Temperature gradients across the Pacific Ocean during the middle Miocene

• Main Authors: Fox, LR, Wade, BS, Holbourn, A, Leng, MJ, Bhatia, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2021
• Subjects: middle Miocene; equatorial Pacific Ocean; SST's; planktonic foraminifera; Mg/Ca; stable isotopes; Antarctic; The Antarctic; Pacific; Antarc*; Ice Sheet; Planktonic foraminifera
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10129766/8/Fox%20et%20al%202021.pdf; https://discovery.ucl.ac.uk/id/eprint/10129766/

Sea surface temperatures (SSTs) of the tropical Pacific Ocean exert powerful controls on regional and global climates. Previous studies have suggested that during warm climate phases, the east-west temperature gradient collapsed. To date, there has been no high-resolution reconstruction of sea surface conditions in both the east and west Pacific Ocean during the Miocene Climate Optimum (MCO) and across the middle Miocene climate transition (MMCT); therefore, our understanding of the mean oceanographic state during this major global climatic shift is limited. Here, we present new SST reconstructions for the eastern Pacific Ocean (15.5–13.3 Ma) which show a clear east-west temperature gradient of ∼4°C during the warmest interval of the Neogene, implying that the oceanographic processes that produce the modern gradient were present and active. There is no shift in the east-west gradient across the MMCT indicating that the gradient was not impacted by global cooling and ice growth. We find a 2°C sea surface cooling in the eastern equatorial Pacific, that lags the benthic foraminiferal δ^{18}O positive shift by 150 kyr, indicating that tropical temperature did not decrease synchronously with the expansion of the Antarctic ice sheet. Reconstructed variations in the δ^{18}O composition of seawater, determined by combining our Mg/Ca and δ^{18}O records, reveal a freshening in the eastern Pacific Ocean after 13.8 Ma, suggesting changes in the hydrological cycle and in tropical fronts in response to the new icehouse regime.