Air-sea CO2 fluxes from pCO2 continuous measurements in a coastal area: the role of atmospheric forcing under different wintry seasons

While confidence in estimating air-sea CO? fluxes in open sea environments is increasing, a large uncertainty remains in defining the role played by coastal ecosystems as CO? sinks or sources. This is due to their highly variable oceanographic and climatic characteristics and to the effects of continental inputs. Within ICOS-OTC network, the PALOMA station, (Northern Adriatic Sea), is continuously collecting sea surface pCO? data since 2012. In the framework of JERICO-NEXT project, PALOMA is working together with several stations located in European coastal seas to explore the role of biological and atmospheric drivers in determining the observed pCO? variability. In this work, we present and discuss the effects of meteorological conditions on CO? air-sea fluxes, using the data collected in four wintry seasons from 2012 to 2016. In winter 2012-2013, the presence of lower temperatures and the occurrence of several events of Bora (wind speed > 15 ms?¹) produced a decrease of the SST down to 8.3 C leading to more favorable conditions for CO? absorption. The following winter was characterized by a higher air temperature, weaker winds, intense precipitation and river discharges larger than the average of the previous decade. These distinct hydrological and meteorological conditions significantly affected the sea surface pCO? that was lower in 2012-2013 (median pCO? ? 324 ± 8.9 ?atm) than in 2013-2014 (median pCO? ? 343 ± 9.0 ?atm). Sea always absorbed CO? from the atmosphere, but average daily fluxes were almost doubled during the colder winter 2012-2013 (F ? - 6.4 mmol-CO? m²d?¹) than in the milder winter 2013-2014 (F ? -3.7 mmol-CO? m²d?¹). Our results highlight the sensitivity of the CO? sink in the northern Adriatic to changes in the meteorological conditions and suggest that its capability of sequestering CO? could dramatically decrease in the next decades under a climate change scenario.