Spatial and temporal variability of the physical, carbonate and CO2 properties in the Southern Ocean surface waters during austral summer (2005-2019)

• Main Authors: /Brandon, Margaux, Goyet, C., Touratier, F., /Lefèvre, Nathalie, /Kestenare, Elodie, Morrow, R.
• Format: Text
• Language: English
• Published: 2022
• Subjects: Southern ocean; Sea surface temperature and salinity; Carbonate system; Air-sea CO 2 flux; Spatial variability; Temporal variability; Antarc*; Antarctic; Antarctique*; Sea ice; Southern Ocean
• Online Access: https://www.documentation.ird.fr/hor/fdi:010086434

In situ measurements of sea surface temperature (SST), salinity (SSS), Total Alkalinity (AT) and Total Carbon (CT) were obtained during austral summer (mid-February to mid-March) from 2005 to 2019 in the Southern Ocean (SO), along a transect between Hobart, Tasmania and Dumont d'Urville French Antarctic Station. The studied transect is divided in four regions from North to South: the Subtropical Zone (STZ), the Subantarctic Region (SAR), the Antarctic Region (AAR) and the Coastal Antarctic Zone (CAZ). Latitudinal distribution of measured SST, SSS, AT, CT as well as calculated pH, CO2 parameters (seawater fugacity of CO2 (fCO2sw), difference between seawater and atmospheric fCO2 (Delta fCO2), CO2 flux (FCO2)) and satellite-derived Chlorophyll a (Chl-a) are dis-cussed. We show that the variability of physical and carbonate parameters in the STZ and north of the SAR are related to the mesoscale activity. In the CAZ, the freshwater inputs from sea-ice melting strongly impact the variability of all parameters. The comparison between physical and carbonate parameters highlights that AT and CT are directly related to the latitudinal variability of SST and SSS. Study of the CO2 parameters shows that the transect is a sink of CO2 during February and March, with a mean FCO2 of-4.0 +/- 2.8 mmol m- 2 d-1. The most negative values of FCO2 are found in the STZ and SAR north of 50 degrees S and in the AAR south of 62 degrees S, where biological activity is high. New simple empirical relationships are developed for AT from SST and SSS and for CT using SST, SSS and atmospheric fCO2 (fCO2atm) for the austral summer in the studied area. Using high resolution SSS and SST from the SURVOSTRAL program, trends of AT and CT are determined in the SAR and the AAR from 2005 to 2019. SST, SSS and AT increase over this period in the SAR, which might be explained by the southward migration of the Subtropical Front. In the AAR, no clear trend is detected. CT increases by 1.0 +/- 0.2 and 0.8 +/- 0.3 mu mol kg -1 yr- 1 in the SAR and AAR ...