science plans source-to-sink (s2s)geomorphology.sese.asu.edu/papers/s2s_science_plan...133 margins...

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MARGINSS c i e n c e P l a nS c i e n c e P l a nS c i e n c e P l a nS c i e n c e P l a nS c i e n c e P l a nsssss

Source�to�Sink

1. Executive Summary

rosion sculpts the landscape, and redis-tribution of the sediment creates the al-

luvial plains, coasts, deltas, and continentalshelves upon which most of the world’spopulation lives and derives much of its en-ergy and water. This transfer of sediment andsolute mass from source to sink plays a keyrole in the cycling of elements such as car-bon, in ecosystem change caused by globalchange and sea-level rise, and in resourcemanagement of soils, wetlands, groundwa-ter, and hydrocarbons. Although the sourceto sink system has been studied in its iso-lated component parts for more than 100years, significant advances in our predictivecapability require physical and numericalmodeling of fluxes and feedbacks based ondata from integrated field studies. TheSource-to-Sink Initiative is an attempt to

quantify the mass fluxes of sediments andsolutes across the Earth’s continental mar-gins by answering the following questions:

1) How do tectonics, climate, sea-levelfluctuations, and other forcing param-eters regulate the production, transfer,and storage of sediments and solutesfrom their sources to their sinks?

2) What processes initiate erosion andtransfer, and how are these processeslinked through feedbacks?

3) How do variations in sedimentary pro-cesses and fluxes and longer-termvariations such as tectonics and sealevel build the stratigraphic record tocreate a history of global change?

The Source-to-Sink Initiative will con-sist of focused investigations on active con-vergent continental margins that produce

Source-to-SinkSource-to-SinkSource-to-SinkSource-to-SinkSource-to-Sink

(S2S)(S2S)(S2S)(S2S)(S2S)

HST

Alongshelfcurrents

nalwa

Overban

depositsGravityflows

y

nalwaves

Geostrophicflows

p

nalwa

iG iGStormeffects

LST

Introduction

S�S Questions

EEEEE

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Source�to�Sink

large amounts of sediment deposited in ad-jacent, closed basins. A suite of inter-connect-able numerical and physical-process modelswith shifting boundaries will be used to testhypotheses concerning process connectionsand to predict the behavior of these sourceto sink systems on time scales ranging fromindividual events to millions of years. Forc-ing and boundary parameters measured in thefield will drive the models, and observationsof system variables will allow comparisonwith model predictions. In this way modelresults will help to interpret data and datawill help test the conceptual understandingembedded within the models.

Rates and mechanisms of sediment pro-duction, transport, and accumulation will bemonitored using high-resolution digital el-evation models, newdating and tracertechniques using cos-mogenic isotopes andoptically stimulatedluminescence, andfield acoustic and op-tical velocimeters formeasuring sedimentvelocity and concen-tration. High-resolution documentation of thespatial structure of the sedimentary recordwill be obtained through swath mapping andCHIRP, combined with sediment coring,which will involve new logging tools suchas GRAPE and FMS. Experimental work inlaboratory settings will allow for the testingof hypotheses under strictly controlled con-ditions, in which forcing and boundary pa-rameters can be systematically varied.

Following community-wide discussions,the Fly River and adjacent Gulf of Papua(Papua New Guinea) and the Waipaoa RiverSystem on the east coast of New Zealand’sNorth Island were chosen for focused research.Selection was based on the ability of the vari-ous study areas to address primary scientific

objectives, the presence of a strong forcingthat produces strong signals, active sedimen-tation spanning the various source to sink en-vironments, active sediment and solutetransfer among environments, system closureto sediment transfer, a high-resolution strati-graphic record, advantageous background dataand scientific infrastructure, manageable lo-gistics, small anthropogenic influence, and so-cietal relevance. After five years the two fo-cus areas will be re-evaluated, at which timefocus priorities may change.

Differences between the two focus ar-eas are noteworthy. The Fly River and Gulfof Papua constitute one of the few modernexamples of a developing foreland basin, andthe Waipaoa drainage basin reflects growthof a terrain by volcanism and vertical uplift.

The Fly/Gulf Sys-tem experiences atropical environ-ment, whereas theWaipaoa is sub-tropical/temperate.Because of differ-ences in oceano-graphic environ-ments, the Gulf of

Papua possesses both siliciclastic and carbon-ate sedimentary environments, whereas theWaipaoa margin contains only siliciclasticsediments. The Fly drainage basin (75,000km2) experiences relatively constant dis-charge, the main perturbations being linkedto ENSO-related droughts, and it is practi-cally unaffected by human activity, althoughrecent mining on the Ok Tedi has provided asediment spike that can be monitored fartherdownstream. In contrast, the Waipaoa sys-tem (2000 km2) is strongly affected by sea-sonal variations in discharge and (particu-larly) by tropical cyclones; and for the past100 years it has been affected by the impactsof European landuse and (to a lesser extent)by dam construction.

“The source to sink system

contains most of our energy

resources and potable water,

and as a result most of Earth’s

human population lives along

the source to sink path”

Processes in the

Source�to�Sink

system

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Source�to�Sink

The Source-to-Sink Initiative will be adecadal effort, with initial studies focusingon delineating the sedimentary fluxes in thesource areas and their near-term and long-term fates. International collaboration withscientists from New Guinea, Australia, andNew Zealand will provide local expertise, ac-cess to local facilities (such as ships and on-land facilities), and help disperse researchcosts. Scientific results will be disseminatedthrough workshops and the MARGINSwebsite, as well as through more traditionalscholarly venues.

The integrated approach fostered by thisstudy should pave the way for greater coher-ence and direction in future studies in sedi-

mentary geology that will go far beyond thescope of source to sink or MARGINS.

2. The Source-to-Sink System

When landscapes are eroded, the resultingsediment and dissolved constituents passthrough a connected suite of geomorphic en-vironments, ultimately to be deposited or pre-cipitated on an adjacent flood plain, marineshelf or abyssal plain. This journey fromsource to sink represents the return limb of amass flux loop that begins when rock is firstexposed to subaerial erosion by tectonic pro-cesses such as crustal thickening or volcanic

processes. The suite of connectedenvironments through which thejourney takes place is the sourceto sink system (Figure 1).

The connected environmentsof the source to sink system areseparated by dynamic boundariesthat shift in response to changes in

sediment fluxes and accommoda-tion (Table 1).

Source

weathering

hillslopeerosion

landslides

glacialerosion

glacial runoffstreams

coralhalimedia

Sinkclin

oforms

deltaic/estuarinetrapping primary

productivity

diagenesis

fluvial transport

floodplains

gravel/sandboundary

shoreline

stratigraphy

fans

shelfbreak

shelfcirculation

reefsbanks

submarinecanyons

openslopes

tidewaterglacier

fjords

contourcurrents

abyssal plains

landslidesdebris flows

turbidity currentsnepheloid layers

shorelineterraces

Modified from JP Walsh

Figure 1. A simple schematic showing the dispersal system. The color of the lettering is coded:sources are indicated by black text, sinks are yellow, processes are shown in white italics, and locationsin white regular typeface.

Terrestrial upland

Terrestrial lowland

Continental shelf

Continental slope

Continental rise and abyssal plain

Transition from gravel-bed to sand-bed streams

Coast (shoreline, estuaries, and deltas)

Shelf-slope break

Slope base

Unit: Boundary:

Table 1. The connected environment units and their dynamicboundaries in the source to sink system (cf. Figure 2).

Scope of the Source�

to�Sink Initiative

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Source�to�Sink

Each environmental unit, which is in-ter-linked with other units by the flux of sedi-ment through the boundaries, may producesediment through erosion or act as a sedi-ment sink through deposition, either tempo-rarily or permanently (Figure 2). The erosionand deposition occur at spatial and temporalscales that vary over at least four orders ofmagnitude, making system behavior espe-cially difficult to predict.

The source to sink system is a particu-larly important historical archive of past andpresent global change. Yet, whether we lookat landscape morphology or the stratigraphythat records its erosion, we see the integraleffect of many events over time. Thus, ourability to tell the story of individual eventsfrom landscape morphology or from thestratigraphic record remains poor. We see thebook of time, and perhaps chapters in the book,but we are only rarely able to read individualpages. Yet it is at the page level that the storytruly unfolds. Sometimes an event is globaland so large, such as the K-T impact event,that it leaves not only footprints, but alsocalling cards. But the stratigraphic record ismore likely to be an unclear succession ofevent-related deposits that are recorded in

ways we cannot yet read, because it is cre-ated by internal and external perturbationsthat constantly propagate through the system.Similarly, the inverse record, i.e. the erodedlandscape, shows the same effects of eventsand their integral effects over time, and it tooremains difficult to interpret.

