Variability of Cold Intermediate Layer Parameters over the Continental Slope off the Crimea Coast Based on Expeditionary Measurements

Yu. V. Artamonov✉, E. A. Skripaleva, A. V. Fedirko

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

✉ e-mail: artam-ant@yandex.ru

Abstract

Purpose. The study aims to analyze the variability features of the cold intermediate layer (CIL) characteristics over the continental slope off the Crimea coast during 2016–2024.

Methods and Results. The analysis is based on hydrological measurement data obtained during cruises of the R/V Professor Vodyanitsky. Seawater temperature and salinity were measured using SBE‑911plus and IDRONAUT OCEAN SEVEN 320 PlusM CTD systems. The core temperature, salinity, density and depth of the CIL were determined from vertical profiles at 279 stations located over isobaths of 200–1500 m. Monthly mean sea surface temperature anomalies relative to climate norms were calculated for the period 2016–2024 using BS HR and UHR SST products from the CMEMS array. The mean core temperature of the CIL over the study period was 8.42 °C, with the core located at an average depth of 91 m on the isopycnic surface of 14.95 cond. units and a salinity of 19.3 PSU. The seasonal cycles of temperature and salinity in the CIL core off the Crimea coast differ from those averaged over the entire Black Sea. The synoptic variations in CIL parameters are nearly an order of magnitude smaller than variations driven by the combined effect of synoptic and interannual variability. The CIL characteristics observed during 2016–2024 exhibit statistically significant linear trends, indicating a general tendency toward an increase in the CIL core depth, temperature, salinity and density. The linear trends account for 35–47% of the total variability in CIL parameters. The cruise confidence intervals for the linear trends (calculated from mean values) are as follows: CIL core depth – 38 m, core temperature, density and salinity –0.88 °C, 0.97 cond. units and 1.36 PSU, respectively. The periods of warming and cooling in the CIL core derived from in situ measurements are in qualitative agreement with interannual sea surface temperature anomaly time series obtained from satellite data both for the coastal zone off Crimea and for the main CIL formation and renewal regions (northwestern shelf and centers of the western and eastern cyclonic gyres).

Conclusions. During the past decade, the CIL core temperature off the Crimea coast exceeded 8 °C, making this isotherm unsuitable as a criterion for defining CIL boundaries. Two main periods of pronounced warming (2019–2021 and 2023–2024) were identified, characterized by simultaneous increases in the CIL core temperature, salinity and density, as well as deepening of the core.

Keywords

Black Sea, continental slope, in situ measurements, spatio-temporal variability, cold intermediate layer, sea surface temperature, satellite measurements

Acknowledgements

The study was conducted within the framework of the state assignment of the FSBSI FRC MHI No. FNNN-2024-0014 “Ocean–atmosphere interaction”. The data were collected using the shared research facility R/V Professor Vodyanitsky operated by the A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS.

Original russian text

Original Russian Text © Yu. V. Artamonov, E. A. Skripaleva, A. V. Fedirko, 2025, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 41, Iss. 6, pp. 788-806 (2025)

For citation

Artamonov, Yu.V., Skripaleva, E.A. and Fedirko, A.V., 2025. Variability of Cold Intermediate Layer Parameters over the Continental Slope off the Crimea Coast Based on Expeditionary Measurements. Physical Oceanography, 32(6), pp. 807-825.

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