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Western Arctic Shelf-Basin Interactions (SBI) Project
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4/12/00 8 21-22 March 2000 Baltimore Inner Harbor, Maryland TUESDAY, 21 MARCH 2000-ALL DAY Day 1 of the Western Arctic SBI Principal Investigators (PI) meeting consisted of brief research overviews and updates by the SBI Phase I PIs. The following summaries outline these presentations, with abstracts available in the meeting books and posted as a pdf file on the SBI web page (http://www.utk-biogw.bio.utk.edu/SBI.nsf ). SUMMARIES FROM PRINCIPAL INVESTIGATORS Knut Aagaard discussed the mooring instrumentation in Bering Strait which measures, among other parameters, velocity, ice thickness, temperature and salinity. He mentioned that Kelly Falkner has an auto sampler for tracers on the mooring apparatus and that Terry Whitledge is planning to install an in situ nutrient analyzer. Some previous observations to date include data that suggest a temperature peak in 1997 which coincides with the coccolithophore take-over and a drop off around 1999. Additionally, there appears to be an annual increase in salinity in July-August from previous winter ice formation, with a gradual decrease in salinity from August to December due to subsequent summer ice melting. Some kind of peculiar salinity effect was taking place in 1991-1992 (lowest levels of decade). The main emphasis for Phase II is to keep monitoring going. Someone asked if the coastal currents were missed by the present monitoring scheme, to which Knut said yes, but there really isn't a large water flow. Is there a salinity memory? Big ice formation, but not all of it goes through the Bering Strait – local melting. Dave Chapman spoke about brine rejection from coastal polynyas and the development of small-scale eddies that carry the resulting dense water offshore. Local bathymetry and ambient currents over the shelf and slope strongly influence both eddy formation and subsequent cross-shelf transport. Ambient currents over the Chukchi Shelf tend to flow eastward and may sweep dense water towards Barrow Canyon. However, ambient currents also have a strong tendency to follow local isobaths which can greatly reduce the down-canyon flux of dense water. Dave and Glen Gawarkiewicz are continuing their numerical modeling studies to examine the processes by which dense water moves across and ultimately leaves the shelf, the water properties produced and the time-scales involved. Questions were raised about tracer studies, time of year for advection and how the interannual variability of the Bering Strait advection affects the Chukchi Sea.
Inflow ambient currents Where? Figure 1. Process modeling for understanding the influence of the Chukchi Sea. Al Plueddemann is investigating the distribution and properties of subsurface eddies found in the Beaufort Gyre. His group used autonomous drifting buoys outfitted with acoustic Doppler current profilers (ADCPs) to measure velocities from 50 m to 300 m depth. The goal is to provide estimates of physical characteristics and dynamical properties, which could be used to distinguish among possible eddy generation mechanisms. Although it appears that the eddies originate on the shelves, neither the generation process nor the mechanism of transporting shelf eddies into the basin is understood. Al is also interested in examining the spatial/vertical differences between anticyclonic vs. cyclonic eddies. Preliminary observations show that eddy encounters were indeed abundant during the buoy drifts, and many of the encounters are suitable for detailed analysis of eddy properties. Depth distribution, time series analysis and the fundamental properties of these eddies are the target of future research support. Jack Whitehead discussed his simulation of boundary currents in real oceans by using a rotating turntable filled with a soft stratified fluid. He slides in a false bottom and introduces salt water. He found there has to be turbulence in order to get the eddies to move off shore. The angle of the L-shaped source influences the level of turbulence and mixing. Then a plume of blue, saltier water is injected into the "lab ocean" and a cyclone (dipole?) movement was observed. It is this movement which draws the eddies off the coast. Any region that tends to have turbulence will see the eddies being swept off the coast. Otherwise, they tend to hug the coastline. Eddies always have a dipolar structure to their movement - cyclone (higher up in stratified region) and anti-cyclone (lower down) side by side. Knut Aagaard verified that he has seen this type of structure in the real setting. Rebbeca Woodgate talked about the Lomonosov Ridge and the pathway of ice/water transport coming out of the Barents Sea and the Atlantic layer. Time series data showed a sharp decrease in temperature and salinity (in the Atlantic layer) during '94-95 at all three mooring sites. It has been found that there was two times more ice that moved into the Barents Sea that year. As it was exported, the