OS41A-0450 0800h
Atlantic Water Seasonal Variability on the Continental Slope of the Laptev Sea
Due to the scarcity of observations, knowledge of circulation, water-mass transformations and exchanges occurring across the continental slope of the Siberian Arctic remains sketchy, and understanding of water dynamics is correspondingly crude. Here, we present our preliminary analysis of observational data obtained from the Laptev Sea continental slope in 2002-2003. The water properties were evaluated using year-long records of water temperature and salinity from the mooring deployed in September 2002 about 200 km northward from the continental shelf brake. CTD surveys from several cruises (1993, 1995, 1996, 2002, 2003 years) were also employed in this analysis. The focus of this study is the seasonal cycle found in the intermediate (150-800m) Atlantic Water layer of the Arctic Ocean. Increase of the Atlantic Water temperature was observed during the cold period whereas during summer months the records show cooling of the layer. We found a strong connection between these cooling and warming events and direction of winds over the slope. Wintertime prevailing off-slope winds cause shift of the warm core of the Atlantic Water towards the slope, and the mooring record indicated warming. Summertime along-slope winds resulted in separation of the Atlantic Water warm core from the slope and decrease of the recorded temperature. These results support the earlier theory by Goodkovich (1961).
http://www.frontier.iarc.uaf.edu/NABOS/
OS41A-0451 0800h
Anisotropic Continuum Model of Granulated Sea Ice
A continuum model describing sea ice as a layer of granulated thick ice intersected by long and narrow regions of thinner ice, leads, is developed. Sea ice is considered to be a two-dimensional granular material, whose deformation occurs through motion of floes generated in ice fracturing under applied stress. We consider dynamics of mesoscale leads generated under tensile stress, whose dimensions is larger than those of floes, so that deformation of the surrounding ice is described through the granular plastic rheology, but still sufficiently smaller than the basin scale, so that they can be modelled using continuum approach. The model consists of the stress expression depending on orientational distribution of lead characteristics, thick ice thickness and rheology. It also includes evolution equations for the orientational distribution of leads, their thickness and width expressed through second-rank tensors. The results of the calculations show that the model produces reasonable behaviour in simple flows. The consideration of the thick ice as granular material elliminates the problem of infinite lead opening under pure shear produced by an earlier model considering thick ice deformation only through ridging.
OS41A-0452 0800h
Annual cycle of dense water cascading in the north-eastern Barents Sea
Dense water cascading, which moves cold and/or salty water down the continental slope, is an efficient way of communication between the coastal and the deep ocean. In the Arctic with respect to its extensive shelf waters, annual freeze-thaw cycle and associated salination and freshening the contribution by cascading in ventilation of the deep water masses was always considered to be remarkably high. Despite this fact comprehensive physical descriptions of the Arctic cascades are extremely rare, due to intermittent nature of the process and complexity of launching winter surveys in the darkness of the Polar Night. The present analysis is based on the recently publicized oceanographic archives, containing oceanographic measurements in 1970-1980s, when the Barents Sea was repeatedly sampled by Russian research vessels in the framework of extended field studies of the Arctic Ocean. Piecing together oceanographic observations in various seasons allowed reconstructing the annual cycle of dense water cascading in this area in connection with causative physical processes. Shelf water attains required for cascading potential by the end of December due to topographic control mechanism, which provides faster cooling in the shallow waters. Early winter cascades originate over the shelf of Novaya Zemlya Archipelago (40-60 m depth). They are driven by temperature, although salination caused by ice formation in the coastal zone, its offshore drift and melting in the warm deep water are critical. Throughout the winter vertically homogeneous source water grows saltier and spreads over deeper areas, including isolated banks, thus providing cold and salty cascades. Active ice formation in the north-eastern Barents Sea terminates in the end of April. By this time, newly formed bottom water fills adjacent bottom depressions. However, significant portion of winter-origin water is still accumulated over shoals. The fate of this water mainly depends on the depth of the productive area. If it is deeper than the lower bound of the seasonal pycnocline, cascading is observed throughout summer and fall in the shape of dense plumes gradually sliding down slope. Model estimations give 7 months as a typical time of complete removal of dense water from the Novaya Zemlya Bank (150 m depth) in the course of cascading. This result is confirmed by the late fall survey demonstrating the remnants of a cascading plume near the seabed separated by the warm water from the developing convective cell near the sea surface.
OS41A-0453 0800h
Wind-forced Interannual Variability of the East-Siberian Sea Hydrography
The East-Siberian Sea (ESS) is situated on the middle of the Siberian Arctic shelf within the zero vorticity contour, separated two predominant large-scale centers of the atmospheric circulation over the Arctic Ocean. This unique position makes ESS hydrography extremely sensitive to the variation of atmospheric vorticity. It provides the basic motivation for revision of historical hydrographic records (1957-2000) from the Laptev and the East Siberian seas in order to evaluate its response to the lager-scale atmospheric circulation patterns. It have been shown that cyclonic atmospheric circulation results in ESS salinity increase due to salty water input from the Chukchi Sea. The Kolyma and Indigirka river runoff plume is forced to move eastward to the New Siberian Islands and the Laptev Sea. Anticyclonic circulation induces Lena River runoff influx into the ESS and redistribution of freshened water further westward along the Siberian coastline. The high correlation between interannual variations of ESS summer salinity and atmosphere vorticity index (0.60 for surface and 0.74 for bottom water layer) have been obtained. For the winter period it is also surprisingly high (0.75 and 0.66) though the land fast ice covers the significant part of the ESS. It allows to speculate that atmospheric forcing appears to be the dominant driver of the East-Siberian Sea hydrography. During winter the land fast ice cover appears to be an effective medium for vertical momentum transfer from the atmosphere into the upper ocean. Apparently the energy flux from the atmosphere to the water through the fast ice provides sufficient forcing to drive winter hydrography interannual variability.
