The Source-to-Sink initiative within MARGINS seeks to advance our predictive capability of sediment and solute fluxes and their fates on the Earth's continental margins. Improved predictions are necessary because this transfer plays a key role in the cycling of elements such as carbon in ecosystems impacted by climate change and sea-level rise, and in the resource management of soils, wetlands, groundwater, and hydrocarbons. At present we cannot anticipate how perturbations in one part of the source-to-sink system will affect another. A quantitative answer, clearly involving modeling, has practical as well as scientific justification. Would, for example, a 50% increase in sediment yield over the next century reverse coastal zone erosion, or would sediment be sequestered on floodplains, thereby increasing up-river flood risk? Would the increased sediment yields from a large earthquake in an upper watershed increase down-stream sedimentation (silting in, for example, shipping channels), and if so, over what duration? And what is the signature of such events in the stratal record?
The key scientific issues impeding better predictive capabilities for the source-to-sink system were identified at two MARGINS Source-to-Sink Workshops and a MARGINS Workshop convened to explore the concept of a Community Sediment Modeling Environment. The scientific issues are contained within three questions:
Question 1: How do tectonics, climate, sea level fluctuations, and other forcing parameters regulate the production, transfer, and storage of sediments and solutes from their sources to their sinks?
Question 2: What processes initiate erosion and sediment transfer, and how are these processes linked through feedbacks?
Question 3: How do variations in sediment processes and fluxes and longer term variations such as tectonics and sea level build the stratigraphic record to create a history of global change?
Methods of Studying S2S Processes:
Based on the workshops and considerable follow-up correspondence, community consensus agreed that S2S studies at selected sites should include:
- Assessment of available data and their suitability for building first-order computational and physical models;
- Field investigation of sediment production, transport and accumulation, and associated mechanics and rates;
- Second-order model building/testing to illuminate mechanisms of sediment transport and stratigraphy generation under various controls;
- Stratigraphic documentation at appropriate spatial resolution to provide desired temporal resolution;
- Monitoring and modeling of active processes are examples of work that should occur throughout the course of the proposed studies. For more detailed information about methods and new technologies, see the Science Plan pages 138 through 143.
(See Science Plans, page 143)
Critical Site Criteria:
- Strong forcing (e.g., heavy rainfall, frequent storms) that produce strong signatures
- Active sediment transfer among environments within a generally closed system
- High resolution stratigraphic record, ideally of some extended duration
- Sufficient background data to allow the formulation of an optimal integrated systems study
- Local scientific infrastructure that permits access to the entire study area
Also desirable would be:
- Analogs with ancient sedimentary environments
- Presence of carbonate environments, in at least one case
- Societal relevance from documentation of the impact of anthropogenic activity on the environments
- Significant differences between the two sites
Source-to-Sink considered more than 20 sites, and selected two active convergent continental margins that produce large amounts of sediment deposited in adjacent, closed basins. Following community-wide discussions, the Fly River and adjacent Gulf of Papua (Papua New Guinea) and the Waipaoa River System on the east coast of New Zealand's North Island were chosen for focused research for the following reasons:
1. Fly River and adjacent Gulf of Papua (Papua New Guinea)
- One of the few modern examples of a developing foreland basin
- Tropical environment
- Mixed siliciclastic and carbonate sedimentary environments
- Relatively constant discharge, with main perturbations linked to ENSO-related droughts
- Practically unaffected by human activity, although recent mining on the Ok Tedi has provided a sediment chemical “spike” that can be monitored farther downstream
2. Waipaoa River System on the east coast of New Zealand's North Island
- Waipaoa drainage basin reflects growth of a terrain by volcanism and vertical uplift
- Sub-tropical/temperate climate
- Predominantly siliciclastic sediments
- Strongly affected by seasonal variations in discharge and (particularly) by tropical cyclones
- For the past 100 years the watershed has been strongly impacted by European land-use and—to a lesser extent—by dam construction
Workshops and Theoretical Earth Institutes (TEIs):
Funding for S2S Science has supported four organizational workshops, with a TEI anticipated for September, 2005). The past workshops were:
- S2S Organizational Meeting I. A four-day meeting organized by Neal Driscoll and Charles Nittrouer and funded by NSF and JOI was held at Lake Quinault, WA, on Sept 28-October 1, 1999 to create the S2S science plan.
- S2S Organizational Meeting II. A follow-up meeting was organized by Driscoll and Nittrouer at Lake Tahoe, on September 11-15, 2000, to gather more community input for the S2S science plan.
- S2S Community Sedimentary Model Science Plan. A two day workshop was organized by James Syvitski, et al., on February 20-22, 2002, to outline a strategy and protocol for constructing a community sediment model (CSM) as part of S2S.