An ability to predict the quantitative be-havior of the source to sink system is impor-tant for a variety of societal reasons. The

source to sink system contains most of ourenergy resources and potable water, and as aresult most of Earth’s human population livesalong the source to sink path. Sedimenteroded in uplands represents a significant lossof agricultural productivity even as it replen-ishes eroding coastlines. Yet we are presentlyunable to anticipate how perturbations in onepart of the system will affect another. Would,for example, a 50% increase in sedimentyield over the next century reverse coastalzone erosion, or would the sediment be se-questered on floodplains, leading to increasedflood risk up river? Would the increased sedi-ment yields from a large magnitude earth-quake in the headwaters of a fluvial systemdisrupt shipping in its lower reaches, and ifso, over what duration? Questions like these

Mou

ntain

s

Plains

Shelf

Slope

Rise

Abyssal

plain

Gravel-sandtransition Coastline

Shelfbreak

Base of slope

Figure 2. Hypsometric configuration of the various environmental units and boundaries in the source-to-sink concept

Societal relevance

Archive of global

change

Predictability

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Source�to�Sink

require accurate quantitative methods forpredicting system behavior over an intimi-dating range of time and space scales. Tobetter explore these questions, as well as toprovide the page-by-page reading of the geo-logic record needed to predict future energyresources, we need improved quantitativemethods for predicting bed characteristicsand architecture that exist in the subsurface.Stratal patterns arising from the interplay ofchanging sea level, sediment supply, and ac-commodation can be crudely predicted fromfirst-generation conceptual and numericalmodels, but more physically based, coupledlandscape-seascape models are needed if weare to predict stratal geometries from recon-structed ancient landscapes and climates.

This problem is compounded by the his-toric disciplinary divisions between geomor-phologists who examine erosion and produc-tion of sediment on land, the oceanographiccommunity, which examines transport anddeposition of marine sediments, the strati-graphic community, which examines thelonger-term record, and the modeling com-munity, which establishes the physical basisfor construction of the sedimentary record.Some of these divisions, notably betweenoceanographers and geomorphologists, oc-cur specifically at the environmental bound-aries listed above, which remain grossly un-derstudied.

The over-arching NSF-MARGINS ap-proach is critical, for only by encouraging

an interdisciplinary community to interact insolving broad problems at selected field sitescan we develop quantitative, 3D, field-testedmodels that are able to predict the responseof a sedimentary system and its deposits toperturbations of variable temporal and spa-tial scales, such as climatic and tectonic vari-ability, and relative sea-level change.

3. What Do We Need to Know aboutthe Source-to-Sink System?

The key scientific issues impeding better pre-dictive capabilities for the source to sink sys-tem were identified at two MARGINSSource to Sink Workshops and a MARGINSWorkshop to define the concept of a Com-munity Sediment Modeling Environment.Similar issues also were identified by an NSFGeology/Paleontology Panel convened in1999 to suggest key problems and majorthrusts for the next decade. The scientific is-sues are contained within three questions:

Question 1: How do tectonics, climate, sealevel fluctuations, and other forcing param-eters regulate the production, transfer, andstorage of sediments and solutes from theirsources to their sinks?

To better manage the landscapes onwhich we live, we need to model linked con-tinental margin systems so we can predictquantitatively the response of these systemsto perturbations (both natural and anthropo-genic). We need to decipher how input sig-nals (e.g., individual storms, floods, or land-slides) are filtered or amplified along a dis-persal system.

For example, it is postulated that sedi-ment delivery to the continental slope occursprimarily at low stands of sea level (Jervey,1988; Posamentier et al., 1989; Lawrence,1993) with a consequent order of magnitudeincrease in sedimentation rates compared to

“We see the book of time, and

perhaps chapters in the book,

but we are only rarely able to

read individual pages. Yet it is

at the page level that the story

truly unfolds”

Key scientific issues

Forcing parameters

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Source�to�Sink

high stands. This increase also has been in-terpreted to result in frequent hyperpycnalflows that may feed deepwater submarinefans and slope aprons (Mulder and Syvitski,1995). However, there is no dynamic modellinking sediment delivery and storage in largerivers on the coastal plain to sediment deliv-ery and storage in the sea. How exactly, forexample, does the sediment transfer vary as afunction of sea level? Rivers can erode andtransport massive amounts of sediment fromthe montane system, independent of sea level,but the site of ultimate sediment accumula-tion (particularly on passive margins) dependson sea level. A definitive answer to this issuerequires an improved understanding of theleads and lags in river response to perturba-tions, and further observations and modelslinking the coastal plain with the subaqueousmargin. Monitoring of present-day sedimentfluxes and compari-son of accumulationrates over longergeologic time scalesby examination ofthe stratigraphicrecord can addressthis question.

As another ex-ample, there are fun-damental uncertain-ties as to how sedi-ment is partitioned between the floodplain,shelf, and slope during major flood events. Thebulk of sediment carried by most modern riv-ers is suspended mud (Milliman and Syvitski,1992), yet the stratigraphic record aboundswith examples of sand-dominated fluvial andshelf deposits, much presumably transportedas bed load or bed-material load. Were theseancient dispersal systems fundamentally dif-ferent from today, or is there a combinationof forcing parameters that yields sandy de-posits from otherwise mud-laden rivers?What controls the proportion of mud depos-

ited in a floodplain versus carried through ariver system and deposited on a muddy shelf?Synchronous monitoring of sediment trans-port in different parts of a source to sink sys-tem is required to address these questions.

Question 2: What processes initiate erosionand sediment transfer, and how are these pro-cesses linked through feedbacks?

Erosion and transport agents are wellknown, but processes that initiate erosionalevents are often less well understood, eventhough they can have significant scientificand societal impact. Moreover, feedbackmechanisms can either increase or decreasethe impact of a particular event.

To cite one example, terrestrial and sub-marine landslides, generated by both earth-quakes and floods, are dominant agents ofsediment transfer and morphological evolu-

tion, as well as con-stituting widespreadhazards in moun-tains and in marineenvironments (thelatter by generatingtsunamis, rupturingpipelines, and dis-rupting communi-cation cables). Pre-sently, however, wehave limited ability

to anticipate landslides and predict their rateof occurrence. What, for example, is the rela-tive importance of earthquake-driven land-slides versus those triggered by floods? Tohelp prepare for landslides and lessen theirimpacts, we need to understand more thor-oughly the processes that cause slope failureand landslides, particularly distinguishingflood-caused versus earthquake caused.While the study of individual landslide gen-esis is crucial, it must be complemented by amore integrated approach of landsliding inthe context of the margin system. This would

“Erosion and transport agents

are well known, but processes

that initiate erosional events are

often less well understood, even

though they can have

significant scientific and

societal impact”

Process initiation

and linkage

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Source�to�Sink

allow for evaluation of how, for instance,incisional events that start at the shorelinepropagate through the landscape (e.g.,Westcott, 1993), triggering submarine land-slides seaward, and fluvial rejuventationlandward, as the perturbation is transmittedthrough the dispersal system. Incision at theshoreline may be initiated by migration oftidal inlets in a barrier system, by landwardmigration of a sediment failure at the conti-nental shelf-slope break, by sea-levelchanges, and also potentially by storms andearthquakes. These processes operate at avariety of time-scales. Sediment failure in theshelf, for example, can be driven by sedimentloading during progradation of an individualmouth bar, such as those that cause growthfaults, and by movement of salt and over-pressured shales (Bhattacharya and Davies,2001). Collapse of sediment at the shelf edgecan also generate tsunamis that may causecoastal erosion that can in turn affect associ-ated rivers. A complete understanding oflandslides, therefore, requires understandinghow the dispersal system is linked to thesource of sediment and specifically howdepositional or erosional events in one partof the system may destabilize the landscapeelsewhere by triggering waves of erosion orsedimentation.

Question 3: How do variations in sedimentprocesses and fluxes and longer term varia-tions such as tectonics and sea level buildthe stratigraphic record to create a historyof global change?

