Steric sea-level fluctuations from remote sensing, oceanic reanalyses and objective analyses in the North Atlantic (original) (raw)
Related papers
Steric Sea Level Changes from Ocean Reanalyses at Global and Regional Scales
Water, 2019
Sea level has risen significantly in the recent decades and is expected to rise further based on recent climate projections. Ocean reanalyses that synthetize information from observing networks, dynamical ocean general circulation models, and atmospheric forcing data offer an attractive way to evaluate sea level trend and variability and partition the causes of such sea level changes at both global and regional scales. Here, we review recent utilization of reanalyses for steric sea level trend investigations. State-of-the-science ocean reanalysis products are then used to further infer steric sea level changes. In particular, we used an ensemble of centennial reanalyses at moderate spatial resolution (between 0.5 × 0.5 and 1 × 1 degree) and an ensemble of eddy-permitting reanalyses to quantify the trends and their uncertainty over the last century and the last two decades, respectively. All the datasets showed good performance in reproducing sea level changes. Centennial reanalyses ...
Steric sea level variations during 1957–1994: Importance of salinity
Journal of Geophysical Research, 2002
Spatially averaged (50°S-65°N) temperature and salinity changes in the 0-3000 m layer during the 1957-1994 period resulted in a sea level rise at a mean rate of about 0.55 mm per year. About 10% of this rate is due to a decrease of the volume mean salinity. The magnitude of total steric sea level (TSSL) changes and the ratio of thermosteric and halosteric anomalies to TSSL anomaly are nonuniform geographically. Salinity effects are critically important to the TSSL changes in some regions of the ocean. For example, the thermosteric anomaly is nearly compensated by the halosteric anomaly in the subpolar North Atlantic. This fact will cause erroneous heat content estimates based on altimetric observations from space if a climatological salinity is assumed. Based on the present historical archive of salinity data, a decrease in global mean salinity has occurred. This increase of fresh water would cause sea level rise at a rate of 1.3 ± 0.5 mm/yr if the added water comes from sources other than floating sea ice.
Journal of Climate
Because 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 tropic...
Estimation of steric sea level variations from combined GRACE and Jason1 data
Earth and Planetary Science Letters, 2007
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 for the GFZ geoids).
Steric height variability in the Northern Atlantic on seasonal and interannual scales
Journal of Geophysical Research, 2008
1] Steric height (SH) variability computed from Argo profiling buoys data for the North Atlantic and period 1999-2006 is analyzed and compared to the variability computed from the satellite altimetry data. It is demonstrated that although the contribution from halosteric contraction is smaller than that from the thermal expansion, it is not negligible in wide areas in the North Atlantic and cannot be discarded (the regression of trends in full steric and thermosteric heights is 0.73). It is found that the SH variability is not really sensitive to increasing the reference level from 1000 to 1500 m. Differences in trend reach several mm/year locally, which is estimated to be below sampling errors (about 1.4 mm/year). The SH trends are between ±1 cm/year locally. The comparison of SH and altimetric height variability shows qualitative agreement of both for the amplitude of the annual harmonics and trend but reveals significant local differences which cannot be explained by bottom pressure variability. The main modes of variability seen in yearly mean patterns of SH and satellite altimetry are also different. It is suggested that sampling/interpolation errors are still too high to reveal a balance between the SH and altimetric height variability at the local level.
Low-frequency Atlantic sea level variability
Global and Planetary Change, 2004
The control run of the Hadley Centre-coupled climate model (HadCM3) is used to establish the sources of multidecadal/ centennial sea level (SL) variations in the northwest Atlantic. It is shown that variations in the sea level for the largest part of this area are related to variations in the thermohaline structure of the upper (c 500 m) part of the ocean. Temperature variations dominate steric sea level variations, while salinity variations are dominant only in the margins of the Labrador Sea and near the Mediterranean outflow. In the Labrador Sea, lower layers in the ocean also contribute to the variability in expansion/contraction of the water column. It is shown that along the North American East Coast, variations in the thermohaline structure of the water column are predominantly related to variations in the wind-driven circulation rather than the thermohaline circulation, which dominates the thermohaline structure in the central parts of the North Atlantic. In the Gulf Stream area and near the Labrador Current, sea level has on the multidecadal/centennial time scale a strong barotropic signal superposed on steric sea level variations.
Comparing the steric height in the Northern Atlantic with satellite altimetry
Ocean Science, 2007
Anomalies of dynamic height derived from an analysis of Argo profiling buoys data are analysed to assess the relative roles of contributions from temperature and salinity over the North Atlantic for the period of 1999-2004. They are compared with dynamic topography anomalies based on TOPEX/Poseidon and Jason altimetry. It is shown that the halosteric contribution to the anomalies of dynamic height is comparable in magnitude to the thermosteric one over the period analyzed. Taking both salinity and temperature into account improves the agreement between zonally averaged trends in the satellite dynamic topography and dynamic height increasing the correlation between them to 0.73 from 0.63 when only temperature variability is taken into account. The implication of this result is that the salinity contribution cannot be neglected in the North Atlantic and that one cannot rely on estimating the thermosteric part by anomalies in the sea surface dynamic topography derived from the satellite altimetry.
Regional patterns of observed sea level change: insights from a 1/4° global ocean/sea-ice hindcast
Ocean Dynamics, 2009
A global eddy-admitting ocean/sea-ice simulation driven over 1958-2004 by daily atmospheric forcing is used to evaluate spatial patterns of sea level change between 1993 and 2001. In the present study, no data assimilation is performed. The model is based on the Nucleus for European Models of the Ocean code at the 1/4°r esolution, and the simulation was performed without data assimilation by the DRAKKAR project. We show that this simulation correctly reproduces the observed regional sea level trend patterns computed using satellite altimetry data over 1993-2001. Generally, we find that regional sea level change is best simulated in the tropical band and northern oceans, whereas the Southern Ocean is poorly simulated. We examine the respective contributions of steric and bottom pressure changes to the total regional sea level changes. For the steric component, we analyze separately the contributions of temperature and salinity changes as well as upper and lower ocean contributions. Generally, the model results show that most regional sea level changes arise from temperature changes in the upper 750 m of the ocean. However, contributions of salinity changes and deep steric changes can be locally important. We also propose a map of ocean bottom pressure changes. Finally, we assess the robustness of such a model by comparing this simulation with a second simulation performed by MER-CATOR-Ocean based on the same core model, but differing by its short length of integration (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) and its surface forcing data set. The long simulation presents better performance over 1993-2001 than the short simulation, especially in the Southern Ocean where a long adjustment time seems to be needed.