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Does the thermohaline circulation weaken in the Adriatic Sea? Ivica Vilibić, Jadranka Šepić Institute of Oceanography and Fisheries, Split, Croatia Nicolas.

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Presentation on theme: "Does the thermohaline circulation weaken in the Adriatic Sea? Ivica Vilibić, Jadranka Šepić Institute of Oceanography and Fisheries, Split, Croatia Nicolas."— Presentation transcript:

1 Does the thermohaline circulation weaken in the Adriatic Sea? Ivica Vilibić, Jadranka Šepić Institute of Oceanography and Fisheries, Split, Croatia Nicolas Proust Student at Institute of Engineering Sciences of Toulon and Var, La Valette, France

2 Motivation Overturning stream function The Mediterranean thermohaline circulation (MTHC) is strongly weakened at the end of the twenty-first century. This behaviour is mainly due to the decrease in surface density and so the decrease in winter deep-water formation. At the end of the twenty-first century, the MTHC weakening can be evaluated as –40% for the intermediate waters and –80% for the deep circulation with respect to present-climate conditions. Somot et al., Climate Dynamics, 2006 Adriatic

3 Motivation A hint is provided by winter of 2012: You are here

4 Motivation However, one harsh winter does not make a transition to the glacial period (regardless of media, some crackpot scientists and record-breaking seawater density in Croatian coastal waters). Our motivation is: To detect and assess long-term AdTHC changes, as being highly relevant to a number of issues (e.g., hydrological cycle in the Med, sea level studies, biogeoscience research,...) Pag Channel, Courtesy of PMF-Zg

5 Outline: - About Adriatic thermohaline circulation (AdTHC) - Major AdTHC driving mechanisms and their trends - AdTHC trends visible in long-term ocean series - Some conclusions, consequences and perspectives

6 About AdTHC The Adriatic is a semi-enclosed basin characterised by both estuarine and anti-estuarine types of THC SAG EAC WAC estuarine AdTHC (driven by freshwater balance) rivers

7 anti-estuarine AdTHC (driven by dense water generation) Vilibić et al., DSR, 2004 About AdTHC Deep convection site (AdDW) Supić and Vilibić, ECSS, 2006

8 anti-estuarine AdTHC (driven by dense water generation) IOF-MHS Virtual Laboratory, 2012 Vilibić et al., DSR, About AdTHC Courtesy of ISMAR Venezia, 16 m Feb 2012

9 anti-estuarine AdTHC – DWG by shelf densification (NAd) Pullen et al., JGR, 2007 Beg Paklar et al., CSR, 2001 Proper quantification of DWG is dependable on model resolution, due to high spatial and temporal variablity of the generating force (bora). Zore-Armanda and Gacic, Ann. Geo., 1987 About AdTHC

10 anti-estuarine AdTHC – DWG by deep convection (SAd) Vilibić and Šantić, OD, 2008 mixed layer depth DW from NAd (NAdDW) About AdTHC

11 anti-estuarine AdTHC – DWG by deep convection (SAd) Vilibić and Šantić, OD, 2008 About AdTHC spring phytoplankton bloom

12 About AdTHC Orlić et al., JGR, 2007 Anti-estuarine AdTHC is thermally-driven through heat losses during bora outbreaks, and is lagged with respect to the forcing for a few months months. Pulsations of dense water outflow generates lagged pulsations of EAC and inflow of saline waters. Croatia Italy Haline forcing Thermal forcing Thermohaline forcing

13 estuarine AdTHC – freshwater balance changes (E, P, R) Overall decrease in river runoff and precipitation, increase in evaporation Cozzi and Giani, CSR, 2011 northern Adriatic river discharges, Po (up) and Adige (down) CRU TS 3.1. precipitation trend, Philandras et al., NHESS, the freshwater deficit increases in the period. The water deficit is due to increases in evaporation driven by increasing SST, while precipitation does not show any consistent trends in the period. Romanou et al., J. Cli., 2010 AdTHC driving mechanisms changes

14 anti-estuarine AdTHC – DWG by heat losses, winds Spatial downscalling is still a demand for proper quantification of long-term changes in heat fluxes and wind stress at the Adriatic dense water generation sites! Middle Adriatic salinity AdTHC driving mechanisms changes Supić et al., Ann. Geo, 2004 anti-estuarine AdTHC – trends in salinity, high interannual variability

15 Variability at lateral boundary – BiOS Gačić et al., GRL, we show that surface flow in the northwestern Ionian co-varies with the density of water masses formed in the Southern Adriatic... AdTHC driving mechanisms changes

16 Data: - Palagruža transect - Stations P1 (528), P2 (529), P3 (216), P4 (206), P5 (199) – number of vertical profiles in brackets temperature, salinity, dissolved oxygen Methods: - removal of 12- and 6-month cycle - linear trends and variability, separately for each station, depth and parameter - significance estimates AdTHC ocean changes An observational study

17 Annual averages in T, S,  t, DO 1 – NAdDW outflow current 2 – LIW inflow current 3,4 – freshened surface waters AdTHC ocean changes ItalyCroatia

18 EMT Interannual and decadal variability, especially in the last two decades AdTHC ocean changes P2, 100 m

19 T, S,  t, DO trends significant at 95% significant at 95% o insignificant AdTHC ocean changes ItalyCroatia

20 T, S,  t, DO trends (pre-EMT period) - The pattern is similar, although different in significance and numbers AdTHC ocean changes

21 Conclusions Q: Does the thermohaline circulation weaken in the Adriatic Sea? A: Probably :) Nature cannot be quantified deterministically. - lower NAdDW production, lower ventilation of deep layers, lower LIW advection today than before 60 years - salinization, heating of surface layers, strengthening of stratification - strong effects on biogeochemistry, ecology of living organisms (especially in deep layers), fisheries,... Jabuka Pit area is very important area for fisheries and biodiversity niche

22 SST difference between and simulated by AOGCM Perspectives Somot et al., GPC, 2008 Zampieri et al., PCE, 2012 Air temperature and precipitation differences between and ensembled over RegCMs winter summer Q: What can be expected in the future?


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