The stratigraphic record is our mainsource of information about the history ofthe Earth’s surface over geologic time, aswell as the repository of major reserves ofgroundwater and hydrocarbons. If the recordis deconvolved correctly, it allows us to re-construct the history of sea level, climate, andtectonics and better predict the properties andoccurrences of reservoirs in the subsurface.

But the fidelity of the stratigraphic record isimperfect, often distorted and containinggaps over a wide spectrum of time scales(Barrell, 1917). Our reconstruction of pastevents is only as good as our understandingof the processes by which they are recordedin sediments. Moreover, recognizing that themodern depositional environment of the shelfreflects the recent past as well as the present,we need to know more about its evolution,particularly since the last glacial maximum(LGM). Our ability to find the next genera-tion of sediment-hosted resources, for ex-ample, will be limited by our ability to pre-dict the locations of potential reservoir bod-ies in the subsurface. Understanding the for-mation of the stratigraphic record is truly asource to sink problem, from the generationof the signal carrier (the sediment) to thepartitioning of fluxes among the whole suiteof margin environments. Integrated studiesof sediment production and accumulationover a time interval for which key controls(e.g., sea level) are relatively well understoodis a crucial step toward developing reliableinterpretive and predictive stratigraphic tools.

In terms of global change, the variousenvironments of the continental margin arealso major reactors in many geochemicalcycles, particularly those of Si, Ca, P, and C.Carbon (both organic and inorganic) cyclinghas important relevance to climate-changemodeling. Margin environments are criticalsites for CO

2 sequestration via weathering re-

actions in source areas as well as by carbon-ate deposition in the shallow and deep oceanenvironments. Quantification of weatheringrates, organic carbon and inorganic carbon-ate production, reactive surface area, andparticle fluxes will provide critical informa-tion for carbon-cycle models and evaluationof global-change scenarios. Carbonate reefsand platforms are particularly sensitive toenvironmental perturbations such as changesin sediment discharge, changes in salinity,

Reconstructing the

record of global

change

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Source�to�Sink

sea-surface temperature, fertilization by nu-trients (anthropogenic and weathering by-products), sea-level change, and topography(James and Kendall, 1992). The dynamics ofmany carbonate systems are fundamentallylinked to input of sediment and nutrients fromupstream terrestrial sources. By choosing amixed clastic-carbonate system, it is possibleto test hypotheses on the relative importanceof the factors that control the stability of car-bonate systems, such as investigating the rela-tive importance of El Niño-type phenomenonversus changes in river-discharge.

The sedimentary wedge that character-izes many continental margins is built fromdepositional systems that relate to the spe-cific environments that comprise source tosink. Localized delta depocenter pro-gradation and along-shelf sediment transportturn sediment point sources into broad con-tinental shelves and provide sediments toreplenish coastlines. To understand how suchprocesses affect margin architecture, we mustacquire observations and develop strati-graphic models that combine knowledgeabout deltaic sedimentation, and shelf andslope depositional processes with tectonismand sea-level variation. River avulsions anddelta lobe switching are linked processes, butthere is significant debate as to the impor-tance of allocyclic controls, such as sea levelchange, versus autocyclic controls, such assuper-elevation of a channel above the flood-plain (Blum and Tornqvist, 2000).

The shoreline is a dynamic boundarythat records the complex interplay betweenrelative sea-level perturbations, physiogra-phy and sediment supply. As such, marginsediments often are contained within an ex-panded section from which both terrestrialand marine signals can be obtained. Qualita-tive models have predicted that the shore-line is farthest seaward when the rate of sea-level drop is a maximum (e.g., Posamentieret al., 1988). Recent morphodynamic experi-

ments have suggested that this result may notalways be the case. A combination ofmorphodynamic and numerical studies link-ing moving boundaries (e.g., the shoreline)will help direct future data acquisition to testmodel predictions, and will yield new in-sights to help mitigate future hazards incoastal environments in response to suchevents as rising sea level.

4. Methods of Investigation

To address these questions, Source-to -Sinkwill proceed as a focused modeling and fieldinvestigation of landscape and seascape evo-lution, and of sediment transport and accu-mulation in two primary field areas wherethe complete source to sink system can beanalyzed. Deciphering the transfer of a sig-nal of an event through a complete and natu-ral source to sink dispersal system will re-quire strong process-based analyses, predic-tive models, and examination of environmen-tal linkages to other segments of the dispersalsystem. At present, for instance, we cannotquantitatively delineate how the segmentsrespond to changes in water discharge orsediment loading. Answers to such questionsrequire us to examine controls on the ratesand processes of floodplain and clinoformsedimentation within a holistic modeling ofthe environment.

Signal transfer through a system can beinvestigated as a “forward” or an “inverse”problem, or both. The forward problem asks:what are the effects of variable sedimentaryprocesses on the signal transferred betweena succession of environments and on the sig-nature imparted to the preserved strata? Incontrast, the inverse problem asks: what sig-natures in the stratigraphic record can be usedto interpret sediment source dynamics in or-der to deduce the role of climate, tectonics,and sea-level variation in its formation? The

S�S and continental

margins

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Source�to�Sink

answer to the forward problem may rangefrom significant transfer of a pulse throughsegments of the dispersal system (top optionin Figure 3) to complete attenuation of thepulse along the dispersal system, such thatlocally generated signals (e.g., from sedimentdynamics) are recorded in the lower segmentsof the system (middle option in Figure 3).The time scales for these two questions gen-

erally fall into one of three time categories:short term (present to 7 ka BP), medium term(7 to 18 ka BP), and long term (>18 ka BP),corresponding to sea-level conditions ofhighstand, transgression, and last glaciallowstand, respectively.

At present, we have little predictive abil-ity to address the forward problem and thuslimited criteria for the inverse problem be-

Figure 3. Several scenarios might explain how a sediment discharge “signal” varies through themorphodynamic segments of sediment dispersal systems. Three scenarios are displayed and can beviewed from a “forward” modeling perspective or an “inverse” modeling perspective, as discussedin the text. The time scale is shown as arbitrary, but needs to be defined in order to identify theprocesses responsible for impacts on the signal transitions. The first row of graphs shows a stronguplands input that progressively attenuates downstream, but is still visible in the marine record. Thismight be the case in the Waipaoa basin. The second row shows a negative signal (e.g. the El Ninosignal in the Fly system) damping completely downstream and being replaced with a signature drivenby tidal, shelf or deep-water transport dynamics. A third scenario shows that even without variationsin source sediment (e.g., Fly during many years), local processes can lead to significant temporalvariation in sediment flux. The two focus sites have strong signals generated, but little is knownabout how the signals are transferred.

Rise & Abyssal PlainMountains Plains Shelf Slope

Rela

tive

Sedi

men

t Lo

ad

earthquakes

reefs

Signal transfer in the

S�S system

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Source�to�Sink

cause of the incomplete nature of the strati-graphic record. Progress can only be madethrough a well-structured, nested researchplan involving collaborative efforts of indi-viduals from disparate backgrounds integrat-ing whole systems, and including allmorphodynamic segments present in thosesystems. By selecting a well-chosen pair offocus sites we ensure that the potentiallyenormous scope of source to sink questionscan be directed towards a tractable solution.

Developing quantitative and physicalmodels for the source to sink System is inte-gral to the strategy of the initiative. Modelswill be used to help define key questions andto test various hypotheses. Model predictionswill help guide aspects of field programs andfield observations will validate/verify modeloutput. Finally, models will allow us to gen-eralize our observations, and thus extend ourunderstanding to other regions. A new gen-eration of numerical modules predicting thetransport and accumulation of sediment inlandscapes and sedimentary basins over abroad range of time and space scales is a highpriority of the Source-to-Sink Initiative. Themodels should be based on algorithms thatmathematically describe the processes andconditions relevant to sediment transport anddeposition in a complete suite of earth envi-ronments, and contain the optimum algo-rithms, input parameters, feedback loops, andprocesses to better predict behavior of thecomplete system (Syvitski et al., 2002). Thegeneral program of investigation for eachselected site will include:

1) Assessment of available data and itsappropriateness for building first-ordercomputational and physical models;

2) field investigation of sediment produc-tion, transport and accumulation, andassociated mechanics and rates;

3) second-order model building/testing toilluminate mechanisms of sediment

transport and stratigraphy generationunder various controls; and

4) stratigraphic documentation at appro-priate spatial concentration to providedesired temporal resolution.

