Dynamics of the subpolar Southern Ocean response to climate change

Abstract

This thesis first focuses on the imprint on sea surface of the interior circulation captured by the Amundsen Undercurrent (AU) and the atmospheric drivers that affect the regions of covariability. Then, we examine more broadly the large scale patterns of the joint forcing from wind and ice that affect the sea level. This is achieved using a novel 16-year long altimetry record of Sea Level Anomaly (SLA) that includes measurements in regions of near-perennial ice cover.

Complemented by a 5-year record of mooring data from two glacial troughs in the Amundsen Sea, we find two robust patterns of co-variability between sea level and the undercurrent. On one hand, seasonal variability displays a Southern Mode modulation, whereby the sea level everywhere on the Antarctic shelf is coherent and anticorrelates with the AU strength. In contrast, on non-seasonal timescales, the undercurrent appears to be linked to ocean dynamics connected to tropical Pacific variability and likely indicative of baroclinic processes. In addition, this work presents a strong argument that remote processes can impact the AU via changes in SLA that propagate along the Antarctic shelf.

We proceed to show that the first two dominant modes of SLA and joint sea ice and wind co-variability are consistent with previous studies that outline a quasi-instantaneous Ekman-driven mass exchange between shelf and the open ocean, as well as between the open ocean and the subtropics, the latter with a 2-month delay. Additionally, we show that teleconnections in the central/SE Pacific associated with the El Nino Southern Oscillation regulate the cross-slope SLA gradient, particularly on timescales longer than a year, and, to a lesser extent, drive an SLA pattern consistent with Zonal Wave 3 forcing, which is known to have a strong connection to sea ice variability.

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Identifiers

ORCID for Alberto Naveira Garabato: orcid.org/0000-0001-6071-605X

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