U13C-0058
Human Influence on Arctic Sea Ice Detectable From Early 1990s Onwards
It has been widely assumed that the recent rapid loss of Arctic sea ice is partly due to human influence, but this hypothesis has not yet been rigorously tested. By comparing observed and multi-model simulated changes in Arctic sea ice extent during 1953-2006 using an optimal fingerprinting method, we find that the anthropogenic signal first emerged in the early 1990s, indicating that human influence could have been detected even prior to the recent dramatic sea ice decline. The anthropogenic signal is also detectable for individual months from May to December, suggesting that human influence, strongest in late summer, now also extends into colder seasons.
U13C-0059
A Convective Cloud Feedback and Spring Arctic Sea Ice Forecasting at High CO2
Winter and spring sea ice dramatically cool the Arctic climate during the the coldest seasons of the year and may have remote effects on global climate as well. Accurate forecasting of winter and spring sea ice has significant social and economic benefits. Such forecasting requires the identification and understanding of all the feedbacks that can affect sea ice. A novel convective cloud feedback has recently been proposed in the context of explaining equable climates, e.g., the climate of the Eocene, that might be important for determining future winter and spring sea ice. In this feedback CO2 -initiated warming leads to sea ice reduction, which which allows increased heat and moisture fluxes from the ocean surface, which destabilizes the atmosphere and leads to atmospheric convection. This atmospheric convection produces high and optically thick convective clouds and increases high-altitude moisture levels, both of which trap outgoing longwave radiation and therefore result in a further warming and sea ice loss. Here it is shown that this convective cloud feedback is active during winter in the coupled ocean-sea ice-land-atmosphere global climate models used for the 1%/year CO2 increase to quadrupling scenario of the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report. It is further shown that the convective cloud feedback plays an essential role in the elimination of maximum seasonal (spring) sea ice in NCAR's CCSM model, one of the IPCC models that nearly completely loses spring sea ice. This is done by performing a sensitivity analysis using the atmospheric component of CCSM, run at a CO2 concentration of 1120 ppm, by selectively disabling the convective cloud feedback and the ocean heat transport feedback. The result is that both feedbacks are necessary for the elimination of spring sea ice at this CO2 concentration.
U13C-0060
Modeling the Formation of the North Water Polynya Ice Bridge
The North Water (NOW) polynya, the largest polynya in the world located in northern Baffin Bay, owes its existence to an ice bridge that forms during later winter. The dynamical conditions and the general characteristics of the ice bridge are studied using an elastic-viscous-plastic (EVP) dynamical sea ice model with an elliptical rheology. The model resolves the ice edge and a stable ice bridge forms only if the yield curve is sufficiently cohesive, the level of cohesion being controlled by the major to minor axis ratio e of the elliptical yield curve. The model solution is robust and invariant with respect to the grid orientation. Results from a sensitivity study with respect to rheological parameters and sea ice thickness show that a minimum uniaxial tensile strength (cohesion) is needed to form a stable arch for a given wind stress. Analysis of the stationary stress state and flow characteristics compare well with theory and observations of granular materials in hoppers. When applied to a realistic representation of the NOW polynya together with the observed wind forcing, the simulated ice bridge form and location match the observations. As the horizontal thickness distribution in Kane Basin depend on sea ice properties and wind stress history, these data could be used as a proxy to validate or tune dynamical model parameters such as e. Adequately simulating sea ice behaviour in constraint areas will become crucial for operational forecasting as navigation increases in a context of rapid Arctic ice retreat and thinning.
