Low confidence in multi-decadal trends of wind-driven upwelling across the Benguela Upwelling System
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Published:2023-10-16
Issue:5
Volume:14
Page:1065-1080
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ISSN:2190-4987
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Container-title:Earth System Dynamics
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language:en
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Short-container-title:Earth Syst. Dynam.
Author:
Bordbar Mohammad HadiORCID, Mohrholz VolkerORCID, Schmidt Martin
Abstract
Abstract. Like other eastern boundary upwelling systems, in the Benguela
Upwelling System, the upwelling along the coastline is primarily
alongshore-wind-driven. In contrast, it is mainly driven by the wind stress
curl farther offshore. The surface wind regime across the Benguela Upwelling
System is strongly related to the South Atlantic Anticyclone that is
believed to migrate poleward in response to anthropogenic global warming.
Using the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis
for 1979–2021, we investigate multi-decadal changes in the South Atlantic
Anticyclone and their impacts on coastal upwelling driven by alongshore
winds, wind-stress-curl-driven upwelling within the coastal zone and total
upwelling as the sum of both across the Benguela Upwelling System. Even
though the detailed structure of surface wind over the coastal zone matters
for both alongshore-wind-driven coastal upwelling and
wind-stress-curl-driven upwelling, we show that it is not of major
importance for the total amount of upwelled water. We found a robust
connection between the anticyclone intensity and the zonally integrated
wind-stress-curl-driven and total upwelling. However, such connection for
the alongshore-wind-driven coastal upwelling is weak. The upwelling in the
equatorward portion of the Benguela Upwelling System is significantly
affected by the anticyclone intensity. In contrast, the poleward portion is
also influenced by the meridional position of the anticyclone. In general,
the impacts of the anticyclone on the local upwelling are more robust during
the austral winter. The multi-decadal trend in the sea level pressure across
the South Atlantic renders a considerable heterogeneity in space. However,
this trend features a small signal-to-noise ratio and can be obscured by
interannual to decadal climate variability. This view is further supported
by the coastal and wind-stress-curl-driven upwelling in several upwelling
cells showing hardly any significant multi-decadal trends.
Funder
Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie
Publisher
Copernicus GmbH
Subject
General Earth and Planetary Sciences
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