C41A-0167 0800h
Ocean Dynamics in Recent Arctic Freshwater Changes
Freshwater changes and redistributions are salient phenomena among recently manifested changes in the Arctic climate system, whose anomalous exports may have significant impact on the deep convection and the Atlantic meridional overturning circulation (Manabe and Stouffer 1988; Hakkiene 1993). Observations and modeling experiments (e.g. Steele and Boyd 1998; McPhee et al. 1998; Zhang et al. 2003) have documented that the Eurasian Basin salinified and the Beaufort Sea freshened while the Arctic Oscillation persisted in its positive phase during the 1990s. Such changes and redistributions of the freshwater storage can predominantly attribute to the redirected Eurasian riverine water input (Steele and Boyd 1998; Zhang et al. 2003) and the changes of sea ice growth and melt (McPhee et al. 1998; Zhang et al. 2003). Horizontal transport in the upper ocean also plays an important role in the forming freshwater storage anomalies (Zhang et al. 2003). On the other hand, from the ocean dynamics point of view, it was hypothesized that freshwater may accumulates or releases corresponding to the fluctuation of overlying atmospheric cyclonic and anticyclonic forcing, namely positive and negative phase of the Arctic Oscillation. Anomalous high (low) sea level pressure may give rise to an enhanced (reduced) convergence and downwelling Ekman pumping to cause an accumulation (release) of freshwater. However, this hypothesis has not been examined intensively due to data availability. In this study, we employed an Arctic sea ice-ocean model to investigate this hypothesis and to examine ocean dynamics' role in the recent freshwater changes.
C41A-0168 0800h
Response of the atmospheric hydrologic cycle over the Arctic to climate change in CCSM3
Through influences on the freshwater content of the Arctic Ocean, the atmospheric hydrologic cycle over the Arctic has the ability to affect climate on a grand scale. The representation of this cycle within version 3.0 of the Community Climate System Model (CCSM3) has been found to be reasonable over the North Atlantic and the majority of Eurasia, although the model's hydrology is flawed within the Mackenzie River Basin. Keeping these strengths and weaknesses in mind, this study relates variability in the Arctic Hydrology to atmospheric circulation in both control and climate change runs of CCSM3. Composite analysis has been used to identify atmospheric circulation patterns associated with basin-scale hydrologic variability. The similarity of these patterns to those found in observations is discussed, as is their adjustment to climate change. Finally, the climate change response of the atmospheric hydrologic cycle is related to other elements of the Arctic freshwater budget.
C41A-0169 0800h
Arctic Terrestrial Hydrology Simulated by CCSM3
General Circulation Models are useful tools to investigate the interactions between the components of the Arctic hydrologic cycle and linkages between these components and the climate system. However, model performance must be assessed before these tools are used. In this paper, simulations of precipitation, evapotranspiration, runoff and streamflow from a control run of the Community Climate System Model, Version 3, are assessed for the Pan-Arctic region and for four major Arctic drainage basins. Spatial patterns of the long-term means and variance, and seasonal cycles of these components of the hydrologic cycle are evaluated. Observation networks in the Arctic are sparse and accurate measurements of many variables are difficult to make. Atmospheric reanalyses provide additional sources of data with which to assess climate model performance. Climate model fields are compared with estimates from the ERA-40 reanalysis, combinations of observed and model data from the Arctic-Rapid Integrated Monitoring System and with gauged streamflow. This work is part of an integrated assessment of the Arctic freshwater budget.
C41A-0170 0800h
Changes in the 21st Century Arctic Freshwater Budget Simulated in a Multi-Member Ensemble with the Bergen Climate Model
Complete mass, heat, and freshwater budgets have been calculated for all regions in the Arctic using output from a 300-year control integration with the Bergen Climate Model (BCM). Comparison with observation shows that the model reasonably well reproduces the observed sea-ice cover and oceanic circulation in the Arctic, although the sea-ice is in general too thin, and the mixed-layer too deep. Furthermore, the runoff, although based on a very simple scheme, is close to observations, both for the Russian rivers and for the Mackenzie River. Also the response to atmospheric forcing such as the Arctic Oscillation is realistic. An ensemble of 5 CMIP2 integrations, where the atmospheric concentration of CO2 is increased by 1% per year, has been performed and the results are compared to the control integration. Of particular interests for the freshwater budget are an almost total disappearance of the summer ice cover, an increased runoff in all major rivers, and an increased export of freshwater to the Nordic Seas and North Atlantic Ocean. Although there is a 10-12% reduction in the Atlantic meridional overturning circulation, there is actually a small increase in the Atlantic inflow to the Nordic Seas and via the Barents Sea to the Arctic Ocean. This may at least partly be attributed to increased westerlies (deeper Icelandic low) in the model simulations.
C41A-0171 0800h
Estimation of Arctic Land Surface Conditions and Fluxes via a Suite of Land Surface Models
River runoff from the Arctic terrestrial drainage system is thought to exert a significant influence over global climate, contributing to the global thermohaline circulation via its effects on salinity, sea ice, and surface freshening in the North Atlantic. Changes in these freshwater fluxes, as well as other components of the Arctic terrestrial hydrologic cycle such as snow cover and albedo, have the potential to amplify the Arctic's response to global climate change. However, the extent to which the Arctic terrestrial hydrological cycle is changing or may contribute to change through feedback processes is still not well understood, in part due to the sparseness of observations of such variables as stream flow, soil moisture, soil temperature, snow water equivalent, and energy fluxes. The objective of this project is to assemble the best possible time series (covering a 20+ year period) of these and other prognostic variables for the Arctic terrestrial drainage basin. While these variables can be estimated with a single land surface model (LSM), the predictions are often subject to biases and errors in the input atmospheric forcings and limited by the accuracy of the model physics. To reduce these errors, we have implemented an ensemble of five LSMs: VIC, CLM, ECMWF, NOAH and CHASM, all of which have been used previously to simulate Arctic hydrology under the Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) Experiment 2e. Model predictions of land surface state variables (snow water content, soil moisture, permafrost active layer depth) and fluxes (latent, sensible, and ground heat fluxes; runoff) are averaged both across the ensemble and over multiple runs, using the best available atmospheric forcing data with and without added random perturbations. Here we evaluate the multi-model ensemble averages in comparison with individual model simulations of variables including snow water equivalent, evaporation, total runoff, and soil thaw depth over the pan-arctic domain, and attempt to evaluate the hypothesis that the ensemble-averaged results are superior to those from any single LSM. In addition, we evaluate individual and multi-model performance in comparison with observations of stream flow, snow areal extent, and other variables as available.
