Causes of the Regional Variability in Observed Sea Level, Sea Surface Temperature and Ocean Colour Over the Period 1993–2011

Abstract

We analyse the regional variability in observed sea surface height (SSH), sea surface temperature (SST) and ocean colour (OC) from the ESA Climate Change Initiative datasets over the period [1993][1994][1995][1996][1997][1998][1999][2000][2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011]. The analysis focuses on the signature of the ocean large-scale climate fluctuations driven by the atmospheric forcing and do not address the mesoscale variability. We use the ECCO version 4 ocean reanalysis to unravel the role of ocean transport and surface buoyancy fluxes in the observed SSH, SST and OC variability. We show that the SSH regional variability is dominated by the steric effect (except at high latitude) and is mainly shaped by ocean heat transport divergences with some contributions from the surface heat fluxes forcing that can be significant regionally (confirming earlier results). This is in contrast with the SST regional variability, which is the result of the compensation of surface heat fluxes by ocean heat transport in the mixed layer and arises from small departures around this background balance. Bringing together the results of SSH and SST analyses, we show that SSH and SST bear some common variability. This is because both SSH and SST variability show significant contributions from the surface heat fluxes forcing. It is evidenced by the high correlation between SST and buoyancy-forced SSH almost everywhere in the ocean except at high latitude. OC, which is determined by phytoplankton biomass, is governed by the availability of light and nutrients that essentially depend on climate fluctuations. For this reason, OC shows significant correlation with SST and SSH. We show that the correlation with SST displays the same pattern as the correlation with SSH with a negative correlation in the tropics and subtropics and a positive correlation at high latitude. We discuss the reasons for this pattern.

Global ocean heat transport dominated by heat export from the tropical Pacific

“…Here we present a novel application of this approach to a recent observational estimate of OHT over the 1992-2011 period. This gridded OHT estimate is part of a global ocean state estimate that agrees, within expected uncertainty ranges, with the bulk of available ocean observations collected between 1992 and 2011, including millions of Argo profiles and complementary satellite data, as well as with atmospheric re-analysis estimates (17)(18)(19)(20)(21)(22)(23)(24).…”

Identifying a human signal in the North Atlantic warming hole

“…1). Two SSTs datasets, which combine satellite and in-situ measurements (the high-resolution NOAA SST 17 and HadISST 18 , Methods), show stronger warming at high and low latitudes than at midlatitudes, resulting in the so-called North Atlantic Warming Hole pattern 6,7,[10][11][12]14,15,19 (Fig. 1a, b).…”

Investigating the predictability of North Atlantic sea surface height

“…Finally, a series of idealised simulations, with selective timescales of the wind and buoyancy forcings, may aid in explaining the dynamical origin of the predictable components. Such ensembles already exist for a range of applications (Gregory et al 2016;Roberts et al 2016;Meyssignac et al 2017). Alternatively, a probabilistic approach as described by Bessières et al (2017) could be used to disentangle the forced and intrinsic variability components, thus, better explaining the dynamical origin of the predictable patterns.…”