Monitoring and modeling of active processesare examples of work that should occurthroughout the course of the proposed stud-ies. This will include high-resolution digitalelevation models (DEMs) and swath imag-ing of both landscapes and seascapes. Moni-toring of the fluxes throughout the system,can be compared with measurements in thechanges between surfaces surveyed beforeand after major events to determine systemresponse. For example, successive high-reso-lution surveys of the seafloor before and af-ter a major storm event can be used to deter-mine how the shelf responds, where erosionoccurs and where deposition occurs. This canbe compared with rates and magnitude ofchanges in coeval landscape and seascapes.This can also be linked to the relative scaleof changes in the floodplain. Documentationof the stratigraphy can proceed in phases byworking through the different storage ele-ments of the morphodynamic segments, andby investigating the temporal resolution ini-tially from the finest-scale deposits of the pastthousand years and later to longer, deeperrecords that extend back to millions of years.Both monitoring and modeling can be greatlyenhanced by capitalizing on existing data andmeasurements taken in selected study sites.

Model development

within the S�S

initiative

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Source�to�Sink

5. New Technologies andOpportunities for Source-to-Sink

Research

For each of the segments of the source to sinksystem, recently developed technology of-fers unprecedented opportunities for newinsight. Several of these key innovative tech-nologies are explained below in their rela-tion to Source-to-Sink scientific objectives.

• High-resolution DEMs, radar inter-ferometric DEMs (broad coverage,lower accuracy) and laser-altimetry(LIDAR, narrow coverage, high accu-racy, very-high resolution) permit the

finer-scale mapping of fluvial dis-persal systems (flow routing), calibrat-ing transport laws, and documentingsurface evolution. Programs such asgoCad and ARCVIEW can be used tomeasure volumetric differences in de-grading landscapes and aggrading sea-scapes. These differences can be usedto measure mass balances amonglinked systems.

• Precision positioning (e.g., DGPS) al-lows us not only to define our positionwithin a few centimeters (Xu et al.,2000), but also permits the reoccupa-tion of study sites, so that short- andmedium-term changes can be studied.

70006500600055005000450040000

20

30

140001300012000110001000090000

20

30

350055007500950015003500550075000

20

30

10

* all vertical scales two-way travel time in milliseconds

Scripp's Subscan Chirp data (May 2001) Lines l16f1 and l16f2 Shots 3500 - 9500 and 1 - 7500

SIS-1000 Chirp (Nov, 1999) Line l105f1 Shots 8100-14200

Huntec Boomer (Nov, 1999) Line l105f1 shots 3900 - 7100

Figure 4. Geophysicalimages acquired offshoreSouth Carolina's GrandStrand, illustrating theimproved resolution andpenetration of theSubscan CHIRP system(top), relative to standardCHIRP data (middle),and a Huntec boomer(bottom). Resolutionincreases from severalmeters in the Huntecrecord to considerablyless than 1 meter in theSubscan record.

Figure courtesy of NealDriscoll, Scripps Insti-tution of Oceanography.

Technology in the

S�S initiative

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Source�to�Sink

• Similarly, swath-mapping—particu-larly the new interferometric swath so-nar system—and the CHIRP seismicprofiler allow marine geologists andgeophysicists to achieve horizontal andvertical resolutions of less than 15-20cm, thus providing unprecedented abil-ity to define fine-scale bathymetry andstratigraphy (Figure 3). Together withDGPS, these new technologies allowus to document the change in seafloormorphology and stratigraphy with time.

• Enhanced coring (e.g., wire-line cor-ing that can be obtained through theOcean Drilling Program) can continu-ously sample long sections of uncon-solidated sediments in diverse environ-ments. New and established loggingtools and geophysical processing (e.g.,GRAPE, FMS, magnetic susceptibility,and the multispectral scanner), more-over, allow continuous acquisition ofdownhole physical properties data.

• Acoustic, electromagnetic, and opticaldevices have been developed to mea-

sure velocity, concentration and grainsize of sediment particles in transport,and high-speed video imaging, particle-image velocimetry used in monitoringphysical experiments can provide valu-able constraints on conceptual, analyti-cal and numerical models.

• Laboratory experimental facilities,such as those recently developed for ex-perimental stratigraphy, allow for thetesting of hypotheses under strictly con-trolled conditions in which forcing andboundary parameters can be systemati-cally varied.

• Recently developed experimental fa-cilities (e.g., large-scale tanks andflumes, Paola et al., 2000) enable un-precedented physical modeling studiesto be posed, especially if constrainedby good field data, as is a central aimof Source to Sink (Figure 5). This isparticularly important because mostprevious modeling studies have beenpurely 2D (e.g., Jervey, 1988; Law-rence, 1993; Wehr, 1993).

Figure 5. Experimental run illustrating the complex interplay between base level, shoreline position,and accomodation. Illustration courtesy of Chris Paola, University of Minnesota.

Methods and

facilities

143143143143143


Source�to�Sink

6. Selection of Focus Sites

Through discussion at various workshops andworking groups, there was general agreementabout the criteria considered essential in theselection of a Source-to-Sink study area.Other criteria were considered important,although perhaps not mandatory:

6.1 Critical Criteria

• Strong forcing that produces strong sig-nals, some of which may be transferredbetween environments - Areas experi-encing rapid uplift and vigorous atmo-spheric forcing (e.g., heavy rainfall,frequent storms) yield large amountsof sediment, often during catastrophicevents. Because they tend to erode andstore less sediment on their floodplains, smaller mountainous rivers tendto have particularly high sedimentyields (Milliman and Syvitski, 1992).As a result, more than 65% of the sedi-ment presently discharged to the glo-bal ocean comes from rivers drainingsouthern Asia and the high-standingislands in Oceania. Rivers draining thehigh-standing islands in the East Indiesand the Philippines alone are estimatedto discharge about more than half ofthe southern Asian fluvial sedimentload (Figure 6).

• Active transfer among environmentswithin a generally closed system - Be-cause larger watersheds tend to storemore sediment and to modulate the ef-fect of individual events, it is preferableto study systems in which the sourcedrains moderate- to small-sized basins(e.g., 103-105 km in area). In this waythe transfer and fate of sediment withinthe study area can be quantified, allow-ing a mass-balance calculation.

Focus site

selection criteria

• High-resolution stratigraphic record —a long record better allows delineationof various-scale events as well as largerchanges in climate and sea level. Ahigh-resolution stratigraphic recordextending back to glacial stage 5e (125ka BP), for example, would allow usto delineate the stratigraphic responseto glacial-interglacial cycles and eu-static sea-level fluctuations.

• Must have sufficient background datato allow the formulation of an optimalintegrated systems study — quantita-tive data concerning rainfall, streamflow, sediment discharge, the oceano-graphic environment as well as a gen-eral understanding of the sedimentarysinks facilitate the formulation of an ef-fective field study. Aerial photographs,digital models, and remotely senseddata also would be extremely helpful.

• Local scientific infrastructure — accessto the entire study area, from source tosink, is necessary. Access to local shipsand land support systems (e.g., shal-low-water boats, field camps) wouldprovide the opportunity to reach areasotherwise inaccessible and also allowus to study the impact of episodicevents, such as floods and storms.

6.2 Other Important Criteria

* Analogs with ancient sedimentary en-vironments - Sites whose environmentsand/or sedimentary deposits can belinked to geological formations clearlywould enhance the uniformitarian as-pects of the study.

* Presence of carbonate environments -By virtue of their usually formingwithin the environment in which theyare deposited, carbonate sediments of-fer unique paleo-environmental and

144144144144144


Source�to�Sink

geochronologic constraints as well aschemical signals, sea-level informa-tion, and other insights. While mixedsiliciclastic-carbonate deposits arecommon in the geologic record, thefactors that control the dominance ofone system relative to the other are onlyqualitatively understood (James andKendall 1992). By supporting a fieldfocus site in which there are mixedsiliciclastics and carbonates, this re-

search will help bridge another gapbetween deep specialist divisions in ourcommunity. Bridging this division isparticularly important in protecting andmanaging the world’s carbonate reefcommunities, which are so stronglyaffected by changes in siliciclastic sedi-mentation.

