406 / 2024-09-16 14:00:31

The east Pacific Oxygen Minimum Zone during the Pliocene

Oxygen Minimum Zone, Pliocene, trace metals, