core theme 1. wp 1.1 task 1.1.1: assessment of millenium-scale simulations and role of external...
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Core Theme 1
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WP 1.1
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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]
Compare simulated key processes of THC dynamics with observations from CT3 [MPI-M]
Design a procedure for coordinated model testing [LOCEAN] and apply to the models [IFM-GEOMAR, LOCEAN, MET-O, MPI-M, NERSC]
Investigate the role of external forcing on THC variability [MET-O, MPI-M, NERSC, IfM GEOMAR]
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17
17.5
18
18.5
19
19.5
20
-3
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-1
0
1
2
3
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1400 1500 1600 1700 1800 1900 2000
SS
(m
ea
n) A
MO
Ind
ex
Year A.D.
ISOW & AMO in phase
vigorous ISOW
sluggish ISOW
warm phase AMO
cold phase AMO
Mean Sortable Silt at Gardar drift(this study)
Reconstructed AMO basedOn three rings (Gray et al., 2004)
WP 1.2 RESULTS - MEAN SORTABLE SILT AT GARDAR DRIFT
Gadar Drift data suggest that basin-wide warm phase is associated with vigorous ISOW flow
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Role of processes
Monthly mean observed (blue) and modelled (red) Faroe Bank Channel overflow
Modeled annual mean Denmark Strait (upper) and FBC (lower) overflow
Olsen et al., 2008
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Role of processes
Modeled annual mean Denmark Strait transport from NCEP forced ocean-only experiment (grey) and assimiltion run with coupled AOGCM (green)
Matei et al., in prep.
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Internal variability vs. External forcing as a pacemaker for Atlantic multidecadal
variability?
Otterå et al 2009
…but this finding appears to be model (and forcing) dependent….
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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]
Design [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]
Assess the role of THC variations on recent changes in North Atlantic heat/fresh water content [MET-O]
Design budget and statistical analysis diagnostics [MET-O] and apply to the models [LOCEAN, MET-O, MPI-M, NERSC]
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Variability: No consensus among state-of-the-art climate models
MPI KCM
100 10100 10
CSIRO GFDL
Power spectra: Maximum Atlantic MOC at 30N, CMIP3 pre-industrial control simulations
Period (yr)Period (yr)Courtesy: Jin Ba
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Role of overflow variations for MOC
Denmark Strait Overflow Transp. and MOC anomalies @ 1085m
3
0
-3Anomaly (Sv)Jungclaus et al., in prep.
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Sensitivity experiment: supress density variations in NS
Denmark Strait Overflow Transp. and MOC anomalies @ 1085m
3
0
-3Anomaly (Sv)Jungclaus et al., in prep.
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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], aided by sensitivity experiments [LOCEAN, MPI-M, NERSC]
Perform partial 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]
Investigate the impact of THC changes on European and Arctic climate [LOCEAN, MET-O, MPI-M, NERSC]
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Ocean-atmosphere feedbacks
Msadek & Frankignoul, 2009
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The WP1.1 model zooNERSC: Bergen Climate Model (BCM):ARPEGE (T42/L31) + MICOM (2.4°, L35)
700yr long control integration 1400-1999 solar and volcanic forcing 1850-1999 solar, volcanic, GHG and aerosol forcing ensembles for selected periods planned scenario integration
MPI-M: MPI-M Earth System Model (COSMOS) ECHAM5 (T31/L19) + MPI-OM, 3°, L40 + carbon cycle)•3000yr long control integration•800-2005 solar, volcanic, land use change, GHG and aerosol forcing (ensemble of 5), •single forcing experiments•alternative solar forcing (ensemble of 3)
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The WP1.1 model zooLOCEAN: IPSLCM4_v2: Atm: 96x71x19, Ocn: 2°x2°
1000yr long control integration 950yr solar and CO2 forcing solar, volcanic and CO2 forcing (running)
higher-resolution runs planned:
METO: HadCM3 1.25° ocean,L205700yr pre-industrial control1500-2000 „natural 500“, solar, orbital, volcanic aerosol, preindustrial GHG (1750), 1750 land surface1750:2000: „all250“: as natural 500 + GHG & aerosol emission history, land-use-change, ozone1860-2000 4 member anthropogenic + natural ensemble
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The WP1.1 model zooIfM GEOMAR: KCM: ECHAM5 (T31/L19) + NEMO 2°x2°/L31)
5000yr long control integration idealized solar forcing runs
higher-resolution runs planned
IN SUMMARY:All modelling groups have provided long integrationsCross-model validation is going on using >1000 yr controlexperiments:Overflow characteristicsSub-polar-gyre characteristicsAMO vs. AMOCSea ice variability
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WP1.1 summary
All modelling groups have provided long integrationsCross-model validation is going on using >1000 yr controlexperiments:Overflow characteristicsSub-polar-gyre characteristicsAMO vs. AMOCSea ice variability
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Things to do
Assess similarities and differences in 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
What causes the differences between the models?