Atlantic layer became more cold and fresh. This big ice effect was also seen in 1969 and indirectly affected the conditions in the Beaufort Sea as well. Lots of discussion with several participants, especially about the Fram Strait. Tom Weingartner discussed SCICEX99 data (submarine cruise). A zigzag fashioned transect was followed across the slope at roughly 133m deep. Tom showed lots of transparencies depicting CTD data (primarily temperature and salinity). The westernmost station (west of Barrow Canyon) showed a halocline @ 125-150 meters and a thermocline @ 200 meters with 0.05 C water below that. The easternmost station (east of Barrow Canyon) showed a significant increase in fresh water and the 0.05 C water completely gone. The current structure was largely to the west at this station. A station just east of the Barrow Canyon showed a classic representation of an eddy area. There was a decrease in the amount of 0.05 C water and very strong counterflow off shore. In summary, it is recognized that there are very strong horizontal and vertical current sheers (changing 20 cm/sec) over the slope which lead to huge variability. The local buoyancy inputs also have effects. Wieslaw Maslowski and Ramsey Harcourt presented model results from basin-scale and Large Eddy Simulation models. Their results from the Pan-Arctic coupled model integration using the 18-km and 30-level grid forced with atmopsheric data for 1979-98 show realistic variability of the sea ice and the upper ocean circulation. This simulation indicates a reversing trend in the sea ice and ocean conditions in the late 1990s compared to that observed in the early 1990s. The Chukchi and Beaufort Seas are important part of this interannual variability. Such findings may help during planning and design of the field experiments during the Phase II of the SBI project. In addition, preliminary results from the 9-km and 45-level coupled model extending from the North Pacific through the Bering/Chukchi Sea and the Arctic Ocean into the North Atlantic have been discussed. They also reported progress with work involving LES modeling (small scale turbulence) with boundary conditions from basin-wide models. Maslowski's team wants to establish a web site where a description of model output and various results will be available and updated for viewing. All interested scientists will be able to download off this site. Knut Stamnes, from the Stevens Institute of Technology, discussed radiative transfer modeling. Stratospheric ozone and cloudiness are important factors influencing and affecting both UV and photosynthetically active radiation (PAR). Stamnes' group used a comprehensive radiative transfer model for the coupled atmosphere-sea ice-ocean (a-s-o) system to determine the radiation environment throughout the a-s-o column. The optical properties of snow were parameterized in terms of snow density and grain-size. Additionally, the optical properties of first-year and multi-year ice were based on detailed ice salinity and temperature measurements. David Kadko investigated the rate of exchange between the Arctic shelves and the Arctic Ocean interior through the use of an isotopic tracer technique. This technique utilizes two naturally occurring radium isotopes (228Ra/226Ra) to measure water column ratios. Since 228Ra only comes from the shelf sediments, it is the best tracer to recognize shelf waters. The decrease ratio of 228Ra/226Ra with distance from the shelf provides a measure of the transport time between the shelf and basin. Based on data calculated from the SHEBA project, the farther the waters are from nearshore regions, the lower the 228Ra/226Ra ratios. The R value for 228Ra/226Ra off the wider Chukchi shelf was in the intermediate range (compared to the narrow Barrow shelf), reflecting the longer/continued input from the underlying sediments. Glenn Cota's main objectives include gaining a better understanding of the mechanisms responsible for the regional/seasonal differences in productivity, to determine net trophic status of regions to evaluate the potential for shelf-basin exchange of organic materials, to establish benchmarks to assess environmental change and to provide validation data for coupled biophysical models in all phases. Additionally, he wishes to focus on hypotheses and research efforts in subsequent SBI phases. Both "top-down" and "bottom-up" approaches will or have been utilized to meet these objectives. The "top-down" approach helps define the available light for photosynthesis by phytoplankton and ice algae; the "bottom-up" model uses water column profiles to estimate seasonal productivity (total and new) and net community trophic status. Patricia Wheeler and Yvette Spitz shared data sets from 1994 AOS Arctic Ocean Section, two 1996 cruises, and SHEBA/JOIS results to describe lower trophic level pelagic dynamics. These data sets and a data assimilation scheme were used to adapt recent improvements to the Atlantic Time Series ecosystem model to the Chukchi Sea ecosystem. One initial focus is to pick parameters that illustrate