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ARCSS/SBI Phase III: Arctic Carbon Cycling and Shelf-Basin Dynamics (March 2006)
Preface: The purpose of this document is to provide the ARCSS Committee and scientific community at large an overview of the results of the community meetings (online, in person) that were used to develop this SBI Phase III synthesis and modeling draft plan for the SBI project.
This document includes: A. Overview statement, B. Overarching themes and questions, C.
Subthemes and questions, and D. Appendices: Appendix I. Key SBI findings, and II. Summary of science community input.
A. Overview Statement: The Pacific Water entering the Arctic through the Bering Strait
Gateway (BSG) has a major impact on the oceanography and productivity of western Arctic shelves and the Canada Basin, as well as far-field influence on the global meridional overturning circulation. The inflow of nutrient-rich Anadyr Water fuels intense biological productivity over the Bering, Chukchi, and Beaufort shelves, the most biologically productive regions in the
Arctic, and supports a rich food web of living resources and human populations. Biological processes over the shelf play a critical role in transforming these imported nutrients into organic matter, with important implications for regional carbon cycling and both regional and global carbon flux. Variation in heat flux through the BSG also appears to exert strong influence on ice cover in the Western Arctic, with large consequences on shelf/slope biological processes. The
Bering Strait inflow is, in turn, modulated by subarctic processes, such as Pacific- and Arcticborn storms and fresh water inputs to the Gulf of Alaska and Bering Sea. Recent observations suggest that this flow is undergoing unprecedented change and contributing to the significant reduction in ice-cover via increased northward fluxes of heat and buoyancy. Linkages between mid-to-high latitude climate processes with the BSG inflow and, in turn, the productivity and carbon cycle of western Arctic Shelves leads to a cascade of physical and biological dynamics affecting the entire Arctic system and beyond. Furthermore, the low salt content of the Pacific inflow restricts its depth range to upper layers where biological processes are the most intense, allowing it to make an important contribution to the Arctic Halocline. An understanding of the dynamics of these fundamental elements of the Arctic System and the strength of linkages between them is therefore vital to understanding the Arctic System as a whole. The importance of biological processes in mediating carbon transformation, cycling and flux in the western
Amerasian Arctic has become apparent through results of the SBI Phase I and II projects and coincident regional sampling by other national and international projects. Clearly, there exists a need to integrate our current knowledge of these major elements of the Arctic, broaden our understanding of the scope of their influence on overall Arctic System processes, and expand this integrated knowledge into a synthesis of the Arctic System.
B. Overarching Themes and Questions
1.
What are the important linkages between processes in the Western Arctic shelf-basin ecosystem(s) and the larger Arctic system? What are the ramifications for the global ocean and climate?
2. How will the large and interconnected changes recently observed in the western Arctic margins propagate through natural and human systems in the Arctic and subarctic? How do these recent changes compare to the past?

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3. How does climate variability over multiple time scales influence the coupled physical, chemical, and biological processes over Arctic shelf/basin systems? How do changes in these processes in turn influence the broader Arctic system?
C. Possible subthemes and questions: Change in the Physical and Biological System
1. Although the Western Arctic appears to play a disproportionately large role in the dynamics of pan-Arctic system, there is a growing need to integrate and synthesize data and processes linking climate forcing, element and heat fluxes through the Bering Strait
Gateway, and shelf/basin carbon cycling in the Western Arctic with the broader Arctic
System. Relevant studies might include:

What are the most significant and critical changes to the Arctic System documented in the modern data records?

What are the forcing connectivity by the atmosphere, land and ocean on shelf-basin exchange through a range of spatial and temporal scales?

What are the impacts of seasonal sea ice extent and its variability on high productivity ecosystems, circulation, and shelf-basin interactions?

How do shelf-basin and inter-basin exchanges communicate change over larger Arctic system scales?

How do the large and interconnected changes observed on the western Arctic shelf and margin affect and propagate through the larger Arctic and subarctic natural and human environment and how do they compare to past changes? and

How does climate variability over decadal to millennial scales influence oceanographic, biogeochemical, and biological processes over arctic shelf/basin systems, and how do these processes influence the broader Arctic System?
2. There is a dynamic barrier at the continental shelf/slope margin, resulting in sharp physical and biological gradients. Understanding the influence of the shelf break barrier on physical and biological processes is crucial for evaluating past system states and predicting future change impacts. Relevant studies might include:

What processes maintain the sharp gradient between the most productive shelves
(Chukchi shelf) adjacent to the least productive basin (Canada Basin) in the world’s ocean?

How are shelf transformation products (salt, nutrients, carbon, zooplankton) fluxed across the shelf break into the basin?

