Diel variability affects the inorganic carbon system in the sea-surface microlayer and influences air-sea CO2 flux estimates

López-Puertas, Ander; Wurl, Oliver; Frka, Sanja; Ribas-Ribas, Mariana (2025) Diel variability affects the inorganic carbon system in the sea-surface microlayer and influences air-sea CO2 flux estimates. Ocean Science, 21 (6). pp. 3471-3485. ISSN 1812-0792

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Abstract

The ocean plays a crucial role in the global carbon cycle by absorbing and storing about one-third of anthropogenic carbon dioxide (CO2). It is estimated that the ocean has sequestered approximately 26 % of CO2 emissions over the last decade, resulting in significant changes in the marine carbon system and impacting the marine environment. The sea-surface microlayer (SML) plays a crucial role in these processes, facilitating the transfer of matter and energy between the ocean and the atmosphere. However, most studies on the carbon cycle in the SML have primarily addressed daily variability and overlooked nocturnal processes, which may lead to inaccurate global carbon estimates. We analysed temperature, salinity, pHT25, and pCO2 using data collected over three complete diel cycles during an oceanographic campaign along the Croatian coast near Šibenik in the Middle Adriatic. Our analysis revealed statistically significant differences (p<0.05) between daytime and nighttime measurements of temperature, salinity, and pHT25. Diel differences in pCO2, were also observed, with patterns largely driven by temperature effects and short-term mixing. These differences may be related to the occurrence of buoyancy fluxes, which are typically more pronounced during the day and could enhance CO2 fluxes, as observed with values of 1.98 ± 2.52 mmol cm−2 h−1 during the day, while at night, they dropped to 0.01 ± 0.02 mmol cm−2 h−1. These findings emphasise the importance of considering complete diurnal cycles to accurately capture the variability in thermohaline features and carbon exchange processes, thereby improving our understanding of the ocean's role in climate change.

Item Type:	Article
Uncontrolled Keywords:	sea surface microlayer; Adriatic sea; CO2 flux; inorganic carbon
Subjects:	NATURAL SCIENCES > Chemistry > Inorganic Chemistry NATURAL SCIENCES > Interdisciplinary Natural Sciences > Marine Science
Divisions:	Division for Marine and Enviromental Research
Projects:	Project title Project leader Project code Project type Biokemijski odgovori površinskog sloja oligotrofnog područja Jadranskog mora na atmosfersko taloženje-BiREADI Sanja Frka Milosavljević IP-2018-01-3105 HRZZ
Depositing User:	Sanja Frka Milosavljević
Date Deposited:	11 Dec 2025 15:03
URI:	http://fulir.irb.hr/id/eprint/10413
DOI:	10.5194/os-21-3471-2025

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