Abstract
AbstractSubmesoscale eddies and fronts are important components of oceanic mixing and energy fluxes. These phenomena occur in the surface ocean for a period of several days, on scales between a few hundred meters and few tens of kilometers. Remote sensing and modeling suggest that eddies and fronts may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0–400 m) revealed enhanced mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical characteristics. Compared to the surrounding waters, the filament was characterized by a distinct phytoplankton bloom, associated with depleted inorganic nutrients, elevated chlorophyll a concentrations, as well as twofold higher phyto‐ and bacterioplankton cell abundances. High‐throughput 16S rRNA gene sequencing of bacterioplankton communities revealed enrichment of typical phytoplankton bloom‐associated taxonomic groups (e.g., Flavobacteriales) inside the filament. Furthermore, linked to the strong water subduction, the vertical export of organic matter to 400 m depth inside the filament was twofold higher compared to the surrounding waters. Altogether, our results show that physical submesoscale mixing can shape distinct biogeochemical conditions and microbial communities within a few kilometers of the ocean. Hence, the role of submesoscale features in polar waters for surface ocean biodiversity and biogeochemical processes need further investigation, especially with regard to the fate of sea ice in the warming Arctic Ocean.
Highlights
Investigating oceanographic dynamics in the Fram Strait is of importance considering the relevance of interacting water masses for the “Atlantification” of the Arctic Ocean (Randelhoff et al 2018; Wang et al 2020)
In addition to physicochemical differences, the Polar and the Atlantic water masses harbor distinct bacterioplankton communities (Wilson et al 2017; Fadeev et al 2018; Müller et al 2018). This region provides an excellent opportunity to investigate how bacterioplankton communities are shaped by submesoscale processes between distinct water masses and how these patterns correspond to the general microbial distribution in the Fram Strait
Using a set of measured parameters, embedded into a high-resolution physical analysis of the filament which we briefly summarize below, we investigated how the submesoscale processes impacted nutrient distribution, phyto- and bacterioplankton community composition, and downward export of particulate organic matter (POC) from the filament
Summary
Observations by satellite remote sensing, autonomous profiling floats, and towed instruments revealed the ubiquity of submesoscale features in the global ocean, confirming previous hypotheses based on numerical models (Ferrari 2011; Lévy et al 2012; Thompson et al 2016) These oceanic motions in surface waters are due to horizontal density gradients, taking the shape of eddies and filaments with a lateral spatial range between a few hundred meters and some tens of kilometers (Sasaki et al 2014). The Strait harbors of two major surface current systems: (1) the East Greenland Current flowing southwards along the Greenland shelf, transporting cold Polar water and sea ice to the North Atlantic (de Steur et al 2009); and (2) the West Spitsbergen Current flowing northwards along the Svalbard Archipelago, transporting relatively warm and saline Atlantic water into the Arctic Ocean (Beszczynska-Möller et al 2012; von Appen et al 2016).
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