• Societal relevance - The results of theinvestigations at the two study sitesshould help document the impact of

12,500

150

400

850

550

250

500

1400

1000

200

500

Fluvial Dischargeof

Suspended Solids to Oceans(Total = 18,300 * 106

t/yr)

30 - 100

100 - 300

300 - 1000

1000 - 3000

> 3000

TSS Yield(t/km2/yr)

190

2240

260

6800

160

240

500

2100

Figure 6. Calculated fluvial discharge of suspended solids to the global ocean (upper left). Of theapproximately 2/3 of the global load emanating from southern Asia, more than half comes fromhigh-standing islands in the East Indies and the Philippines. Illustration after Milliman andFarnsworth (in preparation).

145145145145145


Source�to�Sink

anthropogenic activities on the environ-ment. What is the effect on landscapeevolution, for example, of deforestationor farming, or the effect on water qual-ity or stream flow by dam construction?Landslides and tsunamis are perhapstwo extreme examples of events thatcan have extreme impact on both thesedimentary environment and humancommunities inhabiting those environ-ments.

• Significant differences between twosites - By choosing two sites with dif-ferent climatic regimes, hydrography,sediment sources, oceanographic forc-ing and stratigraphic architectures, wecan better differentiate the qualitativeand quantitative impact of these differ-ent environmental controls. Where pos-sible, drainage basins should have sig-nificant differences in land-use activi-ties and histories. Where perturbationshave occurred - and most drainage ba-sins throughout the world have beenaffected by anthropogenic activities -it is preferable that the changes bequantifiable and should not overwhelmthe natural processes.

6.3 Assessment of Candidate Sites

More than twenty sites were consideredwithin the community as possible candidatesfor a source to sink study. Candidate areasranged from Belize to Alaska and to PapuaNew Guinea. Nearly all candidates, however,failed to meet one or more of the critical cri-teria. The Mississippi River, for example,suffered both its very large size (which tendsto dampen the down-basin effect of even verylarge events) as well as the fact that it con-tains more than 30,000 dams of various sizes,which collectively greatly control the fluvialregime. On the other hand, because of its aridand dammed drainage basin, the BrazosRiver presently supplies relatively smallamounts of modern sediment to its dispersalsystem. Consequently there is little or nosediment transport to the more distal shelfand offshore segments of its system, despitean otherwise excellent offshore seismic andcore subsurface data set that extends back tothe Pleistocene.

The two sites that appeared to satisfy allor at least the most critical criteria were theFly River/Gulf of Papua in Papua NewGuinea, and the Waiapoa dispersal systemin New Zealand. Two adjacent areas (theMarkham River in PNG and the South Is-land of New Zealand) were considered rea-sonable alternative sites that should be re-evaluated after the first five years of theSource-to-Sink program have been com-pleted.

Candidate sites

146146146146146


Source�to�Sink

6.4 Candidate Sites

6.4.1 Fly River/Gulfof Papua (New Guinea)

The Gulf of Papua (GoP) and, in particular, theFly River system provide a unique opportunityto study a major river system that remains in anearly pristine condition (Figure 7). The FlyRiver (drainage basin area 75,000 km2) rises inthe fold and thrust belt of central New Guinea,where mountains locally reach elevations of4000 m. The basin receives up to 10 m of rainin its headwaters and mean annual Fly Riverrunoff approaches 2 m/yr. The two major tribu-taries to the Fly, the Ok Tedi and Strickland,join the Fly along a broad flood plain less than20 m above sea level (Figure 8).

Most of the Fly’s sediment load comesfrom the mountains, with natural loadingdominated by landslides. The natural sedi-ment load of the Fly River delta is estimatedto be 85 x 106 t yr-1 (Pickup et al., 1981),90% of which is fine-grained. Mass wasting

and (to a lesser extent, ENSO variations) maycause significant fluctuations in this load.During El Niño periods, the normally highlevels of Fly River discharges of water, sol-utes and particulates decrease to negligiblelevels, creating a decadal signal whose propa-gation can be studied through the diversesegments of the dispersal system.

Unlike most rivers, the Fly system hasexperienced little deforestation or agricul-tural development and has no dams or artifi-cial levees. The one major anthropogenic per-turbation to the system has been the Ok Tedigold and copper mine, begun in 1985 and by2010 predicted to have introduced 1.7 x 109

t to the watershed. The large influx of sedi-ment in the Fly offers a unique opportunityto examine a large sediment signal, with adistinctive chemical composition, which canbe exploited to document and model sedi-ment transfer processes through the entiresystem. While the vast majority of the sedi-ment thus far has remained within the OkTedi and upper Fly rivers (G. Parker and W.

Figure 7. Location map showing the Fly River, Gulf of Papua, and Markham River in Papua New Guinea.

132° 136° 140° 144° 148° 152°

-12°

-8°

-4°

0°

-8000 -6000 -4000 -2000 0 2000 m

-12°

-8°

-4°

0°

132° 136° 140° 144° 148° 152°

Gulf ofPapua

PAPUANEW GUINEA

IRIANJAYA

AUSTRALIA

Gre

at B

arrie

r Re

ef

FlyRiver

MarkhamRiver

Papua New Guinea

Focus Site

147147147147147


Source�to�Sink

Dietrich, unpublished re-port), it will produce astrong, long-duration sig-nal that differs from short-term stochastic introduc-tion associated with natu-ral loading events.

As a result of miningactivities, there are cur-rently nine flow and sus-pended-sediment gaugingstations along the Ok Tedi-Fly system, some of whichgo back to the early 1980’s.Detailed topographic mapsusing high-resolution aerialphotographs and repeat in-frared surveys also havedocumented changes inmorphology and vegeta-tion. Using differentialGPS, a high-resolutionnetwork of benchmarkshas been established on theFly and Ok Tedi, resultingin a high-quality river pro-file in very flat terrain. Nu-merous cross-sectionshave been established for repeat surveys. TheOk Tedi and Fly floodplains have been topo-graphically mapped through a combinationof aerial photography, laser profiling andground surveying. The extensive data alreadycollected and the established precipitationand hydrologic program in the Fly greatlyincrease the opportunity and possibility ofobtaining accurate sediment budgets throughthe system.

The Fly River delta has the classic funnel-shaped geometry of a tide-dominated system(Galloway, 1975), and has been used as the end-member example in delta classification, al-though in terms of our knowledge about thedifferent delta types, we know the least abouttide-influenced deltas (Bhattacharya and

Walker, 1992). Local tides range from about3.5 m at the mouth to 5 m at the apex (meso- tomacro-tidal). Strong tidal currents cause fluidmuds to be deposited on the floors of distribu-tary channels, which are hypothesized to rep-resent the staging area for distribution to theoffshore shelf clinoform (Dalrymple et al., inpress). The continental shelf contains an ac-tively growing mud-dominated clinoform simi-lar in scale to those associated with other ma-jor rivers (e.g., Amazon, Ganges- Brahmaputra,and Changjiang), and which represents thedominant stratigraphic unit of continental mar-gin architecture around the world (Driscoll andKarner, 1999). Sediments become progres-sively finer in the offshore direction as waveand current velocities diminish. Simulta-

Figure 8. Fly River watershed, also showing Ok Tedi mine, StricklandRiver and present-day estuary, and adjacent Gulf of Papua. Modifiedfrom Dietrich et al (1999).

Fly River

Low human impact

148148148148148


Source�to�Sink

neously, benthic organism abundance increases,and the interbedded physical structure is re-placed by homogenous, bioturbated muds (Har-ris et al., 1996). A preliminary sediment bud-get over a 210Pb timescale (100-yr) indicates thatmodern sediments are partitioned in the follow-ing fashion: Delta Front 24 ± 12x106 metrictons/yr, Prodelta 22 ± 6x106 metric tons/yr, Dis-tal Delta 0.9 ± .2x106 metric tons/yr, which col-lectively represents about 55% of the Fly’s av-erage annual load (Figure 9). An additional 2%is estimated to be transported southward intothe Torres Strait, and some may be sequesteredin the extensive mangrove forests that line theGoP coastline. The “missing” Fly sediment ishypothesized to move northeastward along the

GoP shelf (Harris et al., 1993), where it mixeswith sediments supplied by the Kikori, Purariand other rivers and accumulates on the shelf,probably on clinoform deposits that extendalong the 50-m isobath. High sediment accu-mulation rates (> 1 cm/yr) are known to occurin this region. Geochemical evidence also sug-gests some terrestrial sediment is escaping theshelf into Pandora Trough, but the magnitudeof this loss is unknown. The GoP also providesan excellent locality for Source-to-Sink re-search, including its long marine sedimentaryhistory of foreland-basin evolution (3000 msince the Jurassic).

