environmental variability in response to abrupt climatic ... · 10 km from the north coast of...

Environmental variability in response to abrupt climatic changeduring the Last GlacialndashInterglacial Transition (16ndash8 cal ka BP)evidence from Mainland Orkney

Ashley M Abrook Ian P Matthews Alice M Milner Ian Candy Adrian P Palmer ampRhys G O TimmsCentre for Quaternary Research Department of Geography Royal Holloway University of London Egham Surrey TW200EX UK

AMM 0000-0001-6882-3992Correspondence ashabrookrhulacuk

Abstract The Last GlacialndashInterglacial Transition (LGIT) is a period of climatic complexity where millennial-scale climaticreorganization led to changes in ecosystems Alongside millennial-scale changes centennial-scale climatic events have beenobserved within records from Greenland and continental Europe The effects of these abrupt events on landscapes andenvironments are difficult to discern at present This in part relates to low temporal resolutions attained by many studies andthe sensitivity of palaeoenvironmental proxies to abrupt change We present a high-resolution palynological and charcoal studyof Quoyloo Meadow Orkney and use the Principal Curve statistical method to assist in revealing biostratigraphic change TheLGIT vegetation succession on Orkney is presented as open grassland and Empetrum heath during theWindermere Interstadialand early Holocene and open grassland with Artemisia during the Loch Lomond Stadial However a further three phases ofecological change characterized by expansions of open ground flora are dated to 1405ndash1363 1094ndash108 and 102 cal ka BPThe timing of these changes is constrained by cryptotephra of known age The paper concludes by comparing QuoylooMeadow with Crudale Meadow Orkney and suggests that both Windermere Interstadial records are incomplete and that fire isan important landscape control during the early Holocene

Supplementary material All raw data associated with this publication raw pollen counts charcoal data Principal Curve andRate of Change outputs and the age-model output are available at httpsdoiorg106084m9figsharec4725269

Thematic collection This article is part of the lsquoEarly Career Researchrsquo available at httpswwwlyellcollectionorgccSJG-early-career-research

Received 1 March 2019 revised 16 October 2019 accepted 24 October 2019

The Last GlacialndashInterglacial Transition (LGIT 16ndash8 cal kaBP Rasmussen et al 2014) is a complex period ofpalaeoclimatological and palaeoecological variability Theabundance of research focused on the LGIT which in part isa product of the high stratigraphic and temporal resolutionafforded by many records has generated an improvedunderstanding of dynamic climatic and environmentalshifts (eg Lowe et al 2008 Brooks et al 2012 2016Brooks amp Langdon 2014 Whittington et al 2015 Walker ampLowe 2019) In Britain the LGIT is associated with coldclimates of the Dimlington Stadial (DS Rose 1985)succeeded by relative climatic warmth during theWindermere Interstadial (WI Pennington 1977) a return tocold conditions during the Loch Lomond Stadial (LLS Grayamp Lowe 1977) and a warming climate during the HolocenePalynological data from northern Britain and Scotland (egPennington et al 1972 Lowe amp Walker 1986 Walker ampLowe 1990) largely track these climatostratigraphic phaseswith woody vegetation development during warm phases andArcticalpine open herbaceous vegetation during cold periodsDuring the LGIT abrupt centennial-scale climatic pertur-

bations are observed in Greenland (GI-1d GI-1b 114 ka BPevents Rasmussen et al 2006 2014) and in palaeoclimaticrecords from NW Europe (Brooks amp Birks 2000 Marshall

et al 2002 Brooks et al 2012 2016 Whittington et al2015 Candy et al 2016) However evidence for palyno-logical change at centennial scales during the LGIT isdifficult to discern This may relate to the temporal resolutionof the palynological study lack of palynological sensitivityor the lack of a numerical method that explains considerablevariation within the data Ordination techniques with thefirst axis typically used to define variability may onlyexplain lt40 of the total variation within the data due to theexistence of multiple environmental and ecological gradients(Simpson amp Birks 2012) However Principal Curves (PrCHastie amp Stuetzle 1989 Dersquoath 1999 Simpson amp Birks2012) may distinguish changes in palynological data and aredefined as a smooth one-dimensional curve passing throughan m-dimensional dataspace PrCs capture more variancewithin a dataset than standard ordination techniques and haverecently been used to demonstrate phases of change inpalaeoecological records (Simpson amp Birks 2012 Bennionet al 2015 Shumilovskikh et al 2017)In this study we address issues of vegetation response to

centennial-scale climatic variability and present the lithos-tratigraphy palynostratigraphy charcoal and PrC analysisfrom a sedimentary sequence spanning the LGIT fromQuoyloo Meadow Orkney In particular we use a PrC to

copy 2019 The Author(s) This is an Open Access article distributed under the terms of the Creative Commons Attribution 40 License (httpcreativecommonsorglicensesby40) Published by The Geological Society of London for EGS and GSG Publishing disclaimer wwwgeolsocorgukpub_ethics

Research article Scottish Journal of Geology

Published online December 9 2019 httpsdoiorg101144sjg2019-006 | Vol 56 | 2020 | pp 30ndash46

by guest on August 17 2020httpsjglyellcollectionorgDownloaded from

assist in defining periods of vegetation change during theLGIT and compare the data generated within this study tovegetation and isotopic reconstructions from CrudaleMeadow a site within 6 km of Quoyloo Meaodow (Fig 1)The comparison of these two datasets allows for anunderstanding of the number and impact of different climaticevents within Mainland Orkney during the LGIT

Site context

Consisting of c 70 islands the Orkney Isles are located c10 km from the north coast of Scotland and 80 km SW ofShetland (Fig 1) Quoyloo Meadow (59066417minus3309333 HY250206) is a shallow basin situated in thewest of Mainland Orkney c 22 km NW of Kirkwall Thesite occupies a topographic low within Upper and LowerStromness Flagstones a geological group composed ofmudstone limestone siltstone and sandstone formations(Mykura et al 1976) At its maximum extent the basin is06 times 03 km occupies an area of 01 km2 and lies at analtitude of 30 m asl (Fig 1) The hydrological catchment ofthe site is estimated to be 16 km2 At present an active valleymire occupies the site with one inflow focused from the hillsto the west and one outflow at the northern edge of the basin(Fig 1) However during the late Pleistocene and earlyHolocene the site was characterized by a shallow open-water body with evidence of lacustrine sedimentation(Bunting 1994 Timms et al 2017)The earliest high-resolution pollen-stratigraphic investi-

gation at Quoyloo Meadow was undertaken by Bunting(1994) who reported a 260 cm core sequence with the lowest120 cm attributable to the LGIT From the basal sedimentsno pollen was recovered hinting at either taphonomic issuesor a lack of vegetation surrounding the site during the earliestWI Following catchment stabilization the vegetation wasdominated by low-lying dwarf shrub heathland (Empetrumnigrum) and an open grassland (Poaceae Cyperaceae) TheLLS assemblage was characterized by herbaceous taxa

notably Artemisia and Rumex During the Holocene thevegetation was defined by grassland communities prior to theestablishment of a Betula and Corylus woodland Recentlythe site was reinvestigated as part of a tephrostratigraphicassessment of the archipelago (Timms et al 2017 2018)Timms et al (2017) recovered a similar sequence to Bunting(1994) albeit with a shorter sediment stratigraphy (242 cm)Twelve tephra horizons were identified throughout thesequence (see Timms et al 2017) with a number of thesetephra used to construct a robust age-model for the site

Methodology

Fieldwork and lithostratigraphy

Sediments were extracted from the deepest area of theQuoyloo Meadow basin following depth sounding along aNNE-trending transect (Timms et al 2017) Individualsediment cores were extracted using a Russian corer (50 times5 cm) The core sequence is 242 cm in length as presentedby Timms et al (2017)All cores were described using the Troels-Smith (1955)

sediment classification scheme Sediments were assessed fororganic content using the Loss on Ignition (LOI) method withcombustion at 550degC for two hours Units containing calciumcarbonate were assessed for carbonate percentages using aBascomb calcimeter (Gale amp Hoare 1991) Estimates wereobtained through measuring the amount of carbon dioxideeluted from the sediments following the addition of hydro-chloric acid (Gale amp Hoare 1991) Magnetic susceptibilityestimates were obtained using a Bartington Instruments MS2Ccore-scanning sensor All bulk sedimentological analyseswhere possible were performed at contiguous 1 cm resolution

Palynology

Duplicate cores to those reported by Timms et al (2017)were used in the palaeoecological assessment which havebeen tied to the original sequence based on key marker

Fig 1 Location of Quoyloo Meadow (a) Position of Orkney with respect to the British Isles (b) the location of Quoyloo Meadow and Crudale Meadowwithin Mainland Orkney and (c) topographic map of Quoyloo Meadow and coring location

31Environmental variability in Orkney during the LGIT


horizons and visual stratigraphy The composite QuoylooMeadow sediment profile was analysed for pollen between242 to 131 cm using standard procedures outlined in Faegriamp Iversen (1989) Moore et al (1991) and Munsterman ampKerstholt (1996) This included the addition of Lycopodiumfor pollen concentration estimates the use of densityseparation techniques using sodium polytungstate (SPT ata specific gravity of 20 g cmminus3) and acetolysis Allpalynomorph materials were mounted using glycerine jellyThe record was analysed at a contiguous 1 cm resolutionalthough between 205 and 195 cm the resolution wasdecreased to 2 cm Between 242 and 223 cm the sedimentrecord contained no palynomorphs Pollen identification wasundertaken using an Olympus CX41 binocular microscope at400times magnification with critical identifications at 1000timesmagnification A minimum sum of 300 Total Land Pollen(TLP) was aimed for however this was not always feasiblebetween 2225 and 1955 cm due to low pollen concentra-tions Between these depths TLP sums ranged from 100ndash300TLP Pollen percentage calculations were performed inreference to TLP with aquatic pollen pteridophyte spores andPediastrum (a Non-Pollen Palynomorph NPP) expressed as afunction of TLP + aquatics TLP + pteridophytes and TLP +NPP respectively The latter follows van Geel et al (1980)Pollen type nomenclature follows Moore et al (1991) andStace (2010) All pollen diagram production was undertakenin lsquoC2rsquo V 177 (Juggins 2016) with zones placed visuallyassisted by CONISS (Grimm 1987) using changes inprincipal taxa alongside Pediastrum

Principal Curve analyses

Principal Curves (PrC) were modelled using bothCorrespondence Analysis (CA) and Principal ComponentsAnalysis (PCA) axis one scores following the method ofSimpson amp Birks (2012) All pollen spores and Pediastrumwhose abundances were greater than 5 were selected foranalysis The final curvewasmodelled using CA axis one as thestarting curve in the PrC owing to greater variance beingexplained in the palynological data The data are presentedas stratigraphic plots in the form of PrC outputs and Rate ofChange (RoC) analysesAll numerical analyseswere performedusing the computer programming software lsquoRrsquo and the lsquoRiojarsquolsquoVeganrsquo and lsquoAnaloguersquo packages (Juggins 2017Oksanen et al2019 Simpson amp Oksanen 2019)

