Water mass-structure and variability of the Kane gap in the equatorial Atlantic ocean

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Abstract

The results of a study of the water mass structure in a poorly studied area of the eastern basin of the Tropical Atlantic (Kane Gap) according to data from the 63rd cruise of P/V “Akademik Ioffe” in 2022 are presented in the paper. Variability of the average monthly characteristics of these waters using the GLORYS12v1 reanalysis for 1993–2022 is shown. Intermediate waters in the section are represented by a mixture of Antarctic intermediate water (AAIW) and Mediterranean water (the share of the latter reaches 34%). It has been established that the North Atlantic Deep Water (NADW) is represented by two layers: the Upper NADW with a maximum of salinity and the Middle NADW with a maximum of oxygen. The bottom water layer contains a mixture of Antarctic Bottom Water (AABW), the Lower and Middle components of the NADW. This mixture, coming primarily from the Vema Fracture zone region, is properly to call Northeast Atlantic Bottom Water (NEABW). Its upper limit corresponded to the isotherm of 1.95°С and the Si/P ratio equal to 33. In this work, using the conservative PO, the proportion of AABW in NEABW, which is about 20%, was calculated. According to the GLORYS12v1 on a seasonal scale in the bottom layer, a significant negative relationship was established between the variability of potential temperature and the meridional speed of currents. Significant trend for an increase in the average annual potential temperature (by 0.06 °C) and a decrease in salinity (by 0.005 psu) in general for the period 1993–2022 was revealed.

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About the authors

А. N. Demidov

Lomonosov Moscow State University

Author for correspondence.
Email: tuda@mail.ru

Faculty of Geography

Russian Federation, Moscow

K. V. Artamonova

Lomonosov Moscow State University; Russian Federal Research Institute of Fisheries and Oceanography

Email: tuda@mail.ru

Faculty of Geography

Russian Federation, Moscow; Moscow

S. B. Krasheninnikova

Lomonosov Moscow State University; A.O. Kovalevsky Institute of Biology of the Southern Seas, Russian Academy of Sciences

Email: tuda@mail.ru

Faculty of Geography

Russian Federation, Moscow; Sevastopol

S. А. Dobrolyubov

Lomonosov Moscow State University

Email: tuda@mail.ru

Faculty of Geography, Academician of the RAS

Russian Federation, Moscow

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2. Fig. 1. The position of the stations in the 63rd cruise of the R/V Akademik Ioffe (AI-63) in the Kane Passage. a – schematic map of the Kane Passage, red dots – the position of the stations; b – schematic map of the study area with a bottom water circulation scheme. The red square shows the study area, and the dots – the position of the stations, the gray arrows show the circulation scheme of the Antarctic bottom water (ABW) and the Northeast Atlantic Bottom Water (NEABW) according to [7, 9] for the Cape Verde Basin. Black arrows – the path of NEABW to the study area, reconstructed from the GLORYS12v1 reanalysis

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3. Fig. 2. Distributions of potential temperature, °C (a), salinity, eps (b), dissolved oxygen content, μM/kg (c), silicates, μM/kg (d), θ,S-diagram (d), and phosphate content, μM/kg (e) on section AI63 in the Kane Passage. The gray lines show the boundaries of the water masses, the white line in (d) shows the position of Si/P = 33

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4. Fig. 3. Interannual variability of monthly average values ​​of potential temperature (θ, °C) (a), meridional current velocity (V, cm/s) (b) in the Kane Passage based on the GLORYS12v1 ocean reanalysis for all months of 1993–2022. The inset (on the right) shows an enlarged fragment of 2009–2012. Black dots are based on estimates by different authors from Table 4. Gray fill is the standard deviations for the series of monthly average values ​​of the GLORYS12v1 reanalysis, calculated for 11 months using a sliding window (+5 and –5 months from the central value).

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5. Fig. 4. Periodogram of monthly mean series (a) and variability of filtered detrended monthly mean values ​​of meridional current velocity (V, m/s, blue) and potential temperature (θ, °C, red), for periods of 0.5–1 (b); 2–4 years (c), 10–30 years (d) in the Kane Passage based on the GLORYS12v1 ocean reanalysis

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