Variations in Rates of Biological Production in the Beaufort Gyre as the Arctic Changes: Rates from 2011 to 2016

The Arctic Ocean is experiencing profound environmental changes as the climate warms. Understanding how these changes will affect Arctic biological productivity is key for predicting future Arctic ecosystems and the global CO2 balance. Here we use in situ gas measurements to quantify rates of gross oxygen production (GOP, total photosynthesis) and net community production (NCP, net CO2 drawdown by the biological pump) in the mixed layer in summer or fall from 2011 to 2016 in the Beaufort Gyre. NCP and GOP show spatial and temporal variations with higher values linked with lower concentrations of sea ice and increased upper ocean stratification. Mean rates of GOP range from 8 1 to 54 9 mmol O(2)m(-2)d(-1) with the highest mean rates occurring in summer of 2012. Mean rates of NCP ranged from 1.3 0.2 to 2.9 0.5 mmol O(2)m(-2)d(-1). The mean ratio of NCP/GOP, a measure of how efficiently the ecosystem is recycling its nutrients, ranged from 0.04 to 0.17, similar to ratios observed at lower latitudes. Additionally, a large increase in total photosynthesis that occurred in 2012, a year of historically low sea ice coverage, persisted for many years. Taken together, these data provide one of the most complete characterizations of interannual variations of biological productivity in this climatically important region, can serve as a baseline for future changes in rates of production, and give an intriguing glimpse of how this region of the Arctic may respond to future lack of sea ice. Plain Language Summary The Arctic Ocean is changing rapidly because of global climate change. Sea ice is declining, with the Arctic expected to be ice-free in the summer by the middle of this century. The effect of these environmental changes on the marine carbon cycle is poorly known. In this study, rates of marine photosynthesis and net carbon dioxide drawdown in the summer or fall of 2011-2016 show that ice concentration was the largest environmental predictor of biological productivity, with smaller sea ice concentrations leading to increased rates of photosynthesis and thus likely to higher carbon dioxide drawdown. Additionally, a large increase in total photosynthesis that occurred in 2012, a year of historically low sea ice coverage, persisted for many years. An alternative hypothesis for the large increase in photosynthesis in 2012 is that the data in 2011 were collected before the onset of summer stratification (time when mixed layer depth gets very shallow), whereas data for all subsequent years were collected after this increase in stratification had occurred.