OS41A-0454 0800h
Hydrographic variations of the Pacific Waters in the Canadian Basin
Hydrographic variations of the Pacific Waters in the Canadian Basin are investigated using available CTD and XCTD data sets, SSMI ice concentration, and climatological data (EWG Arctic Ocean Atlas series). Here we focus on the variation of water mass properties of Pacific origin. Pacific Summer Water (PSW), Pacific Winter Water (PWW) and Atlantic Water (AW) are centered at S=31.3psu, 33.1psu respectively. After 1990, temperature of the Pacific Summer Water has been increased about 1.0 degree Celsius per decade. On the other hand the temperature of PWW has been dropped about 0.15 degree Celsius per decade. This negative correlation between PSW and PWW suggested that some dynamical mechanism controls the coherent variability. The variations of PSW and PWW well correlate with the time series of wintertime Arctic Oscillation (AO) index. Positive (negative) AO index corresponds to strengthening (weakening) of Beaufort High (BH). Strong BH enhances the oceanic Beaufort Gyre and leads the increase of northward advection of PSW in the western Canada Basin (Chukchi Borderland: CBL). Consequently large amount of PSW spreads from CBL into the central Canada Basin. Strong easterly associated with strong BH blows the sea ice along the Alaskan Coast in the Chukchi Sea, and activates the formation of coastal polynya between the Point Barrow and Cape Lisburne. Pacific Winter Water via the Alaskan Coast into the Canada Basin is cooled and salinized in the coastal polynya. Consequently, the temperature of PWW in the Canada Basin decreases and the salinity of PWW increases. The salinization in the Canada Basin due to PWW variation causes a deepening of isohaline, suggesting enhancement of baroclinic component of oceanic Beaufort Gyre.
http://www.jamstec.go.jp/arctic/
OS41A-0455 0800h
Circulation in the Landfast Ice Zone of the Alaskan Beaufort Sea
We present 3 years of ADCP and temperature, salinity, and transmissivity data collected year-round on the inner shelf (10 m depth) of the Alaskan Beaufort Sea. The results capture the variable circulation dynamics and water properties induced by seasonal changes in landfast ice and the pulse-like nature of arctic river discharges. An immobile lid of landfast ice, extending from the coast to the 25 m isobath, covers the inner shelf from October - June. When ice is present, currents are along-shore polarized, weak ($<$5 cm/s; but sometimes $>$10 cm/s) and uncorrelated with regional winds. Time-varying along-shore pressure gradients of O(10$^{-7}$) of unknown origin are implied. During the spring river freshet, a highly sheared and strongly stratified under-ice plume spreads offshore at O(10 cm/s) and is accompanied by rapid settling of terrestrial sediments. After ice breakup, swift ($>$25 cm/s) along-shore flows dominate that are correlated with the winds, and accompanied by implied along-shore pressure gradients of O(10$^{-6}$). These currents re-suspend and disperse the sediment load that settled out during the spring freshet. In contrast to earlier results, the mean flow here is negligible, implying a negligible mean along-shore pressure gradient. Our results suggest little cross-shore exchange between the landfast ice zone and the outer shelf in winter and raise questions regarding the role of landfast ice on frictional control of the under-ice circulation and the spreading of under-ice river plumes.
OS41A-0456 0800h
Ocean Circulation and Exchanges Through the Northern Bering Sea - 1979-2001 Model Results
Quantification of ocean circulation and water mass properties in the northern Bering Sea presents several challenges to both modelers and observationalists because of the large, shallow shelf and the relatively high flux of water northward through Bering Strait. We have developed a model with sufficiently high resolution ($\sim$9km) and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in this region. Ocean circulation throughout the Bering Sea is highly variable seasonally, interannually, and possibily interdecadally. However, comparison of model results with observations indicates that it is also responsive to short-term events, such as one occurring during the winter of 2001 with reversed flow in some areas and much reduced sea ice cover. In addition, the modeled vertical water column structure in the northern Bering Sea gives insight into the transport of water northward through Bering Strait into the Chukchi and Beaufort Seas. We compare model output in the Bering Strait region to a time series of moored observations of water mass properties. Eddy kinetic energy fields identify similar regions of the northern Bering Sea for high energy throughout the annual cycle. By comparison, even during autumn and winter when there is sea ice present, the deeper water column maintains high velocity and eddy kinetic energy, while the middle shelf of the Bering Sea is considerably less energetic. Comparison with shipboard observations of near-bottom salinity from late winter through autumn indicates that the model is reasonably representing the major water mass properties in the region. Primary production on the northern Bering shelves is strongly dependent on nutrient sources upwelled from the deep Bering Sea. Using EKE fields and salinity as a proxy for nutrient concentration below the mixed layer, we attempt to identify regions of high primary production.
