CHAPTER 1. INTRODUCTION-DRAFT: UPDATE WITH KEY RESULTS FROM PAR CHAPTERS

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1 CHAPTER 1. INTRODUCTION-DRAFT: UPDATE WITH KEY RESULTS FROM PAR CHAPTERS Grebmeier, J.M. and W. Maslowski (eds) Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, Maryland USA INTRODUCTION The Pacific Arctic Region (PAR) Synthesis effort is a contribution of the Pacific Arctic Group (PAG) to the post-ipy legacy. PAG defines the Pacific sector of the Arctic as the marine area from the Northern Bering Sea into the Chukchi Sea and adjacent Seas, and extending into the deep basins of the Arctic Ocean, with model boundaries from Aleutian Island and deep Bering Sea northward to the Canada Basin. Objectives of the PAR Synthesis are to: 1. present results from research, observation and modeling activities related to the PAG area, both retrospective and IPY efforts 2. share information on current modeling activities covering the PAG synthesis area; work toward a shared modeling system 3. identify status trends, and major new findings and understanding of state and processes in the PAG area 4. using best available model projections, prepare hypotheses regarding the future evolution of the physics and biology of the region 5. prepare scientific conclusions and recommendations to guide future PAG science activities 6. specifically for the PAG region, identify critical marine components of a future Arctic Observing Network Elements of the PAR Syntheses that are important components witin this review include: The geographic area over which data is to be considered: Upstream (Bering Sea) to downstream (Chukchi Sea, portions East Siberian and Beaufort Sea, Canadian Arctic Archipelago, Arctic Ocean) The time period to be considered: Decades leading up to IPY, IPY, and build scenarios decades past IPY Science questions to be addressed by the synthesis and types of data to be included in the synthesis: Pacific-influenced Arctic system status and trends in atmosphere, sea ice, physical forcing, and biogeochemical/biological ecosystem response Linkage between observational data and modeling: Results from PAG Modeling/data fusion workshop and other chapters The products: Special book volume confirmed by Springer for PAG synthesis chapters and special science volumes. The scope: Synthesis through workshops and invited participants 1

2 Who the synthesis is endorsed by: IASC, AOSB, and the ICSU IPY project office as an IPY legacy effort Many successes have come out of the PAR Synthesis workshops to date. A PAR Modeling Workshop held in Sanya, China, in January 2008 resulted in a special issue of Chinese Journal of Polar Science, Vol.9, Additionally, a PAR Biology Workshop held in May 2009 in Seattle, WA, USA resulted in a feature article for EOS (May ) and 2 chapters for the Springer book in progress). Furthermore, a PAR Marine Carbon Cycling Workshop held in June 2009 in Xiamen, China resulted in development of a special issue Deep Sea-Research (in progress, Wei- Jun Cai et al.). In 2010, two orals sessions focusing on ecosystem change in the Pacific Arctic in relation to the Pan-Arctic system took place, one at the AGU Ocean Sciences Meeting in February and the other at the International Polar Year Conference in Oslo in June. The anticipated target groups were disciplinary and interdisciplinary Arctic marine scientists, from physical, biogeochemical and biological oceanographers to higher trophic organism specialists, as well as climate and ecosystem modelers. In both sessions the rooms were filled to over capacity. BACKGROUND Pacific water transiting across the wide Bering, Chukchi and the eastern portion of the East Siberian shelves, and western portion of the Beaufort Sea, is a major driving force for the physical structure, ice extent and thickness, productivity and carbon transport in the Ameriasian Arctic (Figure 1). There are key physical, biogeochemical, and biological oceanographic features that distinguish the Pacific Arctic Sector of the Arctic. These Pacific features have important implications for shelf productivity as well as shelf-basin exchange at the continental margins of these seas, including the influence that Pacific water has downstream and offshore within the upper halocline to the Arctic Basin proper and Canadian Arctic Archipelago. Although some shelf-slope processes are common to all Arctic marginal seas and slopes (e.g., ice formation, brine rejection, advection and eddy production for shelf-basin exchange), the Pacific signature is distinct in its large and small-scale impacts on the Arctic system compared to regions more influenced by the North Atlantic. In particular, the shallow nature of this key throughflow point for Pacific water into the Arctic acts as a valve that can regulate freshwater, heat and nutrient flow to downstream regions. 2