the largest and most coherent spatial and temporal variations. Inorganic nutrients, particulate and dissolved carbon and nitrogen and chlorophyll were all measured parameters. Manuscripts are in the preparatory stages describing the distribution of these materials. The first step in developing the ecosystem model for the Chukchi Sea was based on the Spitz et al. model which incorporates the data in a one-dimensional manner. The Price et al. atmospheric forcing model was used to simulate vertical mixing. As the Chukchi ecosystem model is further developed, it will be extended for use in the Beaufort Sea. Sharon Smith gave an overview of data associated with her project and Nasseer Idrisi discussed the modeling aspects. Sharon reminded everyone that small-body and large-body organisms can impact the distribution of phytoplankton in the shelf-basin region. If small body organisms are dominant, then their grazing will drive the primary production towards a benthic rather than pelagic food web. When comparing two data sets:1950-51 and 1985-86, the warm years ('51 & '86) were dominated by plankton from the Bering Sea and Northern Pacific, while the cold years were dominated by Arctic Ocean species. These observations suggest the need to address interannual variability on a multiyear study basis and studies that cover small spatial/temporal scales. Nasseer Idrisi examined the life cycle of Calanus glacialis and asked two questions: What is the nature of advection onto and off of the shelf? What is the amount of energy available? and how to tie this all together with global climate change and how this would affect the status quo. He then went on to show models of copepod energy budgets during diapause and seasonal energetic requirements. In conclusion, diapausing individuals with high metabolic rates usually do not make it to the next growing season; diapausing individuals with low lipid content who survive to the next growing season probably produce cohorts that go through all life stages in one season and finally, a two-year life cycle requires more energy in a growing season than a one year life cycle. Ken Dunton's research team has designed and implemented a database of benthic habitat data using NODC data, along with other sources. The driving force behind this effort is to link patterns of benthic community structure and biomass in the Chukchi and Beaufort Seas to the physical and biological processes. A GIS software (ArcInfo and Arcview) is being used in the analysis of the temporal and spatial variations found in the benthic community structure and distribution. Additionally, a digital bathymetric base map has been generated onto which the benthic data have been plotted. A project web page is accessible at <http://www.utmsi.utexas.edu/staff/dunton>. The high benthic biomass concentrations are found in the Canadian Beaufort Sea, north of the Mackenzie River and in the Chukchi Sea, just north of the Bering Strait. In contrast, the biomass found along the nearshore of the Alaskan Beaufort Sea shelf is significantly lower. There is a strong correlation between where the marine mammal feeding grounds are and the area of high productivity of the overlying shelf waters. Rodger Harvey et al. are trying to identify the suite of molecular organic markers that can most efficiently track the fate of primary production in the Chukchi and Beaufort Seas. Surface sediments spanning the Arctic Ocean, particularly those collected during the 1994 AOS, are currently being analysed. This data set includes sites along the Chukchi shelf and slope where production predominates. The long-term, historical record of organic deposition can not be gleaned using these molecular markers; however, it is hoped that this procedure will offer a snapshop of the material transported over the underlying sediments. Markers representing diatoms, dinoflagellates, other phytoplankton, as well as higher trophic grazers have been observed. The concentration of phytol (a side-chain of chlorophyll a) is over 10-fold higher on the Chukchi shelf than other sites. Multivariate analysis will be used to target the appropriate suite of organic markers. Then, a historical examination of the downcore records will be studied to look at the long term record of organic inputs. Annelie Skoog has been studying the role of dissolved organic material (DOM) in the Arctic Ocean. DOM in the Arctic Ocean represents the highest concentration compared to any ocean basin, but is mostly unknown on the molecular level. Annelie intends to: 1) determine whether the high DOC levels in the Arctic Ocean include a higher concentration of biologically labile components than found in other oceans, 2) determine the relative biological lability of DOM from riverine inputs to the Arctic Ocean and compare that to DOM formed in situ, and 3) determine which biologically labile compounds in the Arctic have detectable concentrations in order to carry out microbial flux studies. Initial work would have to begin with developing a new method for determining organic acid analysis due