Impact of sampling depth on CO2 flux estimates

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 CO 2 partial pressure (pCO 2 ) measurements at different depths (1, 5, and 10 m) in ocean surface layers to determine CO 2 fluxes (FCO 2 ) 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 FCO 2 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 CO 2 to the atmosphere; nevertheless, our estimates suggest that FCO 2 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 FCO 2 .