What processes on this productive shelf are critical for the tight benthic-pelagic coupling, which supports an incredible biomass of marine mammals that in turn are dependent upon by Native populations for their subsistence and cultural identity?

How are these processes similar/different to continental margins in other arctic regions and/or continental margins in other regions of the world’s oceans?

How will ongoing environmental changes modify the dynamic barrier between the shelf and basin?

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3. Variations in sea ice cover and thickness can initiate a local to system-wide cascade of changes in Arctic physical and biogeochemical processes that are influenced strongly by oceanographic and biological processes over western Arctic shelves. Relevant studies might include:

How will the timing and extent of predicted future changes impact carbon cycling of the
Arctic shelf system?

How will the Arctic system respond to ice retreat beyond the shelf break?

What is the strength and variability of the linkages between important environmental controls of the Arctic system (climate/physical oceanography) and ice cover, ocean biology and other elements of the Arctic system (other dimensions)?

How will these linkages change in the future?

What are the consequences for the Arctic system (carbon, climate, human resource use)?

How will increased natural resource exploitation in the region impact shelf and slope ecosystem dynamics?

How will an increased flux of heat through Bering Strait influence clathrate erosion?
4.
Changing climate may alter the dynamics of pelagic and benthic Arctic systems, with possible mode shifts in their structure and productivity. Relevant studies might include:

How do changes in carbon cycling and pelagic-benthic coupling in the Arctic system, driven by environmental change, influence the structure of Arctic food webs and the population dynamics of important producer and consumer groups?

How will these changes affect Native communities that depend on the current ecosystem state for their subsistence and cultural identity?

How will future climate warming affect the production and export of carbon in Arctic environments and the dynamics of Arctic biological communities?

How will bottom-up versus top-down controls of Arctic biological systems respond to changing Arctic ice and climatic conditions?

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APPENDICES
The following appendices provide a composite summary of material utilized in this draft SBI
Phase III Synthesis document. Appendix I is a summary of key findings from the SBI Phase I and II portions of the SBI Project that were generated during the final SBI PI meeting in
February 2006. Appendix II includes the tropics brought forward during the open science community (online and in person meetings) that were evaluated coincident with the recent findings of the SBI Project in order to draft suggestions for overarching themes and associated subthemes and questions for the SBI Phase III planning effort.
APPENDIX I: KEY SBI FINDINGS
A. Working Group-Physics and Tracer Chemistry
1.
Documenting the existence of the Pacific Water boundary current, which is dynamically trapped to the shelf break.
2.
Identifying different mechanisms of eddy formation from the boundary current, showing that the western Arctic is an “eddy factory” responsible for significant fluxes of mass and properties (nutrients, carbon, zooplankton).
3.
Quantifying Cross-shelf Property fluxes due to upwelling/downwelling.
4.
Revealing that the head of Barrow Canyon is a biological hotspot, with an efficient conduit to depth.
5.
Strong sediment/metabolism gradients vs. depth.
6.
Importance of heat advection for melting ice, rapid ice retreat and associated biological implications.
7.
First time detailed analysis of ice circulation in the western Arctic, documenting source and sink areas, and showing that ice rafting compensates for ablation.
8.
2001-2004 increase in transport, freshwater flux and heat flux through Bering Strait. The
2004 heat flux was the largest since records started.
9.
We are in the heart of a major climate shift where the Chukchi Sea seems to be transforming into another Bering Sea.
10.
DOC is conservative on the timescale of a relatively short residence time on the shelf but not conservative within the long gyre residence time of the Canada Basin.
11.
Identifying the key pathways of source waters for Barrow Canyon.
12.
Pacific-origin storms that veer northward from the Gulf of Alaska tend to excite upwelling along the continental slope of the western Arctic.
B. Working Group-Carbon and Tropic Interactions: Water column
1.
Sea ice algae provide a highly concentrated food source in spring.
2.
Sea-ice primary production and biomass is high on the shelf, low on the slope and basin.
3.
The increase of primary production during the season is driven by open water area, not sea surface temperature. Cloud cover plays a factor, although this is correlated to open water.
4.
In contrast to most ocean shelf systems, terrestrial carbon is an increasing component of the sediment organic carbon pool from shelf to basin.
5.
The microbial loop (DOM, bacteria) in shelf waters is weak and processes a relatively small fraction of primary production.

