Long-Term Trends and Interannual Variability of Wind Forcing, Surface Circulation, and Temperature around the Sub-Antarctic Prince Edward Islands

Tesha Toolsee,Tarron Lamont

doi:10.3390/rs14061318

Abstract

In the Southern Ocean, the sub-Antarctic Prince Edward Islands (PEIs) play a significant ecological role by hosting large populations of seasonally breeding marine mammals and seabirds, which are particularly sensitive to changes in the surrounding ocean environment. In order to better understand climate variability at the PEIs, this study used satellite and reanalysis data to examine the interannual variability and longer-term trends of Sea Surface Temperature (SST), wind forcing, and surface circulation. Long-term trends were mostly weak and statistically insignificant, possibly due to the restricted length of the data products. While seasonal fluctuations accounted for a substantial portion (50–70%) of SST variability, the strongest variance in wind speed, wind stress curl (WSC), and currents occurred at intra-annual time scales. At a period of about 1 year, SST and geostrophic current variability suggested some influence of the Southern Annular Mode, but correlations were weak and insignificant. Similarly, correlations with El Niño Southern Oscillation variability were also weak and mostly insignificant, probably due to strong local and regional modification of SST, wind, and current anomalies. Significant interannual and decadal-scale variability in SST, WSC, and geostrophic currents, strongest at periods of 3–4 and 7–8 years, corresponded with the variability of the Antarctic Circumpolar Wave. At decadal time scales, there was a strong inverse relationship between SST and geostrophic currents and between SST and wind speed. Warmer-than-usual SST between 1990–2001 and 2009–2020 was related to weaker currents and wind, while cooler-than-usual periods during 1982–1990 and 2001–2009 were associated with relatively stronger winds and currents. Positioned directly in the path of passing atmospheric low-pressure systems and the Antarctic Circumpolar Current, the PEIs experience substantial local and regional atmospheric and oceanic variability at shorter temporal scales, which likely mutes longer-term variations that have been observed elsewhere in the Southern Ocean.

Highlights

Licensee MDPI, Basel, Switzerland.With the increase in anthropogenic greenhouse gases in the atmosphere, the world’s ocean, especially the cold Southern Ocean, has been experiencing some major variations in physical conditions [1]
The seasonal cycle of Sea Surface Temperature (SST), winds, and currents has been described in detail by [29], for a wider area around the Prince Edward Islands (PEIs), and here we only provide a brief description of the patterns observed within the averaged 2◦ × 2◦ area (Figure 1)
Since the SST, wind, and geostrophic current products all spanned different lengths of time, we compared the seasonal cycles derived over the full time series against those derived over the period (1993–2016) common to each parameter (Figure 2)

Summary

Introduction

Licensee MDPI, Basel, Switzerland.With the increase in anthropogenic greenhouse gases in the atmosphere, the world’s ocean, especially the cold Southern Ocean, has been experiencing some major variations in physical conditions [1]. The most commonly known impact of the rise in greenhouse gases is the depletion of the ozone layer above the Southern Ocean, which has led to the poleward shift and strengthening of the westerly winds, reflected by the positive trend of the Southern Annular Mode (SAM) [2–5]. Another impact of the rise in anthropogenic published maps and institutional affil-. The delayed warming in the south is related to the poleward strengthening of the westerly wind belt, which has been shown to amplify the Ekman-driven upwelling of the North Atlantic

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Conclusion