Charcoal analysis

Micro- and macro-charcoal analyses were undertakenmatching the resolution of the pollen record However onlymacro-charcoal is presented due to the comparability betweenthe two records Individual cubic centimetres of sedimentwereanalysed followingCarcaillet et al (2007) All macro-charcoalestimates are presented as fragments gt125 microm Charcoal sizedifferentiation was not performed due to the lack of sedimentsretained at 250 microm Charcoal was counted in a segmentedpetri dish using a low power binocular microscope

Chronology

The age model based on tephrostratigraphic informationpresented in Timms et al (2017) has been updated to include

the current best age estimates for the tephra horizonsidentified at Quoyloo Meadow These updated age estimatesand their stratigraphic position within the Quoyloo Meadowsequence were used to construct an age model using ap_sequence depositional model and the IntCal13 calibrationcurve (Reimer et al 2013) within OxCal V 43 (BronkRamsey 2008 2009) No boundaries were added to themodel over areas of lithostratigraphic change and thek_parameter was kept variable

Results

The composite stratigraphy from Quoyloo Meadow ispresented in Figure 2 and Table 1

Sedimentology and stratigraphy

The basal units from the sequence QML-1a and QML-1bare characterized by silty clay sediments with a gradualincrease in organic content QML-1a is characterized by LOIpercentages of lt4 whereas QML-1b exhibits LOIpercentages of lt10 The final unit within the lowerprofile QML-1c is characterized by silts and clays withgreater LOI values of up to 17Throughout QML-2 silt and clay sedimentation dom-

inates However a shift to a dark grey colour is noted fromthe underlying units perhaps reflecting reduced organiccontent as shown by LOI values (lt5) QML-2b exhibits alight brownorange staining which likely relates to thedissolution of basaltic glass shards from a known tephra(Pollard et al 2003 Timms et al 2017)Within QML-3 and QML-5 a shift from minerogenic

sediments to those dominated by high percentages of calciumcarbonate reflects marl sedimentation High CaCO3 percen-tages (gt85) are interrupted within QML-4 as CaCO3

percentages fall to 73 This is coupled with an increase inmagnetic susceptibility and the deposition of a visiblevolcanic ash layer (Timms et al 2017) Overlaying this unitQML-5 returns to high percentages of CaCO3 between 84ndash90 and steadily rising LOI values

Palynology

The pollen spore and NPP percentage and concentrationdiagram has been divided into 11 local pollen assemblagezones (QMP-n) based on 83 samples (Fig 3 and Table 2)

Zone QMP-1 QM1 depth 223ndash217 cm

QMP-1 is dominated by herbaceous taxawith Poaceae valuesoscillating throughout Rumex percentages rise to between 18and 20 Additional herbaceous taxa include CyperaceaeArtemisia Compositae Lactuceae and Saxifragaceae allwith percentages lt10 The main shrub contributor is SalixThe algae Pediastrum exhibit percentages of gt26 through-out the zone TLP concentrations are low throughout QMP-1although total concentrations including all aquatic pterido-phyte and algal indicators peak with 19 100 palynomorphscmminus3 at 2175 cm


QMP-2 demonstrates an increase in arboreal pollen typeswith Betula increasing from 21 to 33 with a brief decline at

32 A M Abrook et al


2115 cm Pinus oscillates between 7 and 18 throughoutValues of Rumex decline from the first zone although at2115 cm percentages increase Additional taxa includeEmpetrum Salix Artemisia Caryophyllaceae andCompositae Lactuceae At 2115 cm percentages ofPediastrum increase to 17 Concentrations are lowthroughout and are comparable to the previous zonealthough a decrease in concentration is noted at 2115 cm


Empetrum percentages rise at the onset of QMP-3 thendecrease from 34 to 14 Betula percentages follow adownward trend whilst Pinus and Cyperaceae values risethroughout Additional taxa include ArtemisiaCaryophyllaceae and Saxifragaceae alongside spores ofSelaginella Throughout the zone percentages of the algaePediastrum are high TLP concentrations peak at 2075 cm at24 100 grains cmminus3 then decrease Total concentrations riseto 125 100 palynomorphs cmminus3 at 2055 cm


Pinus is the principal pollen taxon in QMP-4 peaking at 42towards the middle of the zone The second major taxonArtemisia demonstrates an oscillatory trend wherebysuccessive percentages of 29 9 and 20 are observedPoaceae and Cyperaceae percentages fluctuate between 15and 20 respectively Additional taxa closely resemblethose of the upper levels of QMP-3 with CaryophyllaceaeRumex and Saxifragaceae present Concentrations are as lowas QMP-1 with a TLP average of 4100 grains cmminus3

Fig 2 Stratigraphy of the QM1 sequence from Quoyloo Meadow Loss on Ignition calcimetry and magnetic susceptibility are shown alongside the tephrawithin Timms et al (2017) Abbreviations for tephra from bottom to top TT Tanera Tephra BT Borrobol Tephra PT Penifiler Tephra VA Vedde AshHT Haumlsseldalen Tephra Ask Askja-S Tephra Ash Ashik Tephra SA Saksunarvatn Ash FT Fosen Tephra and AT An Druim Tephra Modified fromTimms et al (2017)

Table 1 Main lithological units from the Quoyloo Meadow sequence

UnitDepth(cm) Sediment classification

Comparable unit(Bunting 1994)

QML-5a 5b 120ndash159 Marl QM-S2 (130ndash207 cm)QML-4 159ndash160 TephraQML-3c 3d 161ndash189 MarlQML-3a 3b 189ndash194 Detrital marlQML-2 194ndash2065 Silty clay QM-S1b (207ndash225 cm)QML-1c 2065ndash208 Silty clay with organics QM-S1a (225ndash260 cm)QML-1a 1b 208ndash242 Silty clay

Adapted from Timms et al (2017) Comparable units from Bunting (1994)




Zone QMP-5 is dominated by Pediastrum The algae peak atthe onset of the zone at 50 and fall to 15 at the zone

terminus Betula percentages are moderate throughout with ahigh of 27 From low percentages Empetrum increases to21 at 1895 cm Poaceae percentages increase to 18

Fig 3 Selected pollen spore and algae profiles from Quoyloo Meadow (a b) pollen spore and algal percentage data (b) macro-charcoal presented as rawcounts and (c) selected pollen concentration data with values shown as times100 grains cmminus3 unless stated LPAZ local pollen assemblage zone TLP TotalLand Pollen

34 A M Abrook et al


Rumex percentages are highest towards the base of the zoneTLP concentrations are higher than QMP-4 and increase to35 100 grains cmminus3 at 1895 cm


QMP-6 is characterized by high values of shrub pollenEmpetrum rises sharply to a sequence high of 50 at1885 cm and then falls to 18 The arboreal component isdominated by Betula which peaks to a sequence high of41 at 1865 cm Herbaceous taxa exhibit percentages lessthan 7 TLP concentrations are high at 1865 cm between30 000 and 40 000 grains cmminus3 Concentrations of Empetrum(23 500 grains cmminus3) and Betula (15 400 grains cmminus3) arehigh


QMP-7 is characterized by elevated percentages of PoaceaeBetula percentages decrease from 25 at 1835 cm to 12 at1657 cm Pinus peaks at different stages throughout thezone with peaks associated with reductions in Filipendulaand Empetrum and increases in Rumex Greater percentagesof Pinus Rumex and Poaceae are associated with increases inconcentrations of these taxa and with decreases in concen-trations of Empetrum


QMP-8 is again dominated by Poaceae with percentagesoscillating between 34 and 50 Corylus achieves percen-tages above 10 and reaches a zone maximum of 19Additional taxa include Cyperaceae Filipendula and RumexThroughout the zone TLP concentrations are variable withmaximum and minimum values of 53 600 grains cmminus3 and18 200 grains cmminus3 A peak in Poaceae to 21 800 grainscmminus3 is observed at 1543 cm


The dominant taxon in QMP-9 is Poaceae with percentagesup to 61 Filipendula is continually recorded withpercentages between 2 and 4 Pinus and Coryluspercentages are generally lower than the previous zonePollen concentrations are largely greater than the previouszone with a TLP peak of 63 100 grains cmminus3 mid-zonereflecting greater concentrations of Betula and Rumex


Poaceae is dominant although percentages decrease to 29at the top of the zone Betula and Pinus are represented byfluctuating percentages and Corylus reaches higher valuesfrom the middle of the zone Salix percentages also risepeaking at 12 at the top of the zone Filicales fluctuatesbetween 6 and 10 throughout TLP concentrations are highwith a maximum of 58 300 grains cmminus3 and Corylus andBetula concentrations increase throughout


The final zone in the sequence is dominated byCorylus whichnearly doubles in percentage from 22 to 40 at the top ofQMP-11 Betula percentages fluctuate between 19 and 29throughout Large increases are observed in percentages ofFilicales spores TLP concentrations are similar to QMP-10


The CA-based PrC explains 81 of the variation within thepalynological dataset Changes in the PrC are directional withthe PrC gradient defined as having Corylus shrubwoodlandand open herbaceous vegetation as the two end-membersVariability in the PrC is confined to a single high-magnitudeoscillation between 206 cm and 193 cm (QML-2 Fig 4)However further episodes of variability can be defined asinflections in the gradient of the PrC and a plateau in thegeneral shift towards lower values (Fig 4) These periods ofchange in the PrC are minor compared to the oscillation

Table 2 Quoyloo Meadow pollen zone information (including the algaePediastrum)

LPAZ Depth (cm) Key indicators

QMP-11 131ndash136 Filicales Corylus BetulaQMP-10 136ndash1445 Poaceae Corylus BetulaQMP-9 1445ndash1505 PoaceaeQMP-8 1505ndash164 Poaceae Corylus PinusQMP-7 164ndash184 Poaceae Pinus BetulaQMP-6 184ndash189 Empetrum Betula PoaceaeQMP-5 189ndash192 Pediastrum Betula Empetrum PoaceaeQMP-4 192ndash202 Pinus Artemisia PediastrumQMP-3 202ndash210 Empetrum Pediastrum CyperaceaeQMP-2 210ndash217 Betula Poaceae PediastrumQMP-1 217ndash223 Pediastrum Poaceae Rumex

Shown are the local pollen assemblage zone (LPAZ) number the depth at which theyoccur in the sequence and the key indicators within each zone

Fig 4 Principal Curve and Rate of Change analysis Grey bars highlightphases of short-term compositional change after Simpson amp Birks (2012)See Figure 2 for key to lithostratigraphy



within QML-2 and their significance is difficult to reconcileNone the less increased variability is noted between 2165and 2105 cm 1885 and 1855 cm 1731 and 1689 cm and1584 and 1543 cm (labelled 1 2 3 4 on Fig 4) Withinthese episodes variability is noted within the Rate of Changeanalysis (RoC Fig 4) suggesting greater compositionalturnover in the palynological dataset Episodes that areconfined to single data points are not considered here