U13C-0061
Variations in Brine Water Export From Arctic Shelves Forced by Atmospheric Circulation Changes
A distinctive water mass generated during winter sea-ice formation was identified in the Laptev Sea and found predominantly in the polynya region. Stable oxygen isotope measurements of the water combined with salinity allows to identify the freshwater sources which contributed. Thereby also the remaining effects of winter sea-ice formation can be identified from samples taken during summer expeditions. Export of Laptev Sea bottom waters can be inferred by tracing the brine enriched shelf water mass to the continental slope. This export of Laptev Sea bottom water shows inter-annual variability in correlation with atmospheric conditions. Years with anticyclonic wind circulation during summer months are favoring an offshore transport of river water at the surface and we find a pronounced signal of brine enriched waters at about 50 m water depth. Years with cyclonic atmospheric circulation during summer months are favoring onshore or alongshore water transport and we find river water fractions at the shelf break are reduced and the pronounced brine signal is missing within the Arctic Ocean halocline at the shelf break. Instead we observe brine-enriched waters in high proportion (up to 30% brine contribution) on the Laptev Sea shelf. Residence times of bottom and subsurface waters on the shelf may thereby vary considerably and an export of shelf waters to the Arctic Ocean halocline might be shut down or strongly reduced during years with "onshore" cyclonic atmospheric circulation, while in years with "offshore" anticyclonic atmospheric circulation brine waters are exported and residence times may be as short as one year. Modeling studies have to test how climate change may affect e.g. the frequency of years with a predominantly "offshore" or "onshore" wind situation, which would both affect the stability of the Arctic halocline. At present we can derive from existing δ 18 O data sets under which conditions bottom waters are exported from the Laptev Sea to the Arctic Ocean halocline. More detailed single year datasets are required to derive information on budgets and quantitative export rates.
U13C-0062
Rate- and State-Dependence of ice-ice Friction in sea ice
The distribution of ice thicknesses in the Arctic is a function of the ice deformation which occurs through ridging, rafting and sliding of ice floes. To determine the relative importance of each of these forms of deformation, it is crucial to have a good model of ice friction. We present data on ice-ice friction from a series of large ice-tank experiments, undertaken at the HSVA ship testing facility in Hamburg, Germany. We focus on the impact of varying the sliding rate, and the hold-time before commencing sliding, following the work of Ruina (1983). We move a 2m square floating ice block, of thickness 25cm, under horizontal normal stress, and detail the force required to move the block and hence the implied friction coefficient μ. Loads are of the order 1kN. We find that the time-averaged friction coefficient shows little rate-dependence, and μ = 0.3-0.4 for a variety of rates (from 1-10cm/s). However, the detailed sliding mechanism varies with rate, and stick-slip behaviour is observed at low rates. The state-dependence is found to be a crucial factor in determining the load required to initiate movement of the ice block. To test for state dependence we apply the side load for a given time interval (the hold time) before starting to move the block. With a hold time of 1000s, the forces are an order of magnitude greater than with a hold time of 10s, and we present data for hold times from 1- 1000s. This work has important implications for sea ice rheology components within global climate models, particularly given that recent satellite observations show that almost all the deformation of Arctic sea ice is due to in-plane frictional sliding. The results outlined above suggest that the static contact time between ice floes may be the key parameter influencing the ensemble movement of sea ice. The work also has value for smaller-scale modelling of sea ice for engineering purposes, for example in predicting forces on offshore structures. As well as presenting our results, we will discuss possible further experiments to extend the range of validity of the work.
U13C-0063
On the large-scale importance of sea ice salinity variations
Sea ice has a non-zero salinity, that varies in space and time. This affects the sea ice thermal properties as well as the ice-ocean salt and freshwater exchanges, which may influence the sea ice mass balance and the polar oceans' characteristics. However, present sea ice models neglect or misrepresent the ice salinity. In this paper, we address the question of the importance of large-scale sea ice salinity variations for the sea ice mass balance and the upper ocean. To examine this question, we formulate salinity variations in the framework of the sea ice thickness distribution theory, using a simple parameterization for brine entrapment and drainage. The latter is tested one-dimensionally and then included in a three-dimensional large-scale ice-ocean model, OPA9-LIM3, which is run over 1970-2006, forced by a combination of atmospheric reanalyses and climatologies. Due to differences in the physical forcings, the model simulates Arctic and Antarctic sea ice salinity fields that profoundly differ, with a seasonal cycle that is found in reasonable agreement with available ice core data. Then, the role of salinity variations is analyzed by comparing the results of the simulation including the interactive salinity with several sensitivity runs using simpler representations of ice salinity. The simulated large-scale sea ice mass balance and upper ocean characteristics are found to be quite sensitive to the representation of ice salinity. In the Arctic, salinity variations induce changes in ice thickness up to one meter in some regions, due to modifications in the sea ice thermal properties. Around Antarctica, through changes in ice-ocean interactions that stabilize the ocean, including salinity variations increases the simulated winter sea ice volume by up to 28%. The model sensitivity to the sea ice salinity is at least as large as a 10% change in summer surface albedo, for example. Given the importance of salinity on the simulated sea ice characteristics, sea ice salinity variations should be included in assessments of the response of the high-latitude oceans to ongoing and future climate change.