OS41A-0457 0800h
Hydrographic Properties in the Bering and Chukchi Seas in the 1999 Summer and Their Comparisons with Climatology
Hydrographic Properties in the Bering and Chukchi Seas in the 1999 Summer and Their Comparisons with Climatology Jiancheng Kang 1) and Xiangdong Zhang2) 1) Polar Research Institute of China, Shanghai 200129, China 2) International Arctic Research Center, University of Alaska Fairbanks, AK99775, USA Correspondence should be addressed to Jiancheng KANG (email: kangjc@sh163.net, kangjc@126.com ) Abstract It has been detected that the high latitude climate system, including ocean, sea-ice and atmosphere, is undergoing remarkable changes. However, hydrographic data in this region is very limited. In July and August 1999, the Chinese Ice-breaker "Xuelong" took a cruise to the Bering and Chukchi Seas, which supplies us an opportunity to examine hydrographic status in the 1999 summer and possible changes of the ocean relative to climatology in this region. Measurements of hydrographic properties, including temperature and salinity, were acquired by the CDT, XCDT and XBT systems. Chemical tracers, such as silicate, phosphate and nitrate, are also obtained simultaneously during the cruise. We made objective analyses of these datasets through quality control and interpolations. The analyzed data shows distinct thermohaline structures between the Bering Sea and the Chukchi Sea and the T-S diagram presents properties of different water masses in these two seas. A notable interesting finding by the comparison of the 1999 cruise data with the climatology is that the temperature in the upper 50m in the Bering Sea decreased and the salinity in the same layers in the Chukchi Sea increased. To verify robustness and explore mechanisms of such hydrographic changes, we planned a continuing collection and analysis of observation data in this region. Keywords: Ocean Hydrographic Climatology, Bering Sea, Chukchi Sea
OS41A-0458 0800h
Horizontal and vertical distribution of freshwater in the Arctic Ocean deduced from historical hydrochemistry
Historical data (1935-2002) of two chemical tracers, oxygen isotope ratio and alkalinity, are combined and freshwater sources of sea ice meltwater (SIM), and other freshwater (OF) are distinguished from each pair of two conservative elements, salinity-oxygen isotope and salinity-alkalinity. The OF consists of mainly river runoff, with addition of precipitation and salinity deficit of inflowing Pacific water. Results give at first startling pictures of both horizontal and vertical distributions of freshwaters from the two designated sources almost throughout the Arctic Ocean. River water sources in Canada Basin: Distribution of OF at the 10 depth shows that river water from the Russian shelf seas flows out of the shelf between the Mendeleyev and the Lomonosov Ridges and exits thorough western part of the Fram Strait. Part of this freshwater enters into the Canadian Basin, where water contains large amount of OF but small fraction of American river water. This may suggest that river water from American continent should exit from the basin relatively fast though the Canadian Archipelago. Vertical mixing of fresh water: The atmospheric cooling and brine rejection during winter converts fresh surface water into denser water with high OF and negative SIM signals. High inventories of both OF and negative SIM, which implies mixing with brine, are found in the Canadian Basin, Baffin Bay and east of Novaya Zemlya in the Kara Sea. These signals in the Kara Sea and the Baffin Bay show occurrence of deep convection in winter, whereas those in the Canadian Basin come from adjacent shallow shelves. In the Canadian Basin, negative SIM distribution is well corresponding to the low temperature layer between surface and Atlantic origin waters. This layer characterized by nutrient maximum with a salinity of about 33.1 and is found to form from the water having salinity of 31-32. Our analysis advocates the importance of shelf water from the East Siberian Sea on formation of water mass in this layer. The shelf water vertically transports both OF and brine from the surface to the deeper layer and accumulates in the Canadian Basin. We appreciate Drs. Murata and Shimada of JAMSTEC for providing unpublished data from the past Arctic expeditions by R/V Mirai.
OS41A-0459 0800h
The Future of the USCG Icebreaker Fleet
The United States Coast Guard (USCG) operates three icebreakers to support science in polar regions: the USCGC HEALY (WAGB-20), the USCGC POLAR STAR (WABG-10) and the USCGC POLAR SEA (WAGB-11). USCGC HEALY, the youngest of the icebreakers, has successfully completed four field seasons in the Arctic Ocean and one deployment to Antarctica since the ship was delivered in late 1999. Operations on board HEALY have improved with each deployment thanks to the feedback provided by science users and the responsiveness of USCG personnel to suggestions for enhancing shipboard support of data and sample acquisition. The POLAR-class icebreakers have been used primarily to support Deep Freeze by carrying supplies to McMurdo Station in Antarctica. Unfortunately, both POLAR STAR and SEA are approaching the end of their useful service life. The main propulsion system of the POLAR SEA has recently been declared unfit to support another trip to Antarctica until at least the 2007 field season, which places an additional burden on the already ailing POLAR STAR and potentially impacts the arctic science schedule of HEALY. The Arctic Icebreaker Coordinating Committee (AICC), which was initially formed to oversee the design and building of the USCGC Healy, now works to liaise and facilitate communications between scientists, funding agencies and facility providers and assist with the planning of polar science projects. Incumbent in this is the requirement that AICC provide continuing oversight for scientific aspects of the potential refitting or replacement of POLAR STAR and POLAR SEA as well as HEALY's scientific spaces and outfitting. The purpose of this presentation is to provide the polar science community with the most recent information about the status of the USCG icebreaker fleet and to solicit, synthesize and present the needs of the community to the Coast Guard to facilitate efficient and effective utilization of U.S. icebreakers.
http://www.unols.org/aicc/
OS41A-0460 0800h
The conservative and non-conservative properties of DOM in the Beaufort Sea
The Beaufort Sea is strongly influenced by the Mackenzie River, which annually discharges large amounts of dissolved organic matter (DOM) to the western Arctic Ocean. We have evidence from water samples collected in 2002 that DOM from the Mackenzie River may be consumed such that DOM behaves non-conservatively up to a salinity of 20 in the Beaufort Sea. Experimental evidence showed that Mackenzie River DOM is highly susceptible to photochemical degradation and we have calculated rates of DOM oxidation and photobleaching. These rates provide upper estimates on the turnover of terrigenous organic carbon in the Beaufort Sea. A possible mechanism is presented that suggests residence time in the surface waters of the Beaufort Gyre as the mechanism by which Mackenzie River DOM may be removed.