C41A-0172 0800h
Atmospheric Modeling Over the Mackenzie, Kuparuk and Lena Watersheds: A Contribution to the NSF ARCSS Freshwater Initiative
Regional atmospheric model simulations over the Mackenzie, Kuparuk, and Lena watersheds have been completed for the time period September 1998 through September 2000 using domains with 50 km and nested 10 km horizontal grid spacing. These simulations are part of a 5-year collaborative project between the University of Colorado, Iowa State University, and the University of Alaska A A>A>ƒ_sA<sup><small>a</small></sup>A>ƒ,<sup><small>a</small></sup>" Fairbanks to model coupled atmosphere A A>A>ƒ_sA<sup><small>a</small></sup>A>ƒ,<sup><small>a</small></sup>" land hydrologic processes over watersheds with continuous and discontinuous permafrost. Output from the atmospheric model simulations will be used to drive a very high resolution land hydrology model, and potential feedbacks between the atmosphere and land process will be studied with a series of uncoupled model experiments. Initial results from the atmospheric model simulations will be presented, with a focus on model validation of the near surface atmospheric state. Particular attention will be given to model errors that are likely to have the largest impact in forcing the land hydrology model. A discussion of differences between the 50 km and 10 km horizontal grid spacing results will also be included.
C41A-0173 0800h
Exploring the Role of Land Surface Changes on the Variability of Pan-Arctic River Discharge
The export of freshwater to the Arctic Ocean plays a key role in both regional and global climates (e.g. via effects on the strength of the North Atlantic Deep Water (NADW) formation that drives the thermohaline circulation). Observed changes in streamflow may be linked both to direct and indirect effects of climate change. For example, a general warming leads to earlier spring runoff, however changes in high arctic vegetation such as increased incidence of brush can lead to increased snow accumulation, and hence sustained runoff later in the summer. Also, vegetation changes can substantially change evapotranspiration. Changes in snow cover extent and the distribution of vegetation and wetlands over the pan-arctic domain affect land-atmosphere energy exchanges, and the seasonality of river flow. Furthermore, recent research has suggested that changes in permafrost extent and the active layer depth may also be affecting river flow. We report a 46-year (1950-95) run of the Variable Infiltration Capacity (VIC) macroscale hydrology model over the pan-arctic land domain, designed to offer insights into the nature and causes of observed long term trends in river discharge. VIC is a semi-distributed grid-based model that parameterizes the processes occurring at the land-atmosphere interface. The most recent version of the model includes several recent improvements specific to cold-land regions. We summarize a set of model runs from which we have estimated the inflow to the Arctic Ocean from all pan-arctic land areas (including the Canadian Archipelago) and an assessment of the capability of the land surface model to simulate the observed changes in gauged streamflow. These results utilize precipitation and temperature fields that incorporate a method of adjustment to reflect the best current understanding of long-term precipitation and temperature trends over the pan-Arctic domain. Finally, we describe an exploratory analysis in which we use the model to evaluate the effects of changes in snow cover extent, land cover classification, and active layer depth on streamflow variability and trends over the last half century.
C41A-0174 0800h
Mapping Snowmelt and Snow Water Equivalent in Arctic Alaska using Microwave Remote Sensing
The transition from snow cover to snow free conditions for the Arctic land surface is the most significant event in the Arctic hydrologic cycle. Due to the spatial scale and inhospitable conditions characteristic of this region, classification of the transition and estimates of snow water equivalent (SWE) are best made with remote sensing techniques. In particular, microwave remote sensing has the advantages of imaging through the frequent cloud cover and long polar nights. Electromagnetic energy at these wavelengths is also extremely sensitive to the presence or absence of free water in a snowpack enabling the timing and extent of snowmelt to be mapped. Remote sensing techniques using a variety of microwave sensors to derive snowpack conditions for the North Slope of Alaska will be presented. The spatial and temporal progression of snowmelt is mapped from both active and passive microwave spaceborne sensors. One such snowmelt map, for the Kuparuk River Basin, is coupled to a snowmelt runoff model (SRM) to simulate the spring-time hydrograph. SWE estimates from microwave remote sensing are also evaluated on the North Slope.
