Distributions of nutrients, trace metals, phytoplankton composition, and elemental consumption in the Ross and Amundsen Seas

Abstract

The Southern Ocean (SO) not only functions as an important carbon sink but also serves as a crucial source of intermediate and deep waters to lower latitudes. The Ross Sea and Amundsen Sea in the West Antarctic are highly productive regions of the Southern Ocean, critically vulnerable to climate change. Hence, comprehending the source-sink patterns of nutrients, particularly trace metals, in these regions is of paramount significance for understanding their ecological effect and the effect on elemental distribution in global ocean. Here, we reported the surface and vertical distributions of phytoplankton composition, Chlorophyll-a (Chl-a), particulate organic carbon (POC), macronutrients, and trace metals (TMs) in the Ross and Amundsen Seas. Deplete dissolved iron concentrations were observed in surface waters averaging 0.17 ± 0.09 nM. High POC and Chl-a were observed that corresponded to elevated Fe in shallow subsurface water (100–300 m), while low POC and Chl-a were found to associate with depleted iron (∼0.1 nM) throughout the upper water column down to 300 m. Sea-ice melting and islands were found to be possible external TMs sources in the Amundsen Sea offshore. Phytoplankton act as a sink for trace metals and regulate the elemental concentration and composition of water bodies, while also being influenced by environmental conditions such as temperature, salinity, and the mixing layer depth. Elemental consumptions in surface water were associated with diatom abundance in both Ross and Amundsen Seas. Based on elemental drawndown ratios in the surface mixed layer, the stoichiometries of the two major phytoplankton functional groups, diatoms and haptophytes, were estimated. Our observations offered insights into the relationships among iron supply, nutrients distribution patterns, and phytoplankton composition in the Southern Ocean.