Global and regional ocean mass budget closure since 2003

Abstract

In recent sea level studies, discrepancies have arisen in ocean mass observations obtained from the Gravity Recovery and Climate Experiment and its successor, GRACE Follow-On, with GRACE estimates consistently appearing lower than density-corrected ocean volume observations since 2015. These disparities have raised concerns about potential systematic biases in sea-level observations, with significant implications for our understanding of this essential climate variable. Here, we reconstruct the global and regional ocean mass change through models of ice and water mass changes on land and find that it closely aligns with both GRACE and density-corrected ocean volume observations after implementing recent adjustments to the wet troposphere correction and halosteric sea level. While natural variability in terrestrial water storage is important on interannual timescales, we find that the net increase in ocean mass over 20 years can be almost entirely attributed to ice wastage and human management of water resources.

Fig. 1. Ocean mass budget timeseries from 2003 to 2022.

a Monthly global ocean mass anomalies from 2003 to 2022, referenced to the 2003–2008 mean for the three ocean mass estimates and five land contributions to OMrecon (offset by −20 mm for clarity). Dashed lines indicate periods where the mass change has been extended from the original data. The colored bars below the panel indicate the periods for the different altimetry missions (S6 = Sentinel-6 Michael Freilich). b Same as a, but 12-month averaged and with the addition of steric-corrected altimetry with the default Microwave Radiometer (MWR) Wet Troposphere Correction (WTC) applied, without (dashed, light purple line) and with (dotted, dark purple line) the halosteric drift correction. c Monthly (thin lines) and 12-month averaged residuals (thick lines) between Omrecon, GRACE, and steric-corrected Altimetry with and without MWR correction (dotted lines). Blue and red dots indicate months affected by La Niña and El Niño, respectively. Gray areas in (a–c) indicate periods with no GRACE observations. d Averaged seasonal mass anomaly for the three ice mass contributions and effect of human water management on naturalized land water storage. e Same as (d), but for naturalized land water storage and the three ocean mass estimates on a different scale. a–e All values are provided in mm global ocean mass change and shaded areas indicate 1σ uncertainties. Data for this figure is provided in the Source Data file.

Fig. 2. Rates of ocean mass change.

a Multivariate El Niño–Southern Oscillation (ENSO) Index (MEI. v2). The ENSO phase is neutral for MEI. v2 index values between −0.5 and 0.5. b Ocean mass change rates (12-month average) for the three ocean mass estimates and natural land water storage (LWS). Dashed lines indicate periods, where the original products have been extended (see methods). c Same as (b), but for the three ice contributions and LWS human. Shaded areas indicate 1σ uncertainties. Data for this figure is provided in the Source Data file.

Fig. 3. Regional ocean mass budgets.

12-month moving averages of the three ocean mass change contributions shown globally (a), for 5 ocean reg.-ions (b–f) and remaining ocean areas (g). The map indicates each ocean region and the global mask applied throughout this study. Shaded areas indicate 1σ uncertainties. The values are relative to the 2003–2008 mean. Data for this figure is provided in the Source Data file.