C41A-0175 0800h
Remote Sensing of Spring Streams on Alaska's North Slope
Spring-fed headwater streams are thought to dramatically affect local aquatic food-web dynamics by providing continual ice-free refugia for species unable to tolerate freezing. Accurate locations of these streams on Alaska's North Slope are needed to investigate associated hypotheses. Thermal springs on Alaska's North Slope are spread over vast, roadless areas and are difficult to identify in summer by aerial survey. Pre-existing data on spring locations are incomplete, largely anecdotal and of insufficient accuracy for use in field sampling. Satellite remote sensing provides capabilities for measuring, monitoring and querying large tracts of remote landscape in an efficient, synoptic manner. Landsat Enhanced Thematic Mapper(ETM) imagery was used to reconnoiter a region of the North Slope using winter scenes, when the contrast between ambient conditions and the springs' thermal signal is easiest to detect. Scenes from February 9, 2002 were selected from the available archive based on cloud cover ($<$10%), and the lowest ambient temperature for dates with adequate archived imagery. Analytical methods were two tiered. A manual examination and interpretation of the imagery detected obvious linear features of relatively high temperature in logical locations for springs. A second examination, using masking and ratio techniques with tabular query, suppressed confounding factors and identified a second set of likely thermal spring locations. A subset coordinate list of candidate sites was developed from these findings, and drove sampling/ground truthing activity in the summer of 2004. All sites visited were confirmed springs and are part of ongoing aquatic food-web research based at Toolik Field Station.
http://www.uaf.edu/toolik/gis/NABS_poster.pdf
C41A-0176 0800h
Groundwater discharge and base flow variability in the Brooks Range, North Slope, Alaska
More than 30,000 liters/sec. of spring water discharges along the eastern part of foothills of the Brooks Range, North Slope, Alaska. These springs flow all year around and cover wide areas with aufeis every winter. In Arctic regions, aufeis is among the biggest temporary storage of freshwater during winter period (more than 8 months). This study examines the historical volume of the aufeis using aerial photographs and satellite imagery as well as MODIS Airborne Simulator (MAS). The energy balance of the aufeis is also an important parameter for estimating perennial aufeis formations. We estimate the Holocene ice volume of aufeis using CaCO3 deposits in the soil. Carbonate material distributions and 13C isotope enrichment signals are indicative of the area occupied by aufeis. Thermal enrichment of the 13C spring water was around 0 to -2 permil at the Hulahula River aufeis area. The 13C isotope of the area immediately outside the aufeis field is around -25 permil and is also very low in carbonate content. The analysis of in-situ soil sample for d13C complemented with remote sensing analyses reveals historic aufeis distributions. The CaCO3 deposits appears to possess a characteristic spectral signature that is evident in the 2300 and 2550 nm wavelength range (two absorption bands 2500-2550 nm and 2300-2350 nm and a band between those two at ~ 2400 nm (2375-2425nm ). The aufeis area was not much greater during historical times such as Little Ice Age (LIA) or Last Glacial Maximum(LGM). However, some of the aufeis and springs (at least Shubik and Sadlerochit springs) survived during LGM. In case of the Sadlerochit spring, the total winter discharge (16,510,000 m3) was almost all turned to aufeis,(15,988,866 m3) preserved as ice on the tundra terrain. Questions of the spring water's ground residence time and infiltration processes are also examined in this study. We collected water from springs, wells, surface water, and precipitation samples for isotope (C, O, H, Sr) and chemical analyses. Preliminary results indicated most of the spring water might come from upper south-facing slope of the Brooks Range (limestone area). Infiltrated meteoric water percolates along the fault between Paleozoic sedimentary rocks and Permo-Triassic sedimentary rocks. A multiple-member mixing model was used to estimate the residence time of groundwater. Their residence times were around 2500 years by statistical correction model. The Kuparuk aufeis (spring) may not follow the same path as other springs. Shallow intra permafrost groundwater system (<30m) was found at Kuparuk springs around aufeis field. The Kuparuk springs residence time was 700 years. A great deal of intra permafrost water has been observed in this area (mean annual ground temperature is-7.8°C at 2003-04). Climatic warming will activate more shallow groundwater system in this area
C41A-0177 0800h
Wind directional dependency of surface energy fluxes over north-eastern Siberia and its implications
In order to better understand the water cycle over tundra, micro-meteorlogical and hydrological observations were carried out over tundra near Tiksi, North-eastern Siberia and seasonal variations of energy budget components were estimated for two years. As an average, net radiation was partitioned for sensible heat flux 25-30%, for latent heat flux 50-55% and for soil conductive heat flux 20%. Those ratios were changed by wind direction. The southwesterly winds were warm and dry, made the sensibe heat flux small or its direction changed to ground surface, and the northeasterly winds were cold, gave the sensible heat flux to the atmosphere from the tundra surface. The southwesterly winds were associated with cyclone intrusions to this area and the northeasterly winds with anti-cyclones. More frequent intrusions of cyclones would decrease the sensible heat flux and increase the latent heat flux. A simple air temperature increase experiments using a simple heat balance model showed the sensible heat flux unchanged and the latent heat flux and conducetive heat flux in soil increased.
C41A-0178 0800h
Connections among atmospheric forcing, river runoff, and oceanological conditions in the Chukchi, East-Siberian and Laptev seas
Available historical meteorological and hydrological data sets mostly unknown to Western scientific society from the Laptev, East-Siberian (ESS), and Chukchi seas, have been collected and combined. All available hydrochemical data have been also accumulated. Comparing land-shelf data for two seminal areas of the Arctic, 1) the Laptev-western ESS, and 2) the eastern ESS-Chukchi Sea, shows a general opposition in ice and hydrological regimes. Thermal state (long-term and interannual variability)of the East-Siberian and Chukchi seas has been studied in connection with land thermal regime and atmospheric forcing. Anomalous "warm", "normal", and "cold" hydrological years were identified in the East-Siberian and Chukchi seas. Efforts are now underway to reveal the connections among the conditions in the East-Siberian, Laptev and Chukchi seas and the ice regime. Carbon dioxide (CO2) distribution and its fluxes are being studied in connection with atmospheric forcing using our own data. Dissolved methane distribution in the surface layer of the East-Siberian sea shows a plume of high concentration driven by Kolyma river runoff. Inflow of Pacific waters in the East-Siberian sea has been studied in different time-scales: from tens of years up to hundreds.
