Tracer-derived freshwater composition of the Siberian continental shelf and slope following the extreme Arctic summer of 2007

We investigate the freshwater composition of the shelf and slope of the Arctic Ocean north of the New Siberian Islands using geochemical tracer data (delta O-18, Ba, and PO4*) collected following the extreme summer of 2007. We find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of Pacific-derived surface water in the westernmost part of the Makarov Basin. We also find larger quantities of meteoric water near Lomonosov Ridge than were found in 1995. Dissolved barium is depleted in the upper layers in one region of our study area, probably as a result of biological activity in open waters. Increasingly ice-free conditions compromise the quantitative use of barium as a tracer of river water in the Arctic Ocean. Citation: Abrahamsen, E. P., M. P. Meredith, K. K. Falkner, S. Torres-Valdes, M. J. Leng, M. B. Alkire, S. Bacon, S. W. Laxon, I. Polyakov, and V. Ivanov (2009), Tracer-derived freshwater composition of the Siberian continental shelf and slope following the extreme Arctic summer of 2007, Geophys. Res. Lett., 36, L07602, doi:10.1029/2009GL037341

Ocean circulation and properties in Petermann Fjord, Greenland

The floating ice shelf of Petermann glacier interacts directly with the ocean and is thought to lose at least 80% of its mass through basal melting. Based on three opportunistic ocean surveys in Petermann Fjord we describe the basic oceanography: the circulation at the fjord mouth, the hydrographic structure beneath the ice shelf, the oceanic heat delivered to the under-ice cavity, and the fate of the resulting melt water. The 1100 m deep fjord is separated from neighboring Hall Basin by a sill between 350 and 450 m deep. Fjord bottom waters are renewed by episodic spillover at the sill of Atlantic water from the Arctic. Glacial melt water appears on the northeast side of the fjord at depths between 200 m and that of the glacier's grounding line (about 500 m). The fjord circulation is fundamentally three-dimensional; satellite imagery and geostrophic calculations suggest a cyclonic gyre within the fjord mouth, with outflow on the northeast side. Tidal flows are similar in magnitude to the geostrophic flow. The oceanic heat flux into the fjord appears more than sufficient to account for the observed rate of basal melting. Cold, low-salinity water originating in the surface layer of Nares Strait in winter intrudes far under the ice. This may limit basal melting to the inland half of the shelf. The melt rate and long-term stability of Petermann ice shelf may depend on regional sea ice cover and fjord geometry, in addition to the supply of oceanic heat entering the fjord. © 2011 by the American Geophysical Union

OCEAN WARMING OF NARES STRAIT BOTTOM WATERS OFF NORTHWEST GREENLAND, 2003-2009

Over the last 60 years, the perception of the Arctic Ocean has changed from a hostile, sluggish, steady, ice-covered environment with little global impact to an ocean that has become increasingly accessible, apparently rapidly changing, only partly ice-covered, and connected to the global meridional overturning circulation. Our new observations demonstrate that waters off Northwest Greenland constitute the final limb in the grand cyclonic circulation of the Atlantic layer in the Arctic Ocean. These waters with an Atlantic water mass signature are warming in Nares Strait to the west of Greenland as they are elsewhere. Estimates of the magnitude and uncertainty of this warming are emerging from both moored observations and historical hydrographic station data. Ocean temperatures sensed by instruments moored 3 m above the bottom between 228 and 366 m depth in Nares Strait suggest a mean warming of about 0.023 ± 0.015,°C per year for the 2003-2009 period at 95% confidence. Salinity changes for the same period are not significantly different from zero. Nevertheless, oscillating bottom temperatures covary with salinities. Mean bottom salinities in Nares Strait exceed 34.56 psu while no water with salinities above 34.51 psu occurs in Baffin Bay to the south. These data indicate a dominantly northern source for the waters sensed by our moorings. Mean bottom temperatures hover near 0,°C, which suggests minimal influence of waters from the northeastern Amundsen Basin in the Arctic Ocean. Thus, we conclude that the observed warming originates from the northeastern Canadian Basin to the southwest of our study area. In addition to these mean conditions, we find large interannual variability. Forexample, significant freshening emerges for the 2003-2006 period that reaches-0.02 ± 0.008 psu per year without significant concurrent temperature trends at three sensor locations. These data contrast with the 2007-2009 observational period when five different sensors all indicate warmer waters (0.063 ± 0.017,°C per year) and saltier waters (0.027 ± 0.01 psu per year), which reverses the 2003-2006 freshening. We speculate that some of these observed changes are caused by a changing ice regime. During the 2003-2006 winters, ice was landfast, while during 2007-2009 it was generally mobile year-round. The warming impacts tidewater glaciers along northern Greenland with sill depths below 300 m, for example, Petermann Gletscher. © 2011 by The Oceanography Society. All rights reserved

Context for the recent massive petermann glacier calving event

On 4 August 2010, about one fifth of the floating ice tongue of Petermann Glacier (also known as "Petermann Gletscher") in northwestern Greenland calved (Figure 1). The resulting "ice island" had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The ice island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glacier's dynamics? Or can it be characterized as part of the glacier's natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance