Steric Sea Level Variations Research Articles

Exploring steric sea level variability in the Eastern Tropical Atlantic Ocean: a three-decade study (1993–2022)

Sea level rise (SLR) poses a significant threat to coastal regions worldwide, particularly affecting over 60 million people living below 10 m above sea level along the African coast. This study analyzes the spatio-temporal trends of sea level anomaly (SLA) and its components (thermosteric, halosteric and ocean mass) in the Eastern Tropical Atlantic Ocean (ETAO) from 1993 to 2022. The SLA trend for the ETAO, derived from satellite altimetry, is 3.52 ± 0.47 mm/year, similar to the global average of 3.56 ± 0.67 mm/year. Of the three upwelling regions, the Gulf of Guinea (GoG) shows the highest regional trend of 3.42 ± 0.12 mm/year. Using the ARMORD3D dataset, a positive thermosteric sea level trend of 0.88 ± 0.04 mm/year is observed, particularly in the equatorial and southern Atlantic regions. The steric component drives the interannual SLA variability, while the ocean mass component dominates the long-term trends, as confirmed by the GRACE and GRACE-FO missions for 2002–2022. For those two decades, the total SLR from altimetry amounts to 3.80 ± 0.8 mm/year, whilst the steric component is reduced to only 0.19 ± 0.05 mm/year, leaving a residual increase in the ETAO of 3.69 ± 0.5 mm/year. The independent mass change from GRACE amounts to 2.78 ± 0.6 mm/year for this region, which just closes the sea level budget within present uncertainty levels. Spatial analysis of the steric components indicates a warming along the equatorial African coast including the GoG and a freshening near Angola. Strong correlations with regional climate factors, particularly the Tropical South Atlantic Index, highlight the influence of persistent climate modes. These findings underscore the urgent need for mitigation and adaptation strategies to SLR in the ETAO, especially for densely populated coastal communities.

Significant Increase in Global Steric Sea Level Variations over the Past 40 Years

Understanding global sea level variations and exploring their causes hold significant importance for future climate change predictions and the sustainable development of mankind, with the steric sea level (SSL) variations being one of the primary contributors to these changes. Here, we utilize four types of temperature and salinity products (i.e., EN4, IAP, SODA, and GDCSM) to investigate the spatiotemporal characteristics of global SSL changes from 1980 to 2020. We also explore the relationship between SSL changes and the El Niño-Southern Oscillation (ENSO) phenomenon. The findings reveal a rising trend of 0.64–0.97 mm/a in global SSL over the past 40 years, and the annual amplitudes of SSL time series are within the range of 0–50 mm. The SSL trend at a depth of 0–100 m exerts the greatest influence on the overall trend. The ENSO phenomenon has an obvious influence on sea level changes both in the equatorial Pacific region and global scale. The changes in the global sea level (GSL) associated with ENSO are primarily caused by changes in SSL. This study benefits the understanding of SSL changes and their connection to climate change, serves as a reference for comprehensively assessing sea level change mechanisms using diverse datasets and remote sensing technology, and further provides a scientific basis for the sustainable development of mankind in coastal areas.

Sources and Sinks of Interannual Steric Sea Level Variability

AbstractUnderstanding the mechanisms of regional steric sea level variability is fundamental to understand the regional sea level variability recorded by satellite altimetry for years and to insure that future projections made by climate models are realistic. Here, we first develop a novel method based on steric sea level variance budget that allows to detect the sources and sinks of the variability. Using the “Estimating the Circulation and Climate of the Ocean” (ECCO V4) state estimate, we then show that interannual steric sea level variability is mainly sustained by interannual fluctuating winds via Ekman transport almost everywhere. The damping of the variability is made by both the interannual fluctuating net heat flux from the atmosphere, that largely dominates the atmospheric freshwater fluxes, and the parametrized effect of eddies. It is also found that the parametrized effect of diffusion on the variability is weak in most regions and that, although globally weak, the fluctuations of atmospheric freshwater fluxes are a source of variance close to the Equator in the Pacific Ocean.

Barystatic and steric sea level variations in the Baltic Sea and implications of water exchange with the North Sea in the satellite era

Satellite altimetry, satellite gravimetry, and in-situ subsurface salinity and temperature profiles are used to investigate the total, barystatic, and steric sea level variations in the Baltic Sea, respectively. To estimate the steric sea level, the density variations are weighted in deeper layers to prevent overestimation of their contribution. We show that the sum of barystatic and steric components exhibits excellent cross correlation (0.9) with satellite altimetry sea level variations and also explains up to 84% of total signal variability from 2002 to 2019. Considering the dominance of barystatic sea level variations in the basin and the limitation of satellite gravimetry in resolving the mass change in water-land transition zones (known as the leakage problem), the mismatch is likely attributed to the inadequate accuracy of the barystatic datasets. The total sea level and its contributors are further decomposed into seasonal, interannual, and decadal temporal components. It is shown that despite its insignificant contributions to seasonal and interannual changes, the steric sea level plays an important role in decadal variations. Additionally, we show that the interannual variations of the barystatic sea level are governed by the North Atlantic Oscillation in the basin. The sea level variation in the North Sea is also examined to deduce the water exchange patterns on different time scales. A drop in the North Sea level can be seen from 2005 to 2011 which is followed by the Baltic Sea level with a ~3-year lag, implying the outflow from the Baltic Sea to the North Sea.

Impacts of the upper-ocean salinity variations on the decadal sea level change in the Southeast Indian Ocean during the Argo era

In the past nearly two decades, the Argo Program has created an unprecedented global observing array with continuous in situ salinity observations, providing opportunities to extend our knowledge on the variability and effects of ocean salinity. In this study, we utilize the Argo data during 2004–2017, together with the satellite observations and a newly released version of ECCO ocean reanalysis, to explore the decadal salinity variability in the Southeast Indian Ocean (SEIO) and its impacts on the regional sea level changes. Both the observations and ECCO reanalysis show that during the Argo era, sea level in the SEIO and the tropical western Pacific experienced a rapid rise in 2005–2013 and a subsequent decline in 2013–2017. Such a decadal phase reversal in sea level could be explained, to a large extent, by the steric sea level variability in the upper 300 m. Argo data further show that, in the SEIO, both the temperature and salinity changes have significant positive contributions to the decadal sea level variations. This is different from much of the Indo-Pacific region, where the halosteric component often has minor or negative contributions to the regional sea level pattern on decadal timescale. The salinity budget analyses based on the ECCO reanalysis indicate that the decadal salinity change in the upper 300 m of SEIO is mainly caused by the horizontal ocean advection. More detailed decomposition reveals that in the SEIO, there exists a strong meridional salinity front between the tropical low-salinity and subtropical high salinity waters. The meridional component of decadal circulation changes will induce strong cross-front salinity exchange and thus the significant regional salinity variations.

Steric Sea Level Variability in the East Asian Seas estimated from Ocean Reanalysis Intercomparison Project Data

In this study, steric height variability in the East Asian Seas (EAS) has been analyzed by using ocean reanalysis intercomparison project (ORA-IP) data. Results show that there are significant correlations between ocean reanalysis and satellite data except the phase of annual cycle and interannual signals of the Yellow Sea. Reanalysis ensemble derived from 15-different assimilation systems depicts higher correlation (0.706) than objective analysis ensemble (0.296) in the EAS. This correlation coefficient is also much higher than that of the global ocean (0.441). For the longterm variability of the thermosteric sea level during 1993-2010, a significant warming trend is found in the East/Japan Sea, while cooling trend is shown around the Kuroshio extension area. For the halosteric sea level, a dominant freshening trend is found in the EAS. However, below 300 m depth around this area, the signal-to-noise ratio of the linear trend is generally less than one, which is related to the low density of observation data.

Multitechnique Assessment of the Interannual to Multidecadal Variability in Steric Sea Levels: A Comparative Analysis of Climate Mode Fingerprints

AbstractBecause of increased emissions of greenhouse gases oceans are warming, causing sea level to rise as the density of seawater falls. Predicting the rates of steric expansion is challenging because of the natural variability of the ocean and because observations are insufficient to adequately cover the ocean basins. Here, we investigate the ability of one ocean reanalysis, two objective analyses, and one combination of satellite geodetic measurements to accommodate data gaps and to reconstruct typical patterns of the steric sea level variability at interannual and multidecadal time scales. Six climate indices are used to identify robust features of the internal variability, using a Least Absolute Shrinkage and Selection Operator (LASSO) regression to select significant predictors of the steric variability. Spatially consistent fingerprints are revealed for all climate indices in the ocean reanalysis dataset, allowing the recovery of most of the steric variability observed in the tropical and North Pacific, as well as large fractions of the Atlantic and Indian Ocean signals. Robust climate mode fingerprints are also identified with high spatial resolution but limited temporal coverage in the geodetic observations. The objective analyses fail to detect many of the patterns expected from climate modes, especially before the Argo era. Climate indices constitute valuable yet underexploited tools to assess the performance of different techniques to reconstruct steric sea levels at interannual and multidecadal scales. Such progress will increase confidence in the historical reconstructions of steric sea levels, which is necessary to improve the closure of regional and global sea level budgets and to validate the predictions of climate models.

Trends and interannual variability of mass and steric sea level in the Tropical Asian Seas

AbstractThe mass and steric components of sea level changes have been separated in the Tropical Asian Seas (TAS) using a statistically optimal combination of Jason satellite altimetry, GRACE satellite gravimetry, and ocean reanalyses. Using observational uncertainties, statistically optimally weighted time series for both components have been obtained in four regions within the TAS over the period January 2005 to December 2012. The mass and steric sea level variability is regressed with the first two principal components (PC1&2) of Pacific equatorial wind stress and the Dipole Mode Index (DMI). Sea level in the South China Sea is not affected by any of the indices. Steric variability in the TAS is largest in the deep Banda and Celebes seas and is affected by both PCs and the DMI. Mass variability is largest on the continental shelves, which is primarily controlled by PC1. We argue that a water flux from the Western Tropical Pacific Ocean is the cause for mass variability in the TAS. The steric trends are about 2 mm yr−1 larger than the mass trends in the TAS. A significant part of the mass trend can be explained by the aforementioned indices and the nodal cycle. Trends obtained from fingerprints of mass redistribution are statistically equal to mass trends after subtracting the nodal cycle and the indices. Ultimately, the effect of omitting the TAS in global sea level budgets is estimated to be 0.3 mm yr−1.

Global sea level variations from altimetry, GRACE and Argo data over 2005–2014

Total sea level variations (SLVs) are caused by two major components: steric variations due to thermal expansion of seawater, and mass-induced variations due to mass exchange between ocean and land. In this study, the global SLV and its steric and mass components were estimated by satellite altimetry, Argo float data and the Gravity Recovery and Climate Experiment (GRACE) data over 2005–2014. Space gravimetry observations from GRACE suggested that two-thirds of the global mean sea level rise rate observed by altimetry (i.e., 3.1 ± 0.3 mm/a from 2005 to 2014) could be explained by an increase in ocean mass. Furthermore, the global mean sea level was observed to drop significantly during the 2010/2011 La Niña event, which may be attributed to the decline of ocean mass and steric SLV. Since early 2011, the global mean sea level began to rise rapidly, which was attributed to an increase in ocean mass. The findings in this study suggested that the global mean sea-level budget was closed from 2005 to 2014 based on altimetry, GRACE, and Argo data.

Steric sea level variability (1993–2010) in an ensemble of ocean reanalyses and objective analyses

Quantifying the effect of the seawater density changes on sea level variability is of crucial importance for climate change studies, as the sea level cumulative rise can be regarded as both an important climate change indicator and a possible danger for human activities in coastal areas. In this work, as part of the Ocean Reanalysis Intercomparison Project, the global and regional steric sea level changes are estimated and compared from an ensemble of 16 ocean reanalyses and 4 objective analyses. These estimates are initially compared with a satellite-derived (altimetry minus gravimetry) dataset for a short period (2003–2010). The ensemble mean exhibits a significant high correlation at both global and regional scale, and the ensemble of ocean reanalyses outperforms that of objective analyses, in particular in the Southern Ocean. The reanalysis ensemble mean thus represents a valuable tool for further analyses, although large uncertainties remain for the inter-annual trends. Within the extended intercomparison period that spans the altimetry era (1993–2010), we find that the ensemble of reanalyses and objective analyses are in good agreement, and both detect a trend of the global steric sea level of 1.0 and 1.1 ± 0.05 mm/year, respectively. However, the spread among the products of the halosteric component trend exceeds the mean trend itself, questioning the reliability of its estimate. This is related to the scarcity of salinity observations before the Argo era. Furthermore, the impact of deep ocean layers is non-negligible on the steric sea level variability (22 and 12 % for the layers below 700 and 1500 m of depth, respectively), although the small deep ocean trends are not significant with respect to the products spread.

