Sea-ice associated carbon flux in Arctic spring

J Ehrlich,I Peeken,F L Schaafsma,B A Bluhm,G Castellani,P Massicotte,H Flores,A Brandt

doi:10.1525/elementa.2020.00169

Abstract

The Svalbard region faces drastic environmental changes, including sea-ice loss and “Atlantification” of Arctic waters, caused primarily by climate warming. These changes result in shifts in the sea-ice-associated (sympagic) community structure, with consequences for the sympagic food web and carbon cycling. To evaluate the role of sympagic biota as a source, sink, and transmitter of carbon, we sampled pack ice and under-ice water (0–2 m) north of Svalbard in spring 2015 by sea-ice coring and under-ice trawling. We estimated biomass and primary production of ice algae and under-ice phytoplankton as well as biomass, carbon demand, and secondary production of sea-ice meiofauna (&gt;10 µm) and under-ice fauna (&gt;300 µm). Sea-ice meiofauna biomass (0.1–2.8 mg C m–2) was dominated by harpacticoid copepods (92%), nauplii (4%), and Ciliophora (3%). Under-ice fauna biomass (3.2–62.7 mg C m–2) was dominated by Calanus copepods (54%). Appendicularia contributed 23% through their high abundance at one station. Herbivorous sympagic fauna dominated the carbon demand across the study area, estimated at 2 mg C m–2 day–1 for ice algae and 4 mg C m–2 day–1 for phytoplankton. This demand was covered by the mean primary production of ice algae (11 mg C m–2 day–1) and phytoplankton (30 mg C m–2 day–1). Hence, potentially 35 mg C m–2 day–1 of algal material could sink from the sympagic realm to deeper layers. The demand of carnivorous under-ice fauna (0.3 mg C m–2 day–1) was barely covered by sympagic secondary production (0.3 mg C m–2 day–1). Our study emphasizes the importance of under-ice fauna for the carbon flux from sea ice to pelagic and benthic habitats and provides a baseline for future comparisons in the context of climate change.

Highlights

The Arctic Ocean harbors a unique ecosystem characterized by organisms that are adapted to an extreme environment comprising polar night, midnight sun, and seasonal or permanent sea-ice cover
Biomass, carbon demand, and production of the seaice biota The biomass of ice algae in ice cores ranged between 10.5 and 41.9 mg C m–2 per station
Except for station 27, the ice-algal demand of these taxa was lower than the ice-algal primary production (Figure 3b)

Summary

Introduction

The Arctic Ocean harbors a unique ecosystem characterized by organisms that are adapted to an extreme environment comprising polar night, midnight sun, and seasonal or permanent sea-ice cover. The composition of the heterotrophic sea-ice fauna (sea-ice meiofauna) varies between regions, seasons, and ice types, some taxa widely occur in Arctic sea ice (Bluhm et al, 2018). Ehrlich et al: Arctic sympagic carbon flux and Hsiao, 1990; Gradinger, 1999a; Bluhm et al, 2018; Ehrlich et al, 2020) These and other sea-ice meiofauna taxa are primarily consumers of ice algae and important links in the transfer of energy from the sea ice to pelagic and benthic food webs (Gradinger, 1999a; Nozais et al, 2001; Grebmeier et al, 2010). Their study showed that sea-ice meiofauna has a low grazing impact on the icealgal spring bloom and leaves the vast majority of organic matter for under-ice, pelagic, and benthic communities

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