Observations of late-winter marine microbial activity in an ice-covered fjord, west Greenland

David Chandler,Shona Mackie

doi:10.5194/essd-12-897-2020

Abstract

Abstract. Direct observations of marine microbial metabolism are sparse in the Arctic, particularly under sea ice during winter. This paper presents the first observations of Arctic winter microbial activity under sea ice in a west Greenland fjord (Lillefjord, ∼ 70∘ N). Here, measured changes in dissolved oxygen (DO) content in light and dark in situ incubations were used to calculate net community productivity, respiration and photosynthesis rates. Data were collected at two fully ice covered sites during February 2013, shortly after the end of the polar night. Averaged over the full study period, dark incubations showed statistically significant decreases in DO of -0.36±0.24 (near shore) and -0.09±0.07 g O2 m−3 d−1 (fjord centre), indicating respiration rates that were 2–20 times greater than rates previously reported under sea ice in the Arctic. Meanwhile, a lack of significant evidence for photosynthesis suggests that the rate of photosynthesis – if it was occurring – was much lower than that of respiration. The data also show no significant evidence of a temporal trend in metabolism rates over the study period; however, ambient seawater DO increased significantly at the fjord centre (0.023±0.013 g O2 m−3 d−1), possibly attributable to processes not occurring in the incubations (such as sea ice algal photosynthesis). These data may improve our understanding of microbial activity in the fjord during winter, and its contribution to Arctic ecosystems under present and future conditions. The data are archived at PANGAEA (https://doi.org/10.1594/PANGAEA.906332, Chandler and Mackie, 2019; https://doi.org/10.1594/PANGAEA.912677, Chandler and Mackie, 2020).

Highlights

There is increasing evidence for rapid climate change in the Arctic, with wide-reaching impacts in both terrestrial and marine environments (Wassmann et al, 2011; McMeans et al, 2013; Post et al, 2013; Comiso and Hall, 2014)
While estimates of marine net primary productivity (NPP) based on satellite retrievals of chlorophyll a have shown a link between reductions in sea ice cover and increases in NPP across much of the Arctic during 1998–2009, details of the processes associated with this change and its effects on higher levels of the food chain remain uncertain (Hansen et al, 2003; Arrigo et al, 2008; Brown and Arrigo, 2012; Vancoppenolle et al, 2013)
The data processing algorithms depend on multiple assumptions that may not be justified or appropriate in all cases (Arrigo et al, 2008); for example there may not be a direct relationship between retrieved chlorophyll a concentration and NPP (Flynn et al, 2013); data are unavailable for ocean wa

Summary

Introduction

There is increasing evidence for rapid climate change in the Arctic, with wide-reaching impacts in both terrestrial and marine environments (Wassmann et al, 2011; McMeans et al, 2013; Post et al, 2013; Comiso and Hall, 2014). The observed reduction in sea ice cover (duration, extent and/or thickness), and the corresponding increase in solar illumination in the upper layers of the Arctic Ocean, is of particular interest. While estimates of marine net primary productivity (NPP) based on satellite retrievals of chlorophyll a have shown a link between reductions in sea ice cover and increases in NPP across much of the Arctic during 1998–2009, details of the processes associated with this change and its effects on higher levels of the food chain remain uncertain (Hansen et al, 2003; Arrigo et al, 2008; Brown and Arrigo, 2012; Vancoppenolle et al, 2013). The data processing algorithms depend on multiple assumptions that may not be justified or appropriate in all cases (Arrigo et al, 2008); for example there may not be a direct relationship between retrieved chlorophyll a concentration and NPP (Flynn et al, 2013); data are unavailable for ocean wa-

Results

Discussion

Conclusion