Revisiting the contemporary sea-level budget on global and regional scales

Abstract

Dividing the sea-level budget into contributions from ice sheets and glaciers, the water cycle, steric expansion, and crustal movement is challenging, especially on regional scales. Here, Gravity Recovery And Climate Experiment (GRACE) gravity observations and sea-level anomalies from altimetry are used in a joint inversion, ensuring a consistent decomposition of the global and regional sea-level rise budget. Over the years 2002-2014, we find a global mean steric trend of 1.38 ± 0.16 mm/y, compared with a total trend of 2.74 ± 0.58 mm/y. This is significantly larger than steric trends derived from in situ temperature/salinity profiles and models which range from 0.66 ± 0.2 to 0.94 ± 0.1 mm/y. Mass contributions from ice sheets and glaciers (1.37 ± 0.09 mm/y, accelerating with 0.03 ± 0.02 mm/y(2)) are offset by a negative hydrological component (-0.29 ± 0.26 mm/y). The combined mass rate (1.08 ± 0.3 mm/y) is smaller than previous GRACE estimates (up to 2 mm/y), but it is consistent with the sum of individual contributions (ice sheets, glaciers, and hydrology) found in literature. The altimetric sea-level budget is closed by coestimating a remaining component of 0.22 ± 0.26 mm/y. Well above average sea-level rise is found regionally near the Philippines (14.7 ± 4.39 mm/y) and Indonesia (8.3 ± 4.7 mm/y) which is dominated by steric components (11.2 ± 3.58 mm/y and 6.4 ± 3.18 mm/y, respectively). In contrast, in the central and Eastern part of the Pacific, negative steric trends (down to -2.8 ± 1.53 mm/y) are detected. Significant regional components are found, up to 5.3 ± 2.6 mm/y in the northwest Atlantic, which are likely due to ocean bottom pressure variations.

Keywords: GRACE; altimetry; budget; sea level; steric.

Fig. 1.

Global mean relative sea level, divided into different contributions. Annual and semiannual harmonics have been fitted and removed and the resulting curves are smoothed with a 3-month running mean (trends are derived from the unsmoothed data). The curves have been offset for clarity.

Fig. 2.

Relative sea-level rise in mm/y in selected coastal zones. The associated polygons are colored according to the estimated total error (Materials and Methods). Wedge areas reflect the absolute magnitude of the different contributions, and negative wedges are shaded. Trends with red numbers indicate nonsignificant (1-σ) total trends, although the individual components may have significant contributions (SI Appendix, Table S4).

Fig. 3.

Time-variable sea-level contributions to the east of the Philippines. Warm (El Niño, red) and cold (La Niña, blue) phases are highlighted whenever the MEI gets larger than 1 or smaller than −1, respectively. The asterisk indicates that the trend is computed over the period where there are Ishii data available (2002–2012). Plots of other regions can be found in the SI Appendix.