Arctic Ocean microbial community structure before and after the 2007 record sea ice minimum.

André M Comeau,William K W Li,Eddy C Carmack,Connie Lovejoy,Jean-Éric Tremblay,Jack Anthony Gilbert

doi:10.1371/journal.pone.0027492

André M Comeau, William K W Li + Show 4 more

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https://doi.org/10.1371/journal.pone.0027492

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Abstract

Increasing global temperatures are having a profound impact in the Arctic, including the dramatic loss of multiyear sea ice in 2007 that has continued to the present. The majority of life in the Arctic is microbial and the consequences of climate-mediated changes on microbial marine food webs, which are responsible for biogeochemical cycling and support higher trophic levels, are unknown. We examined microbial communities over time by using high-throughput sequencing of microbial DNA collected between 2003 and 2010 from the subsurface chlorophyll maximum (SCM) layer of the Beaufort Sea (Canadian Arctic). We found that overall this layer has freshened and concentrations of nitrate, the limiting nutrient for photosynthetic production in Arctic seas, have decreased. We compared microbial communities from before and after the record September 2007 sea ice minimum and detected significant differences in communities from all three domains of life. In particular, there were significant changes in species composition of Eukarya, with ciliates becoming more common and heterotrophic marine stramenopiles (MASTs) accounting for a smaller proportion of sequences retrieved after 2007. Within the Archaea, Marine Group I Thaumarchaeota, which earlier represented up to 60% of the Archaea sequences in this layer, have declined to <10%. Bacterial communities overall were less diverse after 2007, with a significant decrease of the Bacteroidetes. These significant shifts suggest that the microbial food webs are sensitive to physical oceanographic changes such as those occurring in the Canadian Arctic over the past decade.

Highlights

Atmospheric and oceanic processes are directly affected by increasing global temperatures and the Arctic has been the most severely impacted region to date [1]
Once reads were re-sampled and singleton OTUs removed, all three domains showed saturation in the rarefaction analysis, with the Bacteria roughly twice as diverse as the Archaea and the Eukarya representing near 12,000 OTUs at the 98% level (Fig. S1)
We found no significant effect of season, photosynthetically-active radiation (PAR), Chlorophyll a (Chl a) size fraction or geography on the bacterial taxa recovered (Table 1)

Summary

Introduction

Atmospheric and oceanic processes are directly affected by increasing global temperatures and the Arctic has been the most severely impacted region to date [1]. A long-term trend of deceasing minimum extent of summer sea ice was marked by a sharp decline and record low in September 2007. Summer sea ice extent remains below the long-term pre-2007 average [1,2]. Increased stratification of the upper water column due to surface freshening could have a profound effect on nutrient transport into the euphotic zone and decrease the overall productivity of the Arctic Ocean. Evidence for such a change has been reported from the upper 150 m of the Canada Basin, where smaller phytoplankton size-classes are becoming more prevalent [5]

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