Impact of Intermittent Convection in the Northwestern Mediterranean Sea on Oxygen Content, Nutrients, and the Carbonate System

Abstract

The Mediterranean Sea is a semi-enclosed marginal sea characterized by a rapid overturning circulation (Millot & Taupier-Letage, 2005) where deep-water formation processes happen in both the western and eastern basins (Schroeder et al., 2012 and references therein, Pinardi et al., 2019). In the northwestern Mediterranean Sea, the intermediate water masses are characterized by a temperature and salinity maximum in subsurface corresponding to the Levantine Intermediate Waters (LIW) formed in the eastern basin in late February/early March (Lascaratos et al., 1993). This saline and relatively warm water mass spreads at intermediate depths (between 200 and 600 m) over the Mediterranean in a westward pathway, entering the Ligurian Sea and flowing within the Northern Current along the southern French coasts on its way to the Strait of Gibraltar. During its transit from the eastern basin, the consumption of organic matter sinking from the surface decreases the O 2 content in this water mass creating an O 2 minimum in the water column (160-170 μmol kg −1 , Coppola et al., 2018) and lowering pH T and increasing dissolved inorganic carbon (C T ; Álvarez et al., 2014). In the northwestern Mediterranean Sea, which is well ventilated compared to the global ocean (Schneider et al., 2014), Dense Water Formation (DWF) mainly occurs in the Gulf of Lion (Herrmann et al., 2010;Somot et al., 2018), where winter

Assessing seasonal and interannual changes in carbonate chemistry across two time-series sites in the North Western Mediterranean Sea

“…As only CTD downcast performed when samples were taken have been used in this study to derive the MLD, extreme climatic events with bottom-reaching convection reported from 2010 to 2013 and in 2018 in the GoL are not so clearly visible at the two studied sites located outside of the DWF area (see Figure 1 of the Supplementary Material and Section 1). By using Argo float data, Fourrier et al (2022) reported MLD increases to around 2000 m in the winter 2012-2013 and in 2018. Interannual variabilities of temperature and salinity within the mixed layer are presented in Figures 2B, C, G, H.…”

“…From 2010 to 2013, intense deep convection occurred with the maximum mixed layer depth reaching the seafloor every winter at about 2500 m in the Gulf of Lion (GoL) area [Houpert et al, 2016;Testor et al, 2018;Bosse et al, 2021]. In winter 2018, hydrological observations highlighted convection down to at least 1800 m depth in the GoL [Margirier et al, 2020;Fourrier et al, 2022]. In the Ligurian Sea, intermediate mixing events have been observed between 2010 and 2018, with a maximum depth reached by winter convection of 1000 m reported in 2012 and 2013 [Margirier et al, 2020].…”

High-resolution study of the air-sea CO2 flux and net community oxygen production in the Ligurian Sea by a fleet of gliders

“…Here, we used a regional version of CANYON developed for the Mediterranean Sea (CANYON-MED) to predict nutrients and carbonate variables from pressure, temperature, salinity, and oxygen together (with geolocation and date of sampling) measured in the water column by different autonomous platforms (mooring, Argo floats) and ship visits (Fourrier et al, 2020). To improve the accuracy of the predicted variables, an ensemble of ten NN has been proposed (one for each variable) and recently applied in the northwestern Mediterranean Sea (Fourrier et al, 2022) to estimate the trends of nutrients and CO 2 variables (Total Alkalinity or TA, Dissolved Inorganic Carbon or DIC, pH) from surface to deep waters. In this study, the pCO 2sw was derived from DIC and pH at the total scale predicted by CANYON-MED and the CO2SYS v3.0 Matlab toolbox (Sharp et al, 2020).…”

The time series at the Strait of Gibraltar as a baseline for long-term assessment of vulnerability of calcifiers to ocean acidification

“…The former is the result of the transformation process undertaken by the Atlantic surface water as it moves eastward, which makes it saltier, until it sinks to intermediate depths in the Levantine basin, the easternmost basin of the MedSea (Lascaratos, 1993). In contrast, the WMDW is formed in the western Mediterranean basin, as a result of the winter cooling of highly modified surface waters in the Gulf of Lions (MEDOC Group, 1970;Fourrier et al, 2022). Both water masses flow at depth towards the SoG and leave the MedSea, merging in the MOW in the Gulf of Cadiz.…”