Enhanced ocean CO₂ uptake due to near-surface temperature gradients

Area of Science:

• Oceanography
• Climate Science
• Biogeochemistry

Background:

• Oceans absorb approximately 25% of anthropogenic carbon dioxide (CO2) emissions annually.
• Current global CO2 flux estimates often overlook the influence of vertical temperature gradients near the ocean surface.
• Theoretical and laboratory studies suggest temperature gradients significantly affect air-sea CO2 exchange due to CO2 solubility's temperature sensitivity.

Purpose of the Study:

• To provide in-situ field evidence for the effect of vertical temperature gradients on air-sea CO2 fluxes.
• To quantify the impact of near-surface temperature gradients on CO2 uptake in the Atlantic Ocean.
• To validate existing models and theoretical predictions regarding ocean CO2 absorption.

Main Methods:

• Direct and indirect measurement of air-sea CO2 fluxes along transects in the Atlantic Ocean (50°N to 50°S) during 2018 and 2019.
• Comparison of flux measurements with and without the inclusion of vertical temperature gradient data.
• Analysis of the difference between direct and indirect flux estimates.

Main Results:

• Accounting for vertical temperature gradients reduced the discrepancy between direct and indirect CO2 flux measurements from 0.19 to 0.08 mmol m⁻² d⁻¹.
• This adjustment implies an approximate 7% increase in the Atlantic Ocean's CO2 sink, equating to ~0.03 PgC yr⁻¹.
• The findings provide the first in-situ validation of theoretical and modeling studies predicting enhanced ocean CO2 uptake when temperature gradients are considered.

Conclusions:

• In-situ field data confirm that vertical temperature gradients significantly influence air-sea CO2 exchange.
• The study demonstrates a quantifiable increase in the Atlantic CO2 sink due to these gradients.
• Accurate global carbon budget assessments necessitate the incorporation of near-surface temperature gradient effects on ocean CO2 uptake.