OS41A-0461 0800h
Climate Shifts in an Arctic Fjord: Intense Seasonality through Cross-Shelf Exchange
Debate over Arctic climate has focussed on the relative balance between Atlantic, Arctic and fresh water in a system. It is anticipated, and in many cases observed, that the magnitude of each of these sources will vary in time and location. Depending on where the balance lies, a region may become more `Atlantic' (warm and salty) or more `Arctic' (cold and fresh). The impact of this shift in oceanic conditions will have undoubted impact on regional climate, ecosystem structure and biogeochemical cycling. Further, instances of this shift may be recorded in Arctic sediment records providing a palaeo-record of local ocean conditions. In this paper we look at the mechanisms, magnitude and the regional significance of Atlantic Water intrusions into Kongsfjord on the west coast of Spitsbergen. Data from a long-duration, multi-parameter mooring and a database of CTDs are supplemented with model output from the Bergen Ocean Model. On the West Spitsbergen shelf, cold water of Arctic origin lies between the mouth of the fjord and the northward flowing Atlantic water in the West Spitsbergen Current. Common to high-latitude fjords, Kongsfjorden has high freshwater input from glacial melt and experiences seasonality in the sea-ice cover, wind forcing and precipitation. Consequently, the region is an oceanic system that balances Atlantic, Arctic and fresh water. We show that the intrusion of Atlantic origin water into Kongsfjorden occurs rapidly in early summer causing massive changes in the local hydrography of the fjord. In essence, the fjord flips from being an Arctic fjord to an Atlantic fjord. Exchange across the shelf is shown to be through geostrophic control rather than the more usual hydraulic control. This exchange may also be an important sink for heat transported north in the West Spitsbergen Current. Historic data indicate that the hydrographic switch can be to one that is either strongly or weakly Atlantic - i.e. a `cold' state or a `warm' state. Consequently, Kongsfjorden is an ideal site for studying and monitoring change in the Arctic Marine Environment.
http://www.sams.ac.uk
OS41A-0462 0800h
The Northern Bering Sea: An Arctic Ecosystem in Change
Arctic systems can be rich and diverse habitats for marine life in spite of the extreme cold environment. Benthic faunal populations and associated biogeochemical cycling processes are influenced by sea-ice extent, seawater hydrography (nutrients, salinity, temperature, currents), and water column production. Benthic organisms on the Arctic shelves and margins are long-term integrators of overlying water column processes. Because these organisms have adapted to living at cold extremes, it is reasonable to expect that these communities will be among the most susceptible to climate warming. Recent observations show that Arctic sea ice in the North American Arctic is melting and retreating northward earlier in the season and the timing of these events can have dramatic impacts on the biological system. Changes in overlying primary production, pelagic-benthic coupling, and benthic production and community structure can have cascading effects to higher trophic levels, particularly benthic feeders such as walruses, gray whales, and diving seaducks. Recent indicators of contemporary Arctic change in the northern Bering Sea include seawater warming and reduction in ice extent that coincide with our time-series studies of benthic clam population declines in the shallow northern Bering shelf in the 1990's. In addition, declines in benthic amphipod populations have also likely influenced the movement of feeding gray whales to areas north of Bering Strait during this same time period. Finally a potential consequence of seawater warming and reduced ice extent in the northern Bering Sea could be the northward movement of bottom feeding fish currently in the southern Bering Sea that prey on benthic fauna. This would increase the feeding pressure on the benthic prey base and enhance competition for this food source for benthic-feeding marine mammals and seabirds. This presentation will outline recent biological changes observed in the northern Bering Sea ecosystem as documented in a 20-yr environmental time-series in the Bering Strait region.
http://arctic.bio.utk.edu
OS41A-0463 0800h
Observed Changes at the Surface of the Arctic Ocean
The Arctic has long been considered a harbinger of global climate change since simulations with global climate models predict that if the concentration of CO2 in the atmosphere doubles, the Arctic would warm by more than 5°C, compared to a warming of 2°C for subpolar regions (Manabe et al., 1991). And indeed, studies of the observational records show polar amplification of the warming trends (e.g. Serreze and Francis, 2004). These temperature trends are accompanied by myriad concurrent changes in Arctic climate. One of the first indicators of Arctic climate change was found by Walsh et al. (1996) using sea level pressure (SLP) data from the International Arctic Buoy Programme (IABP, http://iabp.apl.washington.edu). In this study, they showed that SLP over the Arctic Ocean decreased by over 4 hPa from 1979 - 1994. The decreases in SLP (winds) over the Arctic Ocean, forced changes in the circulation of sea ice and the surface ocean currents such that the Beaufort Gyre is reduced in size and speed (e.g. Rigor et al., 2002). Data from the IABP has also been assimilated into the global surface air temperature (SAT) climatologies (e.g. Jones et al. 1999), and the IABP SAT analysis shows that the temperature trends noted over land extend out over the Arctic Ocean. Specifically, Rigor et al. (2000) found warming trends in SAT over the Arctic Ocean during winter and spring, with values as high as 2°C/decade in the eastern Arctic during spring. It should be noted that many of the changes in Arctic climate were first observed or explained using data from the IABP. The observations from IABP have been one of the cornerstones for environmental forecasting and studies of climate and climate change. These changes have a profound impact on wildlife and people. Many species and cultures depend on the sea ice for habitat and subsistence. Thus, monitoring the Arctic Ocean is crucial not only for our ability to detect climate change, but also to improve our understanding of the Arctic and global climate system, and for forecasting weather and sea ice conditions. The IABP provides the longest continuing record of observations for the Arctic Ocean.