Charcoal

The charcoal record exhibits a continuous background signalwith specific phases of increased abundance (Fig 3) Charcoalvalues range from 1 to 62 fragments cmminus3 Discrete peaksin charcoal coincide with episodes of variability in thevegetation and PrC record with all charcoal peaks abovethe calculated average deemed important (Fig 3)

Chronology

In total 12 tephra layers given by the QM1 prefix and depthwere identified in the Quoyloo Meadow stratigraphy (Timmset al 2017 2019) Of these nine tephra and their best ageestimates were used to construct a Bayesian age model(Table 3 and Fig 5) Two tephras (QM1 218 and QM1 213)which exhibit a Borrobol-type chemical signature have notpreviously been integrated into a tephrochronological modelat Quoyloo Meadow due to uncertainties with theirstratigraphic placing (see Timms et al 2017) However inlight of their close association across multiple sequences inthe British Isles (Timms et al 2019) and new biostrati-graphic information presented here the age model has beenre-run to include these tephras These two ash layers havebeen correlated to the Borrobol and Penifiler tephrasrespectively The output produced good model agreementacross the sequence and has therefore been used to provideage estimates to support environmental interpretations Themodel suggests that sediments began to accumulate in thebasin from 1525 plusmn 086 cal ka BP (Fig 5)

Interpretation

Stratigraphy

Within this study QML-1 can be attributed to the terminalDimlington Stadial (DS) and Windermere Interstadial (WI)

based on two main lines of evidence First increasing LOIvalues throughout QML-1 suggests an increase in organiccontent This increase likely reflects greater vegetationdevelopment in the Quoyloo Meadow catchment andorincreased lacustrine productivity as a result of climaticamelioration at the onset of the WI (eg Pennington 1986Bunting 1994Whittington et al 2015) However catchment

Table 3 Summary of the tephra data and unmodelled input ranges used to create an age model at Quoyloo Meadow

Name Depth (cm) Unmodelled range (cal ka BP) Modelled range (cal ka BP) μ plusmn σ (this study) Reference (original)

Boundary 120 978ndash774 9024 plusmn 651An Druim Tephra 133 981ndash949 980ndash953 9666 plusmn 66 Timms (2016)Hoslashvdarhagi 133 997ndash948 (Combined) (Combined) Wastegaringrd et al (2018)Fosen Tephra 155 1040ndash100 1027ndash1004 10 164 plusmn 57 Lind amp Wastegaringrd (2011)Saksunarvatn Ash 160 1028ndash1014 1028ndash1015 10 215 plusmn 51 Lohne et al (2014)Askja-S Tephra 188 1092ndash1073 1095ndash1073 10 843 plusmn 78 Kearney et al (2018)Haumlsseldalen Tephra 193 1144ndash1119 1145ndash1118 11 317 plusmn 80 Wastegaringrd et al (2018)Vedde Ash 198 1211ndash1194 1211ndash1193 12 021 plusmn 57 Bronk Ramsey et al (2015)Penifiler Tephra 213 1407ndash1381 1408ndash1382 13 951 plusmn 67 Bronk Ramsey et al (2015)Borrobol Tephra 218 1419ndash1400 1418ndash1399 14 086 plusmn 48 Bronk Ramsey et al (2015)Boundary 242 1706ndash1408 15 246 plusmn 864

Shown are the modelled outputs (954 confidence interval) and μ plusmn 1σ error

Fig 5 Agendashdepth p_sequence depositional model for Quoyloo Meadowwith age uncertainties plotted at 954 confidence intervals and μ plusmn σ Forsoftware see Bronk Ramsey 2017

36 A M Abrook et al


stabilization was not achieved inferred from the continueddeposition of clastic sediments which were likely derivedfrom either loosely bound glacial materials or the weatheringof local geological outcrops in an unstable environment It isalso postulated that the lack of carbonate formationthroughout QML-1 which is observed within QML-3 toQML-5 results from continued clastic sedimentationnullifying carbonate accumulation Second the identifica-tion of two tephra horizons which can be correlated to theBorrobol and Penifiler tephras These tephras have frequentlybeen identified towards the base of Scottish WI stratigraphiesindicating tephra deposition soon after the retreat of theDevensian ice-sheet (eg Turney et al 1997 Pyne-OrsquoDonnell 2007 Matthews et al 2011 Timms et al2019) The apparent late stratigraphic position of thesetephra with respect to the depth of sediment between thebase of the sequence and the Borrobol Tephra suggests thatthe basal sediments were either rapidly accumulating or thatthe basin was exposed prior to the onset of the WI At presentit is difficult to establish which scenario is more likely andthe two scenarios may not be mutually exclusive Howeverthe tentative finding of the Tanera Tephra at the base of thesequence (Timms et al 2019) suggests that at least part ofQML-1a was deposited during the DS and QML-1b duringthe WIQML-2 is attributed to the Loch Lomond Stadial (LLS) on

the basis of continued clastic sedimentation a drop in LOIvalues and the identification of the Vedde Ash a tephrawidely documented from this time interval (eg Lane et al2012 Timms et al 2017 2019) The decrease in LOIsuggests a reduction of organic input into the lake underdeteriorating climatic and environmental conditions Theseconditions are confirmed through a change in pollenassemblage from those dominated by shrubs to thosedominated by herbaceous vegetationThe upper sedimentological units QML-3 to QML-5 can

be attributed to the early Holocene based on the precipitationof calcium carbonate and the identification of early Holocenetephra (Timms et al 2017) In temperate mid-latitudelacustrine settings CaCO3 precipitation is often a productof the increased abundance of macrophytes and greater in-lake productivity as a response to climatic amelioration (egMarshall et al 2002 Palmer et al 2015 Whittington et al2015) The increase in photosynthetic activity removes CO2

from lake waters which acts to increase pH and causessupersaturation of lake waters with respect to calcium andbicarbonate (Kelts amp Hsuuml 1978) The result of this processis the precipitation of CaCO3 The cessation of clasticsedimentation likely demonstrates catchment stabilizationwithin warm climatic conditions of the early Holocene Thesedimentological profile from Quoyloo Meadow is thereforecomparable to that of Bunting (1994) who similarly identifiedassociations with the Late-glacial and Holocene periods

The Quoyloo Meadow palaeoenvironmental record

DS to early WI 1525 plusmn 086ndash1389 plusmn 021 cal ka BP

The Tanera Tephra suggests sediment deposition duringthe DS and the late stratigraphic position of the Borroboland Penifiler tephras within the WI would indicate anexpanded early WI stratigraphy compared to the remainder

of the WI record The lack of pollen between 1525 plusmn 086and 1433 plusmn 035 cal ka BP (242ndash223 cm) could be drivenby (1) unfavourable conditions for pollen production(2) taphonomic issues preventing pollen preservation or(3) the lack of vegetation within the catchment If it isaccepted through increasing organic content that QML-1bcan be attributed to the WI (see lsquoStratigraphyrsquo) climaticconditions would have been favourable for plant floweringgiven that cooler climatic conditions within the high Arcticwere not a barrier to plant flowering at this time (Birks2015) Taphonomic issues can be discounted based onobservations of chironomid head capsules within thesediments which are less structurally resistant thanpollen grains and abundant Lycopodium within the samesamples This suggests that neither field taphonomy orlaboratory process prevented pollen preservationTherefore it is more likely that the absence of pollenindicates that there was limited or no catchment vegetationsurrounding Quoyloo Meadow during the terminal DS andearliest WI which prohibited landscape stabilizationBunting (1994) came to a similar conclusion at QuoylooMeadow suggesting that the erosivity and clastic sedi-mentation were related to the strong wind action on Orkneyin an unvegetated landscape Alternatively continuedclastic sedimentation could result from greater seasonalityand cold winter temperatures at this time increasing theeffect of periglacial activity This explanation cannot bequantified at this stage however due to the lack of asuitable proxyOpen tundra grassland communities developed in the

catchment after 1430 plusmn 033 cal ka BP (2225 cm QMP-1)dominated by Poaceae Rumex Salix Cyperaceae Artemisiaand Compositae Lactuceae with some occurrences ofCaryophyllaceae and Saxifragaceae (Figs 3 and 6) Thisgrassland community reflects the colonization of substratesby pioneering taxa Low pollen concentrations suggest thevegetation coverage was sparse which provides furtherevidence of incomplete catchment stabilization and con-tinued clastic sedimentation with a lack of carbonateaccumulation Constant sedimentological loading likely ledto increased nutrient supply to the lake and algal bloomingas inferred from high Pediastrum abundances (Weckstroumlmet al 2010)As with other records attributed to the WI Pinus is likely

reflective of long-distance transport (eg Birks et al 2005Paus 2010 Whittington et al 2015) Low Pinus concentra-tions suggest the lack of Pinus growing on Orkney despitethe elevated percentages recorded at Quoyloo (19)Elevated percentages of far-travelled taxa have been shownby Birks et al (2005) to result from low local pollenproduction as we propose was the case during the early WIThe same scenario may be true for Betula (Birks et al 2005)However the relative contribution of B nana to the pollenspectrum cannot be determined without macrofossil evi-dence (Birks amp Birks 2000) Considering a lack of evidencefor tree birch establishment in northern Scotland during theWI (Birks amp Birks 2014 Whittington et al 2015) combinedwith the lack of vegetative development in the QuoylooMeadow catchment increases in Betula and reductions inRumex from 1430 plusmn 033 cal ka BP likely represent greatercolonization of B nana



Mid to late WI 1389 plusmn 021ndash1312 plusmn 057 cal ka BP

During the mid-lateWI reductions in Betula pollen are notedwith increases in Empetrum nigrum (Figs 3 and 6) Thischange is mirrored by concomitant increases in organiccontent (Fig 2) Increased E nigrum pollen likely reflectscolonization and proliferation of heathland at QuoylooMeadow reflective of relatively moist climatic conditions(Bell amp Tallis 1973) The spread of heathland may alsoreflect the development of increasingly mature well-drainedalbeit base poor soils (Birks 1970) Continued presence ofPoaceae Cyperaceae Betula and Salix suggests a well-developed heathland mosaic with areas of open vegetationand dwarf-shrub heath in the catchment of QuoylooMeadowThe occurrence of Empetrum during the mid-WI coincides

with widespread heathland expansion throughout Scotland atthis time (eg Pennington et al 1972 Lowe ampWalker 1986Walker et al 1994) This mid-WI heathland expansionprovides further evidence of an expanded basal stratigraphyand the stratigraphically lsquolatersquo positions of the Borrobol andPenifler Tephra as Scottish sites often show heathlandexpansion towards the base of Late-glacial stratigraphies (egWalker amp Lowe 1990 Candy et al 2016) This findingimplies that the remainder of the WI sediment record isrelatively compressed as 65 cm of sediment covers c 800years between the deposition of the Penifiler Tephra and themodelled onset of the LLS Palynological evidence acrossthe Scottish Islands and Highlands during the late WI revealsa double peak or extended phase of Empetrum dominance

with high abundances of Betula and Juniperus (eg Lowe ampWalker 1977 Walker amp Lowe 1990 Mayle et al 1997Whittington et al 2015) Given the small low-reliefcatchment surrounding Quoyloo Meadow once vegetationhad stabilized the landscape it may have starved the basin ofsediment resulting in low sedimentation rates and a shortstratigraphic resolution Alternatively a depositional hiatusoccurred following the mid-WI which may have beencaused by fluctuating lake levels however this is notsuggested here as there are no indicators of lake level changeor abrupt shifts in pollen data Therefore the late WI recordappears to be compressed at Quoyloo Meadow

