Assessment of ocean bottom pressure variations in CMIP6 HighResMIP simulations

Abstract

Ocean bottom pressure (<em>p</em>_b) variations from highresolution climate model simulations under the CMIP6 (Coupled Model Intercomparison Project Phase 6) HighResMIP protocol are potentially useful for oceanographic and spacegeodetic research, but the overall signal content and accuracy of these <em>p</em>_b estimates have hitherto not been assessed. Here, we compute monthly <em>p</em>_b fields from five CMIP6 High-ResMIP models at 1=4° grid spacing over both historical and future time spans and compare these data, in terms of temporal variance, against observation-based <em>p</em>_b estimates from a 1=4° downscaled GRACE (Gravity Recovery and Climate Experiment) product and 23 bottom pressure recorders, mostly in the Pacific. The model results are qualitatively and quantitatively similar to the GRACE-based <em>p</em>_b variances, featuring – aside from eddy imprints – elevated amplitudes on continental shelves and in major abyssal plains of the Southern Ocean. Modeled <em>p</em>_b variance in these regions is ~ 10 %–80 % higher and thus overestimated compared to GRACE, whereas underestimation relative to GRACE and the bottom pressure recorders prevails in more quiescent deep-ocean regions. We also form variance ratios of detrended <em>p</em>_b signals over 2030–2049 under a high-emission scenario relative to 1980–1999 for three selected models and find statistically significant increases in future <em>p</em>_b variance by ~ 30 %–50 % across deep Arctic basins and the southern South Atlantic. The strengthening appears to be linked to projected changes in high-latitude surface winds and, in the case of the South Atlantic, intensified eddy kinetic energy. The study thus points to possibly new pathways for relating observed <em>p</em>_b variability from (future) satellite gravimetry missions to anthropogenic climate change.