U41C-0612
The Relationship Between Sea Ice Variability and Arctic Tundra on the Pan-Arctic, Regional and Site Scales
Recent dramatic reductions in sea ice and changes in Arctic vegetation are well documented and there is growing concern for how these changes will impact the high latitude ecosystem. We hypothesize that reduced sea ice cover during spring/summer leads to a lengthened growing season and the greening of tundra vegetation. To investigate this question, climate analysis techniques are applied to high-resolution passive microwave sea ice concentration and AVHRR land surface temperatures to evaluate the direct relationship between coastal ice and the adjacent land. NCEP/NCAR Reanalysis provides information on the atmospheric circulation, which plays a key role in the local effects of increased open water. The relationship between sea ice and land surface temperature is found to vary with spatial scale and season. Large-scale as well as local circulations play a role in determining the influence of sea ice on the tundra vegetation.
U41C-0613
Seasonal Arctic Ice Forecasting: Can we still use the past to predict the future?
The National/Naval Ice Center, part of the North American Ice Service, produces a Seasonal Outlook each year as an early prediction of that summer's Arctic sea ice conditions. The forecasts for the Western Arctic, including the Alaskan Beaufort Sea coast, are determined using an statistical relationship of an array of monthly mean geopotential heights, sea level pressures, and surface temperatures calculated during the previous winter. These values are then compared with records of previous summers to determine an empirical forecast for the oncoming summer. This method has been essentially the same since it was originally developed in the mid-1970s. Here we examine the forecasts compared with actual conditions, using the opening and closing of the coastal shipping route between Barrow and Prudhoe Bay as the metric. Using NCEP reanalyses , we compute retroactive forecasts for 1948- present and evaluate whether the current method is likely to be well-suited if the dramatic decline in summertime Arctic ice extents continues.
U41C-0614
Tracking the Record Sea Ice Minimum in the Arctic Using National Ice Center Charts
The National/Naval Ice Center (NIC), in Suitland, MD, produces routine analyses of sea ice coverage in the Arctic. We create a Northern Hemispheric analyses based on bi-weekly charts for over 30 individual areas. Weekly charts of several key areas such as the High Arctic, Beaufort Sea, Chukchi Sea, North Sea, and Kara Sea are also produced. To create these charts, analysts at the NIC pool all available data sources including satellite imagery, buoy and shipboard in-situ observations, and models. During the 2007 sea ice season, the NIC charts confirmed observations from other groups (e.g, NSIDC Sea Ice Index, JPL QuikSCAT) that the previous Arctic sea ice minimum recorded in September 2005 was surpassed. NIC charts were also used to monitor the navigability of the both the Northwest Passage and Northern Sea Routes, which are historically ice-infested. Using the NIC sea ice climatology database shows that the routes reached levels of "openness" in 2007 which have not been observed in recent history. http://www.natice.noaa.gov
U41C-0615
Disappearing Sea-Ice and Glacier Mass Balance in the Arctic
Sea-ice extent in the Arctic Ocean has decreased dramatically since 1979. Although negative trends sea-ice are largest in summer months (-9% in September), significant negative trends are seen in all months. Glaciers in the Arctic are also exhibiting increasingly negative mass balances. Anomalous open-water areas, exposed by disappearing ice, promote high surface air temperatures, especially in autumn and winter, and may increase moisture content of surface air masses. Anomalous areas of open-water are found in the Barents Sea and along the Russian coast, areas close to heavily glacierized Arctic islands of Svalbard, Franz Joseph Land, Novaya Zemlya. In this paper we examine the correspondence between records of sea ice extent and long-term records of annual and seasonal glacier mass balance from Arctic Glaciers. Positive correlations are found between summer minimum sea-ice extent and annual mass balance of Svalbard glaciers. Negative correlations are found between summer minimum sea-ice extent and the following year's winter mass balance, suggesting ice- free conditions at the end of summer may enhance winter accumulation on glaciers.