U13C-0064
SEARCH: Study of Environmental Arctic Change--A System-scale, Cross-disciplinary, Long-term Arctic Research Program
The Study of Environmental Arctic Change (SEARCH) is a multi-agency effort to observe, understand, and guide responses to changes in the arctic system. Interrelated environmental changes in the Arctic are affecting ecosystems and living resources and are impacting local and global communities and economic activities. Under the SEARCH program, guided by the Science Steering Committee (SSC), the Interagency Program Management Committee (IPMC), and the Observing, Understanding, and Responding to Change panels, scientists with a variety of expertise--atmosphere, ocean and sea ice, hydrology and cryosphere, terrestrial ecosystems, human dimensions, and paleoclimatology--work together to achieve goals of the program. Over 150 projects and activities contribute to SEARCH implementation. The Observing Change component is underway through National Science Foundation's (NSF) Arctic Observing Network (AON), NOAA-sponsored atmospheric and sea ice observations, and other relevant national and international efforts, including the EU- sponsored Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies (DAMOCLES) Program. The Understanding Change component of SEARCH consists of modeling and analysis efforts, with strong linkages to relevant programs such as NSF's Arctic System Synthesis (ARCSS) Program. The Responding to Change element is driven by stakeholder research and applications addressing social and economic concerns. As a national program under the International Study of Arctic Change (ISAC), SEARCH is also working to expand international connections in an effort to better understand the global arctic system. SEARCH is sponsored by eight (8) U.S. agencies, including: the National Science Foundation (NSF), the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), the Department of Defense (DOD), the Department of Energy (DOE), the Department of the Interior (DOI), the Smithsonian Institution, and the U.S. Department of Agriculture (USDA). The U.S. Arctic Research Commission participates as an IPMC observer. For further information, please visit the website: http://www.arcus.org/search or contact: Helen V. Wiggins: helen@arcus.org, SEARCH Project Office, Arctic Research Consortium of the U.S. (ARCUS); or Peter Schlosser, schlosser@ldeo.columbia.edu, SEARCH SSC Chair.
U13C-0065
Revisiting the Role of Atmospheric Forcing of Fram Strait sea ice export using Daily Data
The recent decline of Arctic sea ice extent has attracted widespread scientific attention. Explanation of this decline is attributed to change in both the thermodynamic component (sea ice melt) and the dynamic component (sea ice export). Our project focuses on the latter – sea ice export through Fram Strait into lower latitudes. Previous studies have shown that the relationship between large-scale atmospheric circulation patterns such as the North Atlantic Oscillation (NAO) and sea ice export through Fram Strait is inconclusive based on monthly data. We utilize daily data from 1979 to 2006 to examine in more detail the relationship between sea level pressure (SLP) and sea ice motion in Fram Strait. We use NCEP Reanalysis data for SLP and Polar Pathfinder 25-km gridded product for sea ice motion. Our results reveal an atmospheric pattern with an east-west distribution of the main centers of action: Barents Low and Greenland High. This east-west dipole is associated with strong northerly winds and therefore promotes increased sea ice export through the Fram Strait. The dipole is stronger in winter, but persists year round. Spectral analysis reveals that the relationship between the SLP and the Fram Strait sea ice export is strongest for the 10-60 day band in all seasons. The east-west SLP dipole has been described in several previous studies as the second EOF of the monthly SLP in the Northern Hemisphere, and scale in association with cold-air outbreaks in Scandinavia on a synoptic scale. We argue that the localized east-west SLP dipole is crucial in forcing sea ice export through Fram Strait, while the relationship between the monthly NAO index and sea ice export might be coincidental.
