Impact of sampling depth on CO2 flux estimates

Abstract

The exchange of trace gases between the atmosphere and the ocean plays a key role in the Earth's climate. Fluxes at the air-sea interface are affected mainly by wind blowing over the ocean and seawater temperature and salinity changes. This study aimed to quantify the use of CO2 partial pressure (pCO(2) ) measurements at different depths (1, 5, and 10 m) in ocean surface layers to determine CO2 fluxes (FCO2 ) and to investigate the impacts of wind-sheltered and wind-exposed regions on the carbon budget. Vertical profiles of temperature, salinity, and pCO(2) were considered during a daily cycle. pCO(2) profiles exhibited relatively high values during sunny hours, associated with relatively high sea temperatures. However, the largest FCO2 corresponded with higher wind speeds. Estimated fluxes between measurements at 1 and 10 m depths decreased by 71% in the sheltered region and 44% in the exposed region. According to the SOCAT dataset, at a depth of 5 m, the Atlantic basin emits approximately 0.29 Tg month(-1) of CO2 to the atmosphere; nevertheless, our estimates suggest that FCO2 at the surface is 12.02 Tg month(-1) , which is 97.6% greater than that at 5 m depth. Therefore, future studies should consider sampling depth to adequately estimate the FCO2