U41C-0616
Satellite-derived distribution of surface chlorophyll biomass and its relation to variability in sea ice cover in the northern Bering Sea
Recent declining trends in sea ice extent in the Bering Sea have a direct impact on spring phytoplankton production. Here, we utilize multi-sensor satellite data to investigate key temporal and spatial linkages between sea ice variability and chlorophyll biomass throughout the northern Bering Sea region, integrating measurements of sea ice extent with phytoplankton blooms. This study incorporates radar, passive microwave and visible/near- infrared satellite measurements of sea ice extent with SeaWIFS and MODIS derived concentrations of chlorophyll- a. Remotely sensed measurements of sea ice cover and chlorophyll-a concentrations are validated with in situ data collected onboard the US Coast Guard Cutter Healy from May through June of 2006 and 2007. Surface phytoplankton blooms are coincident with the onset of sea ice degradation, with good agreement between in situ and remotely sensed concentrations of chlorophyll-a. Once the spring bloom of phytoplankton occurs, surface chlorophyll-a concentrations begin to decline within approximately two weeks. For example, in situ measurements of surface chlorophyll-a concentrations range up to ~29 μg/L at sites measured from 5/18/2007-5/28/2007, but range up to ~13 μg/L at similar sites measured from 6/6/2007-6/13/2007. This is corroborated with measurements of surface nutrient concentrations that significantly decline over the same time period. Recent trends of earlier sea ice break-up and later sea ice formation in the Bering Sea have important implications for the timing of phytoplankton blooms as well as for biological productivity in the Bering Sea at all trophic levels.
U41C-0617
Carbon dioxide fluxes across the atmosphere-water-coastal eroded ice complex in the Arctic Ocean: Laptev and Kara seas
Despite the significant progress that has been made in Arctic biogeochemical studies, large discrepancies still exist between recent estimations of the carbon balance and cycling in the Arctic seas [Romankevich and Vetrov, 2001; Stein and Macdonald, 2003; Macdonald et al., 2006] because reliable data are lacking. The Arctic Ocean has been suggested to be a net sink for atmospheric CO2, favoured by cold, relatively low salinity surface layers). Unfortunately, estimates of annual CO2 uptake from the atmosphere vary widely from 1700 × billions moles (Anderson, et al., 1998) up to 11000 billions moles (Lyakhin and Rusanov, 1983), due to high spatial variability and a difficulty of establishing representative values. To fill this gap with a substantial quantity of good-quality data is one of the primary purposes of this study. During the September 2006 expedition in the Laptev Sea and along the Northern Sea Route five research platforms were used to accomplish field work: the ice-strengthened commercial vessel Kapitan Danilkin, two small vessels, the TB 0012 and the Neptun, an Mi-8 helicopter, and diesel icebreaker Kapitan Dranitsyn. CO2 and CH4 fluxes were measured using micrometeorological methods, enclosure methods, or both. In our CO2 and CH4 exchange study setup, momentum and the fluxes of sensible and latent heat were measured using the eddy-correlation technique, which is the most direct micrometeorological method. Dynamics of the carbonate system was studied using pH- TALK technique. Preliminary results: 1. The coastal area of the Laptev Sea, strongly influenced by coastal erosion and river input of terrestrial carbon (suspended and dissolved), acts as a strong source of CO2 into the atmosphere. CO2 flux from the sea surface/nearshore zone ranged between 0.31 - 0.4 μM/�¼Â²/sec (for comparison, �¡�ž2 release from the tundra soil ranged between 0.03 - 0.18 μM/�¼Â²/sec). The highest rates of �¡�ž2 emission were measured in the freshly-exposed eroded depressions. 2. CO2 fluxes off-shore revealed a mosaic distribution of both intensity and direction of gas exchange, which depended on the characteristics of the underlying water masses. Upper Halocline Water, along with Atlantic Intermediate Water, may act either as a potential source of CO2 to the atmosphere or as a sink.
