Publication Date:
2024-01-30
Description:
Observations from the global ocean have long confirmed the ubiquity of thermohaline inversions in the upper ocean, often accompanied by a clear signal in biogeochemical properties. Their emergence has been linked to different processes such as double diffusion, mesoscale stirring, frontal subduction, and the recently discussed submesoscale features. This study uses the central Baltic Sea as a natural laboratory to explore the formation of salinity inversions in the thermocline region during summer. We use realistic high‐resolution simulations complemented by field observations to identify the dominant generation mechanism and potential hotspots of their emergence. We propose that the strongly stratified thermocline can host distinct salinity minima during summer conditions resulting primarily from the interaction between lateral surface salinity gradients and wind‐induced differential advection. Since this is a generic mechanism, such salinity inversions can likely constitute a typical feature of the upper ocean in regions with distinct thermoclines and shallow mixed layers.
Description:
Plain Language Summary:
The upper ocean is characterized by a well‐mixed surface layer, below which temperature decreases rapidly with depth, forming the so‐called thermocline region. A corresponding salinity increase with depth is typically anticipated for stable density stratification to occur. Temperature and salinity inversions can, however, emerge in the upper ocean. Such thermohaline inversions have been observed in different regions of the world's oceans, and various mechanisms have been proposed to explain their generation. Here, the central basin of the Baltic Sea is used as a natural laboratory to explore the formation of distinct salinity minima in the thermocline region during summer conditions. Using high‐resolution numerical simulations and measurements from a field campaign, we show that inversions are abundant and can emerge throughout the entire basin. They increase with increasing wind speeds and concentrate mainly in regions with strong lateral salinity differences. We propose that thermocline salinity minima can occur during summer when the wind transports saltier water over less saline surface waters. This is a generic mechanism that can therefore be responsible for the formation of the salinity inversions observed worldwide in areas with distinct thermoclines and shallow mixed layers.
Description:
Key Points:
Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline region.
Realistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesis.
Lateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions.
Description:
German Research Foundation
Description:
http://doi.io-warnemuende.de/10.12754/data-2022-0001
Keywords:
ddc:551.46
;
salinity inversions
;
thermohaline intrusions
;
subduction
;
submesoscales
;
differential advection
;
Baltic Sea
Language:
English
Type:
doc-type:article
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