LLS 1312 plusmn 057ndash1146 plusmn 022 cal ka BP

Whilst clastic sedimentation continues throughout the LLS ashift in vegetation assemblage and organic content occurs at1312 plusmn 057 cal ka BP (2065ndash193 cm Figs 2 and 6) Thereduction in LOI throughout QML-2 likely indicates reducedorganic input into the lake body This is supported by themarked change in vegetation during this phase (QMP-3)However an initial phase of both high organic content andabundant Pediastrum likely result from landscape erosionand the input of Interstadial soils (Weckstroumlm et al 2010)following increased periglacial activity under severely coldclimatesOccurring alongside changes in Pediastrum woody

vegetation (Empetrum and Betula) declined with increasingpopulations of Salix Saxifragaceae CyperaceaeCaryophyllaceae and Selaginella selaginoides (Fig 3)

Fig 6 Summary pollen and algal percentage diagram displaying the principal taxa alongside macro-charcoal and the Principal Curve All data presentedagainst age WI Windermere Interstadial LLS Loch Lomond Stadial EH Early Holocene LPAZ local pollen assemblage zone NPP Non-PollenPalynomorph TLP Total Land Pollen

38 A M Abrook et al


These changes suggest the loss of heathland and expansionof an open herbaceous assemblage at the onset of the LLSThe presence of taxa that can survive on disturbed andunstable soils (Caryophyllaceae and Salix) and the appear-ance of S selaginoides reflect a cold climate vegetationassemblage (Heusser amp Igarashi 1994) The increase in Salixpoints to the incidence of late snow lie or exposed landscapes(Wijk 1986 Birks amp Birks 2014) The lingering presence ofEmpetrum perhaps supports the idea of late snow lie withmoisture and protection derived from continued snowpresence However Empetrum will not tolerate continuouslong-lying spring snow (Elvebakk amp Spjelkavik 1995)During this phase charcoal values increased suggesting anincreased fuel source on the landscape following abreakdown of the vegetation community (Fig 6)After 1273 plusmn 056 cal ka BP (2035 cm QMP-4)

Artemisia expanded within the landscape alongsidePoaceae Cyperaceae Caryophyllaceae Rumex andSaxifragaceae (Fig 3) The addition of Artemisia andRumex suggests the establishment of a tundra communityfollowing the onset of the LLS as Artemisia is inferred toreflect dry and cold conditions with the establishment of drywell-drained soils (Birks amp Birks 2014 Whittington et al2015)Within the LLS a vegetational change bracketed by this

Arctic tundra community is noted between 1221 plusmn 034 and1195 plusmn 017 cal ka BP (1995ndash1975 cm) Here reductionsin both the xerophytic Artemisia and Rumex with increasedPinus and minor increases in Empetrum (Figs 3 and 6)suggest an opening of the landscape and contraction ofArcticalpine vegetation (eg Birks amp Birks 2014) Similar tothe earlyWI high Pinus percentages are interpreted to reflectlong-distance transport No evidence suggests that Pinuswasa landscape component during the LLS in Britain and itspresence in Scandinavia has been called into question (egBirks et al 2005) Under a cold stadial climatic regimewherewind shear may have been stronger than under warm climaticconditions (eg Brauer et al 2008) the increase in a far-travelled component may reveal greater apparent dominanceover low pollen producing local herbaceous plants (Birks ampBirks 2000) Low concentrations of pollen during the LLSsupport this explanation However low pollen count sums insamples covering the LLS mean that theories of short-termvegetation change currently are tentative

Early Holocene 1146 plusmn 022ndash902 plusmn 065 cal ka BP

CaCO3 precipitation indicates climatic amelioration duringthe early Holocene which is also clearly recorded in thevegetation (QMP-5) Increased Pediastrum and low landpollen concentrations suggest high levels of catchment soilerosion under low vegetation densities Subsequent expan-sions of Rumex and Salix indicate the re-colonization of theQuoyloo catchment by pioneering taxa following the loss ofthe Arctic tundra assemblage from the LLS (Lowe ampWalker1986 Birks amp Birks 2014) The expansion of Salix in thisinstance may point to areas of exposed ground in thecatchment as opposed to late snow lie which may be lessprevalent within interglacial climatic conditions due to theopen nature of the environment Between 1094plusmn 017 and1075 plusmn 013 cal ka BP (189ndash184 cm QMP-6) Empetrum

and Betula expansion reflects accelerated soil developmentalongside major increases in pollen concentrations suggest-ing the establishment of an extensive dwarf-shrub heathlandGreater LOI values indicate high organic input at this timewhich is a product of an extensively vegetated catchmentInitially during the early Holcene some Betula is interpretedto be B nana Local tree birch may have been presenthowever due to the expansion of shade-intolerant Empetrum(Bell amp Tallis 1973) widespread tree birch colonization wasunlikelyBetween 1075plusmn 013 and 973 plusmn 011 cal ka BP (184ndash

136 cm) Quoyloo Meadow experienced a different vegeta-tion dynamic to most of Scotland due to the lack of woodlanddevelopment (eg Walker et al 1994 Kelly et al 2017) Atthis time reduced populations of dwarf-shrub heathland taxacompared to earlier in the Holocene favoured an expansionof Poaceae alongside Filipendula and the pteridophytesDryopteris and Filicales (Figs 3 and 6) The dominance ofPoaceae indicates the establishment of a grassland commu-nity The establishment of Filipendula suggests relativelywet climatic conditions (Whittington et al 2015) whilst thepteridophytes suggest the establishment of moist and well-drained soils These are taken to reflect a phase of landscapestability in the QuoylooMeadow catchment Throughout thisgrassland phase localized areas of dwarf-shrub heathland andCorylus scrub existed in the catchmentAfter 973 plusmn 011 cal ka BP (136 cm QMP-11) Corylus

expanded which alongside greater incidences of Betula andreduced Poaceae suggests the beginnings of woodlanddevelopment (Fig 6) The lack of birch woodland prior tothis phase likely stems from migratory lags to an islandlocation (Birks 1989) or the out-competing of birch by grassin an environment with strong wind-shear (Bunting 1996)Continued presence of Filipendula Salix Filicales andDryopteris in conjunction with woodland development(Fig 3) suggests areas of moist well-developed soilscontinued into tree clearings or into wetland edges(Bunting 1996) This flora is similar to the present-dayOrkney dales-type community (Chapman amp Crawford1981)

Abrupt palynological change

The PrC at Quoyloo Meadow allows for an understanding ofabrupt change in the palynological record This relates toconsiderable variance being explained by the technique(81) The clearest trend in the PrC is the shift associatedwith the LLS This change reflects increased abundances ofArtemisia Pinus Caryophyllaceae and Selaginella selagi-noides with reductions in Betula and Empetrum Whilst thismillennial-scale change is clearly shown in the zonationapproach as the PrC identifies this shift to open herbaceouscommunities between 1312 plusmn 057ndash1146 plusmn 022 cal ka BP(206ndash194 cm QMP-34) we propose that the technique canbe utilized to identify centennial-scale changes within therecord Due to the short nature of centennial-scale variabilitythese changes are beyond the scope of standard pollenzonation techniques Therefore centennial-scale changesoccur across specific samples within pollen zonesDuring the WI PrC variability is evident between 1405

and 1363 cal ka BP (2165 and 2105 cm) a phase bracketed



by the Borrobol and Penifiler tephras During this periodwithin QMP-2 minor reversions towards higher PrC valuesare observed (Figs 4 and 6) Occurring for specific sampleswithin QMP-2 small increases in Poaceae CyperaceaeRumex and Artemisia with decreases in Betula suggestgreater occurrence of open ground vegetation Increases inthese taxa are interpreted to reflect a brief phase of vegetationchange Coeval with these changes small increases inPediastrum reflect an increase in algal blooming within thelake However the significance of this phase is difficult toascertain as only small changes in pollen andor PrC arenoted which may be a product of noise within the dataset ormore likely stems from open vegetation at Quoyloo Meadowduring the early WI and the lack of clear changes betweenindicators of instability and stability None the less subtlePrC shifts at this time are likely a result of greater landscapedisturbance with increased Pediastrum reflecting increasedsedimentological loading of the lacustrine environmentAll further phases of palynological variability as defined

by the PrC occur in the early Holocene (Figs 4 and 6)However like the WI these phases are subtle and cannot bedelimited from palynological data alone From the PrCpotential phases of palynological change occur between1094 and 108 (189ndash186 cm) at c 105 (173ndash169 cm) and c102 cal ka BP (158ndash154 cm) Between 1094 and 108 calka BP a plateau in the shift towards lower values within thePrC is noted (Fig 6) The PrC appears to be driven byincreases in Pinus with variability in the Empetrum andBetula curves At this time Pediastrum values stabilizeAlthough the changes in the Empetrum curve are confined tosingle samples simultaneous change across multiple pollenspectra also observed in concentration data suggest a periodof vegetation change (Figs 3 and 6) Whilst sedimentationrates may be variable at this time they are unlikely to bewholly responsible for the changes in palynological indicesas both Empetrum (falling) and Betula (rising) displayopposing signals Equally as samples represent between c25ndash60 years vegetation changes are possible Variability inEmpetrum and Betula perhaps indicate a change inhydrological regime at this time as the former requiresmoist and well-drained soils (Bell amp Tallis 1973) with thelatter which includes B nana possibly outcompetingEmpetrum as a pioneering taxon (Birks amp Birks 2014)The increase in charcoal (QMC-4) may further suggest thatfollowing heathland establishment a climatic regime shiftcaused a change in the heathland mosaic and a coevalincrease in fire within the landscapePotential vegetation change at 105 cal ka BP is again

shown by PrC variability However closer scrutiny of thepalynological data reveals that variability is largely driven byvariations in Poaceae Ecologically this phase does notreveal increases in cold or xeric taxa and as pollenconcentrations do not change this variation is likely due tonoise within the datasetBetween 102 and 1014 cal ka BP further variability is

noted in the PrC together with increased charcoal abundance(QMC-5) Throughout this phase expansions in Poaceae andRumex drive changes in the PrC alongside reducedEmpetrum and variable Betula The reduction of Empetrumand variations in Betula suggest a retraction of dwarf shrubheath and an expansion of open grassland communities

Higher concentrations of Poaceae alongside low concentra-tions of Empetrum would support this view (Fig 3)Although a stable grassland community exists prior to thischange in vegetation small increases in the occurrence ofRumex may indicate a phase of greater landscape instabilitywhich appears to correlate with increased burning within thecatchment Therefore at this time a shift in vegetation andgreater fire prevalence occurs at Quoyloo Meadow

