Assessment of Ocean Bottom Pressure Variations in CMIP6 HighResMIP Simulations

Abstract. Ocean bottom pressure (p_b) variations from high-resolution climate model simulations under the CMIP6 (Coupled Model Intercomparison Project Phase 6) HighResMIP protocol are potentially useful for oceanographic and space-geodetic research, but the overall signal content and accuracy of these p_b estimates have hitherto not been assessed. Here we compute monthly p_b fields from five CMIP6 HighResMIP 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 p_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 p_b variances, featuring—aside from eddy imprints—elevated amplitudes on continental shelves and in major abyssal plains of the Southern Ocean. Modeled p_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 p_b signals over 2030–2049 under a high-emission scenario relative to 1980–1999 for three selected models and find statistically significant increases of future p_b variance by ∼30–50 % across the Arctic and in eddy-rich regions of the South Atlantic. The strengthening is consistent with projected changes in high-latitude surface winds and, in the case of the South Atlantic, intensified Agulhas leakage. The study thus points to possibly new pathways for relating observed p_b variability from (future) satellite gravimetry missions to anthropogenic climate change.