C41A-0179 0800h
The West Greenland and Ellesmere Coastal Currents: Spatial Scales of Freshwater Fluxes in Nares Strait From Synoptic Velocity Observations
The Canadian Archipelago constitutes one major pathway of freshwater from the Arctic Ocean into the North-Atlantic. The hypothesized freshwater flux is hypothesized to impact vertical stratification in the ocean and thus the global thermohaline circulation. While this simplification appears reasonable, it involves a number of physical processes all of which are poorly understood in general and most are ignored in the Arctic System Science context that requires integrations over large spatial and temporal domains. What are the physics that transform 0.0 psu salinity (fresh) water at the land-ocean, land-ice, or ice-ocean interfaces to the so-called "fresh" 34.9 psu salinity water at 2000-m depth in the Labrador Sea? How do fresh and thus buoyant waters mix vertically from the surface down and how do they advect horizontally from shallow coastal areas to the deep ocean? These are non-trivial dynamical questions that require appreciation of geophysical fluid dynamics. More specifically, the earth's rotation imposes a very strong dynamical constraint that often prevents across-shelf exchange. It's dynamically hard to move buoyant material from coastal waters to the deep ocean. It also explains why most fresh water is generally found adjacent to coastal regions. Buoyant discharge from point sources (.e.g., a river or the Arctic ocean) or line sources (the ice edge, the melting ice sheet of Greenland) cause circulation that vary at the internal Rossby radius of deformation. This fundamental dynamical scale is generally less than 10-km in most high-latitude ocean systems. Besides buoyant discharges, plumes, and coastal currents, it also scales eddies throughout the ocean. We here provide first examples on the spatial scales of the three-dimensional velocity field in Nares Strait and northern Baffin Island. Our 2003 surveys off western Greenland and Ellesmere Islands using data from the acoustic Doppler current profiler system aboard the USCGC Healy reveal complex but dynamically consistent flow patters that indeed suggest the internal deformation radius of about 5-km as the dominant spatial scale of variability. We find coastally trapped flows both off Ellesmere Island where they advect fresh waters southward and coastally trapped flows off Greenland where they advect fresh waters northward. Spatially variable tidal currents constitute a major source of temporal variability and we predict them using both state-of-the-art numerical models as well as a locally adapted least-squares function fitting. The two methods agree surprisingly well and give us great confidence in both model and data. It also gives confidence that the observed coastally trapped flows represent a significant signal. Biogeochemically motivated studies usually do not resolve the scales of these features in time or space resulting in severely aliased fields.
http://newark.cms.udel.edu/~muenchow/0307adcp
C41A-0180 0800h
Quantifying Uncertainties in Large Scale Water Budget: Case Study in Siberia
Assessment and prediction of Arctic River flows' effects on ocean circulation and climate are hindered by lack of knowledge about the terrestial water balance in remote regions. In this study, we quantify the components of the annual water budget for a large Siberian river basin and -- most importantly -- the uncertainty in the components. The water budget for a watershed can be simplified to basic inputs and outputs: Precipitation (P), Streamflow (Q), and Evapotranspiration (E). Over the long term, assuming negligible change in storage, inputs and outputs should balance, P = Q + E. However, errors in measuring and estimating the components lead to a nonzero closure error, CE = P - Q - E. The uncertainty in the water balance can be quantified by the variance of CE, which is equal to the sum of the component variances (assumed independent). The closure error and its variance were estimated for the 57000 km$^2$ Tom River basin (a subbasin of the Ob River) for five water years, 1981- 1985. We hypothesized that (a) the CE would be negative due to underestimation of P by the sparse, low-elevation precipitation network, and (b) statistical hypothesis testing would show that the CE is not significantly different from 0, due to uncertainty in the components. The basin mean and variance of P were estimated by kriging station observations. The annual mean Q was obtained from discharge measurements at Tomsk, Russia; the uncertainty in Q was based on published estimates of rating curve error bars. The basin mean and variance of E were computed from a derived distribution based on Monte Carlo simulation of the Penman Monteith model, driven by measured meteorological data at Tomsk, and accounting for variation in elevation and vegetation. Annual CEs were negative, ranging from -160 to -325 mm, and the standard deviations ranged from 50 to 60 mm. The CE was significantly different from 0 for all five water years, supporting the belief that annual P is underestimated by the gage network. The level of uncertainty, largely due to E, makes it difficult to assess the accuracy of P. The uncertainties in the components and the CE are an indication of the confidence in statements about the water balance of the region under current or changed conditions.
C41A-0181 0800h
Isotope tracers of freshwater distributions, pathways and timescales within the Arctic Ocean.
We present oxygen isotope, tritium and helium isotope data from the Arctic Ocean. The tritium and helium data are used to calculate apparent ages of the water samples (the time since a water sample was last exposed to the atmosphere), the oxygen isotope data for estimates of freshwater content. The data were gathered mostly during the 1990s, and are part of a growing database of these isotopes. Coverage in the Arctic Ocean is still uneven and incomplete, and ongoing work is aimed at filling these data gaps and establishment of time series at important locations in the Arctic Ocean. However, there is sufficient information in the existing data sets to establish pathways and age estimates for broad sections of the upper 300 meters of the Arctic Ocean. This includes the relatively fresh Polar Waters, which are a source of buoyancy for the Nordic Seas, as well as the Halocline, which constitutes the main stratification of the Arctic water column. In this contribution we present the data on depth and density surfaces. The tritium/He-3 apparent ages are interpreted as a relatively accurate estimate of the first moment of the distribution of transit times between the surface and the sampling site for those waters whose mean ages are less than about 30 years. The delta O-18 values and the tritium are used to track the fate of terrestrial runoff in the Arctic Ocean. The results include a surprising range of apparent ages along isopycnal surfaces, and an unexpected age maximum in the lower halocline over much of the central Arctic Ocean. The former is evidence of dynamical barriers to isopycnal dispersion; the latter indicates relatively rapid horizontal ventilation of the "Atlantic Layer" below the halocline. Some halocline waters show apparent ages beyond the "scale" of the tritium decay clock, indicating either upwelling regions or quasi-stagnant features in a generally more active layer. The data also offer estimates of transit times along the boundary current connecting the Atlantic inflow to the Eurasian Basin with the Canadian Basin, which are complementary to recent work using heat anomalies and CFCs. This information can be applied to studies of pathways and time scales for the propagation of changes at the Arctic Ocean boundaries (e.g., inflow properties through Bering Strait and the Nordic Seas, coastal runoff, atmospheric conditions) into the stratified layers of the Arctic Ocean water column.