- MARGINS Workshop On The Waipaoa Source-to-Sink Focus Area. A workshop for approximately 40 scientists was organized by Steve Kuehl, on May 4-9, 2003, to provide a synopsis of what is known about the system, what needs to be monitored, and to develop an implementation plan for research.
Major Research Activities - Funded Projects:
The following S2S research projects have been NSF funded to date
(proposal start dates in parentheses) from MARGINS and MARGINS-related
panels. They are all in the Papua New Guinea focus area because it was
& Milliman (October, 2003) and Slingerland
(October, 2003): “Collaborative Research: Developing a
Quantitative Understanding of Clinoform Formation, Gulf of Papua”
- Droxler (November, 2003), Bentley
(November, 2003), and Peterson (November, 2003):
“Collaborative Research: Late Quaternary
Siliciclastic and Carbonate Sediments and Sediment Fluxes on the Slopes
and Basin floors of the Ashmore and Pandora Troughs, Gulf of PNG”
(July, 2002), Nittrouer
(July, 2002), and Parker (July, 2002): “Collaborative
Research: Processes Controlling
Depositional Signals of Environmental Change in the Fly River Sediment
Dispersal system: Rates and Mechanisms of Floodplain Deposition”
(MARGINS-related; October, 2002): “Global and Local Controls on
Depositional Cyclicity: Canterbury Basin, New Zealand”
(August, 2001): “MARGINS: Community Sedimentary Model Science Plan for
Sedimentology and Stratigraphy”
Intellectual Progress During MARGINS:
- Pb and Ag from mining activities provide tracers for examining rates of floodplain deposition on the Middle Fly and Strickland Rivers. Preliminary analysis of Pb and Ag in 500 core samples collected in June 2003 from the Strickland floodplain suggests deposition rates approaching 1 cm/yr on the floodplain within one channel width either side of the river.
- Two models of river channel-floodplain co-evolution have been developed to examine storage and removal of sediment from the floodplain. One model shows how feedback between floodplain erosion and deposition drives the system toward an equilibrium state. The other—more detailed model—predicts channel bed and floodplain response to changes in sediment load.
- On margins adjacent to tropical rivers exhibiting low seasonal variability of discharge (e.g., Fly River), variations in marine processes associated with monsoon and tradewind fluctuations appear to control variability in sediment dispersal.
- Sedimentary structures and radioisotopic profiles in Gulf of Papua (GoP) clinoform foreset deposits suggest that fluid mud transport and deposition are taking place.
- Intense reworking of these shallow clinoform topsets by tides and waves, particularly during tradewind conditions, impacts the diagenetic geochemistry of the seabed, allowing intense oxidation of carbon.
- Deep across-shelf channels provide a pathway for removal of sediment and associated carbon from the GoP clinoform topset and an alternative means of cross-shelf sediment dispersal.
- Preliminary analysis of core and CHIRP data reveal two distinct stratigraphic units in the Gulf of Papua foreland basin. On the inner shelf is a modern clinoform that appears to be active. Buried on the middle shelf is a thick sequence of horizontal strata that is being interpreted as an older clinoform that prograded across the shelf in response to relative sea-level rise at a time when tectonic subsidence exceeded eustatic sea-level fall (isotope stage 3 and possibly 4).
- Despite evidence for reworking of shallow parts of the clinoform, deeper parts of the older clinoform appear largely intact, suggesting that these features may make their way into the permanent stratigraphic record.
- Northern Ashmore Trough is a tropical mixed siliciclastic/carbonate system with significant terrigenous inputs, even at present-day. Siliciclastic material comes from rivers discharging on to the GOP shelf. A line of bioherms forming an incipient reef system strongly control the flux of clastics to the trough as a function of sea level.
Map (PDF) prepared by the MARGINS Office, showing the available information on where work has been funded to date in the Gulf of Papua focus area. (Click map for a larger version with explanatory caption.)
Map (PDF) prepared by the MARGINS Office, showing the available information on where work has been funded to date in the Waipaoa focus area. (Click map for a larger version with explanatory caption.)
Major Research Gaps:
Although much of the fieldwork for the Gulf of Papua project has only just begun, and MARGINS funding for the New Zealand project does not begin until FY 2005, we already can identify a number of future research needs:
- To calculate a source-to-sink budget for the Fly River, we need to quantify the sediment storage in the floodplains and subaerial delta. From the confluence of the Fly and Strickland rivers (at Ogwa, 6 m above sea level), it is nearly 450 km to the river mouth. Even a very conservative estimate of sediment accumulation across the delta would suggest that a considerable portion of the Fly's annual sediment load (estimated at Ogwa) may be deposited prior to reaching the ocean. Detailed coring and boring is required, some of which already has been done by PNG scientists and engineers. We are presently attempting to gain access to PNG's own data files.