Define common analyses tools and prepare publication strategy
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WP 1.2: Participants: BCCR and CNRS (Gif-sur-Yvette)
Task 1.2.1. Characterize changes in the deep and intermediate return flow of THC;Determine how much it changed, which components, and why.
Task 1.2.2. Characterize the upper limb of THC—Variations in the inflows to the Nordic Seas.
Task 1.2.3. Characterize climate and thermocline evolution over the last millennium
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Variability in ISOW vigor over the last 1300 years and its relationship to climate
U. Ninnemann, T.L. Mjell, H. Kleiven and I. Hall,
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Bathymetry of the northern North Atlantic and the Nordic Seas. Location of cores MD03-2664/2665 and ODP 983/MC09 are marked with red dots (Modified from Smith and Sandwell, 1997)
Linkages to AMOC?How have Nordic Seas overflows varied?
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Study Area—ISOW variability on Gardar drift
Latitude: 60°19’ NLongitude: 23° 58’ WDepth: 2081 m
GS06-144-09 MC-D
IR
NIIC
Iceland-Scotland Overflow Water (ISOW)
Curry & Mauritzen, 2005
~1400 AD
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Location in the core of ISOW overflow
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Y= 19.833 – 0.00082278x R= 0.43356
I II III IV
~1400-1520 AD
~1521-1618 AD ~1618-1721 AD
~1721-1820 AD
~1820-1937 AD ~1937-1996 AD
WP 1.2 RESULTS - MEAN SORTABLE SILT AT GARDAR DRIFT
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• Multidecadal to centennial variability in ISOW vigor and chemical properties over the last ~600+ years
• ISOW flow variability is coherent across a range of depths and space (not a local signal)
• During the past ~350 years ISOW vigor is in phase with reconstructed AMO on both inter-decadal and centennial timescale—within the error of our age models.
• This strong coherence suggests that low frequency variability in key components of AMOC is coupled to basin-wide temperature perturbations
Summary of Observations
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Eirik sediment drift – DSOW & DWBC variability
~ 2006 AD
~600 AD
Curry & Mauritzen, 2005
GS06-144-03MC A
Latitude: 57°29’ NLongitude: 48° 37’ WDepth: 3432 m
Deep Western Boundary Current (DWBC)
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Mann and Jones (2003)NH tmp. reconstructions
Benthic oxygen isotopesFrom MD03-2664; 3 pt.smooth(Kleiven et al., in prep)
Natural variability in the deep water masses
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WP 1.2.3: Towards the reconstruction of the thermocline
variability in the North Atlantic during the last millennium
T. Bouinot, E. Cortijo, A. Govin, C. ClérouxLSCE/IPSL (Gif/Yvette, France)
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Study sites:
sediment cores
SST August
Already studied
Future work
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How to reconstruct the thermocline variability?
Summer mixed layer
Seasonal thermocline
Temperature
Water depth
Permanent thermocline
Deep-dwelling foraminifera:1. Globorotalia inflata2. Pulleniatina obliquiloculata
1. 2.
Planktic foraminifera1. Globigerinoides ruber2. Globigerina bulloides
2.1.
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Core MD99-2203 (35°N, 75°W, 620 m)
SST August
C. Cléroux, PhD thesis
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Future work: to better trace the extension of the subtropical & subpolar gyres in the North
Atlantic
From Hatun et al. Science 2005
Subtropical gyre water
Subpolar gyre water
MD08-3182Q
MD03-2674Q(56.4°N, 27.8°W, 2830 m)
MD03-2678Q(58.8°N, 26.0°W, 2603 m)
Coretop’s date 2000 a is around
MD03-2674Q 671.5 a ± 30 a 50 cm
MD03-2678Q 308.5 a ± 30 a 35 cm
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Deliverables
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Deliverables
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All WP 1.1 partners have control integrations of 1000 to 6000 years
forced integrations over the millennium are accomplished or ongoing, some forced integrations have been run in ensemble mode
analyses focus presently on the assessment of THC characteristics and mechanisms
Summary WP 1.1
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WP1.2: reconstructions of the strength of the ISOW over last millennium ready, upper ocean T and S in progress.
Reconstruction of integrated overflows south of Greenland as well as upper ocean T, S, and chemical properties in progress
New cores (Gadar Drift and Bay of Biscay) give detailled information on the structure of the thermocline
Hydrographic reconstructions from the inflow region (Faroe transect and Norwegian Sea ready for the last 400-600 years, will be extended back in time
Summary WP 1.2
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Data from WP3 for process understanding:
- Overflow transport timeseries
-Watermass characteristics
monthly basis /
Some key data should be put somewhere together, for instance the data from CT1 on overflow transport / overflow overturning
Give information on variability on time scales most relevant for decadal prediction (CT4)
CT1 and other CTs