C41A-0182 0800h
Annual Freshwater and Heat Content From 2003-2004: First Results from the Beaufort Gyre Observing System
Seasonal variability of freshwater and heat content in the Beaufort Gyre will be presented, and causes of interannual changes will be discussed based on data from the Beaufort Gyre Freshwater Experiment (BGFE; http://www.whoi.edu/beaufortgyre), a prototype Ice-Tethered Profiler (ITP), and using CTD and XCTD data collected between 2001 and 2004. As part of the BGFE and in combination with the JWACS cruises on the CCGS Louis S. St. Laurent, three bottom-tethered moorings were deployed in August 2003 at coordinates 75N and 150W, 78N and 150W and 77N and 140W, and were recovered in August 2004. Year-long time series of sea ice draft (from upward looking sonars mounted at the top mooring float), temperature, salinity, and currents in the 50-2000m layer (from moored profilers), and bottom pressure (from pressure tide gauges) were retrieved from the instruments. Information in the upper ocean above 50 m, were also obtained from four drifting ice beacons which were also installed during the 2003 cruise and have telemetered temperature and salinity data at 10, 25, and 40 m for more than a full year. In order to continue collecting data from the Beaufort Gyre to study multiannual variability, the moorings were refurbished and redeployed in 2004 at the same locations and the buoy array was augmented with an ITP (providing CTD data with 1 meter vertical resolution and 6 hours temporal resolution down to 750 m) establishing the Beaufort Gyre Observing System (BGOS).
http://www.whoi.edu/beaufortgyre
C41A-0183 0800h
The role of moisture transport in the arctic freshwater cycle
This study focuses on understanding the impact of recent Arctic warming to the regional freshwater cycle from the perspective of the atmospheric integrated moisture transport (IMT), estimated based on measurements by multi- spaceborne- sensors. As one of the important components in the polar water/ice balance, IMT is traditionally derived from inadequate rawinsonde measurements. A method is developed to retrieve IMT over oceans using spaceborne scatterometer and microwave radiometer observations. More than five years (from August 1999 to present) daily IMT fields, at 0.5∞x0.5∞ resolution over global ocean, were produced by combining measurements from NASA scatterometer SeaWinds on QuikSCAT (QSCAT) and the Special Sensor Microwave/ Imagers (SSM/I) from Defense Meteorological Satellite Program (DMSP). Retrieved IMT fields have demonstrated credible annual and interannual variations in polar regions. Taking advantage of unprecedented coverage and resolution of satellite data, we were able to depict the temporal and spatial variation of IMT across the boundary of Greenland ice-sheet along a simulated coastline surrounding the Greenland, and revealed its correlation with observed abnormal Greenland ice-sheet melting during 2002 and 2003. The IMT data was also analyzed in the context of global water cycle to explore the linkage between changes in arctic freshwater cycle and global climate.
C41A-0184 0800h
The Biogeochemistry of Dissolved Organic Matter and Nutrients in two Large Arctic Estuaries and Potential Implications for our Understanding of the Arctic Ocean System
The discharge, composition and fate of dissolved organic matter (DOM) and nutrients was investigated in two of the largest Arctic rivers, Yenisei and Ob, in order to assess their role for the biogeochemistry of the Kara Sea, and the potential of terrestrial DOM as tracer for the Arctic Ocean. Ultrafiltered DOM (UDOM) from the 2 river-estuary systems was characterized by high C/N ratios (34 - 49), depleted stable carbon isotope values (less than -26.5 per mill), depleted stable nitrogen isotope values (1.8 - 4.2 per mill), and enriched delta 14C values (84 - 307 per mill). The distribution of DOM and its chemical properties indicated no major loss processes during estuarine mixing but showed considerable variability between the rivers and years suggesting a variable input of plankton-derived DOM. The input of plankton-derived DOM was reflected in elevated neutral sugar yields, decreased C/N ratios, but variable stable carbon isotope values. In contrast, stable nitrogen isotope values appear to be more reliable indicators to distinguish terrestrial from plankton-derived DOM in this estuarine system. Based on stable nitrogen isotope values we estimate that between 6 and 16% of the DOM in the river and estuaries is of plankton origin. Clear differences were found in the chemical composition of DOM size fractions. Plankton-derived DOM was more abundant in the higher molecular weight fractions whereas terrestrial-derived DOM dominated the lower molecular weight fraction. This suggests a more heterogeneous origin of DOM than is revealed from looking at the composition of the bulk DOM. Compiling the information from this study with previous studies indicates that river input of DOM and nutrients is not the main driver of autotrophic and heterotrophic processes in the Kara Sea ecosystem. Consistent with previous reports, we found the terrestrial fraction of river DOM to be largely conservative in the estuaries underscoring the potential of terrestrial DOM as a tracer in the Arctic Ocean, especially when combined with standard hydrographic measurements.