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6.
The high production over the Chukchi shelf, including ice and planktonic diatoms, either falls through the water column unconsumed to the benthos or, at the shelf break, is transported eastward along the shelf break in the prevailing currents or is transported by episodic physical mechanisms into the basin. The relative importance of these two physical pathways presently is not known.
7.
Episodic physical features can transport organic material (plankton, particulates, nutrients) offshore into the basin (eddies, filaments, jets, downwelling) or from the deep basin
(upwelling) onto the shelf both in canyons and along the shelf break. These processes may have important impacts on shelf and basin ecology and community composition (e.g., transport of large bodied copepods from the basin onto the shelves).
8.
Rates of mesozooplankton processes (e.g., reproduction, grazing) are enhanced in the upper slope environment, where shelf-derived and basin-derived zooplankton merge and where mesoscale physical processes (upwelling, eddies) are focused.
9.
Sea ice algae supports the planktonic food web in the spring and can be transported to the shelf beak region from the south for quite a distance.
10.
Heterotrophic protists are ubiquitous, at times have a high biomass, and are an important food resource for zooplankton both in shelf and basin waters.
11.
Heterotrophic protists may have significant grazing impacts on phytoplankton; grazing impacts of mesozooplankton on phytoplankton are minimal.
12.
Mesozooplankton grazing impact is primarily dependent on mesozooplankton biomass; however, prey preferences must be accounted for when calculating mesozooplankton grazing impacts on phytoplankton.
13.
Mesozooplankton prey preferences change seasonally, with microzooplankton preyed on preferentially during the summer and ice algae potentially important during spring.
C. Working Group-Carbon and Trophic Interactions: Sediments
1.
High sediment community oxygen consumption and nutrient release occurs on the shallow
Chukchi shelf under high production zones and at the head of Barrow Canyon.
2.
Barrow Canyon acts as a conduit for particulate organic carbon to move down slope further than in non-canyon regions.
3.
Sediment tracers (sediment oxygen uptake, Be-7, chlorophyll) indicate carbon entrained in down slope currents is moved offshore and then eastward mid-slope into the Beaufort Sea.
4.
New marine carbon utilized over shelf/slope; highest accumulation terrestrial carbon in basin sediments.
5.
Benthic chlorophyll (derived from ice algae?) comprises a large fraction of the POC pool assimilated by benthic fauna living in the Chukchi shelf.
6.
High C-13 depletion of fauna from the eastern Beaufort suggests that terrestrial sources of carbon are important in coastal food webs.
7.
Distinct differences in trophic structure are linked to water mass types; tight coupling between producers and consumers under Bering Shelf water versus wide range in isotopic signatures under Alaska Coastal Current (ACC) and Beaufort near-shore shelf water
8.
Early ice retreat in the Chukchi and increased prevalence of ACC waters on the Chukchi shelf could have profound consequences for benthic secondary production.
9.
Although sedimentary denitrification rates in the SBI region are moderately lower that productive temperate shelves, the very large shelf area to volume ratio of the Arctic Ocean allows denitrification to remove more nitrate from the water column than happens on other

4/14/20 6 shelves.
10.
Denitrification in the Arctic is significant term in the global marine combined budget.
11.
The large negative N* in waters of the western Arctic suggests strong potential limitation to export production and suggests denitrification would act as a negative feedback to climate induced increases in primary production.
12.
Microbial mineralization of allochthonous organic matter plays an important role in benthic food webs.
13.
A significant fraction (10–20%) of primary productivity is exported through the water column below 50 m, though not immediately consumed during benthic carbon respiration, or buried in shelf and slope sediments.
14.
Sinking biogenic particles and associated organic carbon produced over the shelf are largely retained in shelf sediments on seasonal and decadal time-scales, rather than exported to the slope and interior basin.
APPENDIX II: SUMMARY OF SCIENCE COMMUNITY INPUT
1.
SBI results have added step-function data availability for oceanographic and sea ice evaluations in the western Arctic Ocean.
2.
SBI synthesis provides an opportunity for inter-comparison of carbon currency types within production-transport-fate synthesis topics from marine, freshwater and sea ice projects (e.g.,
SBI, Freshwater Integration,SNACS, SASS; international, regional coincident projects with datasets:CASES, CHINARC, JWACS, RUSALCA
3.
There is a need for coupled biochemical/physical modeling of the Arctic Ocean ecosystem at seasonal to interdecadal scales; potential for prediction of scenarios of Arctic climate change and its effects on the Arctic Ocean ecosystem.
4.
SBI Phase III would produce syntheses from the regional to the entire Arctic and, in some cases, the entire global ecosystem in the context of SBI objectives.
5.
Results from the SBI Phase I and II data sets will be an important resource of western Arctic synthesis studies along with data from coincident field programs. Projects would examine broad scale implications of these results in order to develop a better systems understanding of shelf-basin interactions in the Arctic and its connection to global processes.
6.
SBI Phase III coincident with planning for shelf-basin exchange (SBE) studies via international AOSB/CLIC IPY efforts, SEARCH, ISAC and International Polar Year (2007-
2009), SBI synthesis efforts will be both timely in productivity and scope.
7.
What keeps the Shelf-Basin system poised for tight benthic-pelagic coupling?
8.
How does the timing and extent of predicted future changes impact carbon cycling of the
Arctic shelf system? Examples of predicted changes include reduced sea ice, increased freshwater fluxes, higher air and sea temperatures, longer growing seasons, and permafrost thaw. Consequences of such changes might impact: food web structure, food chain length,

