West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability

Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or an ongoing, possibly unstable, response to a past climate anomaly. Lengthening satellite records appear to be incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000 to 2016 near the Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of about four between cool and warm extremes via a nonlinear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice-shelf thinning and retreat of the grounding line, which re-advanced during a post-2011 cool phase. These observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The nonlinear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high

A continuous record of Florida Current temperature transport at 27°N

As part of a newly funded international program to monitor ocean heat transport at mid‐latitudes in the North Atlantic, a continuous estimate of the temperature transport of the Florida Current is required. Since 1982, volume transports have been inferred from voltage measurements monitored by submarine telephone cables across the Straits of Florida. Electromagnetic induction theory suggests that the cable voltage should actually give a more direct measure of conductivity transport than pure volume transport. Due to the strong dependence of conductivity on temperature, this would in theory result in a direct and continuous estimate of the Florida Current temperature transport. This hypothesis is investigated using data from a large number of temperature and velocity sections (58) across the Florida Current at the cable location, leading to a new calibration of the voltage signal for the temperature transport of the Florida Current, crucial for trans‐basin heat flux estimates

Southern Weddell Sea shelf edge geomorphology: Implications for gully formation by the overflow of high-salinity water

Submarine gullies are the most common morphological features observed on Antarctic continental slopes. The processes forming these gullies, however, remain poorly constrained. In some areas, gully heads incise the continental shelf edge, and one hypothesis proposed is erosion by overflow of cold, dense water masses formed on the continental shelf. We examined new multibeam echo sounder bathymetric data from the Weddell Sea continental slope, the region that has the highest rate of cold, dense water overflow in Antarctica. Ice Shelf Water (ISW) cascades downslope with an average transport rate of 1.6 Sverdrups (Sv) in the southern Weddell Sea. Our new data show that within this region, ISW overflow does not deeply incise the shelf edge. The absence of gullies extending deeply into the glacial sediments at the shelf edge implies that cold, high salinity water overflow is unlikely to have caused the extensive shelf edge erosion observed on other parts of the Antarctic continental margin. Instead, the gullies observed in the southern Weddell Sea are relatively small and their characteristics indicative accumulation and subsequent failure of proglacial sediment during glacial maxima

Observations of the vertical and temporal evolution of a Natal Pulse along the Eastern Agulhas Bank

This study re-investigates the work of Lutjeharms et al. [2001,2003] who documented the properties of a Natal Pulse using isopycnal Lagrangian floats. We combined Lagrangian analyses and Eulerian maps derived from objective analysis to better describe the evolution of a Natal Pulse along three density surfaces referred to as the surface (satellite-observed), shallow (isopycnal-1026.8 kg.m−3) and deep (isopycnal-1027.2 kg.m−3) layer. Our observations show that this Natal Pulse extended to a depth of 1000m and was associated with cyclonic relative vorticity values of about 6.5 to 8.5x10−5.s−1 in the surface and shallow layer and 4x10−5.s−1 in the deep layer. This Natal Pulse contributed to cross-shelf exchange through the offshore advection of Eastern Agulhas Bank water near the surface, onshore advection of South Indian Central Water and/or Indian Equatorial Water in the shallow layer and Antarctic Intermediate Water in the deep layer. Sea Surface Temperature maps showed that the downstream progression of the Natal Pulse along the 3000m isobath was related to a readjustment of its rotation axis. This readjustment advected Eastern Agulhas Bank water into the Natal Pulse eddy and triggered a SST cooling of about 3°C in the cyclonic area. The importance of a warm recirculating Agulhas plume originating from the Natal Pulse was highlighted. This warm water plume extended to a depth of 700m and was associated with onshore velocities exceeding those experienced within the Natal Pulse eddy by a factor of two. Our observations indicate that the June/July 1998 Natal Pulse and its associated plumes enhanced cross-shelf exchanges. This article is protected by copyright. All rights reserved