C41A-0185 0800h
A Statistical Examination of Spatial and Temporal Trends in Eurasian Arctic River Discharge
The importance of Arctic river systems to regional and global environments has been well documented. In particular, recently observed increases in freshwater discharge may influence Arctic Ocean ice pack dynamics and, by extension, have a substantial impact on global climate. Despite its critical role as both a driver and an indicator of climate change, many aspects of the Arctic hydrologic cycle are poorly understood. One of the most promising tools in understanding Arctic river discharge is R-ArcticNet v. 3.0, a pan-Arctic database of monthly discharge values for over 8000 hydrologic gauging stations. Many of these stations provide a nearly continuous time series from the early 20th century to the present. In this study, we examine trends in discharge for stations in the Eurasian Arctic at multiple spatial and temporal scales in an attempt to better understand the dynamics of the Arctic hydrologic cycle. The Mann-Kendall test for monotonic trend, a non-parametric test of statistical significance, is used in combination with simple linear regression to examine variations in discharge at monthly, seasonal, and annual time scales for basins ranging in size from 100 to nearly 3 million sq. km. Results of this analysis are mapped using GIS software in order to facilitate the observation of patterns in discharge variation across the Eurasian Arctic as well as to allow comparison with other variables including permafrost extent. Preliminary results suggest that changes in discharge vary substantially from region to region; permafrost extent appears to have little influence on the distribution of increases and decreases in discharge.
C41A-0186 0800h
Discharge and water chemistry of High Arctic rivers in NW Greenland (76$\deg$N, 68$\deg$W)
The volume, temperature, and quality of freshwater runoff from high latitude areas ultimately affect sensitive components of polar oceans, including water stratification, nutrient cycling, and formation of deepwater currents. Freshwater is conveyed from Greenland to the ocean from a multitude of medium-sized rivers for which little is known about discharge and water characteristics. River runoff together with microclimate and soil processes were recorded in a typical high Arctic area in NW Greenland where complete climate records from pre-1978 to the present indicate increases in mean annual air temperature from -12.0$\deg$C to -10.7$\deg$C and precipitation from 65 mm to 120 mm water equivalent between 1993 and 2002. The study will improve understanding of the interaction between climate, landscape processes, and river runoff. The study site extends from the western edge of the Greenland Ice Sheet to Baffin Bay; it covers an area ranging between 10-20 km E-W and 10-15 km N-S, and the elevations reach 700 m. It is a typical high Arctic environment with sparse vegetation and pervasive active patterned ground. Most of the area is covered by glacial drift that resembles the underlying sedimentary and igneous Archean and Proterozoic bedrock. To address how seasonal weather patterns and landscape processes affect runoff and water quality, as well as to examine weathering and carbon budgets in the drainage, we monitor water discharge and suspended load, water temperature, water chemistry (pH, dissolved ions, dissolved organic and inorganic carbon) of three rivers. Two of these rivers originate as melt water runoff from the Greenland Ice Sheet. The third stream is fed by local snowmelt and summer rain events. In addition, climate data along with soil moisture and temperature are recorded with automated stations at two locations. The potential sources of river water are thawing permafrost, local snowmelt, rain, and melting of glacial ice that all have distinct isotopic signatures ($\delta$D and $\delta$$^{18}$O). Stable isotopes therefore, are used to separate the hydrograph into these sources to help us relate discharge pattern and water quality to climate (precipitation, temperature) and landscape processes (thawing of permafrost, weathering, decomposition of organic matter). This presentation focuses on first data set collected from June to September 2004.
C41A-0187 0800h
Multi-Year Observations of Metal Concentrations in Major Arctic Rivers
The PARTNERS project is a multi-year effort to measure several biogeochemical parameters in the six largest rivers that drain the watershed of the Arctic Ocean (Yenisey, Lena, Ob, Mackenzie, Yukon, and Kolyma) as a means to study the origins and fates of continental runoff. Here we report results of analyses of water samples collected in 2003-2004 for a suite of dissolved metals including Ba, Cd, Ce, Co, Cr, Cs, Cu, Fe, Li, Mn, Mo, Ni, Pb, Rb, Re, Sr, Tl, U, V, and Zn. These data demonstrate the variability in metals levels between rivers and the seasonal/interannual variability within individual rivers. The PARTNERS data are compared with previously unpublished measurements of dissolved and particulate concentrations of Cd, Cu, Pb and Zn in samples of water and suspended sediment collected in summer 1998 from the lower reaches of six major Eurasian arctic rivers: the Onega, Severnaya Dvina, Mezen, Pechora, Ob and Yenisey (Guay et al., Marine Chemistry, submitted). These data comprise some of the earliest measurements of trace metals in Eurasian arctic rivers above the estuaries using recognized clean techniques. Significant (a = 0.05) differences were observed between the mean concentrations of metals in the individual rivers, with highest levels overall observed in the Severnaya Dvina and Yenisey. Comparing crustal elemental abundances with ratios of Cd:Zn, Cu:Zn and Pb:Zn in the suspended particulate samples suggests contributions of metals to thses rivers from additional sources besides continental weathering.
C41A-0188 0800h
A Preliminary Evaluation of Carbon Sources and Ages Exported By Major Arctic Rivers
An overall goal of the PARTNERS project is to determine the fate of continental runoff and investigate the biogeochemical make up of runoff originating from different regions of the Arctic. Carbon isotopic (13C and 14C) investigations of bulk carbon pools provide important information on their sources and ages. With respect to global change, shifts in the isotopic signatures of different carbon pools can provide important evidence that the sources and/or processing of terrestrial carbon have undergone fundamental changes. Furthermore, there is a rising concern that as the Arctic warms a portion of the large amount of carbon sequestered in soils and peat might be mobilized to atmospheric and ocean reservoirs. One approach for detect such a mobilization is 14C-aging of major carbon pool in rivers. In this presentation we will evaluate carbon data collected during summer 2003 for 5 major arctic rivers (Ob, Yenisey, Mackenzie, Yukon, and Lena). 14C will be used to estimate average ages of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) being transported in river waters. 13C data will be used to further clarify organic matter sources. Contextual data on alkalinity, pCO2, carbonate, and bicarbonate concentrations in the 5 rivers will also be presented.
C41A-0189 0800h
A Record of Dissolved Metal Concentrations in the Lena River During the Period of Ice Breakup
The PARTNERS project is a 5-year research program (2002-2007) funded by the Arctic System Science Program of the U.S. National Science Foundation. The objective of the PARTNERS project is to measure several biogeochemical parameters in the six largest rivers that drain the watershed of the Arctic Ocean (Yenisey, Lena, Ob, Mackenzie, Yukon, and Kolyma) as a means to study the origins and fates of continental runoff. As part of the PARTNERS field program for 2004, samples were collected on the Lena River in the spring (May-June) during the period of peak discharge and ice breakup. Samples were collected from the bank at the town of Zhigansk (66.75 N, 23.38 E) once daily from May 28th through June 7th, 2004. The river was completely ice covered at the beginning of this period. The river level rose dramatically each day until ice breakup, which occurred on May 30th. Following breakup, the river level began to drop steadily. Visual observation of daily water samples indicated a darkening of the tannic brown color of the river water as discharge levels increased up until breakup, suggesting an increase in DOC concentrations associated with the peak discharge and ice breakup period. Water samples for metals analyses were syringe filtered in the field through 0.45 um polypropylene and 0.02 um Anotop filter discs and acidified under clean conditions upon return to the laboratory. The samples were analyzed by high-resolution ICPMS for a suite of metals including Ba, Cd, Ce, Co, Cr, Cs, Cu, Fe, Li, Mn, Mo, Ni, Pb, Rb, Re, Sr, Tl, U, V, and Zn. Here we report the results from these analyses as a daily time series of metal concentrations bracketing the ice breakup and peak discharge events. During this relatively short amount of time, significant fluctuations in metal concentrations were observed, which are likely related to concurrent fluctuations in DOC concentrations and other changes in river chemistry occurring during this dynamic period of the annual hydrologic cycle in the watershed.
C41A-0190 0800h
Mass Flux of Water, Sediments and Chemical Constituents to the Laptev Sea of the Russian Arctic via the Lena River
The Lena River, one of the world's longest rivers, stretches from southern Siberia, north of Lake Baikal and is the second largest river contributing to the freshwater budget of the Arctic Ocean. During the summer of 2003, ADCP transects of the river's currents, bathymetry and acoustic backscatter were repeated for 500km reaches and at each major tributary, covering over 3,600km of the river's length. Concurrently, multi-parameter CTD casts, water chemistry and sediment concentrations were sampled. Preliminary results show water flow through the river increased with distance from the headwaters (150m$^{3}$/s) and increased greatly with contributions from the many tributaries along the river's length, reaching a peak (over 37,000m$^{3}$/s) 64km before the delta at Stolb. Approximately 94% of the Lena's discharge through the delta was accounted for using ADCP flow calculations from transects in three primary distributaries through the delta. To determine the influence of tidal pumping at the mouth, the principle navigation distributary (Bykovskaya) was resampled at the interface with the Laptev Sea, (mouth of Neelov Bay, near Tiksi), repeatedly over a 40-hour interval revealing a lunar semidiurnal period amplitude of oscillation in flow of the same order magnitude as the `subtidal' discharge. Well-mixed thermohaline profiles were evident in the ebb discharge, but during flood, the water was thermally stratified. The net flux through the mouth accounted for only 70% of the flow to the upper reaches of the same channel (Bykovskaya). A comparison with a historic record of Lena flow places the 2003 samples in phase and approximately equal to the 60-year average. The high resolution ADCP sampling of the currents and acoustic backscatter throughout the measured cross-sections were repeated two-three times per station. Net isopleths of flux will be constructed based on the average of the repeated ADCP transects. The net isopleths will then be used to extrapolate chemistry and suspended sediment data and obtain more comprehensive estimates of mass flux. The results will then be compared with the more traditional method by taking the product of the concentration and the river discharge and will then be compared with similar historic estimates. This study will help to characterize the Lena River flow and discharge to the Laptev Sea of the Russian Arctic.
http://arcticchamp.sr.unh.edu/featuredproject/index.shtml
C41A-0191 0800h
Magnetic Susceptibility Signals to Reconstruct Lena River Freshwater Discharge Events in the Laptev Sea and Neelov Bay, Russian Arctic.
River discharge into the Arctic is known to cause changes in sea ice production and consecutively affect global climate. The Russian Lena River is one of the major contributors into the Arctic Ocean, delivering approximately 770 km$^{3}$/year of freshwater and about 21 x10$^{6}$/year tons of suspended material. Here we present preliminary evidence of fresh water discharge events from the Lena River into the Laptev Sea, Russian Arctic. During two separate coring-oceanographic expeditions in July and September, 2003, over 25 piston, gravity and vibro cores were collected from Neelov Bay and along a transect that extends from the delta floodplain onto the Laptev shelf. Preliminary results from our cores demonstrate that high magnetic susceptibility signals are a good indicator of river sediments deposition and provide an estimate of the number and magnitude of the river discharge. Sedigraph analyses in combination with Wet Sieving analysis (grain size $>$ 3phi) reveal changes in grain size distributions and accurate grain size compositions along the core, which are well correlated with high magnetic susceptibility peaks. Based on lithostratigraphic interpretations and magnetic susceptibility correlations, at least 6 major sections are identified as possible discharge events in two transects that extends from the Lena River Delta into the Laptev Sea Shelf. The magnitude of the magnetic susceptibility peaks appears to reflect the strength of flow and the resulting spatial distribution of sediments during each deposition event associated with each unit. In Neelov Bay, cores in Transect 2 show the possibility that terrestrial material may be from a different source than Bykovskaya channel in the south-east part of the bay. This terrestrial material may be transported from coastal sources by wave refraction or by wind, and/or submarine currents. Future work will help us to understand and reconstruct the chronology of observed sedimentological events.