Detecting Processes Contributing to Interannual Halosteric and Thermosteric Sea Level Variability

Abstract On interannual time scales, regional sea level variability is largely determined by changes in the steric component. The relation between the thermosteric and halosteric components is studied by separating the components into contributions from the mixed layer and, below the mixed layer, into the part that is related to isopycnal motion and that contributes to the steric sea level and the inactive part related to changes of spiciness. The decomposition provides a simple diagnostic to detect and understand physical mechanisms leading to regional sea level changes. In most areas of the world’s oceans, steric sea level variability is dominated by the contribution from isopycnal motion to the thermosteric sea level while halosteric variability relates more to spiciness. Because of the salinity minimum at middepth, different spatial salinity gradients above and below the minimum lead to opposing contributions and thus to a small contribution from isopycnal motion to the halosteric sea level. In nonpolar regions, both active components oppose each other, rendering the thermosteric variability larger than the steric variability. In the Arctic, the variability of both components is governed by spiciness in the Eurasian Basin and isopycnal motion in the Amerasian Basin.

Sea level changes at Tenerife Island (NE Tropical Atlantic) since 1927

Hourly sea level observations measured by five tide gauges at Santa Cruz harbor (Tenerife Island), in the Northeastern Tropical Atlantic, have been merged to build a consistent and almost continuous sea level record starting in 1927. Datum continuity was ensured using high precision leveling information. The time series underwent a detailed quality control in order to remove outliers, time drifts, and datum shifts. The resulting sea level record was then used to describe the low frequency (interannual to decadal) sea level variability at Tenerife. It was found that at interannual and longer time scales, the observed sea level changes are primarily driven by steric sea level variations. Such steric changes are originated by coastal trapped waves induced by longshore winds along the continental coast and propagate poleward. Observed sea level rise at Tenerife was 2.09 ± 0.04 mm/yr since 1927. According to the hydrographic observations in the area, only half of this trend was attributed to steric sea level changes for the top 500 m, at least since 1950.

Decadal and long-term sea level variability in the tropical Indo-Pacific Ocean

In this study, we analysed decadal and long-term steric sea level variations over 1966–2007 period in the Indo-Pacific sector, using an ocean general circulation model forced by reanalysis winds. The simulated steric sea level compares favourably with sea level from satellite altimetry and tide gauges at interannual and decadal timescales. The amplitude of decadal sea level variability (up to ~5 cm standard deviation) is typically nearly half of the interannual variations (up to ~10 cm) and two to three times larger than long-term sea level variations (up to 2 cm). Zonal wind stress varies at decadal timescales in the western Pacific and in the southern Indian Ocean, with coherent signals in ERA-40 (from which the model forcing is derived), NCEP, twentieth century and WASWind products. Contrary to the variability at interannual timescale, for which there is a tendency of El Nino and Indian Ocean Dipole events to co-occur, decadal wind stress variations are relatively independent in the two basins. In the Pacific, those wind stress variations drive Ekman pumping on either side of the equator, and induce low frequency sea level variations in the western Pacific through planetary wave propagation. The equatorial signal from the western Pacific travels southward to the west Australian coast through equatorial and coastal wave guides. In the Indian Ocean, decadal zonal wind stress variations induce sea level fluctuations in the eastern equatorial Indian Ocean and the Bay of Bengal, through equatorial and coastal wave-guides. Wind stress curl in the southern Indian Ocean drives decadal variability in the south-western Indian Ocean through planetary waves. Decadal sea level variations in the south–western Indian Ocean, in the eastern equatorial Indian Ocean and in the Bay of Bengal are weakly correlated to variability in the Pacific Ocean. Even though the wind variability is coherent among various wind products at decadal timescales, they show a large contrast in long-term wind stress changes, suggesting that long-term sea level changes from forced ocean models need to be interpreted with caution.

