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Greenland Climate Research Center

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Leif Toudal Pedersen
added a research item
A portion of the freshwater transport through Fram Strait consists of low-salinity Pacific-derived Arctic water flowing southward along the east coast of Greenland. The pathways of this water are currently unclear. An Ice Tethered Profiler deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected a profile every 3 hr for a year recording conductivity-temperature-depth (CTD) and Colored Dissolved Organic Matter (CDOM) fluorescence. This was accompanied by velocity observations. The CTD data revealed that the subsurface water (~15–85 m depth) characterized by high CDOM resembles the “cold Halostad” in the Canada Basin formed by the injection of Pacific water. A coastal branch of the Pacific water outflow from the Arctic Ocean supplies the Wandel Sea halostad, which shows a clear seasonal pattern. From July to October–November, the halostad is shallow, more saline, warmer, and with less CDOM. Conversely, from November to April, the halostad deepens, cools, freshens and CDOM increases, likely indicating a higher fraction of Pacific winter water. The CTD surveys, wind and current data, and numerical simulations show that the seasonal variation of wind over the continental slope likely controls seasonal changes of this intermediate water layer. Over northeast Greenland, winter winds have a northerly component from November to April, favoring Ekman transport of the Pacific-derived water to the Wandel Sea shelf. In contrast, the prevailing southerly summer winds result in retreat of the Pacific-derived water off the shelf. The landfast ice off-slope extension modifies wind-forcing disrupting seasonal patterns.
Leif Toudal Pedersen
added 2 research items
Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of 5 the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009) satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of 10 floe buoyancy, radar penetration and ice type distribution using both a scattering model and "Archimedes' principle". The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors 15 due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea) the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the 20 relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.
We examine SAR L1b data from the commissioning phase, currently available for the calibration and validation teams. We use CryoSat-2 data to detect leads in the sea-ice in an area north of Svalbard. Furthermore, we classify the sea-ice from computed freeboard values, and evaluate the coherence between the SAR backscatter and the CryoSat-2 data. The surface elevation is extracted from an 80% threshold retracker and a five parameter β-retracker, and this is given with respect to the DTU10 Mean Sea Surface model (MSS). The results are compared with an Envisat ASAR image, and we show that there is a strong correspondence between the freeboard heights and the leads visible in the ASAR image.
Leif Toudal Pedersen
added 9 research items
1] The uptake rates of atmospheric CO 2 in the Nordic Seas are among the highest in the world's oceans. This has been ascribed mainly to a strong biological drawdown, but chemical processes within the sea ice itself have also been suggested to play a role. The importance of sea ice for the carbon uptake in the Nordic Seas is currently unknown. We present evidence from 50 localities in the Arctic Ocean that dissolved inorganic carbon is rejected together with brine from growing sea ice and that sea ice melting during summer is rich in carbonates. Model calculations show that melting of sea ice exported from the Arctic Ocean into the East Greenland current and the Nordic Seas plays an important and overlooked role in regulating the surface water partial pressure of CO 2 and increases the seasonal CO 2 uptake in the area by approximately 50%.
Sea ice flux through the Nares Strait is most active during the fall and early winter, ceases in mid- to late-winter after the formation of ice arches along the strait, and re-commences after breakup in summer. In 2007, ice arches failed to form. This resulted in the highest outflow of Arctic sea ice in the 13-year record between 1997 and 2009. The 2007 area and volume outflows of 87 × 103 km2 and 254 km3 are more than twice their 13-year means. This contributes to the recent loss of the thick, multiyear Arctic sea ice and represents ∼10% of our estimates of the mean ice export at Fram Strait. Clearly, the ice arches control Arctic sea ice outflow. The duration of unobstructed flow explains more than 84% of the variance in the annual area flux. In our record, seasonal stoppages are always associated with the formation of an arch near the same location in the southern Kane Basin. Additionally, close to half the time another ice arch forms just north of Robeson Channel prior to the formation of the Kane Basin arch. Here, we examine the ice export with satellite-derived thickness data and the timing of the formation of these ice arches.
The Arctic is home to a circumpolar community of native people whose culture and traditions have enabled them to thrive in what most would perceive as a totally inhospitable and untenable environment. In many ways, sea ice can be viewed as the glue that binds these northern communities together; it is utilized in all aspects of their daily life. Sea ice acts as highways of the north; indeed, one can travel on these highways with dogsleds and snowmobiles. These travels over the frozen ocean occur at all periods of the sea ice cycle and over different ice types and ages. Excursions may be hunting trips to remote regions or social visits to nearby villages. Furthermore, hunting on the sea ice contributes to the health, culture, and commercial income of a community.