Finally, the Fly River-dominated GoPcan be distinguished by its close proximity

40?

40

2

?

?

?

30 m

30 m

200 mTorres Strait

PAPU

A

NEW

G

UIN

EA

Gulf

of

Papua

FLUID MUD

FLUID

MU

D

Fly

Delt

a

143° 144°

8°

9°

Figure 9. Schematic diagram showing transport pathways for Fly River sediment dispersal. Accordingto this model, floodplain sedimentation is zero and nearly half of the annual load moves alongshoreand offshore to the northeast. Modified from Harris et al. (1993).

Fly River sediment

productivity

149149149149149


Source�to�Sink

to extensive coral reefs and Halimeda banksthat extend northward from the Great Bar-rier Reef, thus providing a unique opportu-nity to study the carbonate- siliciclastic tran-sition (Wolanski et al., 1984).

Scientists from Papua New Guinea andAustralia have been investigating the terres-trial and marine portions of the dispersal sys-tem for more than 20 years. In particular, re-cent and ongoing flow and sediment moni-toring on the Fly River (http://www.Ok-Tedi.com) provide essential flux data as wellas (ultimately) insights as to the impact of amajor anthropogenic activity (the Ok Tedimine). Project TROPICS (Tropical River-Ocean Processes In Coastal Settings) has re-cently studied the fate of solutes and particu-lates entering the Gulf of Papua over Holocenetime scales (http://www.aims. gov.au/pages/research/projects/ project05/tropics/tropics.html). The US-NSF RiOMar program is plan-ning to collaborate with Source-to-Sink inves-tigations in the examination of carbon path-ways through this wet-tropical system.

6.4.2 Waipaoa Dispersal System(New Zealand)

The Waipaoa River margin provides an op-portunity to investigate the signal transfer ofhigh-magnitude perturbations during the lateQuaternary (ENSO driven changes in pre-cipitation, cyclonic storms, and large-scaledestruction of forests from major volcaniceruptions and historical land-use practices)across a relatively closed, small-scale, sedi-mentary system. The system (Figure 10) iscompact (~2570 km2 source, ~900 km2 sink),has a point-source discharge to the ocean, andis virtually closed under present highstandconditions (i.e. sediment budgets can be bal-anced from upland to shelf).

The setting is within the zone of activedeformation associated with the Hikurangi

subduction margin, and encompasses the2200 km2 Waipaoa and 370 km2 Waimatariver basins, which drain the eastern flanksof the Raukumara Range (Figures 10, 11).These drainage basins are positioned abovea major tectonic plate boundary and are un-derlain by deformed Cretaceous and EarlyTertiary mudstones and argillites, early Cre-taceous greywacke, and a thick forearc se-quence of Miocene-Pliocene mudstone andsandstone. Subduction has induced rapiduplift (~4 mm y-1) in the ranges at the headof Waipaoa River (Berryman et al., 2000),where there has been 120 m of downcuttingin the last 15 kyr, much of which was ac-complished in the late Pleistocene and earlyHolocene. Rainfall across the basin is pri-marily controlled by topography, with a meanannual rainfall of 1470 mm from a gaugingstation 48 km upstream from the coast.

Figure 10. Location map showing the Waipaoadispersal system and the eastern South Islanddispersal system.

160°

160°

165°

165°

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170°

175°

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180°

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Eastern South Island

Waipaoa

New Zealand

Focus Site

150150150150150


Source�to�Sink

A remarkable Holocene history of catch-ment erosion events (mainly storm-inducedrainfall) during the past 2 ka has been docu-mented for the east coast of New Zealandfrom Lake Tutira (Eden and Page, 1998),

formed just south of the Waipaoa basin by alarge landslide ~6500 14C years beforepresent (Trustrum and Page, 1992). In the his-torical period these can be tied with recordedlarge storms (e.g., Cyclone Bola) that cause

Figure 11. Topography and bathymetry of the Waipaoa, Waiapu, and Uawa Rivers in the easternNorth Island of New Zealand, showing the onshore and offshore dispersal parts of theWaipaoa dispersalsystem. From Orpin et al., 2002.

Waipaoa River

151151151151151


Source�to�Sink

extensive landsliding. Periods of abundantstorm layers are observed throughout the 2-ka record, which have been hypothesized tocorrespond with ENSO variations (Eden andPage, 1998), although neotectonic move-ments also could be important. New Zealandresearchers are planning to extend the high-resolution storm record to the lake’s originby coring through the thickest part of the lakesediment in 2003. This 6-ky lake record oferosion events is an unique proxy for riverdischarge events, and can be used to drivequantitative models of river input to thecoastal ocean.

Present-day sediment and nutrient fluxesin the Waipaoa system have been stronglyinfluenced by anthropogenic activities. Al-though Maori settlers to the area had dis-rupted the natural vegetation, widespreadclearing of the indigenous forest did not com-mence until after the arrival of Europeancolonists in the late 1820’s, and by 1920 theheadwaters were cleared; today only ~3% ofthe basin remains under primary indigenousforest. The destabilized landscape conse-quently initiated severe hillslope erosion inthe Waipaoa River Basin’s headwaters, whereamphitheater-like gully complexes (up to 0.2km2 in area) developed in the highly shearedrocks. Large volumes of fine sediment aredelivered to stream channels by gully ero-sion and shallow landsliding, and theWaipaoa River has a mean sediment concen-tration of ~1700 mg l-1. The annual averagesuspended-sediment load to Poverty Bay of15 x106 t yr-1 (Hicks et al., 2000) ranksamongst the highest measured in NewZealand, and its sediment yield (5900 t km-2

yr-1) is very high by global standards(Milliman and Syvitski, 1992). Moderateflows (less than the bank-full discharge of~1800 m3 s-1) transport ~75% of the sedimentload. As such the Waipaoa is an ideal systemto study the effects of heavy landuse on thesource to sink system, and may lead to a bet-

ter ability to predict the longer term conse-quences of deforestation that is an epidemicland management problem globally. Further-more, large sediment pulses may be mim-icked by natural events common to the area,such as those thought to occur following amajor volcanic eruption or neotectonic dis-placement.

Fine sediments discharged from theWaipaoa are distributed primarily ashypopycnal plumes and are carried out ofPoverty Bay onto the shelf by the barocliniccirculation (which may be intensified dur-ing periods of high river discharge).Hyperpycnal flows are though to occur dur-ing high discharge events, such as those as-sociated with cyclonic storms (Foster andCarter, 1998). The frequency of hyperpycnalflows during certain times in the past mayhave been considerably lower, as pre-defor-estation discharge was reduced nearly an or-der of magnitude. Such changes should bereflected in distinct sediment dispersal pat-terns, offering the potential to examine theeffect of changing river discharge on the de-velopment of shelf stratigraphy. Study ofhyperpycnal flows is of particular economicinterest because of their potential importancein delivering coarse sediment into deepwaterenvironments. Much of the global energyexploration budget is focused on attemptingto predict the distribution of potential hydro-carbon bearing sandstone reservoirs depos-ited in deep water environments.

The combination of a broad crescentcoast and actively growing anticlines (Lach-lan Ariel; Figure 11) on the outer shelf effec-tively captures sediment on the middle shelf.Post-glacial accumulation rates are high(~1.9m ka-1). A 13 km-wide gap betweenAriel and Lachlan anticlines provides an es-cape route for some sediment, but it is esti-mated that the off-shelf loss of modern mudis small. Sediment escaping onto the conti-nental slope is likely to be retained within a

Strong human

impact on Waipaoa

River system

152152152152152


Source�to�Sink

large amphitheater of a (Pliocene?) collapsestructure formed by collision of the accre-tionary prism with a seamount on the sub-ducting Pacific Plate. Given the shelf andslope entrapment of sediment, conditionsmust be considered favorable for closing themodern Waipaoa budget. The only uncer-tainty relates to sediment transported into thearea by the prevailing along-margin circula-tion. On the shelf, transport is weak andephemeral. However, on the outermost shelfand upper slope, sediments come into con-tact with the southwest-flowing East CapeCurrent. This flow mainly affects sedimentescaping the shelf depocenter and transportrates have yet to be resolved.

