Sea Level Budgets Should Account for Ocean Bottom Deformation.

B D Vishwakarma,J L Bamber,S Royston,R M Westaway,R E M Riva

doi:10.1029/2019gl086492

B D Vishwakarma, J L Bamber + Show 3 more

Open Access

https://doi.org/10.1029/2019gl086492

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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.

Highlights

Changes in sea surface height (SSH) can be explained by a combination of physical processes: the addition or removal of freshwater, change in ocean water volume, a change in ocean bottom topography, and ocean water redistribution driven by changes in the geoid and ocean circulation
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
We show that the new SLB equation is equivalent to the conventional SLB equation under the assumption that the elastic deformation of the ocean floor due to ocean mass change is negligible

Summary

Introduction

Changes in sea surface height (SSH) can be explained by a combination of physical processes: the addition or removal of freshwater (mass change), change in ocean water volume (steric change), a change in ocean bottom topography (bathymetry), and ocean water redistribution driven by changes in the geoid and ocean circulation (cf. Figure 1a). It has been shown that the theoretical elastic OBD due to changes in mass load since 1993 contributes approximately 0.13 mm/year (or 3–4%) to global-mean sea level change (Frederikse et al, 2017). This contribution is comparable in magnitude to the deep steric contribution, which has been identified as one of the top priorities in sea level research (Roemmich et al, 2019; WCRP, 2018). We discuss implications of this updated budget equation for SLB studies using various data products

The SLB Equation

Applying the Updated Budget Equation

Summary and Conclusion