The Chlorophyll-a Content Distribution in the Atlantic Ocean in December 2019 — January 2020 according to Ship Measurements at the Different Hydrometeorological Conditions

Abstract

The horizontal and vertical chlorophyll-a concentrations (Chl) distributions along the ship route of 79th cruise of R/V “Akademik Mstislav Keldysh” in the Atlantic Ocean in December 2019—January 2020 were obtained. Analysis of the observations was conducted for the biogeochemical provinces which were determined by means of the different hydrometeorological conditions for the phytoplankton community functioning.Three methods of Chl measurements were applied: standard extraction method of the seawater samples, the fluorometer underway measurements in the flow-through water system at the depth of 5 m and in-situ profiling fluorometer measurements at stations. Also, measurements of the seawater temperature and salinity in the flow-through water system, the CTD and optical profiling, and ARGO floats were used.The maximum Chl values in the near-surface ocean layer are observed at zones of divergence in the Canary upwelling systems (CNRY) (1.3 mg/m3) and in the Falkland (Malvinas) Current system (4.8 mg/m3), and also in the Drake Strait (1.2 mg/m3). The least Chl values (0.01–0.12 mg/m3) are observed in the tropical, equatorial areas and in the South Atlantic Subtropical Anticyclonic Gyre (SASTG) at the ship route.Vertical Chl profiles with absence of the significant Chl maximum were found. In the CNRY region the Chl values were not changed much within the euphotic zone. While in the region of the Antarctic Circumpolar Current in the Drake Strait and in the offshore stream of the Falkland Current the quasi-homogeneous Chl profiles were observed in the upper layer which is almost 2 times deeper than the euphotic zone.In the profiles with the significant local Chl maximum the most Chl value of 3.5 mg/m3 is observed at the depth about 12 m in the upwelling region on the Patagonian Shelf. In other regions the depth of Chl maximum localization (0.2–0.9 mg/m3) varies widely from 25 to 120 m. In the western part of the SASTG region the absolute Chl maxima were found at the depth of 120 m, that is deeper, then the euphotic zone which is equal to 100 m.