3 Physical Forcing and Hydrographic Dynamics in the Pacific Sector Figure 1. Pacific Arctic Region (PAR; red box), including Bering Strait continental shelf complex and the Canada Basin (CB). Pacificorigin surface waters (red arrows, high nutrients) are observed downstream in the Canada and Makarov Basins (MB), predominantly exiting through the Canadian Arctic Archipelago (CAA) to the North Atlantic Ocean. The Bering Strait continental shelf complex (northern Bering Sea, Bering Strait and northward to the continental margin) is a major gateway from the perspective of ocean, ice, freshwater, and nutrient fluxes, and atmospheric fluxes of heat and moisture (Cooper et al. 1997, Shimada et al. 2005, Woodgate and Aagaard 2005, Woodgate et al. 2005, 2010), as well as fluxes of biological organisms and organic carbon (Grebmeier 2003, Grebmeier et al. 2006, Walsh et al. 2004, 2009). Seasonal evaluation of time series measurements ( ) from the Bering Strait indicate annual variability in salinity (~31.9 to 33 psu), temperature (~-1.8 to 2.3 C), and transport (~0.4 to 1.2 Sv; Woodgate et al. 2005, 2010). Recently it has been determined that the freshwater flux in Bering Strait has been underestimated and should be revised upwards to ~2500 km 3 y -1 (Woodgate and Aagaard 2009?). This means that freshwater in Bering Strait provides ~40% of the total freshwater input to the Arctic Ocean (Woodgate and Aagaard 2005). The nutrient-rich Pacific waters transiting through the Bering Strait are transformed seasonally by oceanographic processes, with far reaching implications for Arctic halocline formation and basin dynamics. Changes in the freshwater flux may also potentially influence global climate systems via connectivity to meridional overturning water on the Atlantic side. Both winter and summer Pacific Water types play variable, yet distinct roles in the transport of heat, freshwater, nutrients, carbon, and biological organisms northwards through the Bering Strait. Shimada et al. (2001, 2005) showed that summer Pacific water is a source of heat to the Pacific Arctic Sector, and it is particularly significant over the Chukchi Borderland. Winter Pacific water is influenced by ice formation and brine rejection, so the timing, extent and location of these processes are intimately tied to halocline formation. The Pacific Arctic Sector is experiencing the greatest seasonal retreat and thinning of sea ice in the Arctic, with September 2007 being the highest sea ice retreat on record (Stroeve et al. 2007). Changes in sea ice formation and thickness influence albedo feedback, brine formation and halocline maintenance, so ice-ocean-atmospheric dynamics are extremely critical for regulating 3

4 climatic conditions in the Arctic, with global ramifications. Recent anomalous spring and summer productivity on the northern Bering Sea shelf has been related to decadal-scale atmospheric/sea ice/oceanographic processes, which may also reflect regime-induced climate changes in the western Arctic (Stabeno and Overland 2001, Overland and Stabeno 2004). These authors report the Bering Sea is shifting to an earlier spring transition based on ice melt and changes in atmospheric circulation patterns. Since changes in the North Pacific Ocean show no long-term non-cyclic trends while the Arctic Oscillation appears to be responding more clearly to changing climate signals, the shallow and dynamic Bering Strait region and adjacent seas are a key location to monitor ecosystem change. Arctic systems can be rich and diverse habitats for marine life in spite of the extreme cold environment. Biogeochemical cycling processes and biological communities are directly influenced by changing sea ice extent, seawater hydrography (nutrients, salinity, temperature, currents), and water column production. The earlier sea ice melt timing and retreat in the Bering Sea and western Arctic will have dramatic impacts on the biological system, such as changes in overlying primary production, carbon transformation, pelagic-benthic coupling, and benthic production and community structure that can have