Impact of sampling depth on CO flux estimates

Area of Science:

• Oceanography
• Climate Science
• Biogeochemistry

Background:

• Air-sea exchange of trace gases is crucial for Earth's climate regulation.
• Oceanic carbon dioxide (CO2) fluxes are influenced by wind speed, sea temperature, and salinity.
• Accurate quantification of CO2 fluxes is essential for understanding the global carbon cycle.

Purpose of the Study:

• To quantify CO2 fluxes (FCO2) using partial pressure of CO2 (pCO2) measurements at various depths (1, 5, and 10 m).
• To investigate the influence of wind-sheltered and wind-exposed areas on oceanic carbon budgets.
• To assess the impact of sampling depth on the estimation of surface CO2 fluxes.

Main Methods:

• Vertical profiles of temperature, salinity, and pCO2 were measured over a daily cycle.
• CO2 fluxes were calculated based on pCO2 differences at different ocean depths.
• Comparison of estimated CO2 fluxes with existing datasets (SOCAT).

Main Results:

• pCO2 levels were higher during warmer, sunnier periods but highest FCO2 correlated with increased wind speeds.
• Estimated FCO2 decreased significantly with depth: 71% in sheltered regions and 44% in exposed regions (comparing 1m to 10m).
• Surface FCO2 estimates were substantially higher (97.6%) than those reported at 5m depth for the Atlantic basin.

Conclusions:

• Sampling depth is a critical factor that significantly affects the accuracy of estimated oceanic CO2 fluxes.
• Previous estimations may underestimate the true CO2 flux due to insufficient consideration of depth-dependent variations.
• Future research on air-sea CO2 exchange must incorporate multi-depth measurements for robust carbon budget assessments.