Sinking Diatom Assemblages as a Key Driver for Deep Carbon and Silicon Export in the Scotia Sea (Southern Ocean)

Abstract

Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global-ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.

Protistan community structure and the influence of a branch of Kuroshio in the northeastern East China Sea during the late spring

“…When considering the relatively sufficient concentration of silicates in the MSW region, which is even higher than the halfsaturation constants for silicate uptake by many diatom species, the silicate-rich nutrient stoichiometry of the water could potentially benefit fast-growing diatoms (Guillard et al, 1973;Paasche, 1973;Paasche, 1975;Tilman and Kilham, 1976). Additionally, it is worth noting that species of the large diatom genus Corethron generally dwell in cold water and employ a strategy of dominating the oligotrophic assemblages by exploiting deep-water nutrients in stratified waters through vertical migration facilitated by controlling their buoyancy (Leventer et al, 2002;Zuñiga et al, 2021). This could partially explain their prevalence at the MSW region stations, where the waters are relatively cold and more vertically stratified.…”

History of Anvers-Hugo Trough, western Antarctic Peninsula shelf, since the Last Glacial Maximum. Part II: Palaeo-productivity and palaeoceanographic changes during the Last Glacial Transition

“…Note that statistical analysis of all species except Chs is based on diatom counts excluding Chs. Like Chs, C. pennatum is a species associated with well-stratified surface waters (Table 2; Crawford, 1995;Leventer et al, 2002;Stickley et al, 2005;Alley et al, 2018;Zúñiga et al, 2021). Sediments captured within cluster DA1a are interpreted to have been deposited during a period of seasonal sea ice formation, with high rates of meltwater input and the formation of a wellstratified water column in the austral spring.…”

Marine Microbiomes: Towards Standard Methods and Best Practices

“…Typically combined with physical and chemical sensors, automated samplers are of particular value in remote and inaccessible areas, such as seasonally ice-covered environments von Appen et al, 2021;Wietz et al, 2021;Ramondenc et al, 2022). For instance, autonomous sediment traps allow linking particle flux with microbial diversity over extended periods, based on microscopic counts (Salter et al, 2007(Salter et al, , 2012(Salter et al, , 2014Nöthig et al, 2020;Zúñiga et al, 2021) and DNA sequencing Bachy et al, 2022;Valencia et al, 2022).…”