Evaporative fractionation of H₂¹⁸O in the polar ocean and the invisibility of large changes of ice volume and sea level in the Saalian δ¹⁸O proxy records

Abstract. The oxygen isotope ratio, δ¹⁸O, as measured in skeletons of oceanic foraminifera, is a proxy for changes in world glacial ice volume and sea level and is of fundamental importance in the study of past climate change. However, in the Late Saalian glaciation the δ¹⁸O proxy reflects neither a large increase in glacial ice volume from 155 ka–142 ka nor the subsequent major deglaciation from 142 ka–136.5 ka in which sea level rose from about −140 m to +4 m at the end of the Drenthe sub stage. This deglaciation was caused by a large reduction in the ice sheet moisture supply due to storm path diversion associated with the loss of thermohaline circulation and the capping of the high latitude North Atlantic with melt water that passed through the Mediterranean Sea from the overflow of a giant ice-blocked Siberian lake. The δ¹⁸O proxy also fails to record the subsequent ice volume buildup of the Warthe substage in which sea level fell about 80 m. The explanation for the invisibility involves the fractionation and sequestration of large mounts of H₂¹⁸O in the effectively isolated and sea-ice-free polar ocean. The sequestration and subsequent release of polar water, enriched in H₂¹⁸O, distorted the fractionation record in the world ocean and destroyed the accuracy of the δ¹⁸O proxy. The proposed physical consequences of the ice-free polar ocean also include a sea-ice-free Labrador Sea and Baffin Bay and an oceanic circulation mode that drove the Drenthe substage glaciation to its maximum extent in Eurasia. The initial cause for the anomalous effects in the δ¹⁸O record was the known ice-flow blockage of all the Siberian rivers that discharge into the polar ocean west of the Lena River. Without adequate stratification by inflowing fresh river water, sea ice was unable to freeze on the deep polar ocean and the fractionation and the physical changes in the polar ocean that are proposed here followed.