Upward nitrate flux and downward particulate organic carbon flux under contrasting situations of stratification and turbulent mixing in an Arctic shelf sea

Abstract

Increased sea ice melt alters vertical surface-mixing processes in Arctic seas. More melt water strengthens the stratification, but an absent ice cover also exposes the uppermost part of the water column to wind-induced mixing processes. We conducted a field study in the Barents Sea, an Arctic shelf sea, to examine the effects of stratification and vertical mixing processes on 1) the upward nitrate flux (into surface layers 5 mmol nitrate m–2 d–1) during a post bloom situation which was associated with a high downward POC flux (40–120 m: 260–600 mg POC m–2 d–1). We suggest that strong wind events during our field study induced vertical mixing processes and triggered upwards nitrate flux, while a combination of down-mixed phytoplankton and fast-sinking mesozooplankton fecal pellets enhanced the downward POC flux. The results of this study underscore the need to further investigate the role of strong, episodic wind events on the upward nitrate and downward POC fluxes in weakly stratified regions of the Arctic that may be ice-free in future.

Keywords

• nitrate flux
• POC export
• sediment trap
• sedimentation
• warming Arctic
• space-for-time substitution