Fossil organic carbon utilization in marine Arctic fjord sediments

Abstract

Abstract Recent research has challenged the traditional view of rock-derived or petrogenic organic carbon (OCpetro) as non-bio-available and bypassing the active carbon cycle when eroded and buried in marine sediments 1 and identified it as a potential source of fossil greenhouse gas emissions to the atmosphere2. Due to rising global temperatures, glacial OCpetro export rates are expected to increase3, thus, increasing the amount of OCpetro accessible to modern microbes in downstream depositional environments like the carbon burial “hot spots” of fjord sediments4. Using compound-specific radiocarbon analysis of fatty acids from intact polar lipids derived from live microbes, we were able to quantify the bio-availability of OCpetro in marine sediments in Hornsund Fjord, Svalbard. Our data indicate that local bacterial communities utilize between 5 ± 2% and 55 ± 6% of OCpetro (average of 25 ± 16%) for their biosynthesis, providing evidence for OCpetro bio-availability and its importance as substrate after redeposition. We hypothesize that the lack of sufficient recently synthesized organic carbon from primary production forces microbes into OCpetro utilization as an alternative energy source. The enhanced input of OCpetro and subsequent utilization by subsurface microbes represents an increasing natural source of fossil greenhouse gas emissions and a potential further positive feedback mechanism in a warming climate.