Hotter and Weaker Mediterranean Outflow as a Response to Basin-Wide Alterations

Time series collected from 2004 to 2020 at an oceanographic station located at the westernmost sill of the Strait of Gibraltar to monitor the Mediterranean outflow into the North Atlantic have been used to give some insights on changes that have been taking place in the Mediterranean basin. Velocity data indicate that the exchange through the Strait is submaximal (that is, greater values of the exchanged flows are possible) with a mean value of −0.847 ± 0.129 Sv and a slight trend to decrease in magnitude (+0.017 ± 0.003 Sv decade−1). Submaximal exchange promotes footprints in the Mediterranean outflow with little or no-time delay with regards to changes occurring in the basin. An astonishing warming trend of 0.339 ± 0.008°C decade−1 in the deepest layer of the outflow from 2013 onwards stands out among these changes, a trend that is an order of magnitude greater than any other reported so far in the water masses of the Mediterranean Sea. Biogeochemical (pH) data display a negative trend indicating a gradual acidification of the outflow in the monitoring station. Data analysis suggests that these trends are compatible with a progressively larger participation of Levantine Intermediate Water (slightly warmer and characterized by a pH lower than that of Western Mediterranean Deep Water) in the outflow. Such interpretation is supported by climatic data analysis that indicate diminished buoyancy fluxes to the atmosphere during the seven last years of the analyzed series, which in turn would have reduced the rate of formation of Western Mediterranean Deep Water. The flow through the Strait has echoed this fact in a situation of submaximal exchange and, ultimately, reflects it in the shocking temperature trend recorded at the monitoring station.

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Characterization of the Atlantic Water and Levantine Intermediate Water in the Mediterranean Sea using Argo Float Data

10.5194/os-2021-68 ◽

2021 ◽

Author(s):

Giusy Fedele ◽

Elena Mauri ◽

Giulio Notarstefano ◽

Pierre Marie Poulain

Keyword(s):

Mediterranean Sea ◽

Thermohaline Circulation ◽

Internal Variability ◽

Warming Trend ◽

Atlantic Water ◽

Western Mediterranean ◽

Water Masses ◽

Intermediate Water ◽

Starting Point ◽

The Mediterranean

Abstract. The Atlantic Water (AW) and Levantine Intermediate Water (LIW) are important water masses that play a crucial role in the internal variability of the Mediterranean thermohaline circulation. In particular, their variability and interaction, along with other water masses that characterize the Mediterranean basin, such as the Western Mediterranean Deep Water (WMDW), contribute to modify the Mediterranean Outflow through the Gibraltar Strait and hence may influence the stability of the global thermohaline circulation. This work aims to characterize the AW and LIW in the Mediterranean Sea, taking advantage of the large observational dataset provided by Argo floats from 2001 to 2019. Using different diagnostics, the AW and LIW were identified, highlighting the inter-basin variability and the strong zonal gradient that characterize the two water masses in this marginal sea. Their temporal variability was also investigated focusing on trends and spectral features which constitute an important starting point to understand the mechanisms that are behind their variability. A clear salinification and warming trend have characterized the AW and LIW in the last two decades (~0.007 and 0.008 yr−1; 0.018 and 0.007 °C yr−1, respectively). The salinity and temperature trends found at subbasin scale are in good agreement with previous results. The strongest trends are found in the Adriatic basin in both the AW and LIW properties. A subbasin dependent spectral variability emerges in the AW and LIW salinity timeseries with peaks between 2 and 10 years.

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The Mediterranean is getting saltier

Ocean Science Discussions ◽

10.5194/osd-11-735-2014 ◽

2014 ◽

Vol 11 (1) ◽

pp. 735-752 ◽

Cited By ~ 2

Author(s):

M. Borghini ◽

H. Bryden ◽

K. Schroeder ◽

S. Sparnocchia ◽

A. Vetrano

Keyword(s):

Deep Water ◽

Mediterranean Basin ◽

Western Mediterranean ◽

Intermediate Water ◽

Deep Water Formation ◽

The Past ◽

Deep Waters ◽

Western Mediterranean Basin ◽

Water Formation ◽

The Mediterranean

Abstract. The deep waters of the Mediterranean Sea have been getting saltier and warmer for at least the past 40 yr at rates of about 0.015 and 0.04 °C per decade. Here we show that two processes contribute to these increases in temperature and salinity. On interannual time scales, deep water formation events in severe winters transmit increasingly salty intermediate waters into the deep water. The second process is a steady downward flux of heat and salt through the halocline-thermocline that connects the Levantine Intermediate Water with the deep water. We illustrate these two processes with observations from repeat surveys of the western Mediterranean basin we have made over the past 10 yr.

