Windy conditions in the Ross Sea polynyas

Abstract

The polar climate is rapidly changing due to rising global temperatures, significantly impacting Antarctic sea ice cover, particularly since 2016. Polynyas, areas of low sea ice concentration surrounded by pack ice, play a crucial role in deep water formation, contributing to the global meridional overturning circulation (MOC). Despite covering only 1% of the sea ice extent, polynyas account for 10% of Antarctic sea ice production. This thesis examines the influence of wind forcing on the area and sea ice production within three coastal polynyas in the Ross Sea: the Ross Ice Shelf Polynya (RISP), McMurdo Sound Polynya (MMSP), and Terra Nova Bay Polynya (TNBP), from 2003 to 2023 (excluding 2012).

Using a flooding algorithm, polynyas are detected based on daily sea ice concentration data derived from satellite observations. The algorithm marks grid cells with sea ice concentration (SIC) below 70% as polynyas if connected to the coast. The study analyses polynya area, sea ice production, and wind data from the regional climate model RACMO 2.4. Monthly sea ice production is estimated using sea ice thickness data.

Key findings include: • The RISP is the largest polynya, accounting for 36% of the total annual polynya area in the Ross Sea, followed by TNBP (27%) and MMSP (15%). • A 40% increase in yearly polynya area was observed from 2003 to 2023, linked to changes in large-scale atmospheric variables and short-term factors like wind speed and air temperature. • High wind speeds are assumed to cause significant ice divergence, leading to larger polynya areas. • The correlation between wind speed and ice production varies among polynyas, with significant correlations in TNBP (r = 0.458) and MMSP (r = 0.357), but not in RISP. • Future projections under the SSP3–7.0 scenario suggest modest changes in ice production and deep water formation, potentially affecting the global overturning circulation.

This study enhances our understanding of polynya processes in a changing climate, highlighting the complex interactions between wind forcing, sea ice production, and polynya dynamics.