The signature of NAO and EA climate patterns on the vertical structure of the Canary Current upwelling system
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Published:2023-03-30
Issue:2
Volume:19
Page:351-361
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ISSN:1812-0792
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Container-title:Ocean Science
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language:en
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Short-container-title:Ocean Sci.
Author:
Georg TinaORCID, Neves Maria C.ORCID, Relvas PauloORCID
Abstract
Abstract. The current study aims to analyse the vertical structure
of the ocean during upwelling events using in situ and modelled data.
Additionally, the influence of climate patterns, namely the North Atlantic
Oscillation (NAO) and the East Atlantic (EA) pattern, on the vertical
structure and their impact on the upwelling activity are assessed for a
period of 25 years (1993–2017). The study focuses on the central part of
the Canary Current (25–35∘ N) with persistent upwelling
throughout the year, with an annual cycle and the strongest events from June to
September. Upwelling is determined using two different approaches: one index is
calculated based on temperature differences between the coastal and the
offshore area, and the other is calculated based on wind data and the resulting Ekman
transport. Different datasets were chosen according to the indices. Stable coastal upwelling can be observed in the study area for the analysed
time span, with differences throughout the latitudes. A deepening of the
isothermal layer depth and a cooling of temperatures are observed in the
vertical structure of coastal waters, representing a deeper mixing of the
ocean and the rise of cooler, denser water towards the surface. During years of a positive NAO, corresponding to a strengthening of the
Azores High and the Icelandic Low, stronger winds lead to an intensification
of the upwelling activity, an enhanced mixing of the upper ocean, and a
deeper (shallower) isothermal layer along the coast (offshore). The opposite
is observed in years of negative NAO. Both effects are enhanced in years
with a coupled, opposite phase of the EA pattern and are mainly visible
during winter months, where the effect of both indices is the greatest. The study therefore suggests that upwelling activities are stronger in winters of
positive North Atlantic Oscillation coupled with a negative East Atlantic
pattern and emphasizes the importance of interactions between the climate
patterns and upwelling.
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
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