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

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


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


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)


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


08-05-200614-04-2006

30-03-200604-03-2006

spring spring phytoplankton phytoplankton

bloombloom


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


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 ... ...


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


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


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?

Documents

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