millennial-scale dynamics of continental peatlands in western canada: pattern, controls and climate...

Millennial-scale Dynamics of Millennial-scale Dynamics of Continental Peatlands in Western Continental Peatlands in Western

Canada: Canada: Pattern, Controls and Climate Pattern, Controls and Climate

ConnectionConnectionZicheng Yu

Lehigh UniversityBethlehem, Pennsylvania

QUEST Workshop on CH4 & Wetlands

14-16 June 2004, Bristol, UK

AcknowledgementsAcknowledgements

Dale Vitt, Kel Wieder, Merritt Turetsky, Dave Beilman, Ilka Bauer, Mike Apps, Celina Campbell, and Ian Campbell for sharing slides, data and ideas.

Climate Change Action Fund (Canada) and National Science Foundation (US) for funding.

Outline of TalkOutline of Talk

Overview of continental peatlands

in western Canada

Accumulation pattern & trajectories

Possible climate & global C cycle

connections

Conclusions

Permafrost peatlands

Open fens

Treed fens

Bogs (treed)

Peatland Types in Western CanadaPeatland Types in Western Canada

Total peatland area = 365,160 km2 (21% landbase)

63% fens28% permafrost bogs9% non-permafrost bogs

% Cover

Vitt et al. (2000)

Peatland Distribution

Non

perm

afro

stbo

gs

Perm

afro

stbo

gs

Tree

d fe

nsSh

rubb

y fe

nsO

pen

fens

-

nonp

atte

rned

Ope

n fe

ns -

patte

rned

C S

tora

ge

(Pg

)

ArcticSubarcticMontaneHigh borealMid-borealParkland

0

2

4

6

8

10

12

14

Total = 48 Pg

Vitt et al. (2000)

Peatland Carbon Storage

Fens are more important C pool and have larger area than bogs in continental Canadian peatlands, as well as bigger CH4 emitters,

but we know much less about these ecosystems than bogs in general

Outline of TalkOutline of Talk

Overview of continental peatlands

in western Canada

Accumulation pattern & trajectories

Possible climate & global C cycle

connections

Conclusions

Because:Observed pattern Infer & understand the processes Projecting future dynamics/trajectories

Time (ka)

Cu

mu

lati

ve M

ass

(g. c

m-2)

Exponential

Linear

Logarithmic

0 4 8 12

0

20

40

60

100

120

80

Why accumulation pattern matters?

(Concave)

(Convex)

Draved Mose, Denmark(data from Aaby & Tauber, 1975)

Age (calendar year BP)

0 1000 2000 3000 4000 5000 6000 7000

Cumulative peat mass (g/cm

2) 0

5

10

15

20

25

Concave Pattern from Oceanic BogsConcave Pattern from Oceanic Bogs

(assuming constant PAR and decay)

“apparent” C accumulation rate

Study Sites

Basal dates from ~80 paludified peatlands

5 sites with hi-resolution peat core analysis

Loss-on-Ignition from Upper Pinto Loss-on-Ignition from Upper Pinto FenFen

Yu et al. 2003

1-cm LOI

n=20 dates

also,

2-cm macro

2-cm isotopes

Peat Depth-Age Curve: Convex at Peat Depth-Age Curve: Convex at UPFUPF

Yu et al. 2003

Opposite to well-documented “concave” pattern

UPF: Convex Pattern

Age (cal yr BP)

0 1000 2000 3000 4000 5000 6000

Cumulative Peat Mass (g/cm

2)

0

10

20

30

What Does This Indicate?What Does This Indicate?

Causes?

• decreasing peat-addition rates from acrotelm, and/or

• increasing catotelm decomposition rate

A Simple Extended ModelA Simple Extended Model

Followed the suggestion by Clymo (2000; Quebec Meeting),

Mepdt

dM tb ** * α−= −

,

where M = cumulative peat mass; p = eventual PAR;

α

= catotelm decomposition rate; and b = PAR coefficient.This equation has an analytical solution,

)(*)( ** ttb eeb

pM α

α−− −

−=

.