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Changes in ventilation of the Mediterranean Sea during the past 25 year

Ocean Science ◽

10.5194/os-10-1-2014 ◽

2014 ◽

Vol 10 (1) ◽

pp. 1-16 ◽

Cited By ~ 37

Author(s):

A. Schneider ◽

T. Tanhua ◽

W. Roether ◽

R. Steinfeldt

Keyword(s):

Mediterranean Sea ◽

Deep Water ◽

Adriatic Sea ◽

Western Mediterranean ◽

Tyrrhenian Sea ◽

Deep Water Formation ◽

Technical Problems ◽

Water Formation ◽

The Mediterranean ◽

Transient Tracer

Abstract. Significant changes in the overturning circulation of the Mediterranean Sea has been observed during the last few decades, the most prominent phenomena being the Eastern Mediterranean Transient (EMT) in the early 1990s and the Western Mediterranean Transition (WMT) during the mid-2000s. During both of these events unusually large amounts of deep water were formed, and in the case of the EMT, the deep water formation area shifted from the Adriatic to the Aegean Sea. Here we synthesize a unique collection of transient tracer (CFC-12, SF6 and tritium) data from nine cruises conducted between 1987 and 2011 and use these data to determine temporal variability of Mediterranean ventilation. We also discuss biases and technical problems with transient tracer-based ages arising from their different input histories over time; particularly in the case of time-dependent ventilation. We observe a period of low ventilation in the deep eastern (Levantine) basin after it was ventilated by the EMT so that the age of the deep water is increasing with time. In the Ionian Sea, on the other hand, we see evidence of increased ventilation after year 2001, indicating the restarted deep water formation in the Adriatic Sea. This is also reflected in the increasing age of the Cretan Sea deep water and decreasing age of Adriatic Sea deep water since the end of the 1980s. In the western Mediterranean deep basin we see the massive input of recently ventilated waters during the WMT. This signal is not yet apparent in the Tyrrhenian Sea, where the ventilation seems to be fairly constant since the EMT. Also the western Alboran Sea does not show any temporal trends in ventilation.

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Inferring deglacial ventilation ages in Western Mediterranean waters using cold-water corals

10.5194/egusphere-egu2020-20171 ◽

2020 ◽

Author(s):

Maria de la Fuente ◽

Luke Skinner ◽

Gemma Ercilla ◽

Elia d'Acremont ◽

Luis Somoza ◽

...

Keyword(s):

