Biogeochemical and ecological variability during the late summer–early autumn transition at an ice‐floe drift station in the Central Arctic Ocean

Nicole L Schanke,Francesco Bolinesi,Giacomo R Ditullio,Peter A Lee,Olga Mangoni,Mario Hoppmann,Philipp Anhaus,Christian Katlein

doi:10.1002/lno.11676

Abstract

AbstractAs the annual expanse of Arctic summer ice‐cover steadily decreases, concomitant biogeochemical and ecological changes in this region are likely to occur. Because the Central Arctic Ocean is often nutrient and light limited, it is essential to understand how environmental changes will affect productivity, phytoplankton species composition, and ensuing changes in biogeochemistry in the region. During the transition from late summer to early autumn, water column sampling of various biogeochemical parameters was conducted along an ice‐floe drift station near the North Pole. Our results show that as the upper water column stratification weakened during the late summer–early autumn transition, nutrient concentrations, particulate dimethylsulfoniopropionate (DMSPp) levels, photosynthetic efficiency, and biological productivity, as estimated by ΔO2/Ar ratios, all decreased. Chemotaxonomic (CHEMTAX) analysis of phytoplankton pigments revealed a taxonomically diverse picoautotrophic community, with chlorophyll (Chl) c3‐containing flagellates and the prasinophyte, Pyramimonas spp., as the most abundant groups, comprising ~ 30% and 20% of the total Chl a (TChl a) biomass, respectively. In contrast to previous studies, the picoprasinophyte, Micromonas spp., represented only 5% to 10% of the TChl a biomass. Of the nine taxonomic groups identified, DMSPp was most closely associated with Pyramimonas spp., a Chl b‐containing species not usually considered a high DMSP producer. As the extent and duration of open, ice‐free waters in the Central Arctic Ocean progressively increases, we suggest that enhanced light transmission could potentially expand the ecological niche of Pyramimonas spp. in the region.

Highlights

Author Contribution Statement: All authors made significant contributions to the data presented in and/or the construction of this manuscript
As late summer progresses into early autumn, freeze-up conditions caused by colder air temperatures will alter the properties of the Arctic Ocean surface waters
Changing environmental conditions have already altered the ecological balance in food web structure, resulting in a shift from sympagic microalgal species, such as sea ice diatoms, to a more planktonic picoeukaryotic-dominated community consisting of small chlorophyll (Chl) b-containing species

Summary

Introduction

Author Contribution Statement: All authors made significant contributions to the data presented in and/or the construction of this manuscript. Micromonas spp. have been shown to significantly increase growth rates at higher temperatures, even under low-light saturation intensities of $ 10 μE m−2 s−1 (Lovejoy et al 2007; Hoppe et al 2018) Other prasinophyte species, such as Pyramimonas spp., have been observed in the sea ice and water column of the open Arctic Ocean (Gradinger 1996; Harðardóttir et al 2014). The continued progression of the Arctic Ocean phytoplankton community from sympagic species toward a more picoplankton-based food web will likely lead to a reduced carbon export flux due to enhanced microzooplankton grazing rates, compared to a microphytoplankton-dominated community (Sherr and Sherr 2002) This change in the Central Arctic Ocean food web structure will likely enhance the microbial loop and regenerated production, thereby significantly impacting various biogeochemical cycles in the region (Worden et al 2015)

Objectives

Methods

Results

Discussion

Conclusion