Permanent Thermohaline Staircases in the Tyrrhenian Sea

Durante, Sara; Schröeder, Katrin; Mazzei, Luca; Pierini, Stefano; Borghini, Mireno; Sparnocchia, Stefania

doi:10.1029/2018gl081747

Cited by 34 publications

(51 citation statements)

References 28 publications

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“…At the beginning of the first phase, IW mainly mixes with AW in the Sicily Channel and the Tyrrhenian entrance, due to the shallowness of these regions. After entering the Tyrrhenian Sea, IW undergoes different mixing processes: (i) the cascading to the bottom of the basin (a process that forms TDW, Sparnocchia et al, 1999) and the consequent vertical mixing with DW and (ii) the diapycnal mixing due to double diffusion in the center of the basin, a peculiar feature of the Tyrrhenian Sea, to which IW contribute as a source of heat and salt (Durante et al, 2019). As a result of these low-energy processes, the fraction of IW at the core of the intermediate layer decreases from 90% at the entrance of the Tyrrhenian basin (IIa) to 76 and 65% in the northern Sardinian Channel (IIb) and the Corsica Channel (III), respectively.…”

Section: Discussionmentioning

confidence: 99%

“…From a hydrological point of view, IW can be considered a useful oceanographic proxy as it is modulated by a variety of processes: DWF in the Gulf of Lion (Schroeder et al, 2006;Testor et al, 2018) and in the Adriatic Sea (Gačić et al, 2001;Chiggiato et al, 2016), interaction with mesoscale structures (Algerian Eddies, Cotroneo et al, 2016), mixing with EMDW and cascading in the Tyrrhenian Sea (Sparnocchia et al, 1999) and double diffusive phenomena in the Tyrrhenian Sea (Durante et al, 2019). IW is crucial in determining the thermohaline characteristics of the deep Mediterranean water (Schroeder et al, 2006) and it responds to long-and short-term climatic changes in the Mediterranean (Toucanne et al, 2012;Schroeder et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

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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“…Buffett et al, 2017), or coarse temporal resolution but long-term records (e.g. Falco et al, 2016;Durante et al, 2019). Moreover, most of the existing studies have not considered the role of thermohaline staircases in the nutrient distribution, because pertinent observations of biogeochemical parameters were hard to be obtained in the water column at relevant temporal and spatial scales.…”

Section: Introductionmentioning

confidence: 99%

Profiling float observation of thermohaline staircases in the western Mediterranean Sea and impact on nutrient fluxes

Taillandier¹,

Prieur²,

D’Ortenzio³

et al. 2020

Preprint

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Abstract. Characterizing the spatio-temporal arrangements of inorganic nutrients is critical to improve our understanding of the marine biological primary production. Among the processes contributing to nutrient distributions, diapycnal diffusion plays a crucial role for the supply of nutrients to the surface productive zone, and for the equilibration of vertical differences in nutrient concentrations induced by large scale thermohaline circulation. This is the case in the western Mediterranean Sea, where Levantine intermediate waters (LIW), that circulate below the surface layer, regionally distribute the nutrient stocks conveyed from the eastern basin or provided by terrestrial inputs, atmospheric deposition, and remineralization of organic matter. In the present study, we focus on the role played by diffusive processes in the LIW fertilization, considering long-term observations of thermohaline staircases. In association with the unprecedented contribution of profiling floats to explore their structural changes, the fine characterization of western Mediterranean thermohaline staircases sampled during the cruise PEACETIME can be carried out from a different perspective. Observations revealed that thermohaline staircases develop over epicentral regions confined inside large scale circulation features and sustained by saltier LIW inflows on the periphery. As observed in the Algerian Basin, these epicentral regions are thought to be site of active mixing, with changes of seawater properties by about + 0.06 °C in temperature and + 0.02 in salinity during the four years of observation. In-situ lateral density ratios are analysed in the view of theoretical predictions to identify and untangle (i) salt fingering as driver of water mass conversion, with (ii) isopycnal diffusion as spreader of heat and salt from the surrounding sources. In the Tyrrhenian Sea, the resulting nutrient fluxes bring upward from deep waters 5 μmol/m2/d in nitrate, which represents one fourth of LIW fertilization by diapycnal diffusion, but remains a secondary contributor to the enrichment of Ionian water inflows.

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“…Thus, we suggest that the spotty saltier in situ values (37.47-37.79) collected on [16][17][18][19] September could represent the signature of upwelled saltier sub-surface waters which were intercepted by the ABACUS glider when navigating across the eastern border of the small eddy centered at 2.21°E 38.61°N. Although SMOS L3 and L4 products retrieve slightly higher SSS in this region in comparison to the rest of the central part of the Mallorca-AC transect, they cannot identify the maximum values observed by the glider, confirming their limits in describing the small scale variability which characterizes the areas of intense local activity.…”

Section: Abacus 1 Surveysmentioning

confidence: 99%

“…In fact, a large anticorrelation between sea level anomalies and phytoplankton biomass has been previously observed in the AB [11], thus suggesting a clear response of biological activity to the shoaling/deepening of isopycnals [12]. As part of the southwestern Mediterranean region, this basin is also known to be particularly responsive to climate change [13,14], and the Mediterranean waters flowing in this area have already shown significant trends at different depths in both temperature and salinity [15][16][17][18].…”

Section: Introductionmentioning

confidence: 95%

In Situ and Satellite Sea Surface Salinity in the Algerian Basin Observed through ABACUS Glider Measurements and BEC SMOS Regional Products

et al. 2019

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The Algerian Basin is a key area for the general circulation in the western Mediterranean Sea. The basin has an intense inflow/outflow regime with complex circulation patterns, involving both fresh Atlantic water and more saline Mediterranean water. Several studies have demonstrated the advantages of the combined use of autonomous underwater vehicles, such as gliders, with remotely sensed products (e.g., altimetry, MUR SST) to observe meso- and submesoscale structures and their properties. An important contribution could come from a new generation of enhanced satellite sea surface salinity (SSS) products, e.g., those provided by the Soil Moisture and Ocean Salinity (SMOS) mission. In this paper, we assess the advantages of using Barcelona Expert Center (BEC) SMOS SSS products, obtained through a combination of debiased non-Bayesian retrieval, DINEOF (data interpolating empirical orthogonal functions) and multifractal fusion with high resolution sea surface temperature (OSTIA SST) maps. Such an aim was reached by comparing SMOS Level-3 (L3) and Level-4 (L4) SSS products with in situ high resolution glider measurements collected in the framework of the Algerian Basin Circulation Unmanned Survey (ABACUS) observational program conducted in the Algerian Basin during falls 2014–2016. Results show that different levels of confidence between in situ and satellite measurements can be achieved according to the spatial scales of variability. Although SMOS values slightly underestimate in situ observations (mean difference is −0.14 (−0.11)), with a standard deviation of 0.25 (0.26) for L3 (L4) products), at basin scale, the enhanced SMOS products well represent the salinity patterns described by the ABACUS data.

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Permanent Thermohaline Staircases in the Tyrrhenian Sea

Cited by 34 publications

References 28 publications

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

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

Profiling float observation of thermohaline staircases in the western Mediterranean Sea and impact on nutrient fluxes

In Situ and Satellite Sea Surface Salinity in the Algerian Basin Observed through ABACUS Glider Measurements and BEC SMOS Regional Products

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