Summary 26 September 2012Core Theme 1

Deliverables

Deliverables

WP 1.1

Tools: Millennium-scale coupled atmosphere-

ocean model simulations (2009)

Model name Horizontal grid (Atm)

Horizontal grid (Ocn)

Vertical levels (Ocn)

Vertical levels (Atm)

Length of control run

BCM 128 x 64 163 x 150 (conforma

l)

35 (isopycn

al)

31 (hybrid) 600

HadCM3 96 x 73 288 x 144 20 (z) 19 (hybrid) 5000

IPSL-CM4 96 x 71 181 x 149(conformal)

31 (z) 19 (hybrid) 1000

KCM 96x48 181x149(conformal)

31 (z) 19 (hybrid) 5000

MPI-M ESM 96 x 48 101 x 120(conformal)

40 (z) 19 (hybrid) 3000

Tools: Millennium-scale coupled atmosphere-

ocean model simulations (CMIP5)

Model name Horizontal grid (Atm)

Horizontal grid (Ocn)

Vertical levels (Ocn)

Vertical levels (Atm)

Length of control run

IPSL-CM5 96 x 95 181 x 149(conformal)

31 (z) 39 (hybrid) 1000

MPI-M ESM 192X96 254 x 220(conformal)

40 (z) 47 (hybrid) 2X1000

Task 1.1.1: Assessment of millenium-scale

simulations and role of external forcing

Compare simulated (signatures of) THC variability on interdecadal to centennial time scales with palaeo-observations from WP1.2 [LOCEAN, MET-O, MPI-M, NERSC]

Characteristics of low-frequency variability in simulations, AMOC and climate modes: Marini et al. (2010), Zanchettin et al. (2010), Park and Latif (2010), Marini et al. (in prep), Park et al. (in prep)

Comparison between simulations and reconstructions:

Sicre et al. (2011), Ottera et al. (2010), Zanchettin et al. (2012), Nuñez-Riboni et al. (2012), Lohmann et al. (in prep), Mjell et al. (in prep)

Task 1.1.1: Assessment of millenium-scale

simulations and role of external forcing

Investigate the role of external forcing on THC variability [MET-O, MPI-M, NERSC, GEOMAR]

Role of strong volcanic eruptions for shaping AMOC variability: Ottera et al. (2010); Zanchettin et al. (2011), Mignot et al. (2011, in prep)

Solar forcing of AMOC changes: Menary et al. (in prep.)

Response to idealized external forcing: Park and Latif (2011)

Millennium simulations: role of external forcing

Ottera et al., 2010

Zanchettin et al., 2011

Task 1.1.2: THC variability on decadal to

centennial time scalesInvestigate mechanisms responsible for low-frequency

THC variability with focus on overflow, deep water formation and its preconditioning [LOCEAN, MET-O, MPI-M, NERSC]

Mechanisms of interdecadal to centennial variability:Menary et al. (2011); Marini et al. (2010), Park and Latif (2010),

Born and Mignot (2011), Medhaug et al. (2012), Langehaug et al. (2012), Escudier et al. (2012), Latif et al. (in rev.), Martin et al. (in rev.), Ba et al. (subm), Brandstator et al. (2011), Keenlyside and Ba (2010)

Task 1.1.2: THC variability on decadal to

centennial time scales

Task 1.1.2: THC variability on decadal to

centennial time scalesDesign [MPI-M] sensitivity experiments to investigate the

impact of changes in overflow and deep water formation on the THC [LOCEAN, MET-O, MPI-M, NERSC]

Lohmann et al. in preparation

Task 1.1.2: THC variability on decadal to

centennial time scales

Assess the role of THC variations on recent changes in North Atlantic heat/fresh water content [MET-O]

Fresh water transports in HadCM3: CT report 2010Ocean heat content changes: Palmer et al. (2011), Robson et

al. (2012)

Arctic/Atlantic exchanges:Eldevik et al. (2009), Jungclaus and Koenigk (2010),

Langehaug et al. (2012b), Langehaug and Falck (2011), Arthun et al. (2012)

Task 1.1.3: Ocean-atmosphere feedbacks and

climatic impact of THC changes

Statistical analysis of lead/lag relationships to investigate the relative role of (un)coupled modes in explaining the low-frequency THC variability [LOCEAN, MET-O, MPI-M, NERSC]

Atmospheric response to MOC variations: Gastineau and Frankignoul (2011a), Gastineau et al. (2011b), Semenov et al. (2010), Jungclaus and Koenigk (2010), Msadek et al. (2011)

Atm leading ocean ocean leading atm

Task 1.1.3: Ocean-atmosphere feedbacks and

climatic impact of THC changes

Perform partially coupled experiments with focus to identify to which extent the Atlantic Multidecadal Oscillation is part of a coupled climate mode [LOCEAN, MET-O, MPI-M, NERSC]

experiments turned out to be too demanding in coupled mode. Experiments with slab ocean done (Msadek et al, 2011), SST-driven atmosphere model experiments at LOCEAN (in prep).

