The impact of the annual continental water-storage cycle on coastal sea-level variations

Author: M.E. Tamisiea, Emma M. Hill, Rui M. Ponte, J.L. Davis, K.J. Horsburgh, T. Howard and S. J. Holgate
December 1, 2007
AGU Fall Meeting, San Francisco

Tamisiea, M.E., E.M. Hill, R. M. Ponte, J. L. Davis, K. J. Horsburgh, S. J. Holgate, T. Howard, 2007. The impact of the annual continental water-storage cycle on coastal sea-level variations, AGU Fall Meeting, San Francisco, December 2007, invited.

Geographic variations in coastal sea-level change, as observed by tide gauges, are driven not only by ocean dynamics and freshwater flux, but also crustal motion and equipotential height variations caused by varying mass loads on the continents. These patterns of sea-level change have been used in the past to infer the mass balance of the large ice sheets. However, GRACE observations suggest that even larger amplitude geographic variations may be produced on shorter time scales by mass changes associated with the hydrological cycle. In this talk, we examine the impact of the hydrological cycle on tide-gauge observations, focusing only on the static variations in sea level. Previous studies have shown that the non-steric, globally-averaged, annual sea-level change is primarily due to mass exchange between the continents and the oceans. This does not imply, though, that the sea level varies uniformly. Indeed, large regional variations in this signal exist along the coasts, depending upon the phase difference between the local water storage cycle and the mean global ocean signal. During late summer, when the annual ocean cycle is at its maximum and the water stored in most of the Northern Hemisphere is at a minimum, the local crustal uplift and equipotential subsidence due to the decrease of mass in the northern latitudes cancels the impact of the increase water volume in the oceans. However, when the ocean signal and hydrological signal are in phase, the loading effects and increased mean sea level contribute to a sea-level annual cycle amplitude of up to 20~mm. In particular, we focus on regions where this signal is the largest, such as the Bay of Bengal and the South China Sea. The results also demonstrate the importance of not assimilating the entire signal present in tide-gauge records into ocean models.