- In both study areas it is critical to understand the temporal variations in fluvial discharge and sediment loads since the last glacial maximum, say post-20ka BP. Initially the Fly River was assumed to be relatively unaffected by human activities, whereas the Waipaoa has felt significant European impact in the past 100+ years. There has been emerging evidence, however, that suggests that the runoff and sediment yield of both watersheds may have been affected by much earlier deforestation and crop cultivation. Some of the earlier shifts in sediment delivery may also reflect climate change, but the data at present are too scarce for us to separate natural from anthropogenic. To address questions concerned with temporal variations in the source, future work should include lake and floodplain boring and coring. The former could address temporal variations in erosion (presumably with both climatic and anthropogenic signals), whereas the latter could quantify the floodplain and delta storage of sediment.
impact of events, both meteorological and geological, needs to be
understood in terms of both the source—how does a drainage basin and
the river draining it respond to an event?— and the sink—how is the
sedimentary architecture impacted by various types of events? The
events can be either meteorological (e.g., storms, ENSO cycles) or
geological (earthquakes, volcanic eruptions), both of which are
known to have affected both the Fly and Waipaoa watersheds.
also needs to be renewed attention on the outer shelf and upper slope;
the transition zone between what—in the absence of shelf subsidence—often represents temporary storage on the shelf and more permanent
storage on the continental slope and rise. Critical in this, of course,
is regional sea-level history, which therefore also involves
paleoclimatologic research (see above). The study of the upper-lower
margin transition ideally could lead to shallow drilling, perhaps
involving cooperation with the Integrated Ocean Drilling Program.
Collaboration and Outreach:
Interdisciplinary scientific research in remote areas requires a broad range of collaborations. These have been forthcoming in both focus areas.
Papua New Guinea
The Gulf of Papua study, for example, involves collaboration with Drs. Robert Aller (SUNY, Stony Brook) and Miguel Goni (University of South Carolina), who are working, respectively, on the early diagenesis and carbon fluxes to the clinoform. We also have benefited greatly from previous and present collaboration with a number of Australian scientists, most notably Drs. Peter Harris (GeoScience, Hobart) and Gregg Brunskill (AIMS, Townsville).
At the same time, we have had an ever-increasing interaction with Papuan scientists and students. To date more than 20 have been on one or more legs of our various cruises, and several have spent periods of time in the United States. In at least one case a PNG scientist (Sioni Sioni, UPNG) will be a lead author on a talk presented at Fall AGU. Below is a list of Papua New Guineans who have participated in the program:
University of Papua New Guinea, Department of Geology:
Hugh Davies, Sioni Sioni, Russell Perembo, Marie Bera, Tina Apami, Jack Atomo, Don Bibaesi, Louisa Dira, Honoria Homu, Rellie Inia, Allan Ila, Alu Ila, Susan John, Magdaline Kepo, Fritz Koroba, Gabriel Laim, Paul Lale, Sarowaget Menggenang, Oala Rarua, Ora Renagi, Deveni Temu, and Ramsey Yehimen
Geological Survey of Papua New Guinea:
Jason Elemunop and James Mokepwesi
As part of the recent Gulf of Papua cruises, there were outreach broadcasts from the ship to a network of middle-school and junior-high school classrooms, in which students had the opportunity to ask scientists (including graduate students) a multitude of questions, ranging from scientific methods to career opportunities. In addition, there were several live broadcasts in which shipboard scientists talked directly with citizen groups around southern California.
Although MARGINS funding for the Waipaoa focus-site study has just begun, already there has been a fruitful collaboration between U.S. and New Zealand land-based and marine scientists. In contrast to Papua New Guinea, considerably more background data have been gathered by NZ researchers. More than 20 years of monitoring of the Waipaoa River by New Zealand scientists, for example, has given us a reasonably good understanding of annual and interannual cycles as well as some idea as to floodplain sedimentation. The Waipaoa 2003 planning workshop noted above included 40 scientists, roughly half each from the U.S. and NZ, including: geomorphologists, geologists, oceanographers, geochemists and hydrologists.
S2S Presentations and Publications:
(Proposal start dates in parentheses)
Milliman, Slingerland, Walsh & Babcock
(October, 2003): “Collaborative Research: Developing a Quantitative
Understanding of Clinoform Formation, Gulf of Papua”
(July, 2002): “Collaborative Research - Processes Controlling
Depositional Signals of Environmental Change in the Fly River Sediment
Dispersal system: Rates and Mechanisms of Floodplain Deposition”
Ogston & Sternberg (July, 2002): “Processes
Controlling Depositional Signals of
Environmental Change in the Fly River Sediment Dispersal System:
Mechanisms and Rates of Shelf Clinoform Development”
(October, 2002): “Global and Local Controls on Depositional Cyclicity:
Canterbury Basin, New Zealand”
Paola & Slingerland (August, 2001): “Margins: Community Sedimentary Model Science Plan for Sedimentology and Stratigraphy”