Interannual Changes in Earth's Dynamic Oblateness (J2): A Metric for Non-Steric Sea Level Rise?

Recent findings regarding changes in the heat content of the global oceans (Lyman et al., 2006) have suggested that the planetary radiative balance may fluctuate and even change sign on interannual time scales. At the same time global general circulation models, and time series of altimeter-determined global sea level, do not appear to reflect the same degree of interannual variability as suggested by the heat content observations. A possible means to reconcile the observational discrepancy is through variations in the rate of non-steric sea level rise induced by transfers of water mass between land ice reservoirs and the global ocean. In this work, we use time series of the Earth's dynamic oblateness (J2) as an independent metric of the redistribution of mass between high and low latitudes. When properly corrected for atmospheric, oceanic and hydrological mass exchange / redistribution and tidal effects, the J2 residual can provide an independent constraint on mass transfers between high latitude land ice and the global ocean. While the long-term rate of land ice ablation cannot be directly determined due to contamination of the J2 signal by post-glacial rebound, interannual fluctuations in high-latitude ice mass balance can be addressed by this method (Dickey et al., 2002). We will assess the uncertainties in this metric of land ice ablation and its relevance for understanding changes in the ocean's heat and mass balances during recent years.