Deep ocean temperatures through time

Abstract. Benthic oxygen isotope records are commonly used as a proxy for global mean surface temperatures during the Late Cretaceous and Cenozoic, resulting estimates have been extensively in characterizing major trends transitions climate system analysing past sensitivity. However, some fundamental assumptions governing this rarely tested. Two key (a) benthic foraminiferal geographically well mixed linked to high-latitude temperatures, (b) correlated with temperatures. To investigate robustness of these through geological time, we performed series 109 model simulations using unique set paleogeographical reconstructions covering entire Phanerozoic at stage level. The run least 5000 years ensure that deep ocean is dynamic equilibrium. We find correlation between good thus data reliable indicators time period, albeit standard error 2 K. This uncertainty has not normally assessed needs be combined other sources when, instance, estimating sensitivity based on ?18O measurements from foraminifera. temperature becomes weaker pre-Cenozoic periods (when paleogeography significantly different present day). reasons include variability source region water (varying hemispheres but also varying latitudes sinking), depth overturning (some extreme warm climates relatively shallow sluggish circulations weakening link ocean), extent polar amplification (e.g. ice albedo feedbacks). Deep sediments prior rare, so extending foraminifera further into deeper problematic, results presented here would suggest such probably an unreliable indicator conditions.