U13C-0066
Trends in Eurasian Arctic runoff timing and their relationship to snow cover changes
Pronounced land surface process changes have occurred in the Arctic and sub-Arctic in recent decades. Apparent earlier ablation of snow cover in spring implies that some of the energy that was once used to melt snow is now absorbed by the ground, thereby lowering the albedo and thus leading to more snowmelt. To date, however, confirmation of such causal explanations for hydrologic trends has been elusive, primarily because of short record lengths and/or absence of requisite data records. We examine changes in the timing of runoff from 53 unregulated Eurasian Arctic streamflow gauges distributed over the Lena, Ob and Yenisei River basins for the period 1958 – 1999. Variables examined include the onset date of the spring runoff pulse, the centroid of timing of spring runoff, and seasonal fractional flows. These results were compared with surface air temperature anomalies and (satellite) snow cover trends to diagnose the sensitivity of runoff in each of the basins to snow cover disappearance, snow-free duration and period of snowmelt. We find that there are consistent trends indicating an earlier onset of runoff in spring across many of the basins, which can be linked to changes in snowmelt timing, and an increase in winter flows, which appears to be related to shorter snow cover duration. Surface air temperature trends have less obvious linkages with the streamflow timing changes, with the exception of the Yenisei basin where an increase in May temperatures are associated with lower snowmelt season runoff, but increases in June temperatures are associated with increased June runoff.
U13C-0067
Comparing Arctic Surface Energy Fluxes and Cloud Cover in the ERA-40, SHEBA, and Other Data Sets
Earth's climate has been changing rapidly in the past few decades. The effects of climate change have been shown to be most noticeable in the Arctic (IPCC 2001). However, the Arctic environment is poorly understood due to several unique factors: relatively high surface albedo, absence of solar radiation during the polar night, extremely cold and dry conditions, and presence of temperature and humidity inversions. In order to understand the response of the Arctic to a changing climate, studies of trends, processes, and feedbacks utilize models and model-observation hybrid data sets. Hence, the accuracy of the processes and feedbacks in these data sets are important. In this study, surface radiative and turbulent fluxes from the ECMWF reanalysis data set (ERA-40; Uppala 2005) are examined from November 1997 through October 1998 over the Arctic Ocean, spanning from 73°N to 76°N latitude and 26°W to 36°W longitude. The reanalysis product is compared to observations taken at the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment (Persson et al. 2002), Russian drifting stations (Lindsay 1998), and the 'Maud' expedition (Sverdrup 1933). In general, the radiative fluxes in ERA-40 agree well with the observations, but with some exceptions that lead to significant differences in the net radiative surface flux and thus in the total surface energy budget. The ERA-40 turbulent fluxes have a similar annual pattern to the observations, but differ in magnitude, again contributing to the error seen in the total surface energy budget. Since clouds have one of the largest impacts on feedback mechanisms, cloud cover from ERA-40 is validated against cloud radar data collected at SHEBA. Finally, the observed relationships between cloud cover and surface fluxes in the SHEBA data are used to validate those in the ERA-40 data.
