Does the thermohaline circulation Does the thermohaline circulation weaken in the Adriatic Sea?weaken in the Adriatic Sea?
Ivica VilibićIvica Vilibić, Jadranka Šepić, Jadranka ŠepićInstitute of Oceanography and Fisheries, Split, Institute of Oceanography and Fisheries, Split,
CroatiaCroatia
Nicolas ProustNicolas ProustStudent at Student at Institute of Engineering Sciences of Institute of Engineering Sciences of
Toulon and Var, La Valette, FranceToulon and Var, La Valette, France
MotivationMotivationOverturning stream functionOverturning stream function
TThe Mediterranean thermohalinehe Mediterranean thermohaline circulationcirculation (MTHC) is strongly weakened(MTHC) is strongly weakened at the end of at the end of thethe twenty-first century. This behaviour is twenty-first century. This behaviour is mainly due tomainly due to the decrease in surface density the decrease in surface density and so the and so the decrease indecrease in winter deep-water winter deep-water formationformation. At the end of the twenty. At the end of the twenty--firstfirst century, the MTHC weakening can be century, the MTHC weakening can be evaluatedevaluated as –40% for the intermediate as –40% for the intermediate waters and –80% for thewaters and –80% for the deep circulation deep circulation with respect to present-climate conditions.with respect to present-climate conditions.
Somot et al., Climate Dynamics, 2006Somot et al., Climate Dynamics, 2006
AdriaticAdriatic
MotivationMotivationA hint is provided by winter of 2012:A hint is provided by winter of 2012:
You are hereYou are here
MotivationMotivationHowever, one harsh winter However, one harsh winter does does not makenot make a transition to the a transition to the glacial period (regardless of glacial period (regardless of media, some crackpot scientists media, some crackpot scientists and record-breaking seawater and record-breaking seawater density in Croatian coastal density in Croatian coastal waters).waters).
Our motivation is:Our motivation is:To detect and assess To detect and assess long-termlong-term AdTHC changes, as being highly AdTHC changes, as being highly relevant to a number of issues relevant to a number of issues (e.g., hydrological cycle in the (e.g., hydrological cycle in the Med, sea level studies, Med, sea level studies, biogeoscience research, ...)biogeoscience research, ...)
Pag Channel, 29-03-2012Pag Channel, 29-03-2012
Courtesy of PMF-ZgCourtesy of PMF-Zg
Outline:Outline:
- About Adriatic thermohaline circulation (AdTHC)About Adriatic thermohaline circulation (AdTHC)- Major AdTHC driving mechanisms and their trendsMajor AdTHC driving mechanisms and their trends- AdTHC trends visible in long-term ocean seriesAdTHC trends visible in long-term ocean series- Some conclusions, consequences and perspectivesSome conclusions, consequences and perspectives
About AdTHCAbout AdTHCThe Adriatic is a semi-enclosed basin The Adriatic is a semi-enclosed basin characterised by both estuarine and characterised by both estuarine and anti-estuarine types of THCanti-estuarine types of THC
SAGSAG
EACEACW
ACW
AC
estuarine AdTHC (driven by freshwater balance)estuarine AdTHC (driven by freshwater balance)
riversrivers
anti-estuarine AdTHC (driven by dense water generation)anti-estuarine AdTHC (driven by dense water generation)
Vilibić et al., DSR, 2004Vilibić et al., DSR, 2004
About AdTHCAbout AdTHC
Deep Deep convection site convection site
(AdDW)(AdDW)
Supić and Vilibić, ECSS, 2006Supić and Vilibić, ECSS, 2006
anti-estuarine AdTHC (driven by dense water generation)anti-estuarine AdTHC (driven by dense water generation)
IOF-MHS Virtual Laboratory, 2012IOF-MHS Virtual Laboratory, 2012
Vilibić et al., DSR, 2004Vilibić et al., DSR, 2004
26-04-201226-04-2012
About AdTHCAbout AdTHC
Courtesy of ISMAR Venezia, 16 mCourtesy of ISMAR Venezia, 16 m
Feb 2012Feb 2012
anti-estuarine AdTHC – DWG by shelf densification (NAd)anti-estuarine AdTHC – DWG by shelf densification (NAd)
Pullen et al., JGR, 2007Pullen et al., JGR, 2007
Beg Paklar et al., CSR, 2001Beg Paklar et al., CSR, 2001
Proper quantification of DWG is dependable Proper quantification of DWG is dependable on model resolution, due to on model resolution, due to high spatial and high spatial and temporal variablitytemporal variablity of the generating force of the generating force (bora).(bora).