Discussion

Palaeoenvironmental and climatic comparisons CrudaleMeadow

As it has been demonstrated that phases of the QuoylooMeadow record are compressed with low sedimentationrates comparisons with additional highly resolved sequencesare necessary to examine the full suite of palaeoenviron-mental changes on Orkney during the LGIT CrudaleMeadow affords this opportunity as not only are thesediments analysed for pollen at high resolution the sitealso contains oxygen isotopic data to establish palaeoclimaticchange (Fig 7 Whittington et al 2015) However thechronology fromWhittington et al (2015) is not sufficientlyprecise to make direct comparisons with Quoyloo MeadowTherefore the two sequences are compared using thepalynological data and supported by changes within thePrCs (Fig 8) The PrC for Crudale Meadow was run usingthe same criteria outlined for Quoyloo MeadowThe base of the record at Crudale Meadow contains high

Poaceae and elevated Betula percentages suggesting an opengrassland with sporadic Betula likely B nana (Whittingtonet al 2015) The transition into a heathland- (Empetrum-)dominated environment occurs within CRU-1 and CRU-2Conversely the open herbaceous vegetation of QMP-1 andpart of QMP-2 is not dominated by Empetrum ThereforeQMP-1 and part of QMP-2 are not represented within theWhittington et al (2015) record Further CRU-1 and CRU-2are reported by Whittington et al (2015) as occurring incalcareous sediment However a reinvestigation of CrudaleMeadow by Timms et al (2018) suggests these calcareoussediments are underlain by clastic sediments not representedin the Whittington et al (2015) study These clasticsediments suggest initial phases of sedimentation in asparsely vegetated landscape The absence of clasticsediments within Whittington et al (2015) coupled withthe difference in pollen assemblages between the two sitessuggests that the record from Quoyloo Meadow pre-dates theCrudale Meadow record Therefore it is reasonable tosuggest that CRU-1 aligns with a later phase of the early WICrudale Meadow does not appear to record the earliest

phase of the WI but may provide superior stratigraphicresolution in other periods ndash specifically in the lateWI whereQuoyloo Meadow appears to be stratigraphically com-pressed In this period Crudale Meadow displays variabilityin the Empetrum curve which is absent from QuoylooMeadow (Fig 8) Considering the proximity of the two sites(c 6 km) similar variability in Empetrummight be expectedAfter the reduction in heathland taxa at the base of CRU-3percentages of Empetrum increase interpreted to reflect arenewed phase of heathland expansion towards the latterphases of the WI (Whittington et al 2015) Therefore if it is

40 A M Abrook et al


Fig 7 Selected pollen percentage data from Crudale Meadow (Whittington et al 2015) Shown alongside the pollen data is the Principal Curve and theδ18O record from the sequence (Whittington et al 2015) LPAZ local pollen assemblage zone

Fig 8 Comparisons between (a) the Quoyloo Meadow palynological Principal Curve and charcoal records and (b) the Crudale Meadow palynologicalPrincipal Curve and climate records Grey bars approximate equivalency between the two sequences with the Saksunarvatn Ash (SA pink bar) used to tiethe records WI Windermere Interstadial LLS Loch Lomond Stadial EH early Holocene



assumed that Empetrum variability is regional at this timethe Crudale Meadow record as reported inWhittington et al(2015) affords greater stratigraphic resolution in comparisonto Quoyloo MeadowFrom these differences we suggest two key observations

First as both Quoyloo Meadow and Crudale Meadow recordclimatic andor palynological variability at an early phase ofthe WI a climatic deterioration occurred at this time on westMainland Orkney Second the depletion in oxygen isotopesand loss of Empetrum during the latter phases of the WI fromCrudale Meadow (CRU-3) reflect a further climatic deteri-oration The compression and lack of resolution in theQuoyloo Meadow record may explain why this deteriorationis not recorded at both sitesPollen records from both sites show an expansion of

Arcticalpine taxa and high compositional turnover duringthe LLS (Fig 8) Greater abundances of and an absence ofvariability in Artemisia at Crudale Meadow suggests either alack of sensitivity to mid-Stadial perturbations or variabilityin the abundancedistribution of Artemisia between sitecatchments However without palaeoclimatic data fromeither site during the LLS this cannot be quantifiedDuring the early Holocene there is strong agreement

between the Quoyloo Meadow and Crudale Meadowsequences with key taxa and both PrCs following a trendtowards greater environmental stability (Fig 8) Both recordsshow the transition from the LLS into the early Holocene andthe expansion of Empetrum heathland suggesting that therecords can be tied with similarities in assumed regionalpollen signals (Fig 8) During this phase the PrCs indicatepalynological variability during the Holocene Whilst this ismanifest as a plateau in the PrC at Quoyloo Meadow (QMP-6 see Abrupt palynological change) the expansion ofheathland and subsequent shift in the PrC occurs alongsidedepletion in the oxygen isotopic curve at Crudale Meadowdefined as the Pre-Boreal Oscillation (PBO CRU-5bWhittington et al 2015) However the shift in the PrC atCrudale Meadow is shown to extend beyond the period ofclimatic variability as inferred by the isotopic excursion Atan approximate mid-point in the plateau within the PrCincreased charcoal abundance suggests an increase in fire atQuoyloo Meadow (Fig 6 QMC-4) If this is extrapolated tothe Crudale Meadow dataset via the alignment of theEmpetrum curve and the PrC fire may be an importantcomponent in understanding continued PrC variability in thelatter stage of and immediately following the climaticoscillation at Crudale Meadow However it is acknowledgedthat this assumes that the charcoal signal is regional and toformally test this hypothesis charcoal analysis needs to beundertaken at Crudale Meadow None the less the tying ofthese two records over this phase of the early Holocenesuggests that in west Mainland Orkney a climatic event asindicated by oxygen isotopic depletion at Crudale Meadowled to a contraction of heathland (Whittington et al 2015)which continued to be modulated by fire It may be thatpositive feedbacks between heathland and fire explain thiscontinued charcoal abundance Using available chrono-logical information this event occurred between 1094ndash108 cal ka BPNo further attempts to correlate the two PrC datasets have

been made although both records show heightened

percentages of Poaceae suggesting that west MainlandOrkney was dominated by open grassland This confirms theviews of Bunting (1994) and Whittington et al (2015) that atreeless landscape persisted until at least after the depositionof the Saksunarvatn Ash (10 210 plusmn 70 cal ka BP Lohne et al2014)

Palaeoenvironmental and climatic comparisons Britainand Europe

The timing of millennial-scale transitions at QuoylooMeadow including the onset of sedimentation at 1525 plusmn086 cal ka BP and the biolithostratigraphic changes thatoccurred during the LLS and early Holocene at 1312 plusmn057 cal ka BP and 1146 plusmn 022 cal ka BP respectivelywithin age uncertainties are comparable to similar millen-nial-scale transitions across Britain and Europe (egMatthews et al 2011 Brooks et al 2012 Muschitiello ampWohlfarth 2015) as well as the Greenland ice-core records(eg Rasmussen et al 2006 2014) The onset of sedimen-tation across many Scottish sequences is notoriously hard toconstrain chronologically as basins were formed followingthe retreat of late Devensian ice and little datable material ispresent within basal sediments (Walker amp Lowe 2019)However as Orkney has been shown to have been ice freebetween 17 and 15 ka BP (Phillips et al 2008 Hughes et al2016) the modelled ages from the base of the QuoylooMeadow record are plausible Whilst it is likely that CrudaleMeadow affords a similar scenario the lack of anindependent chronology precludes this assessmentThe suite of tephra during the WI and early Holocene at

Quoyloo Meadow affords greater precision in constrainingperiods of centennial-scale variability Equally as theQuoyloo Meadow and Crudale Meadow records exhibitsimilar features (see caveats Palaeoenvironmental andclimatic comparisons Crudale Meadow) centennial-scalevariability can be shown across Mainland Orkney A short-lived palaeoecological shift is identified between 1405 and1363 cal ka BP at Quoyloo Meadow The timing of thisevent is comparable to an abrupt climatic event identified inEurope (eg Brooks et al 2012 van Asch et al 2012) andwithin Greenland dated to 1408ndash1394 years b2k (GI-1dBjoumlrck et al 1998 Walker et al 1999 Rasmussen et al2014) In Scotland an early WI climatic deteriorationcomparable to the GI-1d climatic event occurs between1409ndash1365 cal ka BP which has frequently been foundbracketed by the Borrobol and Penifiler tephras (egMatthews et al 2011 Timms et al 2019) Whilst quantifiedclimatic proxies are not presented from Quoyloo Meadow orCrudale Meadow the shift to more open vegetation can beinterpreted as a response to this climatic deterioration whichhas been defined by a 35ndash5degC decline in summer temperatureelsewhere (eg Brooks amp Birks 2000 Brooks et al 20122016) To better understand environmental changes onOrkney at this time quantified climatic data for examplechironomid-inferred summer temperatures are required toestablish the magnitude of climatic change on OrkneyThe centennial-scale climatic and palynological changes

identified during the early Holocene within MainlandOrkney require further explanation as they have frequentlyeither not been identified or have not been constrained

42 A M Abrook et al


chronologically In part this relates to the lack of high-resolution sampling during this phase and multiple plateauxin the radiocarbon curve during the early Holocene (Bjoumlrcket al 1996 Lowe et al 1999) The shift in vegetation andchanges within the PrCs from Orkney between 1094 and108 cal ka BP do not appear to contain any formal climaticcorrelative in Greenland (Rasmussen et al 2014) Howeverclimatic shifts of c 1ndash15degC from Hawes Water (Lang et al2010) and Palaeolake Flixton (Blockley et al 2018) both innorthern England whose chronological uncertainties overlapwith those of the present study suggest a phase of climaticvariability during this time Within continental Europe earlyHolocene climatic variability is shown by short phases ofvegetation change relating to the PBO (114ndash1125 cal kaBP Bjoumlrck et al 1997) This event frequently exhibitsreductions in Betula Pinus and Filipendulawith increases inopen grassland taxa (Bjoumlrck et al 1996 1997) Howevermore recently multiple phases of cool climatic conditionshave been identified across northern Europe between 114ndash108 cal ka BP (eg Andresen et al 2007 Fiłoc et al 2018)suggesting that multiple cool phases characterized this periodof the early Holocene It is therefore probable that changes inheathland PrCs and fire across Orkney at c 109 cal ka BPrelate to pre-Boreal climatic variability observed in Britainand EuropeThe change in the pollen assemblage PrC and charcoal

that occurs at 102 cal ka BP at Quoyloo Meadow has beenpoorly recorded in palynological studies To the best of ourknowledge this is the first instance of environmentalvariability at 102 cal ka BP in Scotland However at103 cal ka BP evidence exists for climatic variability andglacial re-advances across the North Atlantic region (egBond et al 1997 Bjoumlrck et al 2001 Dahl et al 2002 Jessenet al 2008) Evidence from continental Europe suggests thatover the same period vegetation became more openPalynological data from Norway suggest that the landscapewas characterized by open vegetation (Paus 2010) whilstevidence from Poland suggests Pinus forests were tempor-arily replaced by Betula (Fiłoc et al 2018) Thesepalynological changes suggest a period of climatic variabil-ity in Europe Thus the vegetation changes recorded atQuoylooMeadow at 102 cal ka BPmay be linked to climaticchange in the North Atlantic region although the expressionof these changes needs to be further investigated

