Microbial community composition and abundance after millennia of submarine permafrost warming

Julia Mitzscherling,Linda Mahler,Lutz Schirrmeister,Jens Kallmeyer,Maria Winterfeld,Pier P Overduin,Mikhail N Grigoriev,Dirk Wagner,Susanne Liebner,Matthias Winkel,Fabian Horn

doi:10.5194/bg-16-3941-2019

Abstract

Abstract. Warming of the Arctic led to an increase in permafrost temperatures by about 0.3 ∘C during the last decade. Permafrost warming is associated with increasing sediment water content, permeability, and diffusivity and could in the long term alter microbial community composition and abundance even before permafrost thaws. We studied the long-term effect (up to 2500 years) of submarine permafrost warming on microbial communities along an onshore–offshore transect on the Siberian Arctic Shelf displaying a natural temperature gradient of more than 10 ∘C. We analysed the in situ development of bacterial abundance and community composition through total cell counts (TCCs), quantitative PCR of bacterial gene abundance, and amplicon sequencing and correlated the microbial community data with temperature, pore water chemistry, and sediment physicochemical parameters. On timescales of centuries, permafrost warming coincided with an overall decreasing microbial abundance, whereas millennia after warming microbial abundance was similar to cold onshore permafrost. In addition, the dissolved organic carbon content of all cores was lowest in submarine permafrost after millennial-scale warming. Based on correlation analysis, TCC, unlike bacterial gene abundance, showed a significant rank-based negative correlation with increasing temperature, while bacterial gene copy numbers showed a strong negative correlation with salinity. Bacterial community composition correlated only weakly with temperature but strongly with the pore water stable isotopes δ18O and δD, as well as with depth. The bacterial community showed substantial spatial variation and an overall dominance of Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadetes, and Proteobacteria, which are amongst the microbial taxa that were also found to be active in other frozen permafrost environments. We suggest that, millennia after permafrost warming by over 10 ∘C, microbial community composition and abundance show some indications for proliferation but mainly reflect the sedimentation history and paleoenvironment and not a direct effect through warming.

Highlights

Temperatures in high-latitude regions have been rising twice as fast as the global average over the last 30 years (IPCC in Climate Change 2013, 2013) and are predicted to experience the globally strongest increase in the future
In C4, the drill site located closest to the coast, Unit II had the highest pore water salinity, ranging from 0.9 to 17.6 PSU (Table S2), which spans freshwater to mesohaline water but is far below seawater salinities
Substantial permafrost warming is occurring throughout the Arctic today, and the associated response of microbial communities driving biogeochemical cycling and the formation of greenhouse gases is of general interest

Summary

Introduction

J. Mitzscherling et al.: Microbial community composition and abundance. Following the trend of air temperature increase in the Northern Hemisphere, continuous permafrost warmed by about 0.3 ◦C over the last decade at a global scale (Biskaborn et al, 2019). Microbial community composition was reported to be responsive to temperature changes (Luo et al, 2014; Rui et al, 2015; Weedon et al, 2012; Xu et al, 2015; Zhang et al, 2005; Zogg et al, 1997). Microbial community composition can be responsive to temperature and microbial abundance, especially in systems with weak energy constraints. Substantial permafrost warming on long timescales could affect microbial community composition and abundance before permafrost thaws

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Results

Discussion

Conclusion