Zore-Armanda and Gacic, Ann. Geo., 1987Zore-Armanda and Gacic, Ann. Geo., 1987
About AdTHCAbout AdTHC
anti-estuarine AdTHC – DWG by deep convection (SAd)anti-estuarine AdTHC – DWG by deep convection (SAd)
Vilibić and Šantić, OD, 2008Vilibić and Šantić, OD, 2008
mixed layer depthmixed layer depth
DW from NAd DW from NAd (NAdDW)(NAdDW)
About AdTHCAbout AdTHC
anti-estuarine AdTHC – DWG by deep convection (SAd)anti-estuarine AdTHC – DWG by deep convection (SAd)
Vilibić and Šantić, OD, 2008Vilibić and Šantić, OD, 2008
About AdTHCAbout AdTHC
08-05-200614-04-2006
30-03-200604-03-2006
spring spring phytoplankton phytoplankton
bloombloom
About AdTHCAbout AdTHC
Orlić et al., JGR, 2007Orlić et al., JGR, 2007
Anti-estuarine AdTHC is Anti-estuarine AdTHC is thermally-driventhermally-driven through through heat losses during bora heat losses during bora outbreaks, and is outbreaks, and is laggedlagged with respect to the with respect to the forcing for a few months forcing for a few months months.months.Pulsations of dense Pulsations of dense water outflow generates water outflow generates lagged pulsations of EAC lagged pulsations of EAC and inflow of saline and inflow of saline waters.waters.
CroatiaCroatia
ItalyItaly
Haline forcingHaline forcing
Thermal forcingThermal forcing
Thermohaline forcingThermohaline forcing
estuarine AdTHC – freshwater balance changes (E, P, R)estuarine AdTHC – freshwater balance changes (E, P, R)Overall decrease in river runoff and precipitation, increase in evaporationOverall decrease in river runoff and precipitation, increase in evaporation
Cozzi and Giani, CSR, 2011Cozzi and Giani, CSR, 2011
northern Adriatic northern Adriatic river discharges, river discharges, Po (up) and Adige Po (up) and Adige (down)(down)
CRU TS 3.1. precipitation CRU TS 3.1. precipitation trend, 1951-2002trend, 1951-2002
Philandras et al., NHESS, 2011Philandras et al., NHESS, 2011
... ... the freshwater deficit the freshwater deficit increasesincreases in the 1988-2005 in the 1988-2005 periodperiod. T. The water deficit is due he water deficit is due to to increases in evaporationincreases in evaporation driven by increasing driven by increasing SSTSST, while , while precipitation does not show any precipitation does not show any consistent trends in the periodconsistent trends in the period..
Romanou et al., J. Cli., 2010Romanou et al., J. Cli., 2010
AdTHC driving mechanisms changesAdTHC driving mechanisms changes
anti-estuarine AdTHC – DWG by heat losses, windsanti-estuarine AdTHC – DWG by heat losses, windsSpatial downscalling is still a demandSpatial downscalling is still a demand for proper quantification for proper quantification of long-term changes in heat fluxes and wind stress at the of long-term changes in heat fluxes and wind stress at the Adriatic dense water generation sites!Adriatic dense water generation sites!