U13C-0068
Reemergence of sea ice cover anomalies and the role of the sea ice-albedo feedback in CCSM simulations
The dramatic sea ice decline of 2007 and lack of recovery in 2008 raise the question of a "tipping point" for Arctic sea ice, beyond which the transition to a seasonal sea ice state becomes abrupt and irreversible. The tipping point is essentially a "memory catastrophe", in which a dramatic loss of sea ice in one summer is "remembered" in reduced ice thickness over the winter season and leads to a comparably dramatic loss the following summer. The dominant contributor to this memory is presumably the sea ice - albedo feedback (SIAF), in which excess insolation absorbed due to low summer ice cover leads to a shorter ice growth season and hence thinner ice. While these dynamics are clearly important, they are difficult to quantify given the lack of long-term observations in the Arctic and the suddenness of the recent loss. Alternatively, we attempt to quantify the contribution of the SIAF to the year-to-year memory of sea ice cover anomalies in simulations of the NCAR Community Climate System Model (CCSM) under 20th century conditions. Lagged autocorrelation plots of sea ice area anomalies show that anomalies in one year tend to "reemerge" in the following year. Further experiments using a slab ocean model (SOM) are used to assess the contribution of oceanic processes to the year-to-year reemergence. This contribution is substantial, particularly in the winter season, and includes memory due to the standard mixed layer reemergence mechanism and low-frequency ocean heat transport anomalies. The contribution of the SIAF to persistence in the SOM experiment is determined through additional experiments in which the SIAF is disabled by fixing surface albedo to its climatological value regardless of sea ice concentration anomalies. SIAF causes a 50% increase in the magnitude of the anomalies but a relatively small increase in their persistence. Persistence is not dramatically increased because the enhancement of shortwave flux anomalies by SIAF is compensated by stronger turbulent heat flux losses in the cold season. The role of turbulent heat fluxes is somewhat inconsistent with the retrospective 20th century simulations from PIOMAS, in which increased insolation is balanced by longwave heat loss. By fitting the area anomaly time series for the SIAF and no-SIAF integrations to an AR1 process, the change in net feedback due to SIAF is calculated. The change in net feedback implies that SIAF increases the climate sensitivity of September sea ice to external forcing (greenhouse gas increases) by about 20%. The modest increase in sea ice sensitivity is confirmed by further climate change experiments with and without SIAF with the CCSM/SOM model. The small role for SIAF is somewhat surprising given the prevalence of "abrupt loss" events in CCSM climate change simulations. However, it is consistent with claims that the dominant factor in abrupt loss events is the sea ice thickness at the event onset.
U13C-0069
A series of stabilization runs in the 21st Century: Is there a tipping point?
Many scientists and news articles have argued that Arctic sea ice is likely to exhibit threshold-like behavior as it melts back in a greenhouse warming world. Such a tipping point would be an irreversible bifurcation to a new state. 21st century projections with the CCSM3 and many other climate models exhibit very rapid sea ice decline at the end of summer, especially in the most pessimistic scenarios of future anthropogenic greenhouse gas emissions. The rapid decline is best characterized as a dramatic response to a fairly modest change in climate forcing. Sea ice meltbacks at the end of summer as large as observed in 2007 occur about 1% of the time in the early 21st century of simulations with CCSM3. But meltback events of that magnitude never occur in pre-industrial simulations, which suggests that thinner sea ice in a greenhouse warming world will experience larger meltbacks with increasing frequency. Curiously, the variability about the ensemble average exhibits large positive ice anomalies with about the same frequency as large negative ones. The near symmetry in variations about the long-term trend (or lack of significant negative skew) is evidence that the model does not experience threshold-like behavior when it thins. A series of future stabilization runs where greenhouse gas and aerosol levels are held fixed at 2020 and 2030 levels in an A1B scenarios were run. With fixed level of radiative forcing, the sea ice extent declines very slowly for the remainder of the 21st century, with coverage far greater than ensemble members of the standard A1B scenario. Thus it is clear that without a constant increase in radiative forcing, the sea ice in CCSM3 does not continue to rapidly retreat.
