Variability of the ocean heat content during the last millennium - an assessment with the ECHO-g Model

© Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. This work has been possible thanks to the funding by the MCINN projects CGL2005-06097 and CGL2008-06558-C02-C01/CLI, and the MARM project 200800050084028. The manuscript was significantly improved thanks to helpful and insightful comments of four anonymous reviewers. We are grateful to A. Grinsted and S. Jevrejeva for making the MatLab wavelet coherence package and their global sea level reconstructions available, and to A. Kemp for kindly sharing the data from North Carolina with us. We would also like to thank G. Sgubin for interesting discussions and to I. Fast for providing us with the extended FOR1 data.The publication of this article is financed by CNRS-INSU.
Studies addressing climate variability during the last millennium generally focus on variables with a direct influence on climate variability, like the fast thermal response to varying radiative forcing, or the large-scale changes in atmospheric dynamics (e. g. North Atlantic Oscillation). The ocean responds to these variations by slowly integrating in depth the upper heat flux changes, thus producing a delayed influence on ocean heat content (OHC) that can later impact low frequency SST (sea surface temperature) variability through reemergence processes. In this study, both the externally and internally driven variations of the OHC during the last millennium are investigated using a set of fully coupled simulations with the ECHO-G (coupled climate model ECHAMA4 and ocean model HOPE-G) atmosphere-ocean general circulation model (AOGCM). When compared to observations for the last 55 yr, the model tends to overestimate the global trends and underestimate the decadal OHC variability. Extending the analysis back to the last one thousand years, the main impact of the radiative forcing is an OHC increase at high latitudes, explained to some extent by a reduction in cloud cover and the subsequent increase of short-wave radiation at the surface. This OHC response is dominated by the effect of volcanism in the preindustrial era, and by the fast increase of GHGs during the last 150 yr. Likewise, salient impacts from internal climate variability are observed at regional scales. For instance, upper temperature in the equatorial Pacific is controlled by ENSO (El Nino Southern Oscillation) variability from interannual to multidecadal timescales. Also, both the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) modulate intermittently the interdecadal OHC variability in the North Pacific and Mid Atlantic, respectively. The NAO, through its influence on North Atlantic surface heat fluxes and convection, also plays an important role on the OHC at multi
Ministerio de Ciencia e Innovación (MCINN), España
Ministerio de Medio Ambiente, Medio Rural y Marino (MARM), España
Centre national de la recherche scientifique CNRS-INSU
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
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