U41C-0618
Tracing the Atlantic Temperature Signal in the Arctic Ocean
Recent decades were marked by significant changes in the state of the Arctic climate system components, including decrease of the ice cover, increase of surface air temperature, and warning of Atlantic Water layer (AW) in the Arctic Ocean. According to several observation-based studies the process of AW warming had occurred in a series of pulses, separated by intervals of colder water inflow. These warm pulses are anticipated to originate in the Nordic Seas or in the North Atlantic Ocean, since after entering the Arctic Ocean interior AW looses direct contact with the atmosphere. Due to sparse measurements, propagation of warm anomalies across the Arctic Ocean is hard to trace. Several published results are controversial and give large uncertainty in estimation of speed of anomalies propagation. In this theoretical study we show that under certain conditions, a "train" of anomalies moving in a decelerating flow may collapse, resulting in a solitary anomaly far downstream. We applied a hierarchy of analytical and numerical models, based on simplified transport-diffusion equation with prescribed horizontal speed and diffusion coefficient. We estimated typical "collapse" length scales for various frequencies of initial anomalies supply depending on the flow properties. Our results suggest that this mechanism may be applicable for explaining the observed temporal variability of temperature in the AW layer in the Arctic Ocean during the recent decades. Another possible application of our results is explanation of disappearance of the seasonal cycle in the AW. Existence of strong seasonal cycle in AW at the entrance of the Arctic Ocean in Fram Strait and the absence of this variability mode in the Laptev Sea (about 2 thousand kilometers downstream) may be explained by suggested "anomalies collapse" mechanism.
U41C-0619
A 2006-2007 Update on Oceanographic Conditions in the Central Arctic Ocean
Trends in central Arctic Ocean conditions are updated with recently gathered data. In the late 1980s and through the 1990s we saw major shifts in the Arctic Ocean. The influence of Atlantic Water in the Arctic Ocean became more widespread and intense and the pattern of water circulation and ice drift shifted, resulting in a more cyclonic circulation. These changes became manifest in the central Arctic near the North Pole as increases in upper ocean salinity and Atlantic Water temperature. They occurred in concert with a decrease in surface atmospheric pressure. With the aim of helping to track such changes, the North Pole Environmental Observatory (NPEO) has been maintained since 2000. Along with an automated drifting station and a deep ocean mooring near the Pole; NPEO conducts airborne hydrographic surveys that track changes along key sections radiating from the Pole. In a related project, several of us have undertaken in situ ocean bottom pressure measurements and the analysis of Gravity Recovery and Climate Experiment (GRACE) data to track changes in the distribution of ocean mass. Hydrographic measurements made by the NPEO show that between 2000 and 2005, oceanographic condition relaxed toward the pre-1990 state. Morison et al [2006] describe these changes and relate them to a decline in the Arctic Oscillation (AO) index. On the basis of in situ and GRACE bottom pressure trends, Morison et al. [2007] argue that shift back to pre-1990s circulation extended over the whole Arctic Ocean. The Spring 2007 NPEO hydrographic surveys and the 2006-2007 bottom pressure data suggest the trend towards pre-1990s conditions has now, once again, reversed. The new observations show greater salinities and bottom pressure near the Pole, indicative of increased Atlantic water presence. Temperatures have increased in the Atlantic Water core along the Eurasian flank of the Lomonosov Ridge. We will explore these most recent changes and their relation to changes in the ice cover and atmospheric conditions. Refs: Morison, J., M. Steele, T. Kikuchi, K. Falkner, and W. Smethie, 2006, Relaxation of central Arctic Ocean hydrography to pre-1990s climatology, Geophys. Res. Lett., 33, L17604, doi:10.1029/2006GL026826. Morison, J., J. Wahr, R. Kwok, and C. Peralta-Ferriz, 2007, Recent trends in Arctic Ocean mass distribution revealed by GRACE, Geophys. Res. Lett., 34, L07602, doi:10.1029/2006GL029016.
