Impact of sampling depth on CO$$_{2}$$ 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> partial pressure (pCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> ) measurements at different depths (1, 5, and 10 m) in ocean surface layers to determine CO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> fluxes (FCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> ) and to investigate the impacts of wind-sheltered and wind-exposed regions on the carbon budget. Vertical profiles of temperature, salinity, and pCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> were considered during a daily cycle. pCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> profiles exhibited relatively high values during sunny hours, associated with relatively high sea temperatures. However, the largest FCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mrow></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> of CO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> to the atmosphere; nevertheless, our estimates suggest that FCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> at the surface is 12.02 Tg month <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mrow></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:mmultiscripts> </mml:math> , which is 97.6% greater than that at 5 m depth. Therefore, future studies should consider sampling depth to adequately estimate the FCO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mn>2</mml:mn> <mml:mrow></mml:mrow></mml:mmultiscripts> </mml:math> .