to the current poor sensitivity and contamination problems. Ultimately, the combination of classic radiotracer studies and molecular level determinations will make it possible to estimate heterotrophic carbon demand and utilization. Fiona Mclaughlin et al. have been looking at how the upstream events and the far-field effects of the Barents Sea have influenced the Canada Basin waters from 1989-1995. Findings thus far conclude that the composition of the Canada Basin has indeed altered up to 1995 due to: 1) a decrease in Pacific-origin waters, 2) an increase of Atlantic-origin waters, and 3) a change of the Atlantic layer composition, with the Fram Strait Branch (FSB) being colder, fresher and more ventilated than previous years, and the Barents Sea Branch (BSB) being warmer, fresher and more ventilated than previous years. Studies indicate that a large amount of dense water left the shelf – being that the Barents Sea was 2 °C warmer in early 1989 than between 1988-89. These events coincided with atmospheric shift to increased cyclonic circulation in 1989. The effects of a large outflow of dense Barents Sea water were observed some 5000 km downstream in the Canada Basin where the BSB of the Atlantic layer had increased 20% by 1995. Two Arctic atmosphere-ocean modes have been hypothesized: Under the anticyclonic mode, the Arctic atmosphere circulation feed backs onto the Arctic Ocean circulation, causing a boundary current that is thinner and slower and an increase of freshwater export. Under the cyclonic mode, the Arctic atmosphere circulation feed backs on to the Arctic Ocean circulation, causing a boundary current that is thicker and faster and an increase of freshwater export. Dennis Darbys' preliminary results show the importance of examining multiple proxies in the Arctic sediment records in order to understand the environmental changes important to the SBI project. The analyses performed on four cores collected from the Chukchi shelf to the slope yield consistent results which suggest that, during the latest parts of the Holocene period, there was a cooling of the surface water (~7 °C to ~0 °C), and a seasonal sea-ice spreading from ~2 to >11 months per year. Further analysis of a Holocene sediment (core P1) collected on the shelf reveals sea-surface temperature oscillations with at least three warm excursions (>6º C) around 3, 5.5 and 6.5 kyrs BP. More radiocarbon dates will better constrain these events and determine whether they follow predictable climate cycles such as Dansgaard-Oeschger cycles. If so, these climatic cycles could provide the model for extrapolating SBI findings into the future. Other changes observed in the cores include benthic fauna changes (Mg/Ca ratios in ostracodes), organic C and N data, suggesting several excursions indicating the influx of fresh organic matter and evidence that hardly any organic matter input to the sediments occurred prior to the Holocene. The most remarkable aspect of the paleo-record are the large and rapid changes that have occurred in the Holocene of the western Arctic Ocean. These provide benchmarks for SBI Phase II findings. Thorsten Markus from NASA is using SSM/I data to monitor the opening and closing of coastal polynyas. A special algorithm is being used to estimate open water areas in the ice pack, as well areas of thin ice. This method of measurement is very important towards understanding dense water formations in coastal polynyas over the continental shelves. WEDNESDAY, 22 MARCH 2000-MORNING This part of the meeting included a discussion of the draft SBI Phase II implementation plan, with themes divided into three main components: physical, biogeochemical and biological. Knut Aagaard, Lou Codispoti and Ken Dunton, respectively, were asked to share a summary plan with the group. At the start of the morning session and prior to the discussion of the three disciplinary areas, Jackie Grebmeier gave an overview of the program. She reiterated what the focus of the SBI program was, commented on the suggested study areas/sampling sites, and briefly discussed the observational requirements, the potential field measurements, and the program's linkage with other disciplines. She also mentioned plans to hold a Pan-Arctic meeting in the Fall of 2000. As far as the time line is concerned, if Phase II is to begin with field studies by April 2002, then the AO has to go out by December 2000 (Mike Ledbetter said maybe by January 2001) for proposal funds to begin FY October 2001. Therefore, core data sets and/or spatial grids need to get out to web sites very soon or program could be delayed. Knut Aagaard pointed out that there are two "pipes" of through-flow through the Arctic Ocean, with about a 1-1.5 year transit for the waters to reach the interior. He commented that the framework of the current implementation plan provides a great deal of room for proposal writing. This is attractive on one hand; however, he is very concerned about the large responsibility this puts on the review process to sort through the variety of proposals. The discussions then