Sea Level Budgets Should Account for Ocean Bottom Deformation

Abstract

The conventional sea level budget (SLB) equates changes in sea surface height with the sum of ocean mass and steric change, where solid-Earth movements are included as corrections but limited to the impact of glacial isostatic adjustment. However, changes in ocean mass load also deform the ocean bottom elastically. Until the early 2000s, ocean mass change was relatively small, translating into negligible elastic ocean bottom deformation (OBD), hence neglected in the SLB equation. However, recently ocean mass has increased rapidly; hence, OBD is no longer negligible and likely of similar magnitude to the deep steric sea level contribution. Here, we use a mass-volume framework, which allows the ocean bottom to respond to mass load, to derive a SLB equation that includes OBD. We discuss the theoretical appearance of OBD in the SLB equation and its implications for the global SLB.

Keywords: GRACE; altimetry; ocean bottom deformation; sea level budget; solid‐Earth response; steric.

Figure 1

The sea level budget including ocean bottom deformation: (a) schematic diagram of a column of the Earth's solid and fluid envelope. The initial (dashed) and final (solid) state of the ocean bottom (orange) and sea surface (blue); (b) SSH trend from ESA SLCCI altimetry product; (c) steric sea level trend from ensemble mean of four steric data products; (d) ocean mass sea level trend from JPL GRACE Release 06 data; and (e) the OBD trend calculated from our approach. All the maps have been filtered with a 1,000‐km half‐width Gaussian filter and masked over land $+$300‐km buffer for visualization purposes.