Photobiogeochemical cycling of carbon monoxide in the southeastern Beaufort Sea in spring and autumn

Abstract

We investigated the distribution, photoproduction, microbial uptake, and air-sea exchange of carbon monoxide (CO), a key photoproduct of chromophoric dissolved organic matter (CDOM), in open waters of the southeastern Beaufort Sea in autumn 2003 and spring 2004. Diurnal cycles of surface water CO concentration ([CO]) occurred in autumn but not in spring. In both seasons [CO] was well above air-equilibrium at most stations (maximum of 12,500% saturation) and dropped with depth to undetectable levels below 50 m. Mean surface water [CO] and CO water-column burdens (0-50 m) were 0.45 nmol L−1 and 5.0 µmol m−2 in autumn and 4.7 nmol L−1 and 64.8 µmol m−2 in spring, and the sea-to-air CO flux was 33 times higher in spring. The efficiency of CO photoproduction correlated linearly with CDOM across the Mackenzie River estuary, the Mackenzie Shelf, and the Amundsen Gulf. Modeled water-column CO photoproduction in spring was 15 times that in autumn (45.8 vs. 3.0 µmol m−2 d−1). Microbial CO uptake followed first-order kinetics in autumn while Hill-type, saturation, and inhibition kinetics were common in surface waters in spring. Bio-oxidation was the dominant CO loss term in autumn while gas exchange was almost equally important in spring. Higher photoproduction and slower bio-uptake in spring resulted in the wide autumn-spring differences in the [CO] distribution pattern and air-sea CO flux. CO cycling in cold northern waters differs both quantitatively and qualitatively from that in warmer seas.