Seawater carbonate system measurements in the Mediterranean Sea are relatively scarce, especially in its eastern basin. This study describes the monthly variations of carbonate system parameters in the open sea and coastal water column of the eastern Mediterranean Sea during the period February 2018 to January 2019. Water samples were collected for analysis of Total Alkalinity and pHT at the shallow coastal THEMO1 and the deeper open-water THEMO2 (1,500 m bottom depth) stations off the Mediterranean coast of Israel. In the surface layer (<25 m), TA increased with salinity at a rate of +72 μmol·kg−1 and the pCO2(SW) was strongly and positively correlated with temperature. During summertime, surface waters were highly super-saturated with respect to atmospheric pCO2 (pCO2(SW) ∼ 600 μatm), while during winter they were only slightly super-saturated. The estimated net annual CO2 flux from the surface of the eastern Mediterranean Sea to the atmosphere during the study period was +2.8 Tg C·y−1, which is three times greater than a previous estimate made for this region (0.9 Tg C·y−1), and is attributed to the smaller volume of Atlantic water input in the present study compared to the previous one as well as the substantially shallower total dissolved inorganic carbon enriched core of the Levantine Intermediate Water in this study. Based on these results, it is still expected that future warming and salinization, reduced Atlantic Water influx to the eastern Mediterranean Sea, and increased stratification will increase the flux of CO2 to the atmosphere in this region.
Plain Language Summary
This study investigated annual variations in atmospheric CO2 flux from the surface of the eastern Mediterranean Sea based on monthly seawater sampling and carbon chemistry analyses conducted at two locations off the Mediterranean coast of Israel from February 2018 to January 2019. The results indicate that the southeastern Mediterranean Sea was a net source of CO2 to the atmosphere. This behavior was largely driven by seasonal changes in seawater temperature, which controls the saturation concentration of dissolved CO2 in seawater. During summer months, warm surface waters were a strong source of CO2 to the atmosphere, while during winter they were a weak sink. The study estimates that approximately 2.8 million tons of carbon were released annually from the sea to the atmosphere during the study period. This revised and more comprehensive estimate is ∼3 times higher than previous estimates reported for the same region. The increase is suggested to result from recent changes in regional circulation, particularly a reduced inflow of Atlantic Ocean waters into the eastern Mediterranean Sea. Based on these findings, continued warming, increasing salinity, and enhanced stratification of the eastern Mediterranean Sea are expected to further intensify CO2 release to the atmosphere in the future.
Silverman J., Sisma-Ventura,G., Yu J. & Bookman R., 2026. Annual variations of seawater carbonate system in the surface layer of the South-Eastern Mediterranean Sea. Journal of Geophysical Research: Oceans 131: e2025JC023389. doi: 10.1029/2025JC023389. Article (subscription required).