U41C-0620
Response of the Arctic Freshwater Budget to Extreme NAO Forcing
Freshwater release from the Arctic to the deepwater convective regions of the Labrador and Nordic Seas is understood to play an important role in steering decadal global climate variability. An observed freshening of the North Atlantic since the mid-1960s appears to be related to changes in the export of freshwater from the Arctic, and the persistence of a high North Atlantic Oscillation (NAO) during this period. However, the specific response of the Arctic freshwater budget to the NAO is unclear. To investigate this response we use a high resolution (1/3 degree) regional version of the ocean-only MITgcm forced for 12 years with daily NCEP reanalysis data from 1992-2001. At this resolution the model resolves the major Arctic transport pathways, including the Bering Strait and Canadian Archipelago. We ran the model twice, keeping all reanalysis fields the same in both cases, but repeat the wind field of two contrasting NAO years in each run for the extreme negative and positive NAO phases of 1969 and 1989, respectively. Our results highlight a clear response in the Arctic freshwater budget to NAO forcing. Repeat NAO negative wind forcing results in virtually all freshwater being retained in the Arctic. In contrast, repeat NAO positive forcing increases the freshwater export out of the Arctic, primarily via the Fram Strait (54%) and Canadian Archipelago (29%), and results in a total loss in freshwater storage of 14000 km3. We find that the freshwater export via these two pathways increases by virtually the same amount (approx 700 km3 per yr) between the two forcing scenarios, highlighting the important role that the Canadian Archipelago plays in redistributing the freshwater of the Arctic.
U41C-0621
Composition of Upper Arctic Ocean Water Masses North of Ellesmere Island
As part of the Switchyard project CTD measurements and water samples have been collected beneath the sea ice North of Ellesmere Island in the spring between 2005 and 2007. The water samples have been analyzed for oxygen, nutrients, anthropogenic tracers, and oxygen-18. The core water masses have distinct signals in these various constituents and the data have been used to estimate the water mass composition and fresh water sources in the upper few hundred meters of the water column. The seawater component of the upper 100 m is primarily derived from the Pacific Ocean, but also contains about 10% meteoric water. The halocline extends from about 80 m to about 200 m and across this layer the fraction of Pacific water decreases from roughly 90% to ca. 10%; the opposite trend is observed in Atlantic water distribution. The fraction of meteoric water decreases from about 10% at the base of the mixed layer to zero at 200 m. The sea ice melt water fraction is negative in the upper 150 m indicating this is a region of sea ice formation and export.
U41C-0622
Dependence of Evapotranspiration on Meteorological Variables Barrow, Northern Alaska
What are the meteorological variables that best explain the evapotranspiration (ET) in arctic Barrow? How are the correlations distributed across different time scales? These are questions highlighting land-atmosphere, and due to its geography, also ocean interactions. The area experiences nearly saturated surface soils throughout the thawed season, large changes in open water area during the early summer, and is in close vicinity to the seasonally ice covered Chuckchi Sea/Arctic Ocean. Three 3-meter high eddy covariance towers are used in the study conducted in a drained lake basin. Measured air temperature, vapour pressure deficit, wind speed and direction, net and incident solar radiation is tested against ET in different temporal resolutions (30 min to monthly). The statistical method used is the Pearson's product-moment correlation that reflects the degree of linear relationship between two variables. Preliminary results show no significant correlation of mean daily air temperature to ET. Four years of data have been collected, of which three are used to study the dependence of ET on the meteorological variables. The fourth year data is used to validate the multi linear regression model. With historical weather observations, past soil moisture conditions will be estimated through the statistical model. The processes that are of specific importance for the area will be discussed through comparisons to studies in a temperate climate. The study is part of the U.S. NSF SNACS project (Study of Northern Alaska Coastal Systems).
U41C-0623
Attribution of Precipitation Changes in the Mackenzie and Yukon Watersheds During the Second Half of the 20th Century
The method of self-organizing maps (SOMs) is used to investigate changes in precipitation in northwestern North America including the Mackenzie and Yukon watersheds over the time period of 1957-2002. The SOM is used to create a synoptic climatology of 35 unique sea level pressure patterns for this region. The changes in frequency of occurrence for each of these patterns over the time period of study has been determined and the patterns are then related to precipitation in this region. Changes in precipitation are attributed to dynamic (circulation changes), thermodynamic (atmospheric moisture content changes), or a combination of these two mechanisms. Of particular interest are changes in precipitation that occurred after the climatic shift of 1976. In addition, attribution of precipitation changes are also studied in the context of changes in large scale climate indices (AO, PDO). This analysis has been performed over the time period of study to determine if the forcing for precipitation has changed over the analysis period.
