Role of deep convection on anthropogenic CO2 sequestration in the Gulf of Lions (northwestern Mediterranean Sea)

Touratier, Franck; Goyet, Catherine; Houpert, Loïc; Madron, Xavier Durrieu de; Lefèvre, D.; Stabholz, Marion; Guglielmi, Véronique

doi:10.1016/j.dsr.2016.04.003

Cited by 30 publications

(38 citation statements)

References 60 publications

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“…Episodes of oversaturation of sea surface pCO related to atmospheric pCO 2 were reported during short wind gusts and intense vertical mixing events in the Ligurian Sea (Copin-Montégut et al, 2004;Merlivat et al, 2018) and in the central Gulf of Lions open-sea (Touratier et al, 2016). The authors explained those oversaturation episodes by the increase in CO 2 concentration at the ocean surface induced by the mixing of surface CO 2 -poorer waters with deep CO 2 -rich waters.…”

Section: Net Community Productionmentioning

confidence: 98%

“…The accurate representation of the winter mixing of water masses is an essential point for the simulation of the dissolved oxygen dynamics in this region, marked by a strong ventilation of the deep waters that plays a crucial role in its seasonal cycle (Copin-Montégut et al, 2002;Touratier et al, 2016;Coppola et al, 2017;. A validation of the hydrodynamic part of the simulation is described by Estournel et al (2016a), who showed similar spatial distribution of the modelled water column stratification in the entire deep convection area, as well as close modelled time evolution of the temperature profile in the centre of the Gulf of Lions open-sea during the winter, to the observations.…”

Section: Evaluation Of the Modelmentioning

confidence: 99%

“…CC BY 4.0 License. Bégovic, 2002;Schroeder et al, 2008a;Schneider et al, 2014;Stöven and Tanhua, 2015;Touratier et al, 2016;Coppola et al, 2017;. Mavropoulou et al's (2020) study, based on in situ observations over the period 1960-2011, indicated that its variability is one of the main drivers of the interannual variability of the dissolved oxygen (O 2 ) concentration in the deep waters of the western Mediterranean Sea.…”

Section: Introductionmentioning

confidence: 99%

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Oxygen budget for the north-western Mediterranean deep convection region

Ulses¹,

Estournel²,

Fourrier³

et al. 2020

Preprint

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Abstract. The north-western Mediterranean deep convection plays a crucial role in the general circulation and biogeochemical cycles of the Mediterranean Sea. The DEWEX (DEnse Water EXperiment) project aimed to better understand this role through an intensive observation platform combined with a modelling framework. We developed a 3 dimensional coupled physical and biogeochemical model to estimate the cycling and budget of dissolved oxygen in the entire north-western Mediterranean deep convection area over the period September 2012 to September 2013. After showing that the simulated dissolved oxygen concentrations are in a good agreement with the in situ data collected from research cruises and Argo floats, we analyze the seasonal cycle of the air-sea oxygen exchanges, as well as physical and biological oxygen fluxes, and we estimate an annual oxygen budget. Our study indicates that the annual air-to-sea fluxes in the deep convection area amounted to 20 mol m−2 yr−1. 88 % of the annual uptake of atmospheric oxygen, i.e. 18 mol m−2, occurred during the intense vertical mixing period. The model shows that an amount of 27 mol m−2 of oxygen, injected at the sea surface and produced through photosynthesis, was transferred under the euphotic layer, mainly during deep convection. An amount of 20 mol m−2 of oxygen was then gradually exported in the aphotic layers to the south and west of the western basin, notably, through the spreading of dense waters recently formed. The decline in the deep convection intensity in this region predicted by the end of the century in recent projections, may have important consequences on the overall uptake of atmospheric oxygen in the Mediterranean Sea and on the oxygen exchanges with the Atlantic Ocean, that appear necessary to better quantify in the context of the expansion of low-oxygen zones.

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Section: Net Community Productionmentioning

confidence: 98%

Section: Evaluation Of the Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Oxygen budget for the north-western Mediterranean deep convection region

Ulses¹,

Estournel²,

Fourrier³

et al. 2020

Preprint

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“…The capability to absorb atmospheric CO 2 per unit of surface is relatively high in the Mediterranean compared to the global ocean for two main reasons: a shorter ventilation time scale of its bottom waters (Schneider et al, 2014;Stöven and Tanhua, 2014) and a higher total alkalinity that favors the dissolution of air CO 2 (Álvarez et al, 2014b). Carbon sequestration in this basin follows two main pathways, both linked to the IW: (i) the CO 2 absorption and export during DWF events (physical carbon pump) in winter (Touratier et al, 2016;Cantoni et al, 2016) and (ii) the photosynthetic uptake of CO 2 and its subsequent release at depth during remineralization of sinking organic matter (Bethoux et al, 2005), which mostly occurs within the IW (biological carbon pump). The anthropogenic CO 2 has already penetrated the whole water column of the Mediterranean Sea (Schneider et al, 2010;Palmiéri et al, 2015;Hassoun et al, 2015;Sisma-Ventura et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Along-Path Evolution of Biogeochemical and Carbonate System Properties in the Intermediate Water of the Western Mediterranean

