Felix W. Landerer

Regional Dynamic and Steric Sea Level Change in Response to the IPCC-A1B Scenario

This paper analyzes regional sea level changes in a climate change simulation using the Max Planck Institute for Meteorology (MPI) coupled atmosphere–ocean general circulation model ECHAM5/MPI-OM. The climate change scenario builds on observed atmospheric greenhouse gas (GHG) concentrations from 1860 to 2000, followed by the International Panel on Climate Change (IPCC) A1B climate change scenario until 2100; from 2100 to 2199, GHG concentrations are fixed at the 2100 level. As compared with the unperturbed control climate, global sea level rises 0.26 m by 2100, and 0.56 m by 2199 through steric expansion; eustatic changes are not included in this simulation. The model’s sea level evolves substantially differently among ocean basins. Sea level rise is strongest in the Arctic Ocean, from enhanced freshwater input from precipitation and continental runoff, and weakest in the Southern Ocean, because of compensation of steric changes through dynamic sea surface height (SSH) adjustments. In the North Atlantic Ocean (NA), a complex tripole SSH pattern across the subtropical to subpolar gyre front evolves, which is consistent with a northward shift of the NA current. On interannual to decadal time scales, the SSH difference between Bermuda and the Labrador Sea correlates highly with the combined baroclinic gyre transport in the NA but only weakly with the meridional overturning circulation (MOC) and, thus, does not allow for estimates of the MOC on these time scales. Bottom pressure increases over shelf areas by up to 0.45 m (water column equivalent) and decreases over the Atlantic section in the Southern Ocean by up to 0.20 m. The separate evaluation of thermosteric and halosteric sea level changes shows that thermosteric anomalies are positive over most of the World Ocean. Because of increased atmospheric moisture transport from low to high latitudes, halosteric anomalies are negative in the subtropical NA and partly compensate thermosteric anomalies, but are positive in the Arctic Ocean and add to thermosteric anomalies. The vertical distribution of thermosteric and halosteric anomalies is highly nonuniform among ocean basins, reaching deeper than 3000 m in the Southern Ocean, down to 2200 m in the North Atlantic, and only to depths of 500 m in the Pacific Ocean by the end of the twenty-first century.

Long‐term polar motion excited by ocean thermal expansion

[1] Ocean warming is commonly considered unable to excite significant long-term trends in polar motion. Here, however, we argue that this assumption needs to be revised. We demonstrate that steric sea level rise leads to a distinct pattern of horizontal mass redistribution within ocean basins and hence to ocean bottom pressure changes that alter Earth’s inertia tensor on decadal and longer time scales. Based on Earth system model simulations, we estimate that ocean warming leads to polar motion of 0.15 to 0.20 milliarcseconds per one millimeter of thermal sea level rise. This is equivalent to a polar motion rate of about 0.47 milliarcseconds per year towards 155W to 160W for current projections of steric sea level rise during the 21st century. The proposed polar motion signal is therefore not negligible in comparison to other decadal and secular signals, and should be accounted for in the interpretation of polar motion observations. Citation: Landerer, F. W., J. H. Jungclaus, and J. Marotzke (2009), Long-term polar motion excited by ocean thermal expansion, Geophys. Res. Lett., 36, L17603,