Publication Date:
2021-07-04
Description:
Here, we revisit the existing concepts of the vertical structure of deep layers in the Black Sea using data from sensors deployed on profiling floats. The deep transition layer (DTL) between 700 and 1,700 m acts as an interface between the baroclinic layer and the largest bottom convective layer (BCL) of the world oceans. On top of DTL are the warm intermediate layer and deep cold intermediate layer. They both showed strong trends in the last 15 years due to warmer climate and intensification of warmer intrusions from Bosporus. A “salinity wave” was detected in 2005–2009 below ∼1,700 m, which evidenced for the first time the penetration of gravity flow from Bosporus down to the bottom. The layering of water masses was explained as resulting from the different distribution of sources of heat and salt, double diffusion, and balances between the geothermal and salinity flows in the BCL.
Description:
Plain Language Summary:
A total of 5,927 profiles from 31 profiling floats deployed in the Black Sea after 2005 were used to study the thermohaline dynamic. The density ratio, which sets the conditions under which double diffusion could occur qualifies most of the depths below 600 m as a double‐diffusive environment, which was confirmed by the observed staircase structure of vertical profiles. The qualitative differences between the temperature and salinity profiles in DTL are explained by the different distributions of sources and sinks of heat and salt. This layer acts as a transition zone between the bottom convective layer and the baroclinic ocean. A deep cold intermediate layer (DCIL) occupies the top of the DTL. The former became pronounced in recent years as a consequence of the warming of upper water layers. The large salinity variations from 2005 to 2009 observed at the bottom of the DTL evidenced traces of the penetration of the Bosporus plume down to the bottom for the first time. Combining known values of geothermal flow and concepts from the theory of dynamics of salinity‐stratified tanks heated from below made it possible to quantify the mean annual volume of Bosporus water reaching the bottom.
Description:
Key Points:
Profiling floats registered for the first time traces of Bosporus intrusions down to the bottom.
The deep warm and cold intermediate layers are responsive to climate warming.
Different sources of heat and salt dominate the transition between the baroclinic ocean and bottom convection layer.
Keywords:
551.46
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551.46
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baroclinicity
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double diffusion
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geothermal convection
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profiling floats
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sources of heat and salt
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water masses
Type:
article
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