Sea level variations in the South China Sea inferred from satellite gravity, altimetry, and oceanographic data

Sea level variations (SLVs) can be divided into two major components: the steric SLV and the mass-induced SLV. These two components of SLV in the South China Sea (SCS) are studied by using satellite altimetry, GRACE (Gravity Recovery and Climate Experiment) satellite gravity, and oceanographic data on annual and inter-annual timescales. On the annual timescale, the geographic distribution of mass-induced SLV’s amplitude jointly estimated from altimetry and the ECCO (Estimation of the Circulation and Climate of the Ocean) model agrees very well with that from GRACE. GRACE observes obvious seasonal mass-induced SLV in the SCS with annual amplitude of 2.7±0.4 cm, which is consistent with the annual amplitude of 2.7±0.3 cm estimated from the steric-corrected altimetry. On the inter-annual timescales, the mean SLV in the SCS shows a large oscillation, which is mainly caused by the steric effect. The trend of mean SLV inferred from altimetry in the SCS is 5.5±0.7 mm/yr for the period of 1993–2009, which is significantly higher than the global sea level rise rate of 3.3±0.4 mm/yr in the same period. There is no obvious trend signal in the mass-induced SLV detected from GRACE that indicates the water exchange between the SCS and its adjacent seas and land is in balance within the study period.

Steric sea level variations over 2004–2010 as a function of region and depth: Inference on the mass component variability in the North Atlantic Ocean

We investigate the regional‐ocean depth layer (down to 2000 m) contributions to global mean steric sea level from January 2004 to March 2010, using Argo‐based ocean temperature and salinity data from the SCRIPPS Oceanographic Institution database. We find that Indian ocean warming is almost compensated by Atlantic ocean cooling, so that the total global mean steric sea level increases only slightly over the considered period (0.35 ± 0.30 mm/yr). Salinity variations also contribute, at lower rate, to the observed steric compensation. Meanwhile, the Pacific steric sea level increases only slightly (0.35 ± 0.25 mm/yr). In the North Atlantic region, the mass component (estimated by the difference between satellite altimetry‐based minus steric sea level over the same area) is negatively correlated over 2004–2010 with the steric component. During that period, North Atlantic sea level variability seems mostly driven by the North Atlantic Oscillation (NAO). This is unlike during the previous years (1997 to 2004), a period during which we observe significant correlation between North Atlantic sea level and El Nino‐Southern Oscillation (ENSO), with positive sea level corresponding to ENSO cold phases (La Nina).

Mechanisms of interannual steric sea level variability

Processes contributing to interannual steric sea level variability are studied over the period 1993–2004 using an observationally‐constrained ocean state estimate produced by the ECCO (“Estimating the Circulation and Climate of the Ocean”) consortium. The estimate's dynamical consistency allows for the comprehensive attribution of steric changes in terms of advection, diffusion, and surface buoyancy exchange processes. Steric variations are found to be owing more to oceanic transports than to local surface buoyancy fluxes. Advection is responsible for steric variability in the tropical Indian and Pacific oceans. At extratropical latitudes, advection and diffusion appear to be equally important. Local surface buoyancy fluxes can contribute in some regions (e.g., the tropical Atlantic). Analysis of the anomalous wind stress curl shows that extra‐equatorial vertical advection is driven primarily by Ekman pumping. The complexity of the interannual steric budget suggests that anomalous sea level is probably not predictable on the basis of ocean memory alone. Furthermore, proper parameterizations of mixing processes and good estimates of wind‐driven transports both appear to be very important to reliable projections of interannual sea level.

Steric Sea-Level Change and its Impact on the Gravity Field caused by Global Climate Change

It is sometimes assumed that steric sea-level variations do not produce a gravity signal as no net mass change, thus no change of ocean bottom pressure is associated with it. Analyzing the output of two CO2 emission scenarios over a period of 2000 years in terms of steric sea-level changes, we try to quantify the gravitational effect of steric sea-level variations. The first scenario, computed with version 2.6 of the Earth System Climate Model developed at the University of Victoria, Canada (UVic ESCM), is implemented with a linear CO2 increase of 1% of the initial concentration of 365 ppm and shows a globally averaged steric effect of 5.2 m after 2000 years. In the second scenario, computed with UVic ESCM version 2.7, the CO2 concentration increases quasi-exponentially to a level of 3011 ppm and is hold fixed afterwards. The corresponding globally averaged steric effect in the first 2000 years is 2.3 m. We show, due to the (vertical) redistribution of ocean water masses (expansion or contraction), the steric effect results also in a small change in the Earth’s gravity field compared to usually larger changes associated with net mass changes. Maximum effects for computation points located on the initial ocean surface can be found in scenario 1, with the effect on gravitational attraction and potential ranging from 0.0 to −0.7·10−5 m s−2 and −3·10−3 to 6·10−3 m2 s−2, respectively. As expected, the effect is not zero but negligible for practical applications.

