Seasonal transformation and spatial variability of water masses within MacKenzie polynya, Prydz Bay

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Portela, Esther, Rintoul, Stephen R., Bestley, Sophie, Herraiz‐borreguero, Laura, Wijk, Esmee, Mcmahon, Clive R., Roquet, Fabien, Hindell, Mark
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2021
• Subjects: Antarctic polynyas; dense shelf water; water masses; Amery; Amery Ice Shelf; Antarctic; Darnley; East Antarctica; Prydz Bay; Prydz Channel; The Antarctic; Antarc*; Antarctica; Elephant Seals; Ice Shelf; Sea ice; Southern Elephant Seals
• Online Access: https://archimer.ifremer.fr/doc/00739/85134/90102.pdf; https://archimer.ifremer.fr/doc/00739/85134/90103.pdf; https://doi.org/10.1029/2021JC017748; https://archimer.ifremer.fr/doc/00739/85134/

We provide a detailed description of the spatial distribution, seasonality and transformation of the main water masses within MacKenzie Polynya (MP) in Prydz Bay, East Antarctica, using data from instrumented southern elephant seals. Dense Shelf Water (DSW) formation in MP shows large spatial variability that is related to the (i) local bathymetry, (ii) water column preconditioning from the presence/absence of different water masses, and (iii) proximity to the Amery Ice Shelf meltwater outflow. MP exhibits sustained sea ice production and brine rejection (thus, salinity increase) from April to October. However, new DSW is only formed from June onward, when the mixed layer deepens and convection is strong enough to break the stratification set by Antarctic Surface Water above and Ice Shelf Water below. We found no evidence of DSW export from MP to Darnley polynya, as previously suggested. Rather, our observations suggest some DSW formed in Darnley Polynya may drain towards the western Prydz Bay. Then, DSW is exported offshore from Prydz Bay through the Prydz Channel. The interplay between sea ice formation, meltwater input, and sea floor topography is likely to explain why some coastal polynyas form more DSW than others, as well as the temporal variability in DSW formation within a particular polynya. Plain Language Summary Coastal polynyas are regions of open water surrounded by sea ice. They form when strong winds from the Antarctic continent push newly-formed sea ice away from the coast, as rapidly as it forms. Polynyas are therefore important sea ice factories. When sea ice forms, salt is released into the water below, increasing its salinity and density. The densest water in the World Ocean can be traced back to a few coastal polynyas along the Antarctic continent. This dense water formed in polynyas supplies the deep limb of a network of ocean currents that influences climate on global scales. Despite their importance, coastal polynyas remain poorly understood as they are difficult to reach and observe. ...