During sea-level lowstands, the WaipaoaRiver presumably reached the shelf edge, al-though the exact point of discharge is not ob-vious as the course of the ancestral river hasnot been traced entirely across the shelf. If dis-charge was into Poverty Canyon, south of theAriel-Lachlan gap, sediment within the can-yon would be guided to a shallow basin at3000-3200 m depth that has formed betweenthe base of slope and the left bank levee of

Hikurangi Channel. If the lowstand dischargedat a gully near the central part of the gap, thensediment would accumulate mainly within theamphitheater of the collapse structure. Which-ever is the case, the slope conduits lead intobasins where there is a reasonable expecta-tion of closing the budget.

6.5 Differences Between theTwo Study Sites

One of the important criteria in study siteselection were the differences between thetwo sites. At first it may appear that the Flyand Waipaoa sites are closely similar, and itis true that both study sites involve document-ing the input and fate of sediment from rela-tively small mountainous rivers in the SWPacific Ocean. A closer inspection, however,shows many fundamental differences. Forexample:

These and other contrasting sedimentaryconsiderations provide a wide variety of pro-cesses and stratigraphic signatures that will helpdevelop a global understanding for sedimenta-

Figure 12. Seismic sections across the mid-shelf at the Waipaoa, Waiapu, and Uawa Rivers, showingmudstone structural highs on the seaward side, trapping Holocene sediments. From Orpin et al., 2002.

Sea level and

sediment trapping

on Waipaoa shelf

153153153153153


Source�to�Sink

tion, but also will allow greater fundamentalinsights through comparison of the mechanismsand patterns found in the two areas.

7. Implementation Plan

Because the source to sink concept involvesa wide range of terrestrial and marine stud-ies, field work and modeling, the entire inte-grated effort will take at least a decade. Thegeneral outline for these various studies isgiven in Table 3, in which the timelines forvarious activities are indicated. The sequenceof study and relative effort was designed tobuild on the strengths of each site to yield new

understanding in a realistic time frame giventhe length of the Source-to-Sink Program.

Because both the Fly and Waipaoa riv-ers are subject toepisodic events, theFly to ENSO varia-tions in precipitationand the Waipaoa tocyclone activity, it iscritical that the dis-persal system bemonitored for thefull duration of eachstudy. Onshore andoffshore imagingwill help define the

morphologic and stratigraphic frameworkand thereby locate targets for detailed imag-ing and sampling. Onshore sampling and dat-ing would help provide constraints on age ofsurface exposure and material properties.Box, vibra-, and piston-coring of the pre-served stratigraphy will provide age con-straints required for sediment budgets as wellas lithologic information for geophysicaldata. Where longer histories are needed, non-Riser drilling will determine the history andrates of incoming material to the sink; thelocation of these cores will depend greatly

Table 2. Comparison between the two focus areas, Fly River in Papua NewGuinea, and Waipaoa River in New Zealand.

Table 3. Logical progression of studies within focus sites.

Time (years)

1. Monitoring Dispersal System

2. Onshore/Offshore Imaging

3. Onshore Sampling and Dating

4. Sediment Properties/Rates

5. Offshore Non-Riser ODP Drilling

6. Experimental Studies

7. Quantitative Modeling

8. Alternate Platforms/New Drilling

1 2 3 4 5 6 7 8 9 10

Drainage-basin size

Terrestrial and marine climates

Fluvial database

Seasonal river discharge

Anthropogenic impact

Sediment residence time in

drainage basins

Dominant oceanographic variability

Shelf sediments

Shelf stratigraphic architecture

Fly

(75,000 km2), medium

tropical

small

steady

minimal

long

trade winds

siliciclastic, with reef-derived

carbonate facies to the south

clinoform progradation

Waipaoa

(2000 km2), small

sub-tropical

substantial

episodic

considerable

short

cyclonic storms

siliciclastic

basin infill

Implementation of

the S�S Initiative

154154154154154


Source�to�Sink

upon data acquired previously by both im-aging and sediment sampling. Experimentalstudies and particularly quantitative model-ing will provide insights and predictionsabout the dispersal system that can be tested;at the same time, modeling can provide di-rections for the acquisition of seismic andsedimentologic data. Particular attention isbeing devoted to development of the Com-munity Sediment Model (CSM), whose goalis to produce a unified framework model,analogous on some levels to a Global Cli-mate Model. Alternate platforms and newdrilling technology presumably would be ap-plied toward the end of the study, after allthe data and model outputs have been evalu-ated; these final field operations can providekey samples from diverse environments totest model predictions.

Communication and interaction will becornerstones of the implementation policy,to provide opportunities for increased syn-ergy through collaboration and piggyback re-search campaigns. A mid-program evaluationwill occur in the fifth year to determinewhether a course correction is required and,if so, how substantial.

Because, as pointed out earlier, there areconsiderable differences between the Fly/GOPand Waipaoa sites, actual implementation plansfor the two sites will show some differences.

The Fly/GOP focus site is a complete,relatively pristine dispersal system, where wehave the opportunity to address processesoperating along all source to sink morpho-dynamic segments. Although sediment pro-duction rates in the highlands are large byworld standards, the extensive floodplains ofthe lowland Fly and Strickland rivers appearto damp upland production variations, pro-viding an opportunity to investigate damp-ing mechanisms and the associated strati-graphic record. Because historic measure-ments along the river are relatively few, weneed first to understand how changes in wa-

ter discharge and sediment loading impactfloodplain and shelf-clinoform sedimentarysinks, and how escaping sediments impactcarbonate production by coral/algal commu-nities on the shelf and in deeper water. Onlonger time scales, these sedimentary pro-cesses are modified by relative base-levelchanges (caused by tectonics and eustasy).We can address sediment production and se-questration questions in many of themorphodynamic segments of this system onshort (0-7 ka BP), medium (7-18 ka BP), andlong (>18 ka BP) time scales.

It is particularly important at the outsetof the Fly/GOP research to engage both landand marine scientists. This can be accom-plished best by focusing first on fundamen-tal issues addressing sedimentary mecha-nisms on short time scales, which can belinked most strongly to stratigraphy. Of par-ticular significance on short time scales isthe high-amplitude sediment-transfer signalgenerated by the strong El Niño forcing.Based on this strategy, among the short time-scale problems that can be addressed are (inthe downstream direction): siliciclastic sedi-ment production in the uplands, sedimentstorage and transfer in the floodplain, lobeswitching in the delta, clinoform develop-ment on the shelf, and carbonate productionfrom the outer shelf to the deep sea. Theserequire monitoring studies to be initiated firstas well as collection of baseline morphom-etry of present landscapes and seascapesthrough high resolution DEM and seafloormapping. We may also wish to re-map spe-cific morphometric features following largeevents, particularly storms and floods, thatmay occur throughout the duration of thestudy. This places an even greater importanceon the collection of baseline data (e.g.,CHIRP data, High resolution DEM’s) earlyin the individual studies.

On medium time scales, research shouldinvolve the paleoclimatic record in flood-

CSM—Community

Sediment Model

155155155155155


Source�to�Sink

plains and lakes in response to sea-level rise.Shallow coring of the floodplain and lakesediments will accomplish this. Similarly,cores taken at selected sites within the shelfclinoforms can be compared with cores takenfrom the floodplain to examine the similari-ties and differences in how these changes areexpressed. A significant seismic program alsowill be required to map subsurface depositsin 3D. Core data are also critical to calibratelithology, thickness and age of the older strataimaged by these seismic data. These data willalso help quantify the reciprocal carbonateand siliciclastic sedimentation offshore. Thelonger time-scale investigations should in-volve investigation of channel stacking in theflood plain, through collection of deep coresand possibly GPR or seismic data, as well asoffshore seismic data, which will image chan-nel incision of the shelf, and interaction ofshelf-slope carbonate and siliciclastic sedi-mentation over glacial/interglacial cycles.Locations of deeper cores offshore will beselected after processing and preliminary in-terpretation of seismic data.

These will ultimately result in a com-plete characterization of a source to sink sys-tem in which short-term processes can be ex-trapolated back to a stratigraphic record of afew million years. Modeling work will be un-dertaken to simulate this system and test sen-sitivities to processes at a variety of scales,from short-term stochastic processes such asfloods and storms to longer-term processessuch as subsidence, tectonics, and sea level.This will allow us to perform a well-cali-brated test of the relative importance of allo-genic vs. authogenic processes in buildingthe stratigraphic record.