Yu et al. 2003

Age (cal BP)0 1000 2000 3000 4000 5000 6000

0

10

20

30

40

50

60

Age (cal BP)0 1000 2000 3000 4000 5000 6000

Peat Mass (g/cm

2)

0

10

20

30

40

50

60

+50% Decay

-50% Decay

-50% PAR

+50% PAR

Sensitivity to Changes in Decay & Sensitivity to Changes in Decay & PARPAR

Yu et al. 2003

Change in PAR

Age (cal BP)0 2000 4000 6000

Peat-Addition Rate (g m

-2yr

-1)

0

50

100

150

200

250PAR modifier = exp[-b*t]

Time (years)

0 2000 4000 6000

PAR Modifier

0.0

0.2

0.4

0.6

0.8

1.0

b=0.00037 yr-1

0.000185 yr-1

(-50% b)

0.000555 yr-1

(+50% b)

Change in PAR over TimeChange in PAR over Time

191.8 g m-2 yr-1

26.0 g m-2 yr-1

Yu et al. 2003

PAR decrease from initial 192 to eventual 26 g/m2/yr could explain the observed pattern

Summary ISummary I The model suggests that unidirectional decrease

of PAR from 192 to 26 g m-2 yr-1 over that 5400-yr period at UPF could result in the observed convex pattern.

Autogenic drying trend resulted from fen height growth gradually isolates peat surface from water and nutrient sources, causing decreased production, especially for water-demanding rich fen species - esp. in moisture-limiting continental regions.

This analysis indicates that continental peatlands with convex pattern may reach their growth limit sooner than previous model predicts.

Convex Pattern @ Other Sites IConvex Pattern @ Other Sites I

(Kubiw et al. 1989)

Western Canada:

Slave Lake Bog (Kurry & Vitt 1996)

Southwestern Finland:

Pesansuo raised bog (Ikonen, 1993)

Western Siberia:

Salym-Yugan Mire (Turunen et al. 2001)

Convex Pattern @ Other Sites IIConvex Pattern @ Other Sites II

Convex Pattern from Regional SitesConvex Pattern from Regional Sites

(Yu & Vitt, in prep)

Outline of TalkOutline of Talk

Overview of continental peatlands

in western Canada

Accumulation pattern & trajectories

Possible climate & global C cycle

connections

Conclusions

Climate Proxy from Climate Proxy from UPFUPF

(Yu et al. 2003)

UPFW. Canada

(Yu et al. 2003)

Global Climate & C Cycle Connections?

Yu et al. 2003Bond et al. 2001

Indermuhle et al.

1999

Chappellaz et al.1997

Brook et al. 2000

Summary IISummary II Peat accumulation in western Canada shows

sensitive response to Holocene climate variability at millennial time scale.

Peatland carbon dynamics may connect to change in atmospheric CO2 concentrations (Peatlands in western Canada contain ~50 Pg C, which is equivalent to ~25 ppm CO2 if all remained in the atmosphere).

Are there similar pattern in other peatlands of northern latitudes?

Pervasive Climate Controls of Peatland Pervasive Climate Controls of Peatland DynamicsDynamics

A thawed bog shows similar millennial-scale variations

Patuanak Bog (internal lawn)

Connection of Siberian Peatland Initiations and Atmospheric CH4

N = ~200

Smith et al. 2004

Bill Ruddiman’s hypothesis: CO2 increase since 8 ka:

caused by deforestation; CH4 increase since 5 ka:

caused by rice cultivation

Allogenic and Autogenic Controls of Allogenic and Autogenic Controls of Peatland Dynamics: a conceptual modelPeatland Dynamics: a conceptual model

Yu et al. 2003

Autogenic dryingClimate wettingClimate fluctuations

• The different accumulation pattern observed in continental peatlands suggests these peatlands follow different trajectories historically and may respond to climate change differently (compared to well-studied bogs);

• Continental peatlands appear to show sensitive responses to subtle millennial-scale moisture changes during the Holocene;

• Fens seem to be more variable in C accumulation and more sensitive (less self-regulating) to climate variations than bogs;

• Northern peatlands might have had detectable impacts on atmospheric CO2 and CH4 concentrations during the Holocene.

ConclusionsConclusions

• Develop scaling-up models to take advantage of detailed inventory results from western Canada or other regions for regional CH4 emission estimates by peatland types (as a validating tool for global model?);

• Confirm the extent of past climate – peatland – global C cycle connections, particularly using multiple proxies from paired lake-peatland approach (lakes for independent climate reconstructions);

• Understand implications of permafrost (intact, thawing, and thawed) peatlands (and fen-bog transition) for CH4 emission/budget – permafrost is one of the biggest surprises to come in peatland C dynamics;

• Integrate/reconcile down-core paleo data with present-day instrumental C flux measurements.

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