On the freshening of the northwestern Weddell Sea continental shelf

Abstract

Abstract. We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of the three austral winters 1989, 1997, and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ∼64 • S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data from the shallow shelf off the tip of the Antarctic Peninsula, spanning a period of 17 yr, shows a salinity decrease of 0.09 for the whole water column, which has a residence time of <1 yr. We interpret this freshening as being caused by a combination of reduced salt input due to a southward sea ice retreat and higher precipitation during the late 20th century on the western Weddell Sea continental shelf. However, less salinification might also result from a delicate interplay between enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves and increased Larsen C ice loss.

Assessment of the structure and variability of Weddell Sea water masses in distinct ocean reanalysis products

“…The ocean reanalyses that showed a warming trend (MyOcean and SODA) also presented an increase in salinity, while ECMWF showed cooling and freshening trends (Table 4). A freshening trend of the WSBW would be expected as a result of shelf water freshening (e.g., Hellmer et al, 2011;Azaneu et al, 2013) because this bottom water results from shelf water mixing. However, clear salinity changes have not yet been observed in the deep layers of the Weddell Sea (Azaneu et al, 2013); the causes are not yet clearly identified but could be the result of the opposing effects of source waters and dynamic processes masking signal identification.…”

“…Over the past few decades, changes in the thermohaline properties of AABW source waters have been reported, such as freshening of the dense waters in the shelf regions (e.g., Hellmer et al, 2011;Azaneu et al, 2013) and long-term warming of WDW within the Weddell Sea (e.g., Robertson et al, 2002;Smedsrud, 2005). In turn, WSBW in the inner Weddell Sea also experienced warming during the second half of the 1990s (Fahrbach et al, 2004.…”

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

“…These collapses have reduced the restraint of the ice shelves on the flow of grounded tributary glaciers, causing them to accelerate Berthier et al, 2012) and thereby contributing to sea-level rise (Shepherd et al, 2012). Increased freshwater input to the ocean from the collapses and subsequent excess ice discharge may be implicated in the freshening of Antarctic Bottom Water formed nearby (Hellmer et al, 2011;Jullion et al, 2013).…”

Freshwater fluxes in the Weddell Gyre: results from δ 18 O

“…Net precipitation is thought to be intensifying [17,18], although exact trends remain poorly constrained [19,20], while elevated glacial discharge into the region [21] has led to the freshening of both shelf waters [22] and bottom waters [23], primarily linked to increased ice-shelf calving and the speeding up of tributary glaciers in the vicinity of the Larsen ice shelves [24,25].…”