cascading effects to higher trophic levels. For example, recent indicators of contemporary Arctic change in the northern Bering Sea include seawater warming and a reduction in ice extent. Time-series observations indicate a coincident decline in bottom-dwelling clam populations and diving seaducks over the last few decades (Grebmeier and Cooper 2004). In addition, decline in benthic amphipod populations in the Chirikov Basin just south of Bering Strait has likely influenced the movement of migrating gray whales to feeding areas north of Bering Strait during this time period (Moore et al. 2003). Key physiographic aspects of the shelf-slope region of the East Siberian, Chukchi and Beaufort Seas influence shelf-basin exchange and Herald Valley/Canyon and Barrow Canyon are key conduits for transformed Pacific water and associated organisms that transit to the deep Arctic Basin. Eddy formation, boundary current dynamics, and advection are some of the critical transport mechanisms at the shelf-basin interface that facilitate the transfer of salt, heat, nutrients, and various forms of carbon that dictate the current state of the Arctic. Recent findings show increased northward heatflow within the Atlantic water transiting through Fram Strait into the deep Arctic Basin (Schauer et al. 2004), which may induce warmer Atlantic water to move upward at the continental margins of the Chukchi and Beaufort seas. These apparent changes that are being observed in the oceanographic and ice system in this region could lead to dramatic impacts for higher-trophic level fauna, including benthic-feeding animals such as walrus, bearded seals, and gray whales, and pelagic-feeding bowhead and beluga whales that are of cultural and subsistence significance to Arctic Native peoples. High levels of CO 2 have been observed under the winter ice covered, shallow East Siberian Sea shelf, where coastal erosion and biogeochemical transformations have been observed (Semiletov et al. 2004). Retreating sea ice and warming temperature have increased coastline erosion of terrigenous materials into the coastal environment. An increased seasonal open water period in the Arctic will allow an increased wind fetch, thus increasing shoreline retreat. The subsequent input of old, land-produced carbon into the ocean could increase microbial transformation processes as well as dilute the labile marine carbon pool with less-usable terrigenous material, with a potential negative impact on food availability to marine organisms. The cycling of carbon 4

5 (particulate, dissolved, inorganic) is a key concern in these extremely productive regions of the Arctic. Changes in these processes will have cascading impacts to all components of the ecosystem (bacteria to man). Ocean acidification is a potential, large-scale negative impact on the Arctic marine carbon system since increased atmospheric C02 will influence the buffering and corrosive capactity of seawater. Future Challenge The Pacific Arctic Sector is currently experiencing the largest regional changes in Arctic sea ice extent and thickness. A challenge to both the modeling and observational community is to develop workable scenarios to investigate: 1) How will changes in the valve dynamics of the Bering Strait continental shelf complex affect downstream Arctic ecosystems?, 2) Will changes in the timing and extent of ice formation influence halocline formation and thickness, and if so, what are the ramifications of a reduction in the density gradients across the halocline?, 3) Will an increase in freshwater and heat flux via Pacific water flowing through Bering Strait move the Pacific Arctic Region (PAR) to a new stable state and what ramifications would this have for the influence of nutrients, heat, and freshwater on near-field (Pacific sector) ecosystems and downstream (Canadian Archipelago and Arctic basin) ecosystems?, and 4) How will physical and biogeochemical fluxes vary in the Pacific Arctic Region in concert with lower latitude climate variability and change? A key outcome of the PAG modeling/data fusion workshop would be to identify the distinct drivers and responders to change in this region, and to evaluate the downstream impacts on the Arctic system, including its connectivity to the world ocean. Early season ice retreat influences timing of spring bloom and associated lower trophic level consumption of organic carbon that has cascading effects to benthos and higher trophic organisms. There are indications of increased freshwater flux and summer seawater temperatures, both that influence biological processes, and changes in the timing of productivity over shelf and slope regions will rapidly impact trophic structure and carbon transport from shelf to basin. Open ice areas will allow for biological expansion, e.g., fisheries movement northward in Bering Sea, although potential negative impact on benthic-feeding marine mammals and subsistence lifestyle resource exploration and development, e.g., increased oil and gas development in northern Chukchi Sea. There is a need to evaluate whether observed changes are due to climate warming or natural variability need time-series data at select areas of the ecosystem need for standard measurements over a spatial scale to evaluate significance of warming climate and reduced ice extent on biological systems. Need for time-series studies of biological system, currently very limited Incomplete data sets for identifying biological parameters for evaluating change data mining needed for retrospective studies, although with caveat on the quality of available data for comparative studies Implications of changing ice conditions for ecosystems of reduced ice extent could either enhance primary production due to more open areas vs. limit production due to increased wind mixing and reduced stratification possible step-function ecosystem change from one set of species to another, with no way to return to cold-dominated system; resulting in change in carbon cycling northward movement of subarctic-arctic front and associated biological component expansion; enhanced competition increase pelagic-system northward to detriment of benthic 5

6 communities, with potentially negative impact on benthic-feeding marine mammals reduction in ice-associated marine mammal species would have a direction, negative impact on Native subsistence lifestyle in the Arctic References Cooper, L.W., T.T. Whitledge, J.M. Grebmeier, and T. Weingartner (1997), Nutrient, salinity and stable oxygen isotope composition of Bering and Chukchi Sea in and around the Bering Strait. J. Geophy. Res., 102, 12,563-12,574. Grebmeier, J.M. (2003), The Western Arctic Shelf Basin Interactions Project, in The Arctic Research of the United States, National Science Foundation, Vol. 17: Grebmeier, J.M., and L.W. Cooper (2004), Biological Implications of Arctic Change, in Arctic Climate Impact Assessment, Extended Abstracts. Arctic Monitoring and Assessment Programme, Reykjavik, ISBN Also available at Overland, J.E., and P.J. Stabeno (2004), Is the Climate of the Bering Sea Warming and Affecting the Ecosystem? Eos, Trans, 85, Moore, S.E., J.M. Grebmeier, and J.R.Davies (2003), Gray whale distribution relative to forage habitat in the northern Bering Sea: Current conditions and retrospective summary, Can. J. Zool., 81, doi: /z03-043, Schauer, U., E. Farbach, S. Osterhaus, and G. Rohardt (2004), Journal Of Geophysical Research, 109, C06026, doi: /2003jc Semiletov, I.A. Makshtas, and S. Akasofu, E. Andreas (2004), Atmospheric CO 2 balance: The role of Arctic sea ice, Geophys. Res. Letters, 31, L05121, doi: /2003gl Shimada, K., E.C. Carmack, K. Hatakeyama, and T. Takizawa (2001), Varieties of shallow temperature maximum waters in the western Canadian Basin of the Arctic Ocean, Geophys. Res. Lett., 28, 3,441-3,444. Shimada, K., M. Itoh, S. Nishino, F. McLaughlin, E. Carmack, and A. Proshutinsky (2005), Halocline structure in the Canada Basin of the Arctic Ocean, Geophys. Res. Lett., 32, L03605, doi: /2004grl Stabeno, P J., and J.E.Overland (2001), Bering Sea shifts toward an earlier spring transition, Eos,Trans.,AGU,82, 317, 321. Stroeve, J. C., M.C. Serreze, F. Fetterer, T. Arbetter, W. Meier, J. Maslanik, and K. Knowles (2005), Tracking the Arctic s shrinking ice cover: Another extreme September minimum in 2004, Geophys. Res. Lett., 32, L04501, doi: /2004gl Stroeve et al Walsh, J.J., D. A. Dieterle, W. Maslowski, and T.E. Whitledge (2004), Decadal shifts in biophysical forcing of Arctic marine food webs: Numerical consequences, J. Gephys. Res., 109, C05031, doi: /2003jc Woodgate, R. A., and K. Aagaard (2005), Revising the Bering Strait freshwater flux into the Arctic Ocean, Geophys. Res. Lett., 32, L02602, doi: /2004gl Woodgate, R.A., K. Aagaard, and T.J. Weingartner (2005), Monthly temperature, salinity, and transport variability of the Bering Strait throughflow, Geophys. Res. Lett., 32, No. 4, L /2004GL021880, Woodgate et al