| 14 Nov 2025
Surface pCO2 and hydrography in the dense water formation area of the southern Adriatic
Abstract. The rising CO2 concentration in the atmosphere leads to an increase in CO2 uptake in the ocean and to significant changes in seawater chemistry. These changes, in turn, exert profound effects on marine ecosystems across multiple trophic levels. The Mediterranean Sea is considered a hotspot for climate change. Despite such relevance, observations and studies on its carbonate system remain limited, especially in regions that play a crucial role in regulating air-sea CO2 exchange like intermediate and dense water formation areas. The southern Adriatic Sea, a key site for dense water formation in the eastern Mediterranean, hosts the EMSO ERIC and ICOS ERIC South Adriatic observatory (EMSO-E2M3A), operated by the Italian National Institute of Oceanography and Applied Geophysics (OGS). This facility allows the study of physical and biogeochemical dynamics in the deepest area of the Adriatic Sea. The suite of sensors deployed on the surface buoy allows for the characterization of water mass properties, biogeochemical cycles, dense water formation process, and ocean acidification, particularly in relation to carbon sequestration dynamics. Here, time series of meteorological data (e.g., wind speed, wind direction), sea surface physical parameters (e.g., temperature, salinity), dissolved oxygen and partial pressure of CO2 (pCO2sw) and pH from 2014 to 2024 will be presented (https://doi.org/10.13120/y2hw-1j63, Cardin et al., 2025). In particular, quality check and correction and post-processing methods applied to the data will be discussed. The validated surface dataset provides a consistent pCO2sw time series for the Adriatic Sea, with values and seasonal variability in agreement with previous observations across the Mediterranean. Associated temperature, salinity, oxygen, and wind measurements reproduce expected regional patterns, confirming the robustness and suitability of the presented dataset for further biogeochemical and climate-related analyses.
General comments: This is a timely and useful dataset from which the interannual (and seasonal) fluxes of CO2, between the atmosphere and sea, can be calculated without the use of further datasets or model output. It represents a 10-year time series of carbonate chemistry, physical and atmospheric data in the Mediterranean Sea and is unique for the area. The data are easily accessible from the link provided in the text. The paper describes the quality control that has been applied to the data, and how the data may be used in future to provide a flux product.
Specific comments: The CO2 data accuracy is stated as +/- 5uatm (please confirm that this is the manufacturers assessment, ~line 190). Clearly the sensor has larger offsets (Table 1). Do the offsets change between pre and post deployment (due to the biofouling introducing a drift)? Or if this is a constant offset that could be corrected for (as was the case in the Saildrone experiment)?
I would like to see a reference for line 46 (describing the area as a climate change hotspot).
Line 72 suggests the station is an ICOS site, but it is not clear whether a subset of the data is available from the ICOS carbon portal?
Where accuracy was quoted eg: line 132 please clarify if this is a manufacturer assessment
Line 138 suggests that flags are applied to the data (and no corrections are made) – however line 260 references ‘corrected’ data, which may just include the de-spiking so this should be clarified – I get the impression that offsets have not been applied to the data but it would be good to know what difference the offsets would make to the final flux calculation please
line 158 is unclear – what is the ‘which t’ referring to?
The dataset refers to hourly data (though some data – such as CO2 are available 4 hourly)
Line 194 suggests that pre and post calibrations are made at OGS – please quantify the frequency of visits to the site, is it an annual visit?
Line 267 suggests that there are only physical impacts on CO2 – but are there responses due to productivity too (as you report for the oxygen)? Can you explain the double peak in dissolved oxygen or is this the biological impact that you mention?
Line 272 could list the years with higher temperatures in summer (as was done for salinity in the following paragraph) – a little more detail about the anomalies would be useful
Technical corrections: line 76 should read ‘represents an important resource’
likewise, line 95 should be plural for ‘components’
The mooring diagram in figure 1 could be clearer as I was curious to know what depth the biogeochemical measurements extended to
Line 201 should refer to ‘seven data points’ (rather than just seven data)
The Bensi reference is in capital letters (this may be convention for a thesis though?)
The Cardin et al reference (line 402) has ‘et al’ listed when all authors should have been listed. Likewise, Menna et al., Line 494.