Principal Curves in ecological data

Within this paper we have demonstrated the use of PrincipalCurves to assist in capturing significant variance withinpalaeoecological records (eg Simpson amp Birks 2012Bennion et al 2015) Through applying this technique tothe QuoylooMeadow and CrudaleMeadow datasets our aimwas to help delineate abrupt ecological change during theLGIT and to assist in the comparison of the two datasets(Fig 8) However whilst the approach has been successfulcaution is required when comparing across datasets Namelywhere stratigraphic differences occur between two recordsfor example during the late WI at Quoyloo Meadow andCrudale Meadow or where differences in taxon representa-tion occur At Crudale Meadow as Empetrum appearsalongside Artemisia Poaceae and Asteraceae during the WI

as well as during the LLS (despite not being a typical pollentype of Arcticalpine environments) it has the effect ofdriving the PrC towards values that are observed duringphases of catchment instability However it has been shownthat heathland establishment at Quoyloo Meadow isreflective of relatively stable conditions Whilst it isencouraging that the PrC can capture complex data featuresthe output needs to be scrutinized to understand what drivesthe PrC especially when the technique is used forcomparison between sequences None the less we recom-mend the use of PrCs in palaeoecological research

Conclusions

A reanalysis of Quoyloo Meadow allows for an under-standing of vegetation history at both the millennial andcentennial scales The PrC in this respect is vital to helpidentify subtle phases of palaeoecological changewhich maynot be obvious from visual assessments or pollen zonationThe data generated within this study and a comparison withthe nearby site of Crudale Meadow (Whittington et al 2015)have resulted in a number of conclusions

bull A clear biostratigraphic structure of the LGIT exists atQuoyloo Meadow corroborating observations withinBunting (1994) with open herbaceous vegetation andheathland during the Windermere Interstadial anArcticalpine disturbed ground assemblage during theLoch Lomond Stadial and a dwarf shrub heath opengrassland and woodland during the early Holocene

bull The PrC generated from the Quoyloo Meadow datadelineates the Loch Lomond Stadial and potentially afurther three phases of variability in the vegetationrecord These phases are driven by expansion andcontraction in herbaceous or shrub vegetationVariability is shown to broadly correlate with theGI-1d event a climatic deterioration between 1094and 108 cal ka BP also observed in northern Englandand climatic variability at 102 cal ka BP inferred fromthe North Atlantic region

bull In the absence of suitable material for radiocarbondating the use of cryptotephra to develop an agemodel has been invaluable for establishing the timingof events recorded at Quoyloo Meadow and furthershows the versatility of this approach in traditionallylsquohard to datersquo sequences (Timms et al 2019)

bull Through comparing data generated within this studywith the Crudale Meadow record presented inWhittington et al (2015) the sediment records fromboth sites are not completely resolved The earliestWindermere Interstadial does not appear to be presentfrom Crudale Meadow whilst the late WindermereInterstadial is compressed at Quoyloo Meadow

bull During the early Holocene both records appear toshow variability in response to one or more phases ofthe Pre-Boreal Oscillation This event is manifested bya climatic deterioration a change in vegetation and anincrease in fire The increase in fire appears to have animpact on vegetation beyond the duration of theclimatic event



bull The data presented here suggest that a complete profilefrom Orkney can only be obtained through comparingmultiple records and multiple proxies

Acknowledgements The authors would like to thank Jane Bunting andan anonymous reviewer for helpful and constructive reviews to this manuscriptThe authors would like to thank Orkney Brewery for access to the QuoylooMeadow site The authors would also like to express many thanks to KevinEdwards for sharing raw data from Crudale Meadow Thanks also go to MartaPerez-Fernandez within the Department of Geography at Royal HollowayUniversity of London for technical support

Funding AA would like to acknowledge funding from the NaturalEnvironmental Research Council (Grant number NEL0024851) whichenabled the palynological and statistical assessments of Quoyloo Meadow RTwould like to acknowledge funding from Royal Holloway University of Londonin the form of a Reid scholarship and the Quaternary Research Association(QRA) for the receipt of a lsquoNew Research Workers Awardrsquo which assisted in thecollection of Orcadian sediments reported herein

Author contributions AMA Formal analysis (Lead) Funding acqui-sition (Lead) Investigation (Lead) Writing - Original Draft (Lead) Writing ndashReview amp Editing (Lead) IPM Supervision (Equal) Writing ndash Original Draft(Supporting) Writing ndash Review amp Editing (Supporting) AMM Supervision(Equal) Writing ndash Original Draft (Supporting) Writing ndash Review amp Editing(Supporting) IC Supervision (Equal) Writing ndash Original Draft (Supporting)Writing ndash Review amp Editing (Supporting) APP Supervision (Supporting)Writing ndashOriginal Draft (Supporting) Writing ndashReviewampEditing (Supporting)RGOT Formal analysis (Lead) Writing ndashOriginal Draft (Supporting) Writing ndashReview amp Editing (Supporting)

Scientific editing by Martin Kirkbride

ReferencesAndresen CS Bjoumlrck S Jessen C amp Rundgren M 2007 Early Holocene

terrestrial climatic variability along a North Atlantic Island transectpalaeoceanographic implications Quaternary Science Reviews 261989ndash1998 httpsdoiorg101016jquascirev200612017

Bell JNB amp Tallis JH 1973 Empetrum nigrum L Journal of Ecology 61289ndash305 httpsdoiorg1023072258934

Bennion H Simpson GL amp Goldsmith BJ 2015 Assessing degradation andrecovery pathways in lakes impacted by eutrophication using the sedimentrecord Frontiers in Ecology and Evolution 3 httpsdoiorg103389fevo201500094

Birks HH 1970 Studies in the vegetational history of Scotland I A pollendiagram from Abernethy Forest Inverness-Shire The Journal of Ecology 58827ndash846 httpsdoiorg1023072258536

Birks HH 2015 South to north Contrasting late-glacial and early-Holoceneclimate changes and vegetation responses between south and north NorwayThe Holocene 25 37ndash52 httpsdoiorg1011770959683614556375

Birks HH amp Birks HJB 2000 Future uses of pollen analysis must includeplant macrofossils Journal of Biogeography 27 31ndash35 httpsdoiorg101046j1365-2699200000375x

Birks HH amp Birks HJB 2014 Towhat extent did changes in July temperatureinfluence Lateglacial vegetation patterns in NW Europe Quaternary ScienceReviews 106 262ndash277 httpsdoiorg101016jquascirev201406024

Birks HH Larsen E amp Birks HJB 2005 Did tree-Betula Pinus and Piceasurvive the last glaciation along the west coast of Norway A review of theevidence in light of Kullman (2002) Journal of Biogeography 321461ndash1471 httpsdoiorg101111j1365-2699200501287x

Birks HJB 1989 Holocene isochrone maps and patterns of tree-spreading inthe British Isles Journal of Biogeography 16 503ndash540 httpsdoiorg1023072845208

Bjoumlrck S Kromer B et al 1996 Synchronized terrestrial-atmospheric deglacialrecords around the North Atlantic Science 274 1155ndash1160 httpsdoiorg101126science27452901155

Bjoumlrck S Rundgren M Ingoacutelfsson Oacute amp Funder S 1997 The Preborealoscillation around the Nordic Seas terrestrial and lacustrine responsesJournal of Quaternary Science 12 455ndash465 httpsdoiorg101002(SICI)1099-1417(19971112)126lt455AID-JQS316gt30CO2-S

Bjoumlrck S Walker MJ Cwynar LC Johnsen S Knudsen KL Lowe JJ ampWohlfarth B 1998 An lsquoeventrsquo stratigraphy for the Last Termination in thenorth Atlantic region based on the Greenland ice-core record a proposal by theINTIMATE group Journal of Quaternary Science 13 283ndash292 httpsdoiorg101002(SICI)1099-1417(19980708)134lt283AID-JQS386gt30CO2-A

Bjoumlrck S Muscheler R et al 2001 High-resolution analyses of an earlyHolocene climate event may imply decreased solar forcing as an importantclimate trigger Geology 29 1107ndash1110 httpsdoiorg1011300091-7613(2001)029lt1107HRAOAEgt20CO2

Blockley SPE Candy I et al 2018 The resilience of postglacial hunter-gatherers to abrupt climate change Nature Ecology and Evolution 2810ndash818 httpsdoiorg101038s41559-018-0508-4

Bond G Showers W et al 1997 A pervasive millennial-scale cycle in northAtlantic Holocene and glacial climates Science 278 1257ndash1266 httpsdoiorg101126science27853411257

Brauer A Haug GH Dulski P Sigman DM amp Negendank JF 2008 Anabrupt wind shift in western Europe at the onset of the Younger Dryas coldperiod Nature Geoscience 1 520ndash523 httpsdoiorg101038ngeo263

Bronk Ramsey C 2008 Deposition models for chronological recordsQuaternary Science Reviews 27 42ndash60 httpsdoiorg101016jquascirev200701019

Bronk Ramsey C 2009 Bayesian analysis of radiocarbon dates Radiocarbon51 337ndash360 httpsdoiorg101017S0033822200033865

Bronk Ramsey C Albert PG et al 2015 Improved age estimates for key LateQuaternary European tephra horizons in the RESET lattice QuaternaryScience Reviews 118 18ndash32 httpsdoiorg101016jquascirev201411007

Bronk Ramsey C 2017 Oxcal Version 432 httpsc14archoxacukoxcalOxCalhtml [Software] Accessed 2018

Brooks SJ amp Birks HJB 2000 Chironomid-inferred Late-Glacial airtemperatures at Whitrig Bog south east Scotland Journal of QuaternaryScience 15 759ndash764 httpsdoiorg1010021099-1417(200012)158lt759AID-JQS590gt30CO2-V

Brooks SJ amp Langdon PG 2014 Summer temperature gradients in northwestEurope during the Lateglacial to early Holocene transition (15ndash8 ka BP)inferred from chironomid assemblages Quaternary International 34180ndash90 httpsdoiorg101016jquaint201401034

Brooks SJ Matthews IP Birks HH amp Birks HJB 2012 High resolutionLateglacial and early-Holocene summer air temperature records from Scotlandinferred from chironomid assemblages Quaternary Science Reviews 4167ndash82 httpsdoiorg101016jquascirev201203007

Brooks SJ Davies KL Mather KA Matthews IP amp Lowe JJ 2016Chironomid-inferred summer temperatures for the Last GlacialndashInterglacialTransition from a lake sediment sequence in Muir Park Reservoir west-centralScotland Journal of Quaternary Science 31 214ndash224 httpsdoiorg101002jqs2860

Bunting MJ 1994 Vegetation history of Orkney Scotland pollen records fromtwo small basins in west Mainland New Phytologist 128 771ndash792 httpsdoiorg101111j1469-81371994tb04039x