Trace Element ◽

Cold Water ◽

Western Mediterranean ◽

Intermediate Water ◽

Gulf Of Cadiz ◽

Strait Of Gibraltar ◽

Gulf Of Cádiz ◽

The Mediterranean ◽

Spatio Temporal ◽

Reservoir Age

Mediterranean Outflow Water (MOW) acts as a net source of salt and heat into North Atlantic intermediate depths that ultimately contributes to the Atlantic Meridional Overturning Circulation. On this basis, it has been hypothesised that MOW variability might influence global climate. Although several studies have documented major glacial-interglacial changes in deep- and intermediate Mediterranean circulation patterns, little is known about associated impacts on MOW properties, in particular its residence time and geochemical signature. Using a set of cold-water coral samples from along the &#8216;pre-MOW&#8217; and MOW path, i.e. from the Alboran Sea to the northern Galician Bank including the Strait of Gibraltar and the Gulf of Cadiz, we aim to identify changes in both the ventilation state of the water masses flowing out of the Mediterranean and the distribution of coral growth.With this purpose, paired Uranium-series and AMS radiocarbon ages have been obtained in the same coral samples allowing any potential change in the reservoir age to be inferred accurately, as well as allowing a spatio-temporal &#8216;coral map&#8217; to be created. Furthermore, these results have been complemented by trace element measurements in benthic foraminifera from the Alboran coral mound sediment core.Our results show a particular spatio-temporal coral distribution with glacial presence only at the deepest sites of the Gulf of Cadiz (~1000m), followed by ~300m Western Mediterranean (WMed) coral appearance across the deglaciation/mid Holocene (14-4 kyr), to end with a proliferation at the Strait of Gibraltar and Galicia Bank from ~6 kyr towards the present. We hypothesise 1) that ~300m WMed area might have been bathed in Atlantic waters inflow during the glacial due to sea-level drop, returning to LIW (Levantine Intermediate Water) influence over the deglaciation, and 2) that MOW reached deeper areas outside of the Mediterranean Sea in the Gulf of Cadiz during the glacial period. Regarding the reservoir age, little change at the WMed is observed at 150-450m across the deglaciation as compared to the large ventilation excursion detected in the Iberian Margin at ~1000m. However, a ventilation age gradient of ~300 yr related to water depth is observed within WMed corals when appearing at the B&#248;lling-Aller&#248;d, in synchrony with significant changes in hydrographical parameters inferred from foraminiferal trace element from the same area. Overall, our results suggest a water mass reorganization at the surface-intermediate layer of the WMed during the deglaciation and early Holocene, but the ultimate nature of these changes needs yet to be explored by further analysis of Nd isotopes as well as of trace elements beyond the deglaciation.

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A geochemical approach to reconstructing sediment dynamic and thermohaline circulation in the western Mediterranean over the last deglaciation

10.5194/egusphere-egu2020-17722 ◽

2020 ◽

Author(s):

Jose Manuel Mesa-Fernández ◽

Francisca Martínez-Ruiz ◽

Marta Rodrigo-Gámiz ◽

Francisco J. Jiménez-Espejo

Keyword(s):

Thermohaline Circulation ◽

Western Mediterranean ◽

Intermediate Water ◽

Last Deglaciation ◽

Gulf Of Cadiz ◽

Relative Contribution ◽

Gulf Of Cádiz ◽

Mediterranean Outflow ◽

Gibraltar Strait ◽

Alboran Basin

The westernmost Mediterranean basins is an exceptional and sensitive region for reconstructing past climate and oceanographic conditions. Geochemical signatures from diverse sediment records in the Alboran Sea and the Balearic basin, in particular, Ti/ca and Fe/Ca ratios, as proxies for the relative abundance of siliciclastic vs. carbonate fraction, have been investigated. These have also been compared with other previously studied records from the western Mediterranean and the Gulf of Cadiz to elucidate the mechanisms triggering the relative variations between the carbonate and siliciclastic fraction. The lithogenic fraction represents around 70% of the sediment in the Alboran basin, which mainly derived from riverine discharge and coastal erosion. Resuspension of fine sediment particles from the slope and the sea floor by bottom-water currents is a relevant process in these basin. The studied records are located between 850 m and 2400 m below the sea level, under the influence of the Western Mediterranean Deep Water (WMDW), which is restricted to a water depth below 500-600 m and to the Moroccan margin. This deep current is formed in the Gulf of Lion, when the superficial and intermediate waters sink by a density increase, and flow out the basin through the Gibraltar Strait, contributing to the Mediterranean Outflow Water (MOW) along with the Levantine Intermediate Water (LIW). The WMDW formation is enhanced during cold and arid periods. The comparison with other previously studied records, support important variations of the mechanisms triggering the relative contribution of carbonate and siliciclastic fractions during the last 20,000 yrs. The, Ti/Ca and Fe/Ca ratios increased during cold and arid periods, such as the Heinrich Event 1 (HE1) and the Younger Dryas (YD). These changes are more prominent in the Balearic basin and the eastern Alboran basin than in the western Alboran basin and the Gulf of Cadiz. Thus, we hypothesized that the increase in the Ti/Ca and Fe/Ca ratios is rather related to the enhanced WMDW production and more remobilization of fine siliciclastic sediments.

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Modeling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

Ocean Science ◽

10.5194/os-3-77-2007 ◽

2007 ◽

Vol 3 (1) ◽

pp. 77-89 ◽

Cited By ~ 6

Author(s):

M. A. Ahumada ◽

A. Cruzado

Keyword(s):

Mediterranean Sea ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Western Mediterranean ◽

Ocean Model ◽

Intermediate Water ◽

Princeton Ocean Model ◽

The Mediterranean ◽

Northwestern Mediterranean

Abstract. The Princeton Ocean Model – POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea – OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers, the model results have confirmed that Levantine Intermediate Water (LIW) and Western Mediterranean Deep Water (WMDW) follow essentially a cyclonic path during all year.

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The Mediterranean is becoming saltier

Ocean Science ◽

10.5194/os-10-693-2014 ◽

2014 ◽

Vol 10 (4) ◽

pp. 693-700 ◽

Cited By ~ 53

Author(s):

M. Borghini ◽

H. Bryden ◽

K. Schroeder ◽

S. Sparnocchia ◽

A. Vetrano

Keyword(s):

Deep Water ◽

Mediterranean Basin ◽

Western Mediterranean ◽

Intermediate Water ◽

Deep Water Formation ◽

The Past ◽

Western Mediterranean Sea ◽

Deep Waters ◽

Western Mediterranean Basin ◽

Water Formation

Abstract. The deep waters of the western Mediterranean Sea have become saltier and warmer for at least the past 40 years at rates of about 0.015 and 0.04 °C per decade. Here we show that two processes contribute to these increases in temperature and salinity. On interannual timescales, deep water formation events in severe winters transmit increasingly salty intermediate waters into the deep water. The second process is a steady downward flux of heat and salt associated with salt finger mixing down through the halocline–thermocline that connects the Levantine Intermediate Water with the deep water. We illustrate these two processes with observations from repeat surveys of the western Mediterranean basin we have made over the past 10 years.

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Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Ocean Science ◽

10.5194/os-10-439-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 439-457 ◽

Cited By ~ 25

Author(s):

T. Stöven ◽

T. Tanhua

Keyword(s):

Deep Water ◽

Eastern Mediterranean ◽

Western Mediterranean ◽

Inverse Gaussian ◽

Ionian Sea ◽

One Dimensional ◽

Levantine Basin ◽

The Mean ◽

The Mediterranean ◽

Transient Tracer

Abstract. Ventilation is the primary pathway for atmosphere–ocean boundary perturbations, such as temperature anomalies, to be relayed to the ocean interior. It is also a conduit for gas exchange between the interface of atmosphere and ocean. Thus it is a mechanism whereby, for instance, the ocean interior is oxygenated and enriched in anthropogenic carbon. The ventilation of the Mediterranean Sea is fast in comparison to the world ocean and has large temporal variability. Here we present transient tracer data from a field campaign in April 2011 that sampled a unique suite of transient tracers (SF6, CFC-12, 3H and 3He) in all major basins of the Mediterranean. We apply the transit time distribution (TTD) model to the data in order to constrain the mean age, the ratio of the advective / diffusive transport and the number of water masses significant for ventilation. We found that the eastern part of the eastern Mediterranean can be reasonably described with a one-dimensional inverse Gaussian TTD (IG-TTD), and thus constrained with two independent tracers. The ventilation of the Ionian Sea and the western Mediterranean can only be constrained by a linear combination of IG-TTDs. We approximate the ventilation with a one-dimensional, two inverse Gaussian TTD (2IG-TTD) for these areas and demonstrate a possibility of constraining a 2IG-TTD from the available transient tracer data. The deep water in the Ionian Sea has a mean age between 120 and 160 years and is therefore substantially older than the mean age of the Levantine Basin deep water (60–80 years). These results are in contrast to those expected by the higher transient tracer concentrations in the Ionian Sea deep water. This is partly due to deep water of Adriatic origin having more diffusive properties in transport and formation (i.e., a high ratio of diffusion over advection), compared to the deep water of Aegean Sea origin that still dominates the deep Levantine Basin deep water after the Eastern Mediterranean Transient (EMT) in the early 1990s. The tracer minimum zone (TMZ) in the intermediate of the Levantine Basin is the oldest water mass with a mean age up to 290 years. We also show that the deep western Mediterranean has contributed approximately 40% of recently ventilated deep water from the Western Mediterranean Transition (WMT) event of the mid-2000s. The deep water has higher transient tracer concentrations than the mid-depth water, but the mean age is similar with values between 180 and 220 years.

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