Sea ice presence is linked to higher carbon export and vertical microbial connectivity in the Eurasian Arctic Ocean

Claudia Wekerle,Eduard Fadeev,Anya M Waite,Christina Bienhold,Ian Salter,Morten H Iversen,Simon Ramondenc,Eva-Maria Nöthig,Antje Boetius,Laura Hehemann,Andreas Rogge

doi:10.1038/s42003-021-02776-w

Abstract

Arctic Ocean sea ice cover is shrinking due to warming. Long-term sediment trap data shows higher export efficiency of particulate organic carbon in regions with seasonal sea ice compared to regions without sea ice. To investigate this sea-ice enhanced export, we compared how different early summer phytoplankton communities in seasonally ice-free and ice-covered regions of the Fram Strait affect carbon export and vertical dispersal of microbes. In situ collected aggregates revealed two-fold higher carbon export of diatom-rich aggregates in ice-covered regions, compared to Phaeocystis aggregates in the ice-free region. Using microbial source tracking, we found that ice-covered regions were also associated with more surface-born microbial clades exported to the deep sea. Taken together, our results showed that ice-covered regions are responsible for high export efficiency and provide strong vertical microbial connectivity. Therefore, continuous sea-ice loss may decrease the vertical export efficiency, and thus the pelagic-benthic coupling, with potential repercussions for Arctic deep-sea ecosystems.

Highlights

1234567890():,; The Arctic Ocean is currently undergoing unprecedented changes due to advancing climate warming
We studied microbial communities associated with settling aggregates in contrasting sea ice conditions between June 24th and July 16th 2016 at the Long-Term Ecological Research (LTER) observatory HAUSGARTEN in the Fram Strait
The Particulate organic carbon (POC) fluxes showed peaks (>10 mg m−2 d−1) early in the productive season (March, April, and May), during the period when sea ice is present in the region and defined as iceassociated carbon export, and again later in the season (June, July, and August) during the ice-free period due to POC export of pelagic production[31]

Summary

Introduction

1234567890():,; The Arctic Ocean is currently undergoing unprecedented changes due to advancing climate warming. Primary production models suggest that with the northward propagation of ice-edge blooms along leads and polynyas, the impact of ice-algae and under-ice phytoplankton blooms on productivity is likely to increase[18], with ecological consequences for pelagic and benthic ecosystems[16,19] It remains unclear what ecological effects an earlier and a stronger retreat of the ice-edge will have for carbon export on the Arctic shelf seas and margins. Beyond the supply of energy and nutrients, sinking particles can play a key role in determining the structure and functioning of microbial communities in the deep sea by importing microbes from surface waters[22,23,25] To date, such so-called vertical microbial connectivity has mainly been demonstrated in temperate and tropical oceanic settings[22,23,24,25,26,27]. With increasing evidence of functional microbial groups exported from surface waters into the deep sea, alterations in vertical microbial connectivity may impact biogeochemical processes of the deep ocean and the seafloor

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Conclusion