Chemical and biological vertical distributions within central Arctic (>82°N) sea ice during late summer

We assessed the distribution of biota (autotrophs and heterotrophs) and associated carbonate chemistry variables in Arctic sea ice at latitudes >82 degrees N during late summer and early autumn 2018. The sampled sea ice was relatively thick (average 1.4 m) with variable snow cover (mean 7 cm) and low bulk salinities throughout. Most measured variables, including carbonate chemistry parameters, were low in the upper half of the ice cores, but increased with depth. Measurements of particulate organic carbon (POC), chlorophyll a (chl a), bacterial abundance, and particulate extracellular polysaccharide (pEPS) in the cores strongly suggested that detrital carbon was the major particulate organic pool. Near the ice-water interface, autotrophic material comprised ca. 50% of the total POC, whereas pEPS and bacterial carbon accounted for ca. 8 and 1% of the total POC, respectively. Under-ice water was nutrient poor, providing only a small input of nutrients to support autotrophic growth, at least during the time of our sampling. While the Arctic Ocean has substantial interannual variability in sea-ice concentration and thickness, these measurements enrich the available database and suggest that during years when autumn sea ice is >1 m thick, sea-ice biota are limited in activity and biomass.

Automated summary

We examined the distribution of biota and carbonate chemistry variables in Arctic sea ice during late summer and early autumn 2018. The sea ice sampled was thick and had low bulk salinities, with most variables increasing with depth. Our measurements indicated that detrital carbon was the main organic pool in the ice cores. Near the ice-water interface, autotrophic material comprised around 50% of the total particulate organic carbon. Nutrient availability in the under-ice water was limited, suggesting limited activity and biomass of sea-ice biota when autumn sea ice is thicker than 1 m.