Importance of self-attraction and loading in the annual cycle of ocean bottom pressure

Author: Nadya Vinogradova, Rui M. Ponte, M.E. Tamisiea, J.L. Davis and Emma M. Hill
December 1, 2009
AGU Fall Meeting, San Francisco

Vinogradova, N., R.M. Ponte, M.E. Tamisiea, J. Davis, and E.M. Hill, 2009. Importance of self-attraction and loading in the annual cycle of ocean bottom pressure. AGU Fall Meeting, San Francisco, December 2009.

The water cycle explains the average mass-flux component of the global mean annual cycle observed from altimetry. However, this water is not distributed uniformly throughout the ocean. When water is stored either in the atmosphere or on the continents, it causes both crustal deformations and changes in the equipotential surface of the oceans that lead to regional variations in sea level. These self-attraction and loading (SAL) effects cause the regional annual cycle to depend upon the balance between the local water storage and the background global average. In contrast to the mass flux's dominant contribution to the global average sea level, at any given point dynamic ocean signals are typically much larger than those that would be expected due to the mass flux. Bottom pressure variations, on the other hand, generally have smaller amplitude variations than sea level, and the SAL signal in bottom pressure can be as large as dynamic ocean signals. We compare the annual cycle inferred from bottom pressure recorders to an increasingly complex estimate derived from models: ocean dynamics from ECCO results, ECCO plus a globally-averaged mass flux estimate, and an estimate with full account of SAL effects. We demonstrate that, on average, the agreement with the observations improves with the increasing complexity of the model and conclude that interpreting ocean bottom pressure records requires accounting for the SAL effects.