went in the direction of how much time? Four sites for mooring placement have been identified with a desire to place another one at the westernmost point (in Russian waters). A five year time span for the field program appears appropriate, with synthesis time between major field efforts recommended. Lou Codispoti first provided a brief update of the OAII program (he is the new Chair) and congratulated Jackie for being appointed to the Arctic Research Commission. He emphasized that the terms arctic system and global change are included in the main objectives of OAII. SHEBA, SBI and SEARCH are part of OAII, with SEARCH evolving into its own entity. He pointed out that there are enormous amounts of changes going on in the Bering Sea, including coccolithophore blooms which have caused a shift in the lower trophic structure of the Bering Sea, massive die-offs of short-tail sheerwaters and about a 98% reduction in the nesting success rate of eider ducks. Similar to Knut, Lou is very concerned about the time-series events. How they are worded as the goals for this project will be very important. Many questions were raised to be dealt with primarily in the SCC meeting. Also, it was pointed out that there is a need for core measurements, with appropriate QA/QC for data quality. Ken Dunton summarized the biology components and spent time trying to identify the study areas on which we really needed to concentrate. The importance of sea ice cover to biological processes was also discussed. Sue Moore presented a brief overview of current marine mammal studies in the SBI area and topics for further work. After some limited discussion on the implementation plan, the meeting adjourned for transport to the USGC HEALY for lunch, then a short afternoon session in the ship's conference room, and ship tours. WEDNESDAY, 22 MARCH 2000-EARLY AFTERNOON SESSION ON THE HEALY So, what type of field program do we propose?. Various mooring sites were placed on the map, including Toshi Takizawa's JAMSTEC moorings, which would be available for biological sensor placement. Another suggested mooring site was in the high production zone (SE Chukchi Sea) or at Hanna Shoals. Eddy Carmack also labeled moorings that the Canadians have in place. The following comments/ideas were shared: 1. Terry Whitledge raised the question about more slope surveying. 2. Eddy Carmack suggested having a mooring at stn. A (ongoing time station) and a sediment trap at the polynya east of Mackenzie River. 3. Al Plueddemann, Tom Weingartner, Terry Whitledge, Robie Macdonald and Glenn Cota discussed back and forth the placement of instrumentation in or near the polynyas, the importance of polynyas in biological processes and the need to look at the impact of lateral sheers. 4. Annelie Skoog raised questions about a riverine placement of a mooring at MackenzieRiver. 5. Rodger Harvey said let's keep the influence of the Mackenzie River in mind and connect with the areas of high productivity. Contrasting the two different areas was what attracted him to the SBI project in the first place. 6. Eddy Carmack drew a box covering the region around the broad Mackenzie Canyon and the other canyon on the east side of the Mackenzie river (line C - repeat hydrography). 7. Paul Wassman suggested a focus on the typical markers of the Arctic Ocean – North of the box that Eddy drew (keep away from the exception to the rule)! Concentrate on the Beaufort Sea area; do routine work in the Bering-Chukchi Sea area. 8. Knut Aagaard asked something about the lagrangian measurements- tells about non-conservative processes and diffusion information; a very strongly advective system. 9. Al Plueddemann suggested it is criticial to instrument the bottom to look at the dense waters formed in the polynya zones, especially with the remote sensing capabilities presented to us. 10. Glen Gawarkiwicz is interested in the upwelling/downwelling processes around fast currents, and mentioned the importance of the lateral sheers: cross–shelf exchange dynamics are very sensitive to the sheers, because they can create eddies locally. 11. Igor Melnikov suggested moving the mooring placement just south of Wrangel Island. 12. Ken Dunton asked Eddy if his moorings were far enough east for sampling in the Beaufort Sea – need contrast with Bering-Chukchi system. 13. Knut Aagaard came back with comment that it all is a huge investment to do all the process work. 14. Igor Melnikov was asked about collaborative efforts with the Russians. 15. Knut Aagaard raised a question about dissolved oxygen and having time series for oxygen; he mentioned he thought there is a decreased O2 concentration as low as 16% in winter. 16. Jackie Grebmeier has found some purely anoxic sediments in the region (SE Chukchi Sea and Barrow Canyon), but they are transient. The overall discussion centered around the moorings acting as the skeleton of the program, with the body composed of seasonal and interannual survey and process studies. At this point, the meeting was adjourned for smaller group tours of the ship organized by Jim Swift. |