U13C-0070
Positive trend in the mean speed and deformation rate of Arctic sea ice, 1979- 2007
Using buoy data from the International Arctic Buoy Program, we found that the sea ice mean speed over the Arctic has substantially increased over the last 29 years (+17 per cent per decade for winter; +8.5 per cent for summer). We check that these trends were not affected by temporal or spatial sampling bias. A strong seasonal dependence of the mean speed is also revealed, with a maximum in October and a minimum in April, i.e. out of phase, lagging by 6 months with respect to the sea ice extent seasonal variability. The sea ice mean strain rate, deduced from the dispersion of buoys trajectories, also increased significantly over the period (+51 per cent per decade for winter; +52 per cent for summer). We check that these increases in both sea ice mean speed and deformation rate are unlikely a consequence of a stronger atmospheric forcing, as the mean wind speed over the Arctic did not increase significantly over the period. Instead, they suggest that sea ice kinematics plays a fundamental role in the albedo feedback loop and sea ice decline: increasing deformation means stronger fracturing, hence more lead opening and therefore a decreasing albedo. This accelerates sea ice thinning in summer and delays refreezing in early winter, therefore decreasing the mechanical strength of the cover and allowing even more fracturing and larger drifting speed and deformation, and possibly a faster export of sea ice through the Fram Strait. The September minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking, as we found that for both winter 2006-2007 and summer 2007, exceptionally large deformation rates affected the Arctic sea ice cover, in agreement with a much faster than expected drift of the polar schooner Tara during its journey along the transpolar current.
U13C-0071 INVITED
Arctic Sea Ice Loss: Atmospheric Forcing and Response
The accelerating retreat of Arctic sea ice in recent decades is a pre-eminent signal of climate change. What role has the atmospheric circulation played in driving the sea ice decline, and how will future Arctic sea ice loss affect the global atmospheric circulation and climate? To address the first question, we document the evolution of Arctic sea ice concentration trends since 1979 in light of changing atmospheric circulation conditions, in particular an upward trend in the wintertime Northern Annular Mode during the first half of the record and a downward trend during the second half. The results indicate that concurrent atmospheric circulation trends contribute to forcing winter and summer sea ice concentration trends in many parts of the marginal ice zone during both halves of the record. However, there is also an emerging signal of overall Arctic sea ice decline since 1979 in both winter and summer that is not directly attributable to a trend in the overlying atmospheric circulation. To address the second question, we have conducted simulations with a state-of-the-art atmospheric general circulation model at high resolution with specified Arctic sea ice conditions for the late 20th century and projected for the late 21st century. The simulations show that although future loss of Arctic sea ice is greatest in summer and autumn, the response of the net surface energy flux is largest in winter. Since the energy fluxes communicate the sea ice loss to the atmosphere, it follows that the largest atmospheric response also occurs in winter. This response consists of atmospheric boundary layer warming over the adjacent continents due to horizontal heat transport by sub-monthly transient motions; temperature advection by the monthly mean atmospheric circulation acts as a negative feedback. Despite the warming, snow depth increases over Siberia and northern Canada due to increased precipitation in early winter. Although the model exhibits a significant atmospheric circulation response in winter, its spatial and vertical structure varies from month to month; no significant circulation response occurs in summer.
U13C-0072
Arctic Perennial and Winter Multiyear Ice on a Precipitous Decline
Knowledge about the state of the Arctic perennial and multiyear ice cover is important because they are the mainstay of the Arctic sea ice cover. Perennial ice is ice that survives the summer and consists mainly of second year and the older multiyear ice types. The rapid rate of decline in the perennial ice cover has been reported and examined previously and with the precipitous decline in 2007 and again in 2008, the Arctic Ocean has become an intense area of climate change result. The perennial ice area in 2007 was observed to be 27% less than the previous record low established in 2005 and was 38% less than climatological average. The sea surface temperature (SST) in the Arctic has also been on the rise at about 0.7 per decade with the SST at the Chukchi Sea region being observed by satellite data to be anomalously higher than average by about 5 oC. This is an indication that ice-albedo feedback effects in the region are already being observed and that a recovery of the perennial ice cover in the foreseeable future may not be possible. To gain insight into the state of the multiyear ice cover, we take advantage of the large contrast in the emissivity of first year and multiyear ice in winter and assess the variability and trend of the older multiyear ice type. The contrast is largest in February when the ice is cold and dry and the technique and is most pronounced between first year and the older multiyear (3 years or older) ice types. The retrieved area of winter multiyear ice is about 2 million km2 less than that of the perennial ice area observed during the previous summer indicating that only the older and thicker types of multiyear ice are included. The trend of the retrieved multiyear ice cover for the period 1979 to 2007 is observed to be about -14%/decade which indicates a significantly faster decline than the perennial ice cover. This suggests that the thicker component of the perennial ice cover is declining even more rapidly that the perennial ice. The area and extent of the perennial ice in 2008 appears to be the second lowest if not the lowest during the satellite era. The persistence of low values during the recent decade and especially in 2007 and 2008 is a manifestation of a generally thinner Arctic ice cover in the recent years than in the 1980s. This phenomenon together with the observed rapid rise in SST suggest that the impact of ice-albedo feedback is becoming an important factor that needs to be considered in the changing Arctic.
