MOLECULAR PROXIES RECORD TRENDS IN SOUTHERN OCEAN PALEOTEMPERATURES FOR THE CAMPANIAN THROUGH PALEOCENE

Gradual cooling characterizes the trend in Late Cretaceous climate for southern high latitudes, likely associated with the progressive breakup of Gondwana and widening of the Southern Ocean basin. However, a lack of high-resolution paleotemperature records has constrained assessment of factors controlling this cooling trend. Recovery of Campanian through Paleocene organic-rich sediments (~78 – 60 Ma) from the Transkei Basin (Hole U1581B), offshore South Africa, during IODP Expedition 392 now enables reconstruction of ocean paleotemperatures recording climatic evolution of the late Cretaceous Southern Ocean. Analysis of GDGTs originating from Nitrososphaerota and alkenones derived from haptophyte algae afforded temporal records for sea surface temperatures (SST) based on TEX₈₆ and U^K'₄₀ molecular proxies. U^K'₄₀ represents an analog of the U^K'₃₇ proxy based on the ratio of C₄₀ rather than C₃₇ di- and triunsaturated alken-2-ones. The coherence between TEX₈₆ and U^K'₄₀ supports the efficacy of the U^K'₄₀ as a Cretaceous temperature proxy and the high sedimentation rate of the sequence captures trends in SSTs. evidence for progressive cooling in the TEX₈₆ record is consistent with other temperature reconstructions for the late Cretaceous. In addition, SSTs stratigraphic profiles for the Transkei Basin reveals several discrete cooling steps during the late Campanian and at the Campanian-Maastrichtian boundary not previously observed for this time interval. Moreover, the location of Hole U1581B suggest that these data may help define the development of the Southern Ocean gyre, which likely influenced the gradual decrease in southern mid-to-high-latitude temperatures.