et al. 2020

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A basin-scale oceanographic cruise (OCEANCERTAIN2015) was carried out in the Western Mediterranean (WMED) in summer 2015 to study the evolution of hydrological and biogeochemical properties of the most ubiquitous water mass of the Mediterranean Sea, the Intermediate Water (IW). IW is a relatively warm water mass, formed in the Eastern Mediterranean (EMED) and identified by a salinity maximum all over the basin. While it flows westward, toward and across the WMED, it gradually loses its characteristics. This study describes the along-path changes of thermohaline and biogeochemical properties of the IW in the WMED, trying to discriminate changes induced by mixing and changes induced by interior biogeochemical processes. In the first part of the path (from the Sicily Channel to the Tyrrhenian Sea), respiration in the IW interior was found to have a dominant role in determining its biogeochemical evolution. Afterward, when IW crosses regions of enhanced vertical dynamics (Ligurian Sea, Gulf of Lion and Catalan Sea), mixing with surrounding water masses becomes the primary process. In the final part of the investigated IW path (the Menorca-Mallorca region), the role of respiration is further masked by the effects of a complex circulation of IW, indicating that short-term sub-regional hydrological processes are important to define IW characteristics in the westernmost part of the investigated area. A pronounced along-path acidification was detected in IW, mainly due to remineralization of organic matter. This induced a shift of the carbonate equilibrium toward more acidic species and makes this water mass increasingly less adequate for an optimal growth of calcifying organisms. The carbonate buffering capacity also decreases as IW flows through the WMED, making it more exposed to the adverse effects of a decreasing pH. The present analysis indicates that IW evolution in the sub-basins of the WMED is currently driven by complex hydrological and biogeochemical processes, which could be differently impacted by coming climate changes, in particular considering expected increases of extreme meteorological events, mainly due to the warming of the Mediterranean basin.

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“…For example, estimates of change in pH of bottom waters since the preindustrial era range between −0.005 and −0.06 (Palmiéri et al, 2015) and up to as much as −0.14 for full profile estimates (Touratier and Goyet, 2011). Techniques for estimating ocean acidification in the Mediterranean Sea thus far include the following: (1) hind-casting, using highresolution regional circulation models (Palmiéri et al, 2015), the TrOCA approach as applied to cruise-based profile data (Krasakopoulou et al, 2011;Touratier and Goyet, 2011;Touratier et al, 2016), and others (Howes et al, 2015); (2) partially reconstructed time series (Marcellin Yao et al, 2016); (3) comparative study periods (Luchetta et al, 2010;Meier et al, 2014); and (4) sensor-based observations over a short study period (Flecha et al, 2015). Ocean acidification time series of consistent sampling over many years are lacking for the Mediterranean Sea (The MerMex Group, 2011), particularly along the coast where river discharge influences the carbonate system (Ingrosso et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Coastal ocean acidification and increasing total alkalinity in the northwestern Mediterranean Sea

et al. 2017

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Abstract. Coastal time series of ocean carbonate chemistry are critical for understanding how global anthropogenic change manifests in near-shore ecosystems. Yet, they are few and have low temporal resolution. At the time series station Point B in the northwestern Mediterranean Sea, seawater was sampled weekly from 2007 through 2015, at 1 and 50 m, and analyzed for total dissolved inorganic carbon (C T ) and total alkalinity (A T ). Parameters of the carbonate system such as pH (pH T , total hydrogen ion scale) were calculated and a deconvolution analysis was performed to identify drivers of change. The rate of surface ocean acidification was −0.0028 ± 0.0003 units pH T yr −1 . This rate is larger than previously identified open-ocean trends due to rapid warming that occurred over the study period (0.072 ± 0.022 • C yr −1 ). The total pH T change over the study period was of similar magnitude as the diel pH T variability at this site. The acidification trend can be attributed to atmospheric carbon dioxide (CO 2 ) forcing (59 %, 2.08 ± 0.01 ppm CO 2 yr −1 ) and warming (41 %). Similar trends were observed at 50 m but rates were generally slower. At 1 m depth, the increase in atmospheric CO 2 accounted for approximately 40 % of the observed increase in C T (2.97 ± 0.20 µmol kg −1 yr −1 ). The remaining increase in C T may have been driven by the same unidentified process that caused an increase in A T (2.08 ± 0.19 µmol kg −1 yr −1 ). Based on the analysis of monthly trends, synchronous increases in C T and A T were fastest in the spring-summer transition. The driving process of the interannual increase in A T has a seasonal and shallow component, which may indicate riverine or groundwater influence. This study exemplifies the importance of understanding changes in coastal carbonate chemistry through the lens of biogeochemical cycling at the land-sea interface. This is the first coastal acidification time series providing multiyear data at high temporal resolution. The data confirm rapid warming in the Mediterranean Sea and demonstrate coastal acidification with a synchronous increase in total alkalinity.

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Role of deep convection on anthropogenic CO2 sequestration in the Gulf of Lions (northwestern Mediterranean Sea)

Cited by 30 publications

References 60 publications

Oxygen budget for the north-western Mediterranean deep convection region

Oxygen budget for the north-western Mediterranean deep convection region

Along-Path Evolution of Biogeochemical and Carbonate System Properties in the Intermediate Water of the Western Mediterranean

Coastal ocean acidification and increasing total alkalinity in the northwestern Mediterranean Sea

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