Bunting MJ 1996 Holocene vegetation and environment of Orkney In HallAM (ed) The Quaternary of Orkney Field Guide Quaternary ResearchAssociation Cambridge 20ndash29

Candy I Abrook A Elliot F Lincoln P Matthews IP amp Palmer AP 2016Oxygen isotopic evidence for high-magnitude abrupt climatic events duringthe Lateglacial Interstadial in north-west Europe analysis of a lacustrinesequence from the site of Tirinie Scottish Highlands Journal of QuaternaryScience 31 607ndash621 httpsdoiorg101002jqs2884

Carcaillet C Perroux AS Genries A amp Perrette Y 2007 Sedimentarycharcoal pattern in a karstic underground lake Vercors massif French Alpsimplications for palaeo-fire history The Holocene 17 845ndash850 httpsdoiorg1011770959683607080526

Chapman HM ampCrawford RMM 1981 Growth and regeneration in Britainrsquosmost northerly natural woodland Transactions of the Botanical Society ofEdinburgh 43 327ndash335 httpsdoiorg10108003746608108685370

Dahl SO Nesje A Lie Oslash Fjordheim K amp Matthews JA 2002 Timingequilibrium-line altitudes and climatic implications of two early-Holoceneglacier readvances during the Erdalen Event at Jostedalsbreen western NorwayThe Holocene 12 17ndash25 httpsdoiorg1011910959683602hl516rp

Dersquoath G 1999 Principal curves a new technique for indirect and direct gradientanalysis Ecology 80 2237ndash2253 httpsdoiorg1018900012-9658(1999)080[2237PCANTF]20CO2

Elvebakk A amp Spjelkavik S 1995 The ecology and distribution of Empetrumnigrum ssp hermaphroditum on Svalbard and Jan Mayen Nordic Journal ofBotany 15 541ndash552 httpsdoiorg101111j1756-10511995tb00190x

Faegri K amp Iversen J 1989 Textbook of Pollen Analysis 4th edn John Wileyand Sons Chichester

Fiłoc M Kupryjanowicz M Rzodkiewicz M amp Suchora M 2018 Responseof terrestrial and lake environments in NE Poland to Preboreal cold oscillations(PBO) Quaternary International 101ndash117 httpsdoiorg101016jquaint201602052

Gale S amp Hoare P 1991 Quaternary Sediments Petrographic Methods for theStudy of Unlithified Rocks Belhaven and Halsted Press New York

Gray JM amp Lowe JJ 1977 The Scottish Lateglacial Environment a synthesisIn Gray JM amp Lowe JJ (eds) Studies in the Scottish Late-GlacialEnvironment Pergammon Press Oxford 163ndash181

Grimm EC 1987 CONISS A FORTRAN 77 program for graphicallyconstrained cluster analysis by the method of incremental sum of squaresComputers amp Geosciences 3 13ndash35 httpsdoiorg1010160098-3004(87)90022-7

Hastie T amp Stuetzle W 1989 Principal curves Journal of the AmericanStatistical Association 84 502ndash516 httpsdoiorg10108001621459198910478797

Heusser CJ amp Igarashi Y 1994 Quaternary migration pattern of Selaginellaselaginoides in the North Pacific Arctic and Alpine Research 26 187ndash192httpsdoiorg1023071551783

44 A M Abrook et al


Hughes AL Gyllencreutz R Lohne OslashS Mangerud J amp Svendsen JI 2016The last Eurasian ice sheetsndasha chronological database and time-slicereconstruction DATED-1 Boreas 45 1ndash45 httpsdoiorg101111bor12142

Jessen CA Rundgren M Bjoumlrck S Andresen CS amp Conley DJ 2008Variability and seasonality of North Atlantic climate during the earlyHolocene evidence from Faroe Island lake sediments The Holocene 18851ndash860 httpsdoiorg1011770959683608093521

Juggins S 2016C2 Version 177 Software for ecological and palaeoecologicaldata analysis and visualisation Newcastle University Newcastle upon Tyne[Software] Accessed 2016

Juggins S 2017 httpscranr-projectorgwebpackagesriojariojapdf riojaAnalysis of Quaterary Science Data Version 09-21 CRAN [Software]Accessed 2019

Kearney R Albert PG Staff RA Paacutel I Veres D Magyari E amp BronkRamsey C 2018 Ultra-distal fine ash occurrences of the Icelandic Askja-SPlinian eruption deposits in Southern Carpathian lakes New age constraintson a continental scale tephrostratigraphic marker Quaternary ScienceReviews 188 174ndash182 httpsdoiorg101016jquascirev201803035

Kelly TJ Hardiman M Lovelady M Lowe JJ Matthews IP amp BlockleySPE 2017 Scottish early Holocene vegetation dynamics based on pollen andtephra records from Inverlair and Loch Etteridge Inverness-shireProceedings of the Geologistsrsquo Association 128 125ndash135 httpsdoiorg101016jpgeola201602008

Kelts K amp Hsuuml KJ 1978 Freshwater carbonate sedimentation In Lerman A(ed) Lakes Chemistry Geology Physics Springer New York 295ndash323

Lane CS Blockley SPE et al 2012Was the 121 ka Icelandic Vedde Ash oneof a kind Quaternary Science Reviews 33 87ndash99 httpsdoiorg101016jquascirev201111011

Lang B Bedford A Brooks SJ Jones RT Richardson N Birks HJB ampMarshall JD 2010 Early-Holocene temperature variability inferred fromchironomid assemblages at Hawes Water northwest England The Holocene20 943ndash954 httpsdoiorg1011770959683610366157

Lind EMampWastegaringrd S 2011 Tephra horizons contemporary with short earlyHolocene climate fluctuations new results from the Faroe IslandsQuaternaryInternational 246 157ndash167 httpsdoiorg101016jquaint201105014

Lohne OslashS Mangerud J amp Birks HH 2014 IntCal13 calibrated ages of theVedde and Saksunarvatn ashes and the Younger Dryas boundaries fromKraringkenes western Norway Journal of Quaternary Science 29 506ndash507httpsdoiorg101002jqs2722

Lowe JJ amp Walker MJC 1977 The reconstruction of the Late-Glacialenvironment in the southern and eastern Grampian Highlands In Gray JMamp Lowe JJ (eds) Studies in the Scottish Late-Glacial EnvironmentPergammon Press Oxford 101ndash118

Lowe JJ amp Walker MJC 1986 Late-Glacial and early Flandrianenvironmental history of the Isle of Mull Inner Hebrides ScotlandTransactions of the Royal Society of Edinburgh Earth Sciences 77 1ndash20httpsdoiorg101017S0263593300010725

Lowe JJ Birks HH et al 1999 The chronology of palaeoenvironmentalchanges during the Last Glacial-Holocene transition towards an eventstratigraphy for the British Isles Journal of the Geological Society London156 397ndash410 httpsdoiorg101144gsjgs15620397

Lowe JJ Rasmussen SO et al 2008 Synchronisation of palaeoenvironmentalevents in the north Atlantic region during the Last Termination a revisedprotocol recommended by the INTIMATE group Quaternary ScienceReviews 27 6ndash17 httpsdoiorg101016jquascirev200709016

Marshall JD Jones RT Crowley SF Oldfield F Nash S amp Bedford A2002 A high resolution Late-Glacial isotopic record from Hawes Waternorth-west England climatic oscillations calibration and comparison ofpalaeotemperature proxies Palaeogeography PalaeoclimatologyPalaeoecology 185 25ndash40 httpsdoiorg101016S0031-0182(02)00422-4

Matthews IP Birks HH Bourne AJ Brooks SJ Lowe JJ Macleod A ampPyne-OrsquoDonnell SDF 2011 New age estimates and climatostratigraphiccorrelations for the Borrobol and Penifiler Tephras evidence from AbernethyForest Scotland Journal of Quaternary Science 26 247ndash252 httpsdoiorg101002jqs1498

Mayle FE Lowe JJ amp Sheldrick C 1997 The Late Devensian Late-Glacialpalaeoenvironmental record from Whitrig Bog SE Scotland 1Lithostratigraphy geochemistry and palaeobotany Boreas 26 279ndash295httpsdoiorg101111j1502-38851997tb00856x

Moore PD Webb JA amp Collinson ME 1991 Pollen Analsyis BlackwellScientific Oxford

Munsterman D amp Kerstholt S 1996 Sodium polytungstate a new non-toxicalternative to bromoform in heavy liquid separation Review ofPalaeobotany and Palynology 91 417ndash422 httpsdoiorg1010160034-6667(95)00093-3

Muschitiello F amp Wohlfarth B 2015 Time-transgressive environmental shiftsacross Northern Europe at the onset of the Younger DryasQuaternary ScienceReviews 109 49ndash56 httpsdoiorg101016jquascirev201411015

Mykura W Finn D amp May F 1976 British Regional Geology Orkney andShetland Institute of Geological Sciences HMSO NERC Edinburgh

Oksanen J Blanchet FG et al 2019 httpscranismacjpwebpackagesveganveganpdf Community Ecology Package Ordination Diversity andDissimilarities Version 25-6 CRAN [Software] Accessed 2019

Palmer AP Matthews IP et al 2015 The evolution of Palaeolake Flixton andthe environmental context of Star Carr NE Yorkshire Stratigraphy andsedimentology of the Last Glacial-Interglacial Transition (LGIT) lacustrinesequences Proceedings of the Geologistsrsquo Association 126 50ndash59 httpsdoiorg101016jpgeola201410002

Paus A 2010 Vegetation and environment of the Roslashdalen alpine area CentralNorway with emphasis on the early Holocene Vegetation History andArchaeobotany 19 29ndash51 httpsdoiorg101007s00334-009-0228-4

Pennington W 1977 The Late Devensian flora and vegetation of BritainPhilosophical Transactions of the Royal Society Series B Biological Sciences280 247ndash271 httpsdoiorg101098rstb19770109

Pennington W 1986 Lags in adjustment of vegetation to climate caused by thepace of soil development Evidence from Britain Plant Ecology 67 105ndash118httpsdoiorg101007BF00037361

Pennington W Haworth EY Bonny AP amp Lishman JP 1972 Lakesediments in northern Scotland Philosophical Transactions of the RoyalSociety of London Series B Biological Sciences 264 191ndash294 httpsdoiorg101098rstb19720012

Phillips WM Hall AM Ballantyne CK Binnie S Kubric PW ampFreeman S 2008 Extent of the last ice sheet in northern Scotland tested withcosmogenic 10Be exposure ages Journal of Quaternary Science 23 101ndash107httpsdoiorg101002jqs1161

Pollard AM Blockley SPE ampWard KR 2003 Chemical alteration of tephrain the depositional environment theoretical stability modelling Journal ofQuaternary Science 18 385ndash394 httpsdoiorg101002jqs760

Pyne-OrsquoDonnell SDF 2007 Three new distal tephras in sediments spanningthe Last GlacialndashInterglacial Transition in Scotland Journal of QuaternaryScience 22 559ndash570 httpsdoiorg101002jqs1066

