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

Abstract

Episodic high wind events have a potential for significantly mixing surface water partial pressure of CO2 (pCO2). Their effect on estimates of air–sea CO2 flux, especially in the coastal ocean, has not been adequately assessed. Here we show the response of surface water pCO2 and CO2 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, pCO2 in the surface water increases by 30–50μatm and CO2 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 pCO2 measurements suggest that the most likely responsible mechanisms for the observed pCO2 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 CO2 exchange. In such coastal environments the presence of shallow depths and short horizontal spatial scales of variation facilitate the exchange of pCO2 both vertically within ocean layers and horizontally across ocean basins, which can then alter air-sea pCO2 difference across the ocean surface during high wind events and affect gas exchange.