Institute of OceanographyUniversity of HamburgHamburg Germany

Reading, United Kingdom

Institute of OceanographyUniversity of HamburgHamburg Germany

Reading, United Kingdom
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Lei R.,Polar Research Institute of China | Tian-Kunze X.,Institute of OceanographyUniversity of HamburgHamburg Germany | Wang J.,National Oceanic and Atmospheric Administration | Kaleschke L.,Institute of OceanographyUniversity of HamburgHamburg Germany | Zhang Z.,Polar Research Institute of China
Journal of Geophysical Research: Oceans | Year: 2016

SSM/I sea ice concentration and CLARA black-sky composite albedo were used to estimate sea ice albedo in the region 70°N-82°N, 130°W-180°W. The long-term trends and seasonal evolutions of ice concentration, composite albedo, and ice albedo were then obtained. In July-August 1982-2009, the linear trend of the composite albedo and the ice albedo was -0.069 and -0.046 units per decade, respectively. During 1 June to 19 August, melting of sea ice resulted in an increase of solar heat input to the ice-ocean system by 282 MJ·m-2 from 1982 to 2009. However, because of the counter-balancing effects of the loss of sea ice area and the enhanced ice surface melting, the trend of solar heat input to the ice was insignificant. The summer evolution of ice albedo matched the ice surface melting and ponding well at basin scale. The ice albedo showed a large difference between the multiyear and first-year ice because the latter melted completely by the end of a melt season. At the SHEBA geolocations, a distinct change in the ice albedo has occurred since 2007, because most of the multiyear ice has been replaced by first-year ice. A positive polarity in the Arctic Dipole Anomaly could be partly responsible for the rapid loss of summer ice within the study region in the recent years by bringing warmer air masses from the south and advecting more ice toward the north. Both these effects would enhance ice-albedo feedback. © 2016. American Geophysical Union. All Rights Reserved.


Schaffer J.,Alfred Wegener InstituteHelmholtz Center for Polar and Marine ResearchBremerhaven Germany | Kanzow T.,University of Bremen | Jochumsen K.,Institute of OceanographyUniversity of HamburgHamburg Germany | Lackschewitz K.,elmholtz Center for Ocean Research KielKiel Germany | And 3 more authors.
Journal of Geophysical Research: Oceans | Year: 2016

The Denmark Strait Overflow (DSO) contributes roughly half to the total volume transport of the Nordic overflows. The overflow increases its volume by entraining ambient water as it descends into the subpolar North Atlantic, feeding into the deep branch of the Atlantic Meridional Overturning Circulation. In June 2012, a multiplatform experiment was carried out in the DSO plume on the continental slope off Greenland (180 km downstream of the sill in Denmark Strait), to observe the variability associated with the entrainment of ambient waters into the DSO plume. In this study, we report on two high-dissipation events captured by an autonomous underwater vehicle (AUV) by horizontal profiling in the interfacial layer between the DSO plume and the ambient water. Strong dissipation of turbulent kinetic energy of O( 10-6) W kg-1 was associated with enhanced small-scale temperature variance at wavelengths between 0.05 and 500 m as deduced from a fast-response thermistor. Isotherm displacement slope spectra reveal a wave number-dependence characteristic of turbulence in the inertial-convective subrange ( k1/3) at wavelengths between 0.14 and 100 m. The first event captured by the AUV was transient, and occurred near the edge of a bottom-intensified energetic eddy. Our observations imply that both horizontal advection of warm water and vertical mixing of it into the plume are eddy-driven and go hand in hand in entraining ambient water into the DSO plume. The second event was found to be a stationary feature on the upstream side of a topographic elevation located in the plume pathway. Flow-topography interaction is suggested to drive the intense mixing at this site. © 2016. American Geophysical Union. All Rights Reserved.


Gabrielski A.,Institute of OceanographyUniversity of HamburgHamburg Germany | Badin G.,Institute of OceanographyUniversity of HamburgHamburg Germany | Kaleschke L.,Institute of OceanographyUniversity of HamburgHamburg Germany
Journal of Geophysical Research C: Oceans | Year: 2015

The single-particle dispersion of sea ice in the Fram Strait region is investigated using ice drift buoys deployed from 2002 to 2009 within the Fram Strait Cyclones and the Arctic Climate System Study campaigns. A new method to estimate the direction of the mean flow, based on a satellite drift product, is introduced. As a result, the bias in the dispersion introduced by the mean flow is eliminated considering only the displacements of the buoys in the cross-stream direction. Results show an absolute dispersion growing quadratically in time for the first 3 days and an anomalous dispersion regime exhibiting a strongly self-similar scaling following a 5/4 power law for time scales larger than 6 days persisting over the whole time series of length 32 days. The non-Gaussian distribution of the velocity fluctuations with a skewness of -0.15 and a kurtosis of 7.33 as well as the slope of the Lagrangian frequency spectrum between -2 and -1 are in agreement with the anomalous diffusion regime. Comparison with data from the International Arctic Buoy Program yields similar results with an anomalous dispersion starting after 10 days and persisting over the whole time series of length 50 days. The results suggest the presence of deformation and shear acting on the sea ice dispersion. The high correlation between the cross-stream displacements and the cross-stream wind velocities shows the important role of the wind as a source for the anomalous dispersion. © 2015. American Geophysical Union.

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