C41A-0192 0800h
Amplified carbon release from vast West Siberian peatlands by 2100
The potential impacts of climate change on peatland carbon cycling are subject to ongoing debate. Since the Last Glacial Maximum, northern peatlands have behaved primarily as a net sink of atmospheric carbon, storing up to $\sim$455 Pg C or one-third of the global soil carbon pool. However, the likely fate of this carbon under a warming climate remains a major unanswered question in Arctic Science and is particularly relevant in West Siberia, which contains the world's largest stores of peat carbon, exports massive volumes of freshwater and dissolved organic carbon (DOC) to the Arctic Ocean, and is warming faster than the Arctic as a whole. Here we present extensive DOC measurements from 96 watersheds distributed throughout West Siberia, providing data on a much larger spatial scale than previous studies and for the first time explicitly examining stream DOC in permafrost environments. Our results show cold, permafrost-influenced watersheds release little DOC to streams. However, we find drastically higher values in warm, permafrost-free watersheds, rising as a function of peatland abundance. The two regimes are demarcated by the position of the -$2\deg$C air temperature isotherm, which is also approximately coincident with the permafrost boundary. Climate models predict near-doubling of these warm areas in West Siberia by 2100, suggesting up to 700$%$ increases in stream DOC concentrations and 2.7-4.3 Tg yr$^{-1}$ increases in DOC flux from the region.
C41A-0193 0800h
Terrestrial and Ecological Impacts of Rain-on-Snow and Melt-Freeze Events in the Circumpolar Arctic
Incidents of rain-on-snow and melt-freeze events have been shown to have dramatic impacts on the heat budget of arctic permafrost, frequency of avalanches in mountainous regions, and the health of native caribou and reindeer populations. Latent heat from freezing rainwater that has percolated through the snow pack warms the soil surface, while ice layer formation in the snow pack can lead to snow instability and difficulty of movement and forage for reindeer and caribou populations. These same mechanisms allow melt-freeze events to have similar impacts. To date however, both the relative importance of these two mechanisms, and their extent in the circumpolar Arctic, have yet to be evaluated. We characterize past occurrences of and trends in rain-on-snow and melt-freeze events for the circumpolar arctic using meteorological station data and the European 40-Year Reanalysis, and we place a particular emphasis on the typical synoptic features of these events, and their control by the larger-scale patterns of the atmospheric circulation. We also present analysis of a future climate scenario using daily output from the CCSM3 model under an enhanced greenhouse gas environment which shows an increase in total area with rain-on-snow events, as well as an increase in the frequency of rain on snow and melt freeze events for much of the high northern latitudes. We use each of these characterizations as inputs to a permafrost and snow pack model to quantify the past and future terrestrial and ecological impacts of these events in the circumpolar arctic.
C41A-0194 0800h
Historical human demands for freshwater in the Arctic
The overall objective of this research is to understand how humans rely on freshwater at local and regional scales in selected parts of the Arctic, how these dependencies have changed in the recent past, and how they are likely to change in the future. This study is taking place on the Seward Peninsula where climate induced changes in the hydrologic cycle are currently being observed. This presentation will document results to date on historical industrial and domestic water demand on the Seward Peninsula. Preliminary results suggest that water use in the Nome Mining District decreased proportionally with the decline of placer mining operations. Water was used in placer gold mining operations on the Seward Peninsula to run hydraulic giants and sluice boxes. Because water was one of the limiting factors in mining operations, a series of ditches diverted nearly all available surface water in the Nome mining district between 1905 and 1914 for industrial use. The domestic water demand, that is, water used for drinking, cooking and cleaning, increased over the past 40 years as piped water and sewer systems were installed in many villages. Domestic demand can increase by 900% when a community installs piped water. The increase in demand corresponding to this change of delivery system can be seen in the difference between water consumption in a village with a central watering point, such as Wales, and a village such as Brevig Mission, where every house is connected to a piped water and sewer system. Historical pressures on the freshwater resource are being used to better understand the vulnerability of the resource now and in the future. This study is being funded under the NSF Arctic System Science Program, Human Dimensions of the Arctic (OPP-0328686).
C41A-0195 0800h
Snowmelt Hydrology of a Headwater Arctic Basin Revisited
Nine months of snow accumulation in the Alaskan Arctic guarantees that the snowmelt event will be a significant annual hydrologic event. These breakup floods constitute a majority of the maximum annual floods, although rainfall floods will generate the peak floods of record for small to intermediate sized headwater catchments. A paper published after the initial five years of study (1985-1989) concluded that redistribution of the snowpack by wind, direction of the prevailing winds and lack of subsurface storage produced runoff responses that resulted in significantly high values. The average maximum snowpack leaving the Imnavait Creek catchment as runoff immediately following ablation ranged from 0.50 to 0.66. What have we learned from 15 more years of data collection for this small headwater basin? First, our initial conclusions are still true. Further, this additional data allows us to re-examine the annual variability of the snow water equivalent (SWE) and timing of ablation, and the hydrologic runoff response. Over the 20-year period of record, the SWE has ranged from 69 mm to over 185 mm (standard deviation of 33 mm) and the window of ablation is from late April to June 10, or about six weeks. Both of these ranges are much greater than those observed during the first 5 years. Also, the runoff ratio over this period varies from 0.44 to 0.80 with a standard deviation of 0.11. This recent increase in variation may or may not be due to a changing climate. The subtle impact of a warming climate may be lost in the large inter-annual variation of hydrologic variables; however this reanalysis does permit better quantification of the natural variability and the 20-year data set is now beginning to provide the basis for evaluating longer-term trends.