[MIS14-P29] Mechanism of sea-ice production variation in Amundsen Sea Polynya
Keywords:Antarctic Ocean, coastal polynya, Amundsen Sea Polynya
In this study, we compare the ice production in the ASP with atmospheric parameters and fast ice extent to investigate factors for causing ice production variation. Ice production estimated from heat flux calculation with daily thin ice thickness from AMSR-E/AMSR2 data (Nihashi and Ohshima, 2015; Nihashi et al., 2017) is used. For fast ice, monthly extent detected from AMSR-E/AMSR2 data is used. We also use ice production estimated using thin ice thickness by an improved algorithm in which ice types (active frazil and thin solid ice) are considered (Nakata et al., 2019). As atmospheric data, we use ERA5.
Ice production is positively correlated with wind speed regardless of daily or monthly data with the coefficient of 0.54-0.73. Here, we use a wind component with the highest correlation; components of the wind vector are projected in all directions of every 1° from 0° (northerly wind) clockwise to 360°, and then, correlation coefficients are calculated. The wind component is oriented to the west rather than to the offshore (north) against the land. This is a direction towards the offshore against the shoreline defined by both the land and fast ice. This result supports the analysis using only AMSR-E data (Nihashi and Ohshima, 2015). If ice production in which thin ice types are considered is used, the wind component is oriented toward further west when active frazil is dominant. This direction is to the offshore against the fast ice. Further, active frazil tends to form along fast ice. On the other hand, the wind component is northward (to the offshore against land) when thin solid ice is dominant. Multiple regression analysis is performed on the ice production using air temperature, wind speed, and fast ice extent averaged over the freezing season (May-August). Ice production can be explained by these parameters with R=0.77. This indicates that ice production in the ASP before the satellite observation era can be reproduced to some extent from atmospheric data by using this regression line. The results presented in this study suggest that fast ice plays a vital role in the formation and variation of the ASP. Continuous monitoring of Antarctic coastal polynyas and fast ice from passive microwave satellite sensor is quite meaningful understanding climate change.