Polar Southern Ocean dynamics from satellite altimetry

Abstract

The polar Southern Ocean is a region of complex interactions between the ocean, atmosphere, and cryosphere which have great influence on climatically important processes such as sea ice formation, ice shelf melt, and the production of Antarctic Bottom Water. These processes has been shown to have far-reaching consequences, though the exact nature of their driving mechanisms is not well understood. This is partly due to the inhospitable nature of the region, which makes research voyages difficult, dangerous, and costly; resulting in a sparse distribution of in situ measurements restricted to only a few locations. Furthermore, conventional satellite altimetry is incapable of taking measurements in the presence of sea ice, leading to a lack of data in winter months and a bias towards summer. This study aims to address this.

Here, a specially-processed dataset from CryoSat-2 enables measurements of sea surface height to be taken from specular returns from sea ice leads. These are used to provide a picture of polar Southern Ocean dynamics throughout the year. The first objective of this study is to assess the ability of this dataset to capture the seasonal-to-interannual variability of sea surface height in the polar Southern Ocean. It is shown that the altimetry data has this ability. Comparison with climate indices and in situ data reveal that this is a valuable new tool for the investigation of ocean dynamics in the presence of sea ice.

The second objective uses this dataset to analyse the variability and drivers of the Antarctic Slope Front, a frontal system around much of Antarctica’s shelf that plays an important role in regulating shelf water properties. Analysis shows that its transport is maximum in April – June and minimal in December – February. This seasonality is near-ubiquitous around the continent, and it is hypothesised it is rapidly propagated around Antarctica along f/H (f is the coriolis parameter, H is the water depth) contours. Wind stress is identified as a major driving mechanism and a composite of wind stress, sea ice concentration, and sea ice drift data is produced. Maximum Covariance Analysis identifies modes of covariance between it and the altimetry and reveals two separate responses to changes in surface stress, each with a different effect on the Southern Ocean. Both of these modes are shown to be important for Southern Ocean dynamics, and could influence climatologically important processes there.

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Identifiers

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

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