Comment on “On the steric and mass‐induced contributions to the annual sea level variations in the Mediterranean Sea” by David García et al.

[1] Garcia et al. [2006] (hereafter referred to as GCDVG) present an analysis of mass-induced sea level variation (SLVmass) of the Mediterranean Sea based on satellite altimetry, ocean modeling and Gravity Recovery and Climate Experiment (GRACE) gravity measurements. In particular, GCDVG find consistency between altimeter sea level variations corrected for steric effects and changes in oceanic mass derived from Gravity Recovery and Climate Experiment (GRACE). GCDVG show that the annual cycle of the sea level variability (SLVtotal) is dominated by changes in its steric part (SLVsteric) and that the basin average of mass (SLVmass) is maximum in February. They conclude that, when the sea level is rising (falling) the Mediterranean Sea is actually losing (gaining) mass. [2] GCDVG appear to use an unrealistically large estimate of steric sea level variability (SLVsteric) and neglect changes in continental water storage that can significantly affect GRACE measurements over the Mediterranean Sea. These issues are examined in turn below by reviewing relevant individual basin averages of the Mediterranean Sea in comparison to results of other studies. In particular, while also finding consistency between altimetry and GRACE measurements, Fenoglio-Marc et al. [2006] (hereafter referred to as FKB), in a similar study of the Mediterranean Sea, find steric effects only accounting for about 60% of the total annual sea level variability and the annual cycle of SLVmass having a maximum in November.

Steric Sea-level Variations Inferred from Combined Topex/Poseidon Altimetry and GRACE Gravimetry

In this study, we propose to estimate the steric sea-level variations over a < 2-year period (April 2002 through December 2003) by combining global mean sea level (GMSL) based on Topex/Poseidon (T/P) altimetry with time-variable geoid averaged over the oceans, as observed by the GRACE (Gravity Recovery and Climate Experiment) satellite. In effect, altimetry-derived GMSL changes results from two contributions: Steric (thermal plus salinity) effects due to sea water density change and ocean mass change due to water exchange with atmosphere and continents. On the other hand, GRACE data over the oceans provide the ocean mass change component only. The paper first discusses the corrections to apply to the GRACE data. Then the steric contribution to the GMSL is estimated using GRACE and T/P data. Comparison with available thermal expansion based on in situ hydrographic data is performed.

Estimation of steric sea level variations from combined GRACE and Jason-1 data

We estimate the mean steric sea level variations over the 60°S–60°N oceanic domain for the recent period (from August 2002 to April 2006), by combining sea level data from Jason-1 altimetry with time-variable gravity data from GRACE. The observed global mean sea level change from satellite altimetry results in total from steric plus ocean mass change. As GRACE measurements averaged over the ocean represents the ocean mass change component only, the difference between GRACE and altimetry observations provides an estimate of the mean steric sea level. Two different sets of GRACE geoid solutions (the GRGS EIGEN-GL04 and the GFZ EIGEN-GRACE04S products) have been used. Each GRACE data set ranges over approximately 3 yr or more (August 2002–April 2006 for the GRGS geoids and February 2003–February 2006 for the GFZ geoids).We first focus on the seasonal variations. The two GRACE data sets agree very well in terms of mean annual mass variation, both in amplitude (approximately 7.3 mm equivalent sea level) and phase (maximum on October 14). For both time spans, Jason-1 sea level minus GRACE ocean mass has an annual amplitude of approximately 5.8 mm with a maximum on March 11. The latter signal compares well with the steric annual sea level estimated from the World Ocean 2004 climatology and the Ishii et al. [M. Ishii, M. Kimoto, K. Sakamoto, and S.I. Iwasaki, Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses, Journal of Oceanography, 62 (2) (2006) 155–170.] ocean temperature data. We also examine the interannual fluctuations of the Jason-1 minus GRACE sea level. The two resulting steric sea level time series (based on the two GRACE data sets) agree well. The inferred steric sea level curve exhibits an increasing trend during the last 3.5 yr (August 2002–April 2006), of the same order of magnitude as the 1993–2003 steric sea level trend computed with in situ hydrographic data. However, over the last 3.5 yr, we note a strong discrepancy between altimetry minus GRACE and in situ-based steric sea level trend, the latter exhibiting a negative slope. The cause for such a discrepancy is yet unknown but may be related to inadequate sampling of in situ ocean temperature measurements.