This type of integrated modeling over or-ders-of-magnitude spatial and temporal scaleshas never been attempted before, partly be-cause of a lack of well-constrained field ex-amples against which to build the models, asis a key goal of the Source-to-Sink Initiative.

The specific sediment yield for theWaipaoa river ranks among the highest in theworld, consequently, even small-scale per-turbations in the terrestrial environmentshould create a strong depositional signal.Because of the small size of the drainagebasin, the residence time of sedimentary ma-terial within the terrestrial environment isrelatively small, and therefore changing dis-charge conditions should rapidly propagateto the shelf depocenter. As a result, theWaipaoa system represents a sedimentaryend-member where the potential for preser-vation of climatic, geologic, and anthropo-genic signals on the shelf is high. Despitethis potential, we need to understand howoperative marine processes filter the chang-ing discharge conditions to determine thedominant control on the formation of shelfstratigraphy. Thus, a combination of terres-trial and marine observations and modelingshould be undertaken to define the terrestrialsignals, determine the dominant marine trans-port processes, and resolve the shelf strati-graphic record.

Episodic and highly concentrated riveroutflow into an energetic coastal environ-ment ultimately will allow the communityto examine the role of marine transport pro-cesses in modulating strong signals emanat-ing from the drainage basin. Monitoring andmodeling studies will be required to under-stand the mechanisms of sediment dispersalfrom Poverty Bay to the open shelf, and theresulting depositional signatures. Near bot-tom observations are key to understandingpresent-day sediment dispersal patterns (e.g.,instrumented tripods, swath mapping, high-resolution seismic) and will provide realis-tic constraints for sedimentary models whichneed to be developed in order to predict dis-persal and accumulation patterns beyond thetemporal range of these observations.

A large body of research already existsregarding the geologic framework and Ho-

Differences in

implementation

between Focus Sites

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locene environmental conditions in the terres-trial part of the Waipaoa system (e.g., Fosterand Carter, 1997; Eden and Page, 1998). Us-ing these present data, process and samplingstudies can begin in the uplands and flood-plain regions. Information also exists for theoffshore part of the Waipaoa system, but dataare fewer. Waipaoa studies would build on pastand continuing work of New Zealand scien-tists in three significant areas: 1) Holoceneclimate record and landscape evolution, aswell as mechanisms and patterns of sedimentproduction (Landcare Research; http://www.landcare.cri.nz); 2) flow and sediment dis-charge monitoring (Gisborne District Coun-cil and the National Institute of Water & At-mospheric Research, NIWA); 3) nature andamount of along-margin and off-shelf trans-port and sediment storage on the continentalslope (NIWA; http://www.niwa.cri.nz). Thesestudies represent a significant contributionfrom New Zealand partners and provide ampleopportunities for collaborative efforts to makesignificant scientific advances toward theSource-to-Sink objectives.

A combination of methods will be neededto understand better the Waipaoa system. Shal-low and deep coring of lacustrine and shelfenvironments along with chronostratigraphicanalyses will be needed to define the inputsand sedimentary architecture. Numerous te-phra layers and pronounced textural variationsin marine cores off the Waipaoa will enhanceour ability to constrain shelf stratigraphy. Theerosion of regolith following large magnitudeevents that generate massive landsliding (e.g.,7.8 magnitude Napier earthquake of 1931) ischaracterized by an abundance of Tertiarypollen, which thus provides a means for iden-tifying them in the shelf record (Wilmshurstand McGlone, 1996). The chronostratigraphiccontrol afforded by tephrachronology, alongwith coring and high-resolution seismic stud-ies, will facilitate construction of sedimentbudgets that can be used to constrain estimates

of riverine inputs over the Holocene. Conse-quently, investigations should focus on theupland source regions, the floodplains, coast,and shelf. Ongoing studies of the continentalslope by NIWA, in collaboration with USMARGINS scientists, will help to address thepossibility of off-shelf transport, and to closethe offshore portion of the dispersal systemduring the Holocene. Before process and sam-pling studies can begin, however, geophysi-cal characterization of the shelf needs to becarried out, principally by swath bathymetryand high-resolution seismic profiling, withlimited ground-truthing. This would be fol-lowed by more detailed sampling and obser-vational studies. During this phase, it will becritical to coordinate closely the terrestrial andmarine studies to address how changing ter-restrial inputs and the dominant transport pro-cesses affect the segregation, dispersal andpreservation of strata.

8. International Cooperation

The success of both focus studies will dependgreatly on our foreign partners. Without theirhelp in supplying previously acquired terres-trial and marine data, without their assistancein providing field support, such as boats andfield camps, and without (particularly in thecase of Papua New Guinea) permission towork in their territorial waters, these studieswould be impossible.

In the Fly River study we rely on threeprime groups for support. The Ok Tedi Minegroup have been extremely forthcoming insharing their hydrologic data from the Fly,and they also have given access to their riverboats and even helicopters, the only practi-cal ways in which field operations can be ac-complished in the coastal lowlands. ThePapua New Guineans themselves, particu-larly faculty at the University of Papua NewGuinea, Port Moresby, have been helpful in

International

collaboration

NIWA�US

Ok Tedi Mine group

University of PNG

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obtaining permission to work in the country.Finally, the Australians have had a long-timeinterest in the Fly River, particularly as itstands at the northern end of the Great Bar-rier Reef; any change in the fluvial and/ordispersal paths of the Fly River system couldhave major impacts on the reefs to the south.As such, the Australians have conductedmany research programs in the Gulf of Papua.Several Australian cruises, in fact, providedthe first opportunities for American scientiststo work in Papua New Guinean waters. Thesevarious links will be continued in future stud-ies, particularly as the assistance of Ok Tediand the Australians is critical for us to obtainsmall-draft boats that can work in river andcoastal environments.

The success of any study of the WaipaoaRiver and adjacent offshore basin dependsstrongly upon New Zealand scientists. Flu-vial data are available from Landcare, whileaccess to New Zealand ships will come fromclose ties with NIWA (see previous section).The NIWA link to ships of opportunity is par-ticularly critical, since it is our assumptionthat episodic events, most likely tied to cy-clones, have a major effect on both the riverand the transport of its sediment to the off-shore basins. As US UNOLS ships are sched-uled far ahead of any actual cruise, our onlyopportunity to study these major events andtheir effects on the dispersal and sedimen-tary systems most likely could come onlyfrom using New Zealand ships. As in the caseof Australians, New Zealand scientists willbe working as our research partners, andtherefore ship costs should be less than if wewere forced to lease a third-party ship.

9. Education and Communication

Educational opportunities should be vigor-ously incorporated within Source-to-Sink.Graduate students are expected to participate

through the funded research activities. How-ever, special attempts should be made to ex-tend the terrestrial and marine research ef-forts to benefit younger and older scientists.Within NSF there are additional resources forundergraduate and post-graduate education.After an initial round of research is approved,plans will be developed for running under-graduate field camps for study of earth sur-face processes in conjunction with the re-search activities. Similarly, the opportunitywill exist for professional field trips (~2weeks) by interested scientists, especiallyuniversity professors and secondary educa-tors.

The MARGINS Office (currently at theWashington University in St. Louis) main-tains an active website (www.margins.wustl.edu) that can provide information de-scribing past, present, and future field pro-grams and experiments as well as access tothe existing databases. In this way both in-formation of future opportunities and exist-ing data can be accessed quickly, thus pro-viding “instant” communication betweengeomorphologists, marine geologists,stratigraphers, and modelers.

An NSF-sponsored program entitledDigital Library for Earth Systems Education(DLESE) is a web-based operation that pro-vides the basis by which many of the resultsby Source-to-Sink participants during thenext 10 years. Unique opportunities wouldbe dynamic figures, such as laboratory simu-lations of mass flows or time-series videoobservations of the seabed. This “text” wouldbe used for the field camps and field trips,and would be available to anybody throughthe web. Other means for dissemination ofresults include Theoretical and Experimen-tal Institutes (TEI), which are basically shortcourses. Regular sessions at national/inter-national meetings should be planned. And theMARGINS web site will receive materialsfrom Source-to-Sink studies.

Outreach

MARGINS Office

and website

DLESE

Theoretical

Institutes

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References

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