Quantatative analysis of microbial abundance within Arctic fjord sediments assessed through direct counting

Microbes found in the marine sediments are responsible for the production of nearly half of the carbon dioxide found in the atmosphere (Arrigo, 2005). The fjords of Svalbard (79°N) are not considered typical marine sediments because high iron content influences unique subsurface redox chemistry. Radiotracer studies have shown that these sediments contain active bacterial sulfate-reducing communities (Finke et al., 2016). In addition to bacteria, archaeal cells within these sediments have been in aggregates encompassed by sulfate-reducing bacteria (Ravenschlag et al., 2001). These anaerobic organisms participate in mediating environmental biogeochemical cycles, including the oxidation of methane (Ravenschlag et al., 2001) and iron reduction (Vandieken et al., 2006). These observations have led to the understanding of the important role that these microbes play in global nutrient cycling and have led to recent interest in how these communities will respond to glacial retreat associated with climate change (Arrigo, 2005). However, the abundance of microbes across the fjords in Svalbard is relatively unknown. Here, we show the abundance of in sediments from two virtually unstudied fjords, Van Keulenfjorden and Kongsfjorden. We found a general trend of lower microbial abundance after around 10 cm in depth. For relative abundance, we saw numbers around 10^7 cells per ml in Van Keulenfjorden, which is slightly lower than counts of 16S copy numbers acquired through quantitative PCR (qPCR). Our results demonstrate that there are varying levels of microbial abundance in the fjord sediments of Svalbard. Moving forward, this research could help contribute to a better understanding of the effect that these microbes have on nutrient cycling at both a local and global level by coupling abundance data with functional analyses. Furthermore, we hope that this research will enhance the ability of predicting the effects that climate change and glacial runoff have on these microbial communities and carbon cycling in the Arctic Circle.