U13C-0073
Increasing Baseflow From Possible Permafrost Thawing and Increasing Mean Annual Streamflow in the Northwest Territories, Canada
Increasing surface air temperatures from anthropogenic forcing are melting permafrost in high latitudes and intensifying the hydrological cycle. Long-term streamflow records (at least 30 yrs) from 23 stream gauges in the Canadian Northwest Territories (NWT) indicate a general significant upward trend in baseflow of 0.5- 271.6 %/yr and the beginning of significant increasing mean annual flow (seen at 39% of studied gauge records), as assessed by the Kendall-τ test. The NWT exports an average discharge of at least 308.6 km3/yr to the Beaufort Sea, of which at least 120.9 km3/yr is baseflow. We propose that the increases in baseflow and mean annual streamflow in the NWT were caused predominately by climate warming via permafrost thawing that enhances infiltration and deeper flowpaths and hydrological cycle intensification. To provide hydroclimatic context, we present evidence of a statistically significant positive link between the Arctic Oscillation and annual NWT streamflow at the interannual-to-decadal timescales.
U13C-0074
Arctic Sea Ice Melt in the Summer of 2008
There has been a marked decline in the summer extent of Arctic sea ice over the past few decades. To
enhance our understanding of this decline, autonomous ice mass balance buoys were deployed in the sea
ice cover as part of the North Pole Environmental Observatory, the Beaufort Gyre Environmental
Observatory, and the Developing Arctic Modeling and Observing Capabilities for Long-term Environmental
Studies Program. These buoys monitor changes in snow deposition and ablation, ice growth, and ice surface
and bottom melt. Results during the summer of 2008 showed considerable spatial variability in the amount of
surface and bottom melt. In the vicinity of the North Pole the amounts of surface and bottom ablation were
comparable to values observed in recent years. Modest (less than 0.5 m total) amounts of melting were
observed north of Greenland. Melting in the Southern Beaufort Sea was quite large, with 0.85 m of surface
melt and more than 1 m of bottom melt. Reduced ice concentration in this region led to a buildup of solar
heat in the upper ocean. This absorbedsolar heat was released gradually and also through abrupt episodes
when peak bottom melt rates exceeded several cm per day.
http://www.crrel.usace.army.mil/sid/IMB
U13C-0075
Creating Arctic Sea Ice Protected Areas?
As Arctic sea ice retreats and the Northwest Passage and Northern Sea Route open, the Arctic will experience more extensive human activity than it has ever encountered before. New development will put pressure on a system already struggling to adapt to a changing environment. In this analysis, locations are identified within the Arctic that could be protected from resource extraction, transportation and other development in order to create refuges and protect remnants of sea ice habitat, as the Arctic transitions to ice-free summer conditions. Arctic sea ice forms largely along the Siberian and Alaskan coasts and is advected across the North Pole towards Fram Strait, the Canadian Archipelago and the Barents Sea. In addition to the future loss of ice itself, contaminants entrained in sea ice in one part of the ocean can affect other regions as the ice drifts. Using observations and models of sea ice origins, trajectories and ages, we track sea ice from its origins towards marginal ice zones, mapping pathways and termination locations. Critical sea ice source areas and collection regions are identified with the goal of aiding in the protection of the remaining Arctic sea ice habitat for as long as possible.