ALBERT

Description: The ocean plays an important role in modulating the mass balance of the polar ice sheets by interacting with the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given that the flux of warm water onto the continental shelf and into the sub-ice cavities is steered by complex bathymetry, a detailed topography data set is an essential ingredient for models that address ice–ocean interaction. We followed the spirit of the global RTopo-1 data set and compiled consistent maps of global ocean bathymetry, upper and lower ice surface topographies, and global surface height on a spherical grid with now 30 arcsec grid spacing. For this new data set, called RTopo-2, we used the General Bathymetric Chart of the Oceans (GEBCO_2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the International Bathymetric Chart of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves, and sub-ice cavities, RTopo-2 now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at a good representation of the fjord and shelf bathymetry surrounding the Greenland continent. We modified data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ, and Sermilik Fjord, assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off Northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79° N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey data for the region. Radar data for surface topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centres of Technical University of Denmark (DTU), Operation Icebridge (NASA/NSF), and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves, RTopo-2 largely relies on the Bedmap-2 product but applies corrections for the geometry of Getz, Abbot, and Fimbul ice shelf cavities. The data set is available in full and in regional subsets in NetCDF format from the PANGAEA database at doi:10.1594/PANGAEA.856844.

Description: The ocean plays an important role in modulating the mass balance of the polar ice sheets by interacting with the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given that the flux of warm water onto the continental shelf and into the sub-ice cavities is steered by complex bathymetry, a detailed topography data set is an essential ingredient for models that address ice-ocean interaction. We followed the spirit of the global RTopo-1 data set and compiled consistent maps of global ocean bathymetry, upper and lower ice surface topographies and global surface height on a spherical grid with now 30-arc seconds resolution. We used the General Bathymetric Chart of the Oceans (GEBCO_2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the International Bathymetric Chart of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves and sub-ice cavities, RTopo-2 now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at a good representation of the fjord and shelf bathymetry surrounding the Greenland continent. We corrected data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ and Sermilik Fjord assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79° N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey data for the region. Radar data for surface topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centers of Technical University of Denmark (DTU), Operation Icebridge (NASA/NSF) and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves, RTopo-2 largely relies on the Bedmap-2 product but applies corrections for the geometry of Getz, Abbot and Fimbul ice shelf cavities. The data set is available in full and in regional subsets in NetCDF format from the PANGAEA database at https://doi.pangaea.de/10.1594/PANGAEA.856844.

Description: 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( math formula) 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 ( math formula) 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.

Description: More than 25% of mean global sea level rise is caused by mass loss of Greenland Ice Sheet (GrIS). A significant part of this melt is attributed to the interaction between marine terminating glaciers of the GrIS and the surrounding warm ocean waters. However, the sources and pathways of the warm waters on the shelf, their variability and mechanisms of the heat transfer involved are variable regionally and yet largely unknown. In this work, we focus on the 79-North Glacier (79-NG), a major glacier in North-East Greenland that was subject to an increased melt in the last years. Recent observations show that Atlantic Intermediate Water (AIW) warmer than 1°C reaches the 79NG via the trough system on the East Greenland continental shelf. In particular, these observations indicate that AIW reaches the glacier rather through the southern Norske Trough than through the northern Westwind Trough. Here we employ Lagrangian modelling and analysis using a high resolution FESOM (Finite Element Sea Ice-Ocean Model) simulation. Particle trajectories representing warm AIW mass are calculated to determine the pathways of this water mass on the adjacent shelf in the Norske Trough, and we analyze the water property changes along the trajectories. Moreover, to identify the sources of the AIW in the vicinity of the 79-NG, we compute backward particle trajectories

Description: More than 25% of mean global sea level rise is caused by mass loss of Greenland Ice Sheet (GrIS). A significant part of this melt is attributed to the interaction between marine terminating glaciers of the GrIS and the surrounding warm ocean waters. However, the sources and pathways of the warm waters on the shelf, their variability and mechanisms of the heat transfer involved are variable regionally and yet largely unknown. In this work, we focus on the 79-North Glacier (79-NG), a major glacier in North-East Greenland that was subject to an increased melt in the last years. Recent observations show that Atlantic Intermediate Water (AIW) warmer than 1°C reaches the 79NG via the trough system on the East Greenland continental shelf. In particular, these observations indicate that AIW reaches the glacier rather through the southern Norske Trough than through the northern Westwind Trough. Here we employ Lagrangian modelling and analysis using a high resolution FESOM (Finite Element Sea Ice-Ocean Model) simulation. Particle trajectories representing warm AIW mass are calculated to determine the pathways of this water mass on the adjacent shelf in the Norske Trough, and we analyze the water property changes along the trajectories. Moreover, to identify the sources of the AIW in the vicinity of the 79-NG, we compute backward particle trajectories.

Description: The 79-North Glacier (79-NG), a major glacier in North-East Greenland that was subject to an increased melt in the last years. The rate of ice loss by basal melting at marine-terminating glaciers is linked to the flow of warm water masses to the glacier that enhance basal melting. However, the sources and pathways of the warm waters on the shelf, their variability and mechanisms of the heat transfer involved are variable regionally and still clearly known. We use Lagrangian particle simulations based on output from a high resolution FESOM (Finite Element Sea Ice-Ocean Model) model to backtrack the source water masses of the warm water inflow to the 79NG. The Lagrangian particles visualize pathways of these waters. They also disclose intense eddy mixing processes in the Fram Strait and the vivid changes of temperature and salinity along the water mass trajectories.

Description: More than 25% of mean global sea level rise is caused by mass loss of Greenland Ice Sheet (GrIS). A significant part of this melt is attributed to the interaction between marine terminating glaciers of the GrIS and the surrounding warm ocean waters. Recent moored and ship-based observations suggest that Atlantic Intermediate Water (AIW) warmer than 1°C reaches the 79NG via the trough system on the East Greenland continental shelf, and that the southern route through the Norske Trough, is preferred. The origins and pathways of these warm AIW are elusive however due sparseness of observations from this remote and harsh environment. Here we use a a high resolution FESOM (Finite Element Sea Ice-Ocean Model) and a suite of Lagrangian model and analysis tools to study the water pathways to the NEGIS and 79NG. We deploy 1915 Lagrangian particles at the Norske Trough and track them backwards to the Fram Strait and further, to the Atlantic and Arctic origins of these waters. The particle trajectories reveal that the warm water in the Trough is a mixture of three source waters: about 60% of particles crossed the northern section (80.64°N) towards the Arctic sea, about 20% crossed the Fram section (78.5°N) southward to the North Atlantic, and nearly 10% entered through an alternative route, the Westwind Trough. We calculate the travel time and water property changes of AIW along the trajectories. The released particles with temperature higher than 2°C reached Fram section after 200 days and colder water (1-2°C) take half this time (100 days). The interannual variability of particle crossings the Fram section has good agreement with the observed variability of AW temperature anomalies in Fram Strait at depth of 250m. Using Lagrangian statistics, we assess the role of the eddy mixing processes at the Fram Strait and that of the mesoscale recirculations in the Trough system.