http://iabp.apl.washington.edu
OS41A-0464 0800h
The North Pole Environmental Observatory: A Community Resource for Tracking Change in the Arctic Marine Environment
The North Pole Environmental Observatory (NPEO) was first established in 2000 as means of long-term tracking of change in the central Arctic Basin. The multiple investigators of NPEO intend the site to provide information and field research opportunities to a broad range of investigators. It is not limited to a single location, but is a distributed observatory consisting of three parts: an automated drifting station installed near the Pole that samples air-ice-ocean conditions as it drifts across the Amundsen and Nansen basins to Fram Strait, a deep ocean mooring approximately 25 km from the Pole; and repeated airborne hydrographic surveys that track changes along key sections radiating from the Pole. The North Pole region is sensitive to a changing Arctic climate. In the 1990's hydrographic data gathered in the area showed a strong increase in upper ocean salinity associated with a more cyclonic Arctic Ocean circulation. They also showed a large increase in Atlantic Water temperatures at depth. The decrease in sea ice thickness up through the `90s has also been apparent at the Pole. Hydrographic measurements made by the NPEO have shown that the conditions since 2000 have tended to relax toward pre-1990 climatology but that the changes still partly persist, particularly at deeper depths. The moored records from the first three years show both multi-year trends and rapid changes. These suggest a close connection of the interior ocean that overlies the abyssal plain with the boundary current that rings the Eurasian Basin. Atmospheric and ice measurements show a mix of 1990s like conditions and a return to climatology. For example, while 2003 shows a minimum ice extent in the Beaufort Sea, the North Pole region had a particularly cold summer. NPEO is scheduled to continue through 2008 and we hope this presentation will encourage other investigators to take advantage of the opportunities it provides. The automated drifting station and its installation provide opportunities for others to test new instrument designs and automated platforms in the presence of a wealth of background observations at minimal incremental logistics cost. The North Pole mooring provides a unique view of the Arctic Ocean from the surface to the sea floor. The array is well suited for additional instrumentation that will broaden that view, including measurements from other disciplines. The hydrographic sections provide opportunities for added sampling and drifting buoy deployments. We make data from NPEO available to the research community available as rapidly as possible.
http://psc.apl.washington.edu/northpole/index.html
OS41A-0465 0800h
Dissolved Oxygen Extrema in the Arctic Ocean Halocline from the North Pole to the Lincoln Sea
Dissolved oxygen profiling by new generation sensors was conducted in the Arctic Ocean via aircraft during May 2003 as part of the North Pole Environmental Observatory (NPEO) and Freshwater Switchyard (SWYD) projects. At stations extending from the North Pole to the Lincoln Sea north of Ellesmere Island, such profiles display what appear to be various oxgyen maxima (with concentrations 70 percent of saturation or less) over depths of 70 to 110 m in the halocline, corresponding to salinity and temperature ranges of 33.3-33.9 and -1.7 to -1.5 deg C. The features appear to be widely distributed: Similar features based on bottle data were recently reported for a subset of the1997-1998 SHEBA stations in the southern Canada Basin and in recent Beaufort Sea sensor profiles. Oxygen sensor data from the August 2002 Chukchi Borderlands (CBL) and 1994 Arctic Ocean Section (AOS) projects suggest that such features arise from interleaving of shelf-derived, oxygen depleted waters. This generates apparent oxygen maxima in Arctic basin profiles that would otherwise trend more smoothly from surface near-saturation at the surface to lower concentrations at depth. For example, in the Eurasian Basin, relatively low oxygen concentrations are observed at salinities of about 34.2 and 34.7. The less saline variant is identified as part of the lower halocline, a layer originally demarcated by a Eurasian Basin minimum in "NO", reinforced by additional inputs in the Canada Basin. The more saline and thus denser variant appears to arise from transformations of Atlantic source waters over the Barents and/or Kara shelves. Other low-oxygen waters are generated in the vicinity of the Chukchi Borderlands, from Pacific shelf water outflows that mix into Eurasian waters that entered the Makarov Basin over the Lomonosov Ridge. One such input is associated with the well-known silicate maximum that historically has been associated with a salinity of about 33.1. Above that (32-33 salinity range), there is a layer moderately elevated in temperature (summer Bering Sea water) that we show is also oxygen depleted. We propose that these low oxygen waters influence the NPEO and SWYD profiles to varying extents in a manner reflective of the large-scale circulation. The patterns of halocline circulation we infer from the intrusive features defy a simple boundary-following cyclonic flow. These results demonstrate the value of the improved resolution made feasible with continuous oxygen profiling. In the drive to better understand variability and change in the Arctic Ocean, deployment of appropriately calibrated CTDO packages offers the promise of important new insights into circulation and ecosystem function.