Middle Adriatic salinityMiddle Adriatic salinity
AdTHC driving mechanisms changesAdTHC driving mechanisms changes
Supić et al., Ann. Geo, 2004Supić et al., Ann. Geo, 2004
anti-estuarine AdTHC – trends in salinity, high anti-estuarine AdTHC – trends in salinity, high interannual variabilityinterannual variability
Variability at lateral boundary – BiOSVariability at lateral boundary – BiOS
Gačić et al., GRL, 2010Gačić et al., GRL, 2010
... ... we show that surface flow in thewe show that surface flow in the northwestern Ionian conorthwestern Ionian co--varies with varies with the density of waterthe density of water masses masses formed in the Southern Adriaticformed in the Southern Adriatic ... ...
AdTHC driving mechanisms changesAdTHC driving mechanisms changes
Data:Data:- Palagruža transectPalagruža transect- Stations P1 (528), P2 (529), P3 (216), Stations P1 (528), P2 (529), P3 (216), P4 (206), P5 (199) – number of vertical P4 (206), P5 (199) – number of vertical profiles in bracketsprofiles in brackets- 1952-20101952-2010- temperature, salinity, dissolved oxygentemperature, salinity, dissolved oxygen
Methods:Methods:- removal of 12- and 6-month cycleremoval of 12- and 6-month cycle- linear trends and variability, linear trends and variability, separately for each station, depth separately for each station, depth and parameterand parameter- significance estimatessignificance estimates
AdTHC ocean changesAdTHC ocean changes
An An observational observational
studystudy
Annual averages in T, S, Annual averages in T, S, tt, DO, DO1 – NAdDW outflow current1 – NAdDW outflow current2 – LIW inflow current2 – LIW inflow current3,4 – freshened surface waters3,4 – freshened surface waters
AdTHC ocean changesAdTHC ocean changesItalyItalyCroatiaCroatia
EMTEMT
Interannual and Interannual and decadal variability, decadal variability,
especially in the especially in the last two decadeslast two decades
AdTHC ocean changesAdTHC ocean changes
P2, 100 mP2, 100 m
T, S, T, S, tt, DO trends 1952-2010, DO trends 1952-2010• • significant at 95%significant at 95%oo insignificant insignificant
AdTHC ocean changesAdTHC ocean changesItalyItalyCroatiaCroatia
T, S, T, S, tt, DO trends 1952-1989 (pre-EMT period), DO trends 1952-1989 (pre-EMT period)- The pattern is similar, although different in - The pattern is similar, although different in significance and numberssignificance and numbers
AdTHC ocean changesAdTHC ocean changes
ConclusionsConclusions
Q: Q: Does the thermohaline circulation weaken in the Adriatic Sea?Does the thermohaline circulation weaken in the Adriatic Sea?
A: Probably :) Nature cannot be quantified deterministically.A: Probably :) Nature cannot be quantified deterministically.
- lower NAdDW production, lower NAdDW production, lower ventilation of deep layers, lower ventilation of deep layers, lower LIW advection today than lower LIW advection today than before 60 yearsbefore 60 years
- salinization, heating of surface salinization, heating of surface layers, strengthening of layers, strengthening of stratificationstratification
- strong effects on strong effects on biogeochemistry, ecology of biogeochemistry, ecology of living organisms (especially in living organisms (especially in deep layers), fisheries, ...deep layers), fisheries, ...
Jabuka Pit area is Jabuka Pit area is very important area very important area for fisheries and for fisheries and biodiversity nichebiodiversity niche
SST difference between 2070-2090 and SST difference between 2070-2090 and 1961-1990 simulated by AOGCM1961-1990 simulated by AOGCM
PerspectivesPerspectives
Somot et al., GPC, 2008Somot et al., GPC, 2008
Zampieri et al., PCE, 2012Zampieri et al., PCE, 2012
Air temperature and precipitation Air temperature and precipitation differences between 2070-2090 and differences between 2070-2090 and 1961-1990 ensembled over RegCMs1961-1990 ensembled over RegCMs
winterwinter
summersummer
Q: What can be expected in the future?Q: What can be expected in the future?