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.

An improved and homogeneous altimeter sea level record from the ESA Climate Change Initiative

“…2). In this area, trends are mainly of thermosteric origin (Legeais et al, 2016b;Meyssignac et al, 2017) in response to increased easterly winds during the last 2 decades associated with the decreasing Interdecadal Pacific Oscillation (IPO)/Pacific Decadal Oscillation (e.g. Merrifield et al, 2012;Palanisamy et al, 2015a;Rietbroek et al, 2016).…”

Reconstruction of Local Sea Levels at South West Pacific Islands—A Multiple Linear Regression Approach (1988–2014)

“…Steric changes can be due to surface buoyancy fluxes, mixing, and adiabatic motions of the isopycnals caused by adjustments to wind‐driven circulation (Meyssignac et al, ; Piecuch & Ponte, ). Wind stress curl produces divergence or convergence of the surface layer (Ekman pumping), which is balanced by vertical “heaving” of the thermocline.…”

“…At interannual‐to‐interdecadal time scales, the thermosteric sea level variability is mostly induced by the internal reorganization of ocean water masses in response to the wind stress curl forcing (Stammer et al, ). Based on previous studies (e.g., Forget & Ponte, ; Meyssignac et al, ), wind stress curl is therefore considered as the dominant predictor of thermosteric sea level, and hence of sea level in the region.…”

“…The residual of thermosteric sea level variability from that induced by wind stress curl anomalies is due to buoyancy forcing at the air‐sea surface, and the intrinsic ocean variability (Meyssignac et al, ). To capture thermosteric sea level variability induced by surface heat forcing, the local SST is added as a potential predictor (Meyssignac et al, ). The other predictors include the wind stress in the vicinity of the island, representing the wind setup, and the halosteric component for salinity changes.…”

Forcing Mechanisms of the Interannual Sea Level Variability in the Midlatitude South Pacific during 2004–2020

“…Previous studies have emphasized that interannual sea level variations in the South Pacific are essentially due to steric fluctuations (e.g., [12,13]), resulting from temperature and salinity changes in the ocean. Changes in the thermosteric (temperature-related) component only are the main contributor of sea level change in the South Pacific at these time scales (e.g., [14,15]). Nevertheless, contributions from the halosteric (salinity-related) component have been shown to play a sizable role in several areas, such as the western equatorial Pacific and near the western boundary currents (e.g., [13,15,16]).…”