OS41A-0466 0800h
Intensification of the Atlantic Deep Circulation by the Canadian Archipelago Throughflow
In the northern high latitudes, where deep water formation occurs, horizontal freshwater transport in the form of seawater and sea ice is a major component of the freshwater budget. The horizontal freshwater transport controls the surface salinity in this region, and thus has a significant impact on the deep water formation process and the resultant Atlantic deep circulation. In this study, we focus on the freshwater transport through the Canadian Archipelago, and investigate how the intensity of the Atlantic deep circulation depend on opening and closing of the Canadian Archipelago. An ice-ocean coupled model is used; it consists of the oceanic component COCO3 (CCSR Ocean Component Model version 3) and the sea ice component including dynamics and thermodynamics. The horizontal resolution is 1 degree. Restoring surface salinity to observed data is not employed. When the Canadian Archipelago is opened, the Atlantic deep circulation strengthens by 21 %. The deep water formation in the northern North Atlantic is responsible for the enhancement. The flow of a low salinity water through the Canadian Archipelago does not directly affect the deep water formation in the northern North Atlantic, since it flows only in the western part of the Labrador Sea. The confinement of the flow in the western Labrador Sea is caused by the reproduction of the cyclonic circulation there. Instead, the surface salinity in the deep water formation region is affected by the East Greenland Current, which flows from the Fram Strait along the east coast of Greenland and increases its salinity by opening the Canadian Archipelago. Consequently, the deep water formation is activated there and the Atlantic deep circulation strengthens. Thus, it is suggested that the Canadian Archipelago throughflow does not directly suppress the deep water formation in the northern North Atlantic, but indirectly activate it by the increase in salinity of the East Greenland Current.
OS41A-0467 0800h
An Autonomous Network Measuring Changes in the Thickness of the Arctic Sea Ice Cover
Recent observational and modeling studies indicate that the Arctic sea ice cover is undergoing significant climate-induced changes, affecting both its extent and thickness. The thickness, or more precisely, the mass balance of the ice cover is a key climate change indicator, since it is an integrator of both the surface heat budget and the ocean heat flux. Accordingly, efforts are underway to develop and deploy autonomous systems designed to observe changes in the mass balance of the ice cover. We are in the early stages of deploying a network of autonomous ice mass balance buoys (IMB). An IMB buoy consists of sensors to measure snow accumulation and ablation, ice growth and melt, and internal ice temperature plus a satellite transmitter. In some cases a Web cam is added allowing the evolution of surface conditions to be observed. IMB buoys have been deployed each spring during the past five years from the North Pole Environmental Observatory and in several other areas including a few in the Beaufort Sea and Central Basin. Preliminary observations indicate that there is significant regional and interannual variability in the mass balance, with considerable differences in ice growth, as well as the relative amounts of surface and bottom ablation. North Pole buoys have recorded significant interannual variability in surface ablation, with values ranging from 5 to 35 cm. Results from the Beaufort Sea show year to year variations in bottom melt of 25 to 60 cm. Data from autonomous IMB buoys will be integrated with other in situ observations, satellite remote sensing information, and numerical modeling results to provide a comprehensive picture of changes to the Arctic sea ice cover.
OS41A-0468 0800h
Seasonal and Interannual Variability of the Arctic Ocean Upwelling
Ekman layer transport in the Arctic Ocean is a main mechanism for redistributing fresh water in the upper Arctic Ocean. Its divergence, i.e., upwelling, is an important process for heat and salt fluxes to the surface mixed layer. The daily Ekman layer transport and the upwelling field in the Arctic Ocean have been calculated by using both satellite and buoy data from 1978 to the present. The upwelling varies profoundly over the whole Arctic Basin on the seasonal time scale. In the Beaufort Sea in the winter season, there are strong offshore transport and upwelling along the shelf regions and downwelling in the interior region. The winter upwelling field was reversed in the summer. This seasonal cycle appears to explain an unexpected seasonal salinity variation in the upper Beaufort Sea in 1996-98 when IOEB buoy data showed that the salinity was maximum in the summer and minimum in the winter. The upwelling field also varies significantly on interannual and decadal time scales in response to changes in the atmosphere and ice motion. Such low-frequency changes affect the heat and salt flux to the mixed layer and the hydrographic structure, including the state of the Arctic halocline.
OS41A-0469 0800h
Weekly to Interannual Variations of Sea-Ice Draft at the North Pole Environmental Observatory
A 2-year time series of sea-ice draft D(t) was estimated from measurements made by Upward Looking Sonars (ULS) from 10 April, 2001 to 21 April, 2003. The moorings were located at the North Pole Environmental Observatory (NPEO: 89.56 N, 66.65 E in year 1; 89.45 N, 53.63 E in year 2). Sample statistics and probability density distributions (PDFs) of D(t) have been estimated by grouping the data in nonoverlapping, two-week intervals with probability weighting proportional to the ice speed recorded simultaneously by an Acoustic Doppler Current Profiler (ADCP). In the first year the sample mean draft varied from 3.7 meters in early April to 2.3 meters in late August, with an overall annual mean of 3.0 meters. The sample mean draft estimated for 15 September, 2001 is 2.3 meters, a value near the middle of the seasonally adjusted estimates derived from submarine sonar profiles near the North Pole in the 1990's (Rothrock, et al., 1999). The evolution of modal draft in year 1 lags behind the sample mean, with extrema of 2.3 meters in late June, 2001 and 1.6 meters in early January, 2002. The open water fraction (OWF), estimated by counting ice drafts smaller than .05 meters, exceeded 1 percent from mid-June to early October, and for a brief period in late December. The maximum OWF of 13 percent occurred in July, 2001. The mean ice draft was larger throughout most of the second year, especially in summer. The sample mean ice draft for 15 September, 2002 is 3.2 meters, i.e. 90 cm greater than in the preceding year, and just outside the envelope of the Rothrock values for the 1990's. Analysis of the ice draft time series, monthly mean maps of multiyear ice concentration estimated from SSM/I data, and monthly mean anomaly maps of sea level pressure suggests that ice advection played a major role in these interannual differences.