WP1.1 has assessed the THC as represented in the various models and millennium-scale reconstructions

representation of processes

characteristics of internal variability

climate response to THC changes

THC response to external forcings

WP1.1 demonstrated that model simulation and process study are instrumental to understand mechanisms identified in observations and reconstructions

WP1.1 demonstrated that (simulated) natural variability of THC has a significant impact on the winter atmospheric circulation in the NH

WP1.1 demonstrated that there is more to the THC than just the conveyor-belt image!

Core Theme 1 J. Jungclaus & H. Kleiven

“Quantifying and modeling THC variabilityusing palaeoclimate observations and Simulations”

WP 1.2 (Kleiven, Geo and BCCR)THC and related climate variables during the last Millennium from Palaeo observations

Deliverables

D13 Providing a time series of the variability of integrated exchanges with the Nordic Seas and the intensity of the individual deep branches of the THC over the last millennium from paleo data (Month 24)

D20 Providing a data set describing the spatial evolution of SST and thermocline variability associated with changes in the THC at multi-decadal resolution in the North Atlantic during the last millennium (month 36)

Task 1.2.1 Characterize changes in the deep limb of THC-Determine how much it changed, which components, and why?

ISOW and DSOW both show multidecadal-centennial variability over the past millennium. ISOW covaried with AMO over the past 600yrs, DSOW changes during largest N.Atlantic coolings

Task 1.2.2 Characterize the upper limb of THC-Variations in the inflows to the Nordic SeaInflow covaries with NAO/AMO and simulations suggest role for advective anomalies (intergyre/gyre)?

Task 1.2.3 Characterize climate and thermocline evolution over the last millenium

North Atlantic surface climate covary with AMO over past millennium/signal amplification near SPG points toward sensitivity/involvement of SPG.

Reconstructing ocean circulation and climate based on the “Gardar Drift” Tor Lien Mjell (1), Helene R. Langehaug (2), Odd Helge Otterå (3), Tor Eldevik (4), Ulysses. S. Ninnemann (1,5), Helga (Kikki) F. Kleiven (1,5), Ian Hall (6) in prep

Using simulations of the last millennium to understand variability seen in paleo- observations: In-phase variation of Iceland-Scotland overflow strength and Atlantic Multidecadal Oscillation Katja Lohmann1, Juliette Mignot2, Helene R. Langehaug3,4, Johann H. Jungclaus1, Odd Helge Otterå4, Yongqi Gao3,4, Tor Lien Mjell4,5, Ulysses Ninnemann4,5 and Helga (Kikki) Flesche Kleiven4,5, to be submitted

ISOW vigor over the last millennia and its relationship to climate. Mjell, T.L., Ninnemann, U.S., Kleiven, H.F., Rosenthal, Y. and Hall, I.R. Variability in In prep. North Atlantic climate and deep water variability since 600 A.D. Kleiven, H.F., Rosenthal, Y. and Ninnemann, U.S. In prep

Lund et al. (Nature, 2006)

Changed volume transport(1SV=106 cubic m./sec) in the Gulfstream outside Florida over the Little Ice Age

State of the art pre THOR:Changes in the volume transport of the Gulfstream during the Little Ice Age

On a mission….

R/V Mariond Dufresne

Eirik sediment drift, south of GreenlandNew marine ocean data spanning the Little Ice Age ~ 1980 AD

~600 AD

Curry & Mauritzen, 2005

GS06-144-03MC A

57°29’ N, 48° 37’ WDepth: 3432 m

(Figure modified after Curry and Mauritzen, 2005) 15 yrs sample resolution, 13 AMS 14C dates

Reconstructed sea surface temperatures 600-2003 A.D.

Western settlementdeclined

Eastern settlementdeclined

Bottom water flow speed (mean sortable silt in RED) bottom water chemistry (benthic 13C in GREEN)

Deep water variability

Observe a close coupling between surface climate and the properties of proto North Atlantic Deep Water, primarily on centennial timescales.

The surface property changes clearly affect the density and could strongly influence vertical convection.

Today vertical convection in the subpolar gyre and Labrador Sea are important for global deep water ventilation and contribute to the meridional overturning circulation.

Climate – deep water coupling

• The presence and evolution of these drifts are intimately linked with the deep ocean circulation pattern and intensity, sediment supply, and the local topography of the area

• Drift pattern mirror the path of the bottom currents

FD = Feni DriftHAD = Hatton DriftGD = Gardar DriftBD = Bjørn DriftSD = Snorri DriftGLD = Gloria DriftED = Eirik Drift

Modified after Faugères et al., 1993

STUDY AREA

NADW

Modified after Kleiven et al. (2008)

Modified after Kleiven et al. (2008)

Red = GS06144-09 MC-D Blue = Gray et al., 2004

ISOW AND CLIMATE RECONSTRUCTIONS OVER THE LAST 2KYR

This ocean-climate coupling supports the hypothesis that AMO involves, and is potentially driven by, variations in AMOC

THOR is a project financed by the European Commission through the 7th Framework Programme for Research, Theme 6 Environment, Grant agreement 212643 http://ec.europa.eu/index_en.htm