Multidecadal freshening and lightening in the deep waters of the Bransfield Strait, Antarctica

Abstract

The deep waters of the Bransfield Strait receive considerable amounts of water from the Weddell Sea continental shelf. The restricted connections to the surrounding ocean and relatively easier access makes the Bransfield Strait an important proxy region for monitoring changes in the dense Weddell Sea shelf water masses, which are an important precursor of Antarctic Bottom Water (AABW). Long‐term hydrographic data from the period 1960s–2010s showed freshening and lightening of the deep water masses of the Bransfield Strait, which was likely caused by large freshwater inputs originating from the western shelf of the Weddell Sea. The rates of freshening and lightening were −0.0010 ± 0.0005 yr−1 and −0.0016 ± 0.0014 kg m−3 yr−1 for the central basin, respectively, and −0.0010 ± 0.0006 yr−1 and −0.0029 ± 0.0013 kg m−3 yr−1 for the eastern basin, respectively. The deep waters showed a high degree of interannual thermohaline variability, which appeared to be caused by changes in the proportions of source water mass mixing between the years. Statistically significant negative correlations between salinity/neutral density fields and the Southern Annular Mode (SAM) were observed (−0.56 and −0.62 for the central basin, respectively, and −0.58 and −0.68 for the eastern basin, respectively) between 1980 and 2014. During SAM positive phases, communication between the Weddell Sea and the Bransfield Strait is reduced, which leads to less saline and lighter water masses in the Bransfield Strait; however, the opposite trends are observed during SAM negative phases.

Managing fishery development in sensitive ecosystems: identifying penguin habitat use to direct management in Antarctica

“…Results from the model of Young et al (2017) highlight the presence of relatively slow-moving water in regions of shallow bathymetry, compared with more rapid flows at the shelf-edge and in deeper oceanic regions; these findings accord well with existing hydrographic models and empirical studies (e.g., Dinniman and Klinck 2004, Heywood et al 2004, Dotto et al 2016. Transport between off-shelf and on-shelf waters is complex, but is almost certainly a vital process regulating the flow of krill into the foraging range of chinstrap penguins.…”

“…Circumpolar Deep Water and warm surface waters from the Bellingshausen Sea enter the Bransfield Strait from the southwest, mainly to the west of the South Shetland Islands. The NEMO model recreates well, the Antarctic Circumpolar Current Southern Boundary to the north of the South Shetland Islands, the Antarctic Slope Front, and the Coastal Current (Thompson et al 2009, Dotto et al 2016.…”

Three decades of deep water mass investigation in the Weddell Sea (1984–2014): Temporal variability and changes

“…Mackas et al (1987), Tomczak and Large (1989), and Tomczak (1997, 1998) considerably improved the method allowing for more robust applications. Since then, the OMP analysis has been successfully applied throughout the global ocean to determine the relative water mass fractions of contribution on (i) regional (e.g., Huhn et al, 2008;Jenkins et al, 2014;García-Ibáñez et al, 2015;van Caspel et al, 2015;Dotto et al, 2016), (ii) ocean basin (e.g., Poole and Tomczak, 1999;Kerr et al, 2009a;Pardo et al, 2012;Santos et al, 2016;Ferreira and Kerr, 2017), and (iii) global (e.g., Johnson, 2008) scales. The method was also effectively used to distinguish water mass fractions of mixtures and eventual biases in Southern Ocean studies using numerical modeling and ocean reanalysis products (e.g., Kerr et al, 2009bKerr et al, , 2012b.…”

Ocean forcing of glacier retreat in the western Antarctic Peninsula

“…The regimes have different temporal variabilities, with CDW variations originating in the transport and mixing of water from the Antarctic Circumpolar Current, and BSW variations originating in atmosphere-ocean interaction and sea ice formation over the Weddell Sea shelf (28). Ocean heat content in the Bellingshausen Sea is known to have increased, attributed to an increase in CDW upwelling onto the shelf, a decrease in heat loss to the atmosphere, and a slow warming of the CDW offshore of the shelf (29,30).…”