OS41A-0470 0800h
Arctic Logistics Information and Support: ALIAS
The ALIAS web site is a gateway to logistics information for arctic research, funded by the U.S. National Science Foundation, and created and maintained by the Arctic Research Consortium of the United States (ARCUS). ALIAS supports the collaborative development and efficient use of all arctic logistics resources. It presents information from a searchable database, including both arctic terrestrial resources and arctic-capable research vessels, on a circumpolar scale. With this encompassing scope, ALIAS is uniquely valuable as a tool to promote and facilitate international collaboration between researchers, which is of increasing importance for vessel-based research due to the high cost and limited number of platforms. Users of the web site can identify vessels which are potential platforms for their research, examine and compare vessel specifications and facilities, learn about research cruises the vessel has performed in the past, and find contact information for scientists who have used the vessel, as well as for the owners and operators of the vessel. The purpose of this poster presentation is to inform the scientific community about the ALIAS website as a tool for planning arctic research generally, and particularly for identifying and contacting vessels which may be suitable for planned ship-based research projects in arctic seas.
http://alias.arcus.org
OS41A-0471 0800h
Supercooling in the mixed layer beneath Arctic pack ice from modern and historical measurements
In the central Arctic, the oceanic heat flux from the seawater to the pack ice depends mostly on the seawater temperature elevation above freezing (dT). Long-term temperature and salinity observations from modern drifting platforms (primarily SALARGOS, IOEB, JCAD buoys and SHEBA) indicate that the annual cycle of dT in the mixed layer beneath the ice pack is significantly related to the solar zenith angle (with 1 month time lag). During winter when there is no solar input, the seawater temperature is expected to be very close to the freezing temperature at a given salinity, but the observations indicate that small positive biases in dT are common, especially in the Transpolar Driftstream. Meanwhile, supercooling where dT is negative by more than 0.01 \deg C was indicated in only 0.2% out of 6450 daily average values, and in only 4 out of 30 modern platforms. In order to extend the record backward in time, dT was also computed from hydrographic data obtained by Russian North Pole (NP) drifting stations and western AIDJEX and FRAM drifting stations. Surprisingly, virtually every station and over 31% of the observations from the NP stations and over 11% of the observations from AIDJEX indicate supercooling by more than 0.01 \deg C. In this study, the methods of data collection, accuracy of the measurement techniques, and considerations of natural variability are analyzed to gain a better understanding of the data quality and to merge the modern and historical records.
OS41A-0472 0800h
Meridional Overturning Exchange with the Nordic Seas
The flow of Atlantic water towards the Arctic crosses the Greenland-Scotland Ridge in three current branches. By the heat that it carries along, it keeps the subarctic regions abnormally warm and by its import of salt, it helps maintain a high salinity and hence high density in the surface waters as a precondition for thermohaline ventilation. In mid 1990's an extensive monitoring program for all three branches was lunched as a Nordic contribution to WOCE and is still going on. The western branch, the Irminger Current, has been monitored by means of traditional current meters moorings on a section crossing the current northwest of Iceland. A number of ADCPs have been moored on a section going north from the Faroes, crossing the Faroes Current. The eastern branch, the Continental Slope Current, is monitored by ADCPs moorings across the Faroe-Shetland Channel. CTD observations from research vessels along all the current meter sections are obtained on seasonal basis. Here we present for the first time the results from all the branches and offer numbers for the Atlantic water transport as well as seasonal and interannual variations. In addition we offer numbers for the dense overflowe trough the faroe Bank Channel.
http://www.bjerknes.uib.no/research/MOEN/index.html
OS41A-0473 0800h
The Nordic Seas 2002 Survey: Water Mass Comparisons with Previous Surveys
The Nordic Seas survey completed by Icebreaker Oden and R/V Knorr during April-June 2002 provides not only nearly complete lateral and vertical coverage of the Nordic Seas but also an excellent basis for comparisons with earlier surveys. The classic Greenland Sea Deep Water, which has been steadily eroded ever since the early 1980s, is essentially gone today. In the 2002 data, salinities on deep isopycnals show little variability across the Nordic Seas, except for influence of saline waters from the Arctic Ocean and dense waters from Storfjorden, with essentially no remaining signal from what was earlier a strong, fresh deep water source in the central Greenland Sea. The vertical structure of the water masses across the Nordic Seas clearly show a remarkable transition of the Greenland Sea from its appearance in nearly all pre-1990s data. Nordic Sea winter-produced intermediate waters exhibit no companion temporal decrease in presence: in 2002 there were typically slightly greater thicknesses of key intermediate layers, with about the same (high) average dissolved oxygen concentrations, as in the 1980s data, albeit in 2002 with slightly higher average salinities. It is interesting that the central Greenland Sea vertical structure has shifted from a quasi-one-layer regime to a two-layer one, even though upper salinities are relatively high in recent data. This fosters speculation regarding the possible role of warmer air temperatures, particularly in winter, in bringing about the regime transition.