U41C-0624
Rising minimum flows in northern Eurasian rivers suggest a growing influence of groundwater in the high-latitude water cycle
A first analysis of new daily discharge data for 111 northern rivers from 1936-1999 and 1958-1989 finds an overall pattern of increasing minimum daily flows (low-flows) throughout Russia. The increases are generally more ubiquitous than are increases in mean flow, occur in summer as well as winter, and occur in non-permafrost as well as permafrost terrain. A subset of 12 unusually complete river discharge records from 1935-2002 suggests that the most recent minimum-flow increases since 1985 are largely unprecedented in the historical record, at least for this small group of stations. Hydrograph baseflow separations were not performed. However, if minimum-flows are presumed at least correlative with groundwater and unsaturated zone inputs to river discharge, then the data suggest a broad-scale mobilization of such water sources in the late 20th century. It is unknown whether this phenomenon simply reflects increased precipitation throughput, or indicates that some other process is at play; what is known is that low-flows are rising in many watersheds across Russia. We speculate that reduced intensity of seasonal ground freezing, together with precipitation increases, could drive much of the +7 percent late twentieth-century increases in Eurasian river discharge to the Arctic Ocean http://lena.sscnet.ucla.edu
U41C-0625
Application of the VIC hydrologic model to explore the role of permafrost in observed Eurasian Arctic streamflow changes
Eurasian river discharge into the Arctic Ocean has increased since the 1930s, potentially impacting deep water formation in the North Atlantic and consequently the strength of the thermohaline circulation. However, long-term streamflow and precipitation trends are inconsistent, particularly for river basins underlain with permafrost, which suggests another source of water. We apply the VIC model to explore the potential contribution of permafrost melt to observed streamflow trends. In so doing, we have made various improvements to the model to handle decadal-scale permafrost dynamics. The use of a zero-flux computational bottom boundary allows for long-term temperature changes in the model's deeper soil layers, while the placement of the model's bottom boundary at several times the thermal damping depth minimizes the build- up of heat storage along the boundary. To improve computational efficiency, we distribute the thermal nodes used to solve the sub-surface heat equation exponentially with depth, and perform a grid transformation to solve the system in linear space. We solve the system implicitly to ensure numerical stability at time-steps larger than one hour, which also improves computational efficiency. Finally, we incorporate an excess ground ice and surface subsidence algorithm, in which porosity and soil depth decrease as excess ground ice melts. To explore the degree to which permafrost melt may have contributed to observed streamflow increases, we adjust the concentration of ground ice at various depths in the soil column until simulated streamflow trends match observed. In this way, we can comment on the plausible contributions of precipitation, evapotranspiration, and sub-surface storage changes to observed streamflow increases in select permafrost basins. We show results for our test basin, the Aldan River basin, an unregulated tributary to the Lena River. The Aldan River basin, 89 percent of which is underlain by continuous permafrost, has had significant streamflow increases since the mid 1940s. We demonstrate that permafrost melt may have been an important contribution to streamflow increases beginning in the 1950s to 1960s.
U41C-0626
Freshwater Sources and Transit Times in the Near-surface Waters of the Canadian Basin
The surface waters of the Canadian Basin constitute a pool of buoyant, relatively fresh, waters that are important to the dynamics of the Arctic Ocean as well as to the vertical stratification of the Nordic and Labrador seas. In this contribution we use multiple tracers (isotopes of oxygen, helium and hydrogen as well as dissolved anthropogenic gases) to look at sources and residence times of the freshwater component of the upper 500 meters of the Canadian Basin. New data from the 2005 Arctic Ocean Sciences trans-Arctic cruise are presented and analyzed in the context of data from prior cruises. The data offer a more detailed illustration than previously available of the buoyancy sources and surprising horizontal gradients of the residence times in the buoyant lens over the Arctic.
U41C-0627
PRESENT PERMAFROST EXTENT in ALASKA UTILIZING NUMERICAL MODELING
Area underlain by permafrost in Alaska varies from continuous in the north through sporadic and warmer ground in the south. A changing climate makes estimating thermal response and predicting changes in extent in the transitional areas valuable for wildlife management as well as human infrastructure resiliency. Out recent research has focused on the Seward Peninsula of Alaska. Where average air temperatures are just below freezing and the permafrost is very warm, an area susceptible to dramatic change in response to a warming climate. In this paper the focus expands to the state of Alaska using two methods of estimating extent: the Geophysical Institute Permafrost Lab method (GIPL model is based on the modified Kudryavtsev approach) and the TTOP method originally derived by Smith and Riseborough. Current meteorological data is based on the present observational record.
U41C-0628
Surface Water Storage Change as Evidence of Groundwater Gradients
Much of the Alaskan Arctic and Subarctic receives a minimal amount of annual precipitation. Changes to regional precipitation patterns and the general transient warming expected in the next century's lake hydrology and the associated wetlands place the risk of lakes perforating the permafrost boundary on the forefront. Lake change on the Alaskan landscape due to permafrost degradation is going to be important to local ecosystems and in, for example, providing habitat for migratory waterfowl in the next decades and centuries. Permafrost presence, absence, and thickness are interconnected in the deciphering of groundwater gradients and projection of surface water presence, absence, disappearance, and appearance on the Alaskan landscape. Detailed efforts have been made to produce datasets of presence or absence of the permafrost on the Seward Peninsula and further efforts are in place to do the same for the entire state. Continuous permafrost can provide an impervious barrier to groundwater movement and most groundwater-surface water interaction occurs in areas of discontinuous permafrost. With permafrost thawing and open talik formation in discontinuous permafrost regions, surface water formerly perched above the permafrost can drain into the subpermafrost groundwater. In contrast, in areas where the local hydraulic gradient is upwards, subpermafrost groundwater may discharge at the surface as the confining layer of permafrost degrades and an open talik forms. Lake change, in the absence of changes in evaporation and surface flow, are governed by the local vertical flux of water. In this study we compile observations of surface water storage change in Alaska and conjecture that shrinking/ disappearing lakes are evidence of supra-permafrost groundwater downwelling. The resulting dataset serves as verification for our model of groundwater dynamics. The planned method for determining the ground water gradient and degree to which vertical percolation will be restricted is to analyze digital terrain information with hydrology, permafrost, soils, geology, and current climate data. To start the groundwater gradient computations we will focus on areas with known hydrologic phenomena and elaborate on a vector based gradient map referencing the steepness of the terrain and the precipitation on the surrounding higher elevations. Once the present groundwater and surface water situation is captured, based on the future subsidence of the permafrost in areas on the landscape, we propose to forecast the wetness and dryness across Alaska, capturing the uniqueness of each watershed's turn toward wetter and then drier over the next decades and centuries.
U41C-0629
Modeling Runoff on the North Slope of Alaska Using the HBV Model
The Arctic fresh water hydrologic cycle is dominated by the melting of the seasonal snow cover and scattered precipitation events during the summer months. The HBV model has been applied in the Imnavait and Upper Kuparuk basins, located in the headwaters of the Kuparuk River on the North Slope, to examine runoff during spring and summer months. HBV is a semi-distributed conceptual model and was developed in 1975 by the Swedish Meteorological and Hydrological Institute. Simple data inputs and robust predictive capacity make HBV an attractive method for modeling discharge, particularly in basins with limited data. Current work has focused on calibrating the Imnaviat model with greater precision using historical meteorological and discharge data from 1988 to present. We are now developing new models for the larger Upper Kuparuk and Putuligayuk watersheds on the North Slope. Additional uses for the model include predicting discharge for ungaged North Slope basins east of the Kuparuk such as the Kadleroshilik and the Kavik. Parameter calibration initially begins with HBV-light, a scaled-down version of the model which is used to examine parameter sensitivity using a Monte Carlo procedure. Principle component analysis is then used to examine the interaction between the parameters and each year of the model run. An optimized set of parameters common to all calibrating years is developed and tested on additional data from gaged and ungaged basins. Existing research on ablation characteristics and precipitation correction is used to modify the associated parameters in HBV. Permafrost affects, such as the timing of active layer development, are integrated into the runoff response routine to produce a more accurate physical representation. Challenges associated with modeling larger watersheds include more spatially distributed processes and limited available data for model calibration.