4/14/20 7 trophic efficiency, sediment mineralization/sediment oxidation state, benthic biomass, and carbon export and sequestration.
9.
What processes maintain the sharp gradient between the most productive shelves adjacent to the least productive basin in the world’s ocean? How will ongoing environmental changes modify this gradient? Examples of mechanisms include physical processes, external physical forcing, food web structure and processing.
10.
Variation in ice cover and thickness, mediated by solar insolation and advected heat flux through the Bering Strait, initiates a local to system-wide cascade of changes in arctic oceanographic and biological processes. How do linkages between these (or other) important environmental controls of the arctic system vary with ice cover, ocean biology, and other elements of the arctic system (other dimensions) and how will these linkages be affected by future climate change?
11.
What is the strength of linkages between important environmental controls of the arctic system (climate/physical oceanography) with ice cover, ocean biology and other elements of the Arctic system (other dimensions) and how will these linkages change in the future?
12.
Changing climate may alter the dynamics of pelagic and benthic Arctic systems, with possible mode shifts in their structure and productivity. How will future climate warming affect the production and export of carbon in Arctic environments and the dynamics of arctic communities?
13.
How will the Arctic system respond to ice retreat beyond the shelf break?
14.
How will bottom-up versus top-down controls of Arctic biological systems respond to changing Arctic ice and climatic conditions.
15.
How do changes in carbon cycling and pelagic-benthic coupling in the Arctic system, driven by environmental change, influence the structure of Arctic food webs and the population dynamics of important producer and consumer groups?
16.
Arctic change will influence cycles: water, carbon and heat, which impact the Arctic system.
What questions can we put forward and answered with SBI and other available data sets related to the carbon cycle that will improve our understanding of the Arctic system, whether regionally, circum-arctic, or globally?
17.
Will our enhanced understanding of ice and physical margin dynamics through SBI data synthesis, along with other relevant data sets, enable us to evaluate the impact of future process changes on shelf-basin interactions that would feedback to the Arctic system?
18.
What are the broad scale impacts of a warming of the influx waters passing through Bering
Strait and the implications for the Arctic sea ice regime and ecosystems, including regional, central Arctic and downstream areas? How can Bering Strait inflow and downstream impacts influence global overturning circulation (climate, ecosystem, ocean-human interactions)?

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19.
Results from SBI have revealed that the shelf-edge boundary current in the Canada Basin is highly turbulent and subject to intense offshore flux of mass, nutrients, and other properties.
Are these processes generic to the entire Arctic boundary current, and what are the largescale ramifications for the ecosystem of the Arctic Ocean interior?
20.
How can observations in the western Amerasian Arctic collected during SBI and coincident studies be used for regional assessments and modeling of key forcing functions and system responses? Is it possible to expand this to a pan-Arctic perspective?
21.
Bioavailable DOM and POC are rapidly produced in shelf waters during spring and summer and some of this DOM/POC is transport to the basin. Through SBI studies we know that rates of utilization of DOM are relatively low in shelf waters compared to POC. Terrigenous
DOM discharged to the Arctic Ocean by rivers has a modern radiocarbon age and is abundant in shelf and polar surface waters. We need to understand the role of increased seawater temperature on carbon cycling in river and marine waters and the impact this will have on the Arctic Ocean carbon cycle.
22.
There are temporal differences in the contribution of photic zone metabolism to carbon fluxes in the SBI study area. How would perturbations that alter the frequency or duration of these contrasting modes of metabolic balance impact carbon sinks and sources in this region of the Arctic Ocean?
23.
What are the implications of such a modal shift on the Arctic carbon cycle?
24.
Increase seawater temperature could enhance both primary (plant) and secondary
(zooplankton, bacterial) production, thus enhanced water column cycling and limiting benthos, movement towards pelagic vs. benthic-dominated region in Amerasian Arctic with implications to higher trophic populations and human utilization.