Changes of Decadal SST Variations in the Subpolar North Atlantic under Strong CO2 Forcing as an Indicator for the Ocean Circulation’s Contribution to Atlantic Multidecadal Variability

Hand, Ralf; Bader, Jürgen; Matei, Daniela; Ghosh, Rohit; Jungclaus, Johann H. (2020). Changes of Decadal SST Variations in the Subpolar North Atlantic under Strong CO2 Forcing as an Indicator for the Ocean Circulation’s Contribution to Atlantic Multidecadal Variability. Journal of Climate, 33(8), pp. 3213-3228. American Meteorological Society 10.1175/JCLI-D-18-0739.1

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The question of whether ocean dynamics are relevant for basin-scale North Atlantic decadal temperature variability is the subject of ongoing discussions. Here, we analyze a set of simulations with a single climate model consisting of a 2000-yr preindustrial control experiment, a 100-member historical ensemble, and a 100-member ensemble forced with an incremental CO2 increase by 1% yr−1. Compared to previous approaches, our setup offers the following advantages: First, the large ensemble size allows us to robustly separate internally and externally forced variability and to robustly detect statistical links between different quantities. Second, the availability of different scenarios allows us to investigate the role of the background state for drivers of the variability. We find strong evidence that ocean dynamics, particularly ocean heat transport variations, form an important contribution to generate the Atlantic multidecadal variability (AMV) in the Max Planck Institute Earth System Model (MPI-ESM). Particularly the northwest North Atlantic is substantially affected by ocean circulation for the historical and preindustrial simulations. Anomalies of the Labrador Sea deep ocean density precede a change of the Atlantic meridional overturning circulation (AMOC) and heat advection to the region south of Greenland. Under strong CO2 forcing, the AMV–SST regression pattern shows crucial changes: SST variability in the northwestern part of the North Atlantic is strongly reduced, so that the AMV pattern in this scenario is dominated by the low-latitude branch. We found a connection to changes in the deep-water formation that cause a strong reduction of the mean AMOC and its variability. Consequently, ocean heat transport convergence becomes less important for the SST variability south of Greenland.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography > Physical Geography > Unit Climatology
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography
08 Faculty of Science > Institute of Geography > Physical Geography

Graduate School:

Graduate School of Climate Sciences

UniBE Contributor:

Hand, Ralf

Subjects:

900 History > 910 Geography & travel

ISSN:

0894-8755

Publisher:

American Meteorological Society

Funders:

[UNSPECIFIED] German Federal Ministry of Education and Research ; [UNSPECIFIED] Horizon 2020

Projects:

[UNSPECIFIED] RACE II
[UNSPECIFIED] CLIMPRE Inter-Dec

Language:

English

Submitter:

André Hürzeler

Date Deposited:

28 May 2020 15:30

Last Modified:

18 Mar 2021 02:30

Publisher DOI:

10.1175/JCLI-D-18-0739.1

Related URLs:

BORIS DOI:

10.7892/boris.142262

URI:

https://boris.unibe.ch/id/eprint/142262

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