Evolution of the dynamics, area, and ice production of the Amundsen SeaPolynya, Antarctica, 2016-2021

Polynyas are key sites of ice production during the winter and areimportant sites of biological activity and carbon sequestration during thesummer. The Amundsen Sea Polynya (ASP) is the fourth largest Antarcticpolynya, has recorded the highest primary productivity, and lies in anembayment of key oceanographic significance. However, knowledge of itsdynamics, and of sub-annual variations in its area and ice production, islimited. In this study we primarily utilize Sentinel-1 synthetic aperture radar (SAR) imagery, sea ice concentration products, and climate reanalysis data, along with bathymetricdata, to analyze the ASP over the period November 2016-March 2021.Specifically, we analyze (i) qualitative changes in the ASP'scharacteristics and dynamics, as well as quantitative changes in (ii) summerpolynya area, and (iii) winter polynya area and ice production. From ouranalysis of SAR imagery we find that ice produced by the ASP becomes stuckin the vicinity of the polynya and sometimes flows back into the polynya,contributing to its closure and limiting further ice production. The polynyaforms westward off a persistent chain of grounded icebergs that are locatedat the site of a bathymetric high. Grounded icebergs also influence theoutflow of ice and facilitate the formation of a "secondary polynya" attimes. Additionally, unlike some polynyas, ice produced by the polynya flowswestward after formation, along the coast and into the neighboring seasector. During the summer and early winter, broader regional sea iceconditions can play an important role in the polynya. The polynya opens inall summers, but record-low sea ice conditions in 2016/17 cause it to becomepart of the open ocean. During the winter, an average of 78 % of iceproduction occurs in April-May and September-October, but large polynyaevents often associated with high, southeasterly or easterly winds cancause ice production throughout the winter. While passive microwave data ordaily sea ice concentration products remain key for analyzing variations inpolynya area and ice production, we find that the ability to directlyobserve and qualitatively analyze the polynya at a high temporal and spatialresolution with Sentinel-1 imagery provides important insights about thebehavior of the polynya that are not possible with those datasets.