PCO2 and CO2 exchange during high bora winds in the Northern Adriatic

摘要

Episodic high wind events have a potential for significantly mixing surface water partial pressure of CO_2 (pCO_2). Their effect on estimates of air-sea CO_2 flux, especially in the coastal ocean, has not been adequately assessed. Here we show the response of surface water pCO_2 and CO_2 fluxes during high bora wind in the Northern Adriatic for a range of conditions including: stratified and oversaturated with respect to atmospheric CO2, stratified and undersaturated, and non-stratified and undersaturated. Three representative bora cases of 1.5-2day duration with wind speeds over 10ms-1 indicate that in all three studied cases, regardless of pre-bora conditions, pCO_2 in the surface water increases by 30-50μatm and CO_2 flux magnitudes peak up to 4 folds (-22.6 and -24.1mmolm-2day-1 day in the winter cases and 29mmolm-2day-1 in the summer case) over the magnitude of the mean annual value. Oceanic data measured simultaneously to surface pCO_2 measurements suggest that the most likely responsible mechanisms for the observed pCO_2 increases were oceanic vertical mixing and/or oceanic horizontal advection. Our study contributes to a very limited set of observations currently available on the biogeochemical response to episodic high wind events in coastal areas and their role in CO_2 exchange. In such coastal environments the presence of shallow depths and short horizontal spatial scales of variation facilitate the exchange of pCO_2 both vertically within ocean layers and horizontally across ocean basins, which can then alter air-sea pCO_2 difference across the ocean surface during high wind events and affect gas exchange. ?Episodic high bora winds significantly affect coastal mixing and carbon dynamics.?Surface water pCO_2 is increased by mixing and advection of water during bora.?High winds enhance air-sea CO_2 flux magnitude at the study site up to 4 folds.