OS41A-0474 0800h
Observed and modeled evolution of the deep water properties in the Nordic seas and the Arctic Ocean since the middle of the 20th century
Observations of hydrographic properties and transient tracer distributions during the past few decades revealed a remarkable decrease in the formation rate of Greenland Sea Deep Water (GSDW). On the basis of simple time-dependent mass balance calculations (box models) it has been concluded that this reduction in GSDW production by roughly 80 percent occurred rapidly at around 1980 (+-2 years). Further observations revealed that the change in GSDW production led to reorganizations in the circulation and exchange of deep waters in the coupled system of the GIN seas and the Arctic Ocean. This in turn resulted in significant changes in deep water properties, moving the T/S characteristics of the waters found in the deep Greenland Sea (below ca. 1500 to 2000 meters depth) outside the classical definition of GSDW. Although many studies have addressed the reason for the change in GSDW formation no conclusive answer has been found. In this contribution we address the further evolution of the deep waters in the Nordic seas using hydrographic and transient tracer data, in conjunction with simple box model simulations. We derive deep water formation and exchange rates for the past decade to extend previous work, which used data collected through the mid 1990's. Additionally, we project the evolution of the deep water characteristics under a variety of scenarios for the deep water formation rate in the Greenland Sea.
OS41A-0475 0800h
An Update on USCGC HEALY (WAGB-20) and its Capabilities
The USCG Healy (WAGB-20) is the US academic research vessel supporting arctic research. The Healy's keel was laid at Avondale shipyard in 1996. An extensive science evaluation coordinated by the UNOLS Office was conducted in 2000. The first science legs were conducted in 2001 and the status of the Healy was reported by Swift et. al (2002) in EOS. Since then the UNOLS Arctic Icebreaker Coordinating Committee has worked with the Coast Guard, the ship, the National Science Foundation and the user community to encourage a number of significant improvements which have been made to the vessel including substantial upgrades to the science data acquisition and logging system, installation of a significantly improved science seawater system, installation of a dual frequency echo sounder with swept (Chirp) subbottom capability replacement of the 300 KHz ADCP with a 75 KHz broad band ADCP, substantial upgrades to the ship's satellite data receiving system and numerous communication system upgrades. Future upgrades in various stages of planning include upgrades to the lab spaces for improved efficiency and space utilization, improvements in the climate control chambers, more cooling water for incubators, upgrade or replacement of the multibeam seafloor mapping system, improved high latitude communications, and enhancements to the data acquisition, quality control and real-time monitoring capabilities among other things.
http://www.uscg.mil/pacarea/healy/
OS41A-0476 0800h
Tidal and Inertial Variability in Arctic sea ice drift and Deformation
A dominant aspect of sea ice deformation and drift in the high latitudes is the presence of significant semi-diurnal tidal and inertial variability. Recent observations using synthetic aperature imagery (Kwok et. al., 2003) have shown Winter semi-diurnal variability near the North Pole to be almost continuous with peak to peak variations in divergence of about 0.2 % common. Whether or not such variability is tidal or inertial in origin is a matter of considerable debate. To elucidate this problem a barotropic ice-ocean tidal model with an oceanic boundary layer including imbedded sea ice is constructed for the Arctic Ocean. The tidal model utilizes an implicit B grid solver and is driven with M2 forcing at the southern boundary. While still retaining inertial variability in the oceanic boundary layer, the imbedding procedure of Heil and Hibler (2002) is modified so that in the absence of any ice interaction or surface stress there is no turning angle between the ice and the oceanic boundary layer. To elucidate the relative role of tides, ice mechanics and boundary layer inertial fluctuations on semi-diurnal variability in the ice deformation, a hiearchy of numerical experiments over a several month long period are carried out. Experiments include cases with and without an imbedded boundary layer and with and without ice mechanics. The results are analyzed in conjunction with observed hourly buoy drift and qualitatively compared to fluctuating deformation near the North pole.
OS41A-0477 0800h
A Multi-Tracer Analysis for the Study of the Movement and Mixing of Fresh Waters in a Shallow Arctic Estuarine System
Water samples were collected through 2-m thick ice in the shallow waters of the coastal Beaufort Sea during the spring maximum flow of the Kuparuk and Sagavanirktok rivers, Alaska, in late May to early June 2004. Sampling was carried out over an area of about 800 km$^2$ at water depths of 0.5, 1.0, 1.5, 2.5, 4, 6, 7, and 10 meters below the ice layer, depending on the total depth of the water column. Continuous profiles of temperature and salinity (CTD) and current measurements at key depths were obtained. Water from the two rivers and from sea ice has geochemical characteristics that are different from ambient seawater as well as from each other. Concentrations of conservative tracers, such as salinity, temperature and oxygen isotopes, as well as semi-conservative tracers, such as barium and dissolved silica are used to distinguish and measure seaward mixing of various source waters. For example, concentrations of dissolved silica in the Kuparuk River (13\pm1$\mu$M), the Sagavanirktok River (24\pm5$\mu$M) and sea ice (1.0\pm0.5$\mu$M) provide distinct signatures relative to the deeper Polar Mixed Layer (PML) with silica levels of 7.6\pm0.8$\mu$M. Similar trends are demonstrated with the other tracers. Mixing was traced horizontally (x, y) and vertically (z) throughout the sampling area, and temporally (t) at selected sites. A 1-2 m thick lens of predominately fresh water could be traced 10-12 km offshore. Combined use of the various tracers shows dissipation of geochemically different freshwater signals into the ambient PML of the Beaufort Sea during the spring floods.