Rasmussen SO Andersen KK et al 2006 A new Greenland ice corechronology for the last glacial termination Journal of Geophysical ResearchAtmospheres 111 httpsdoiorg1010292005JD006079

Rasmussen SO Bigler M et al 2014 A stratigraphic framework for abruptclimatic changes during the Last Glacial period based on three synchronizedGreenland ice-core records refining and extending the INTIMATE eventstratigraphy Quaternary Science Reviews 106 14ndash28 httpsdoiorg101016jquascirev201409007

Reimer PJ Bard E et al 2013 IntCal13 and Marine13 radiocarbon agecalibration curves 0ndash50000 years cal BP Radiocarbon 55 1869ndash1887httpsdoiorg102458azu_js_rc5516947

Rose J 1985 The Dimlington StadialDimlington Chronozone a proposal fornaming the main glacial episode of the Late Devensian in Britain Boreas 14225ndash230 httpsdoiorg101111j1502-38851985tb00724x

Shumilovskikh LS Novenko E amp Giesecke T 2017 Long-term dynamics ofthe East European forest-steppe ecotone Journal of Vegetation Science 29416ndash426 httpsdoiorg101111jvs12585

Simpson GL amp Birks HJB 2012 Statistical learning in palaeolimnology InBirks HJB Lotter AF Juggins S amp Smol JP (eds) TrackingEnvironmental Change Using Lake Sediments Volume 5 Data Handlingand Numerical Techniques Kluwer Academic Dordrecht The Netherlands249ndash327

Simpson GL amp Oksanen J 2019 httpscranr-projectorgwebpackagesanalogueanaloguepdf Analogue and Weighted Averaging Methods forPalaeoecology Version 017-3 CRAN [Software] Accessed 2018

Stace C 2010 New Flora of the British Isles 3rd edn Cambridge UniversityPress Cambridge

Timms RGO 2016 Developing a refined tephrostratigraphy for Scotland andconstraining abrupt climatic oscillations of the Last Glacial-InterglacialTransition (Ca 16-8 ka BP) using high resolution tephrochronologies PhDthesis Royal Holloway University of London

Timms RGO Matthews IP Palmer AP Candy I amp Abel L 2017 A high-resolution tephrostratigraphy from Quoyloo Meadow Orkney ScotlandImplications for the tephrostratigraphy of NW Europe during the Last Glacial-Interglacial Transition Quaternary Geochronology 40 67ndash81 httpsdoiorg101016jquageo201606004

Timms RGO Matthews IP Palmer AP amp Candy I 2018 Toward atephrostratigraphic framework for the British Isles A Last Glacial toInterglacial Transition (LGIT c 16ndash8 ka) case study from Crudale MeadowOrkney Quaternary Geochronology 46 28ndash44 httpsdoiorg101016jquageo201803008

Timms RGO Matthews IP Lowe JJ Palmer AP Weston DJMacLeod A amp Blockley SPE 2019 Establishing tephrostratigraphicframeworks to aid the study of abrupt climatic and glacial transitions a casestudy of the Last GlacialndashInterglacial Transition in the British Isles (c 16ndash8 kaBP) Earth-Science Reviews 192 34ndash64 httpsdoiorg101016jearscirev201901003

Troels-Smith J 1955 Characterisation of unconsolidated sediments GeologicalSurvey of Denmark Series 5 1ndash73

Turney CSM Harkness DD amp Lowe JJ 1997 The use of microtephrahorizons to correlate Late-glacial lake sediment successions in ScotlandJournal of Quaternary Science 12 525ndash531 httpsdoiorg101002(SICI)1099-1417(19971112)126lt525AID-JQS347gt30CO2-M

van Asch N Lutz AF Duijkers MC Heiri O Brooks SJ amp Hoek WZ2012 Rapid climate change during the Weichselian Late-Glacial in Irelandchironomid-inferred summer temperatures from Fiddaun Co Galway



Palaeogeography Palaeoclimatology Palaeoecology 315ndash316 1ndash11httpsdoiorg101016jpalaeo201111003

van Geel B Bohncke SJP amp Dee H 1980 A palaeoecological study of anupper Late Glacial and Holocene sequence from ldquoDe Borchertrdquo TheNetherlands Review of Palaeobotany and Palynology 31 367ndash448 httpsdoiorg1010160034-6667(80)90035-4

Walker MJC amp Lowe JJ 1990 Reconstructing the environmental history ofthe Last GlacialndashInterglacial Transition evidence from the Isle of Skye InnerHebrides ScotlandQuaternary Science Reviews 9 15ndash49 httpsdoiorg1010160277-3791(90)90003-S

Walker MJC amp Lowe JJ 2019 Lateglacial environmental change in ScotlandEarth and Environmental Science Transactions of The Royal Society ofEdinburgh 110 173ndash198 httpsdoiorg101017S1755691017000184

Walker MJC Bohncke SJP Coope GR OrsquoConnell M Usinger H ampVerbruggen C 1994 The DevensianWeichselian Late-glacial in northwestEurope (Ireland Britain north Belgium The Netherlands northwestGermany) Journal of Quaternary Science 9 109ndash118 httpsdoiorg101002jqs3390090204

Walker MJC Bjoumlrck S et al 1999 Isotopic lsquoeventsrsquo in the GRIP ice core astratotype for the Late Pleistocene Quaternary Science Reviews 181143ndash1150 httpsdoiorg101016S0277-3791(99)00023-2

Wastegaringrd S Gudmundsdoacutettir ER et al 2018 Towards a Holocenetephrochronology for the Faroe Islands North Atlantic QuaternaryScience Reviews 195 195ndash214 httpsdoiorg101016jquascirev201807024

Weckstroumlm K Weckstroumlm J Yliniemi LM ampKorhola A 2010 The ecologyof Pediastrum (Chlorophyceae) in subarctic lakes and their potential aspaleobioindicators Journal of Paleolimnology 43 61ndash73 httpsdoiorg101007s10933-009-9314-y

Whittington G Edwards KJ Zanchetta G Keen DH Bunting MJFallick AE amp Bryant CL 2015 Lateglacial and early Holocene climates ofthe Atlantic margins of Europe Stable isotope mollusc and pollen recordsfrom Orkney Scotland Quaternary Science Reviews 122 112ndash130 httpsdoiorg101016jquascirev201505026

Wijk S 1986 Performance of Salix herbacea in an alpine snow-bed gradientJournal of Ecology 74 675ndash684 httpsdoiorg1023072260390

46 A M Abrook et al


assist in defining periods of vegetation change during theLGIT and compare the data generated within this study tovegetation and isotopic reconstructions from CrudaleMeadow a site within 6 km of Quoyloo Meaodow (Fig 1)The comparison of these two datasets allows for anunderstanding of the number and impact of different climaticevents within Mainland Orkney during the LGIT

Site context

Consisting of c 70 islands the Orkney Isles are located c10 km from the north coast of Scotland and 80 km SW ofShetland (Fig 1) Quoyloo Meadow (59066417minus3309333 HY250206) is a shallow basin situated in thewest of Mainland Orkney c 22 km NW of Kirkwall Thesite occupies a topographic low within Upper and LowerStromness Flagstones a geological group composed ofmudstone limestone siltstone and sandstone formations(Mykura et al 1976) At its maximum extent the basin is06 times 03 km occupies an area of 01 km2 and lies at analtitude of 30 m asl (Fig 1) The hydrological catchment ofthe site is estimated to be 16 km2 At present an active valleymire occupies the site with one inflow focused from the hillsto the west and one outflow at the northern edge of the basin(Fig 1) However during the late Pleistocene and earlyHolocene the site was characterized by a shallow open-water body with evidence of lacustrine sedimentation(Bunting 1994 Timms et al 2017)The earliest high-resolution pollen-stratigraphic investi-

gation at Quoyloo Meadow was undertaken by Bunting(1994) who reported a 260 cm core sequence with the lowest120 cm attributable to the LGIT From the basal sedimentsno pollen was recovered hinting at either taphonomic issuesor a lack of vegetation surrounding the site during the earliestWI Following catchment stabilization the vegetation wasdominated by low-lying dwarf shrub heathland (Empetrumnigrum) and an open grassland (Poaceae Cyperaceae) TheLLS assemblage was characterized by herbaceous taxa

notably Artemisia and Rumex During the Holocene thevegetation was defined by grassland communities prior to theestablishment of a Betula and Corylus woodland Recentlythe site was reinvestigated as part of a tephrostratigraphicassessment of the archipelago (Timms et al 2017 2018)Timms et al (2017) recovered a similar sequence to Bunting(1994) albeit with a shorter sediment stratigraphy (242 cm)Twelve tephra horizons were identified throughout thesequence (see Timms et al 2017) with a number of thesetephra used to construct a robust age-model for the site

Methodology

Fieldwork and lithostratigraphy

Sediments were extracted from the deepest area of theQuoyloo Meadow basin following depth sounding along aNNE-trending transect (Timms et al 2017) Individualsediment cores were extracted using a Russian corer (50 times5 cm) The core sequence is 242 cm in length as presentedby Timms et al (2017)All cores were described using the Troels-Smith (1955)

sediment classification scheme Sediments were assessed fororganic content using the Loss on Ignition (LOI) method withcombustion at 550degC for two hours Units containing calciumcarbonate were assessed for carbonate percentages using aBascomb calcimeter (Gale amp Hoare 1991) Estimates wereobtained through measuring the amount of carbon dioxideeluted from the sediments following the addition of hydro-chloric acid (Gale amp Hoare 1991) Magnetic susceptibilityestimates were obtained using a Bartington Instruments MS2Ccore-scanning sensor All bulk sedimentological analyseswhere possible were performed at contiguous 1 cm resolution

Palynology

Duplicate cores to those reported by Timms et al (2017)were used in the palaeoecological assessment which havebeen tied to the original sequence based on key marker

Fig 1 Location of Quoyloo Meadow (a) Position of Orkney with respect to the British Isles (b) the location of Quoyloo Meadow and Crudale Meadowwithin Mainland Orkney and (c) topographic map of Quoyloo Meadow and coring location






Charcoal analysis


Chronology



Results







Palynology






32 A M Abrook et al



















34 A M Abrook et al

























Charcoal


Chronology


Interpretation

Stratigraphy








36 A M Abrook et al






















38 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al





Charcoal analysis


Chronology



Results







Palynology






32 A M Abrook et al



















34 A M Abrook et al

























Charcoal


Chronology


Interpretation

Stratigraphy








36 A M Abrook et al






















38 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al



















34 A M Abrook et al

























Charcoal


Chronology


Interpretation

Stratigraphy








36 A M Abrook et al






















38 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al

























Charcoal


Chronology


Interpretation

Stratigraphy








36 A M Abrook et al






















38 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al






















38 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al




















Discussion





40 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al
















42 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al







Conclusions






















































44 A M Abrook et al




























































46 A M Abrook et al















































44 A M Abrook et al




























































46 A M Abrook et al




























































46 A M Abrook et al


environmental variability in response to abrupt climatic ... · 10 km from the north coast of...

Documents