Variability of the CO2 Flux on the Water-Atmosphere Interface in the Black Sea Coastal Waters on Various Time Scales in 2010–2014

Abstract

Due to the present tendency to the increased carbon dioxide content in the atmosphere, one of the priorities in hydrochemical research consists in studying the gas exchange in the water-atmosphere system. At that, quantity assessment of the marine areas' role in the CO2 transport requires taking into account water spatial heterogeneity based on its ability to invade or evacuate carbon dioxide. Represented are the results of estimating intensity and direction of the CO2 flux between the sea and the atmosphere in the Black Sea coastal waters in 2010-2014 executed based on the in situ hydrochemical studies and reanalysis of meteorological data. The results of direct measurements of the CO2 equilibrium partial pressure in the water surface layer and in the atmosphere near-surface layer were used for the first time for calculating the CO2 flux in the Black Sea waters. The results of analysis of the CO2 flux variability on different time scales are represented. The performed calculations show that the CO2 evacuation prevails in a warm season, whereas its invasionin a cold season. During the off-season transitions, the water area state is close to equilibrium. The timing limits of the seasons are not constant and vary practically each year. Probable reasons of a CO2 flux seasonal variability are considered. Possible role of the abiogenic, biogenic and anthropogenic factors is assessed as a cause of the observed intensity fluctuations of the CO2 exchange between the sea and the atmosphere. It is shown that on the synoptic time scale, the CO2 flux is characterized by a narrower oscillations' amplitude as compared to its seasonal and inter-annual variability. It is noted that smallscale temporal variability of the CO2 flux is more pronounced during the cold season. The features of the carbon cycle in the Black Sea coastal waters are considered. Possibility of using information on the CO2 flux intensity and direction for assessing the water area ecological state is discussed.