A Tracer Study of the Thermohaline Circulation of the Eastern Mediterranean

Roether, Wolfgang; Roussenov, Vassil; Well, Roland

doi:10.1007/978-94-011-0870-6_16

Cited by 53 publications

(26 citation statements)

References 12 publications

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“…The input function of tritium originated from Roether et al (1992) and was extended in time by R. Steinfeld (unpublished data). It was newly adjusted by Stöven and Tanhua (2013) using tritium Roether et al (2013a) derived from a slightly different approach.…”

Section: The Transit Time Distribution Conceptmentioning

confidence: 99%

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

et al. 2014

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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, SF 6 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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Section: The Transit Time Distribution Conceptmentioning

confidence: 99%

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

et al. 2014

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“…Med. constrained by transient tracers commonly used tritium input function (TIF) for the North Atlantic was obtained by Dreisigacker and Roether (1978) and further developed for the EMed by Roether et al (1992). Based on this data set, another TIF for the EMed was created by R. Steinfeldt (unpublished data) where the data after 1974 was extrapolated by using the decay function of tritium.…”

Section: Radioactive Transient Tracersmentioning

confidence: 99%

“…2.4.3). The TIF by Dreisigacker and Roether (1978) and Roether et al (1992) is a rough estimate of the complex regional impact factors and provides a mean input of tritium into the surface layer of the ocean. Nevertheless, this input function is the best existing approach and the results of the offset corrected input function clearly show that the shape of the curve tends to be correct.…”

Section: Ig-ttdmentioning

confidence: 99%

Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Stöven

Tanhua

2014

Ocean Sci.

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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 (SF 6 , 3 H and 3 He) 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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“…The model produces a stable climate without the use of flux adjustments, though a very small drift remains in the deep ocean (Pardaens et al 2003). Convection in HadCM3 is parametrised by the Rahmstorf (1993) scheme, and the overflow over the GIS ridge is modified by using the Roussenov convection scheme (Roether et al 1994). These parametrisations lead to overflows over the GSR that are reasonable for a model of limited resolution (Wood et al 1999;Thorpe et al 2004), with deep water formed in the Labrador and in the GIN seas (Wood et al 1999).…”

Section: Model Experimentsmentioning

confidence: 99%

Sensitivity of climate response to variations in freshwater hosing location

2009

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In a recent intercomparison of the response of general circulation models (GCMs) to highlatitude freshwater forcing (Stouffer et al., J Climate 19(8):1365-1387, a number of the GCMs investigated showed a localised warming response in the high-latitude North Atlantic, as opposed to the cooling that the other models showed. We investigated the causes for this warming by testing the sensitivity of the meridional overturning circulation (MOC) to variations in freshwater forcing location, and then analysing in detail the causes of the warming. By analysing results from experiments with HadCM3, we are able to show that the high-latitude warming is independent of the exact location of the additional freshwater in the North Atlantic or Arctic Ocean basin. Instead, the addition of freshwater changes the circulation in the sub-polar gyre, which leads to enhanced advection of warm, saline, sub-surface water into the Greenland-IcelandNorwegian Sea despite the overall slowdown of the MOC. This sub-surface water is brought to the surface by convection, where it leads to a strong warming of the surface waters and the overlying atmosphere.

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A Tracer Study of the Thermohaline Circulation of the Eastern Mediterranean

Cited by 53 publications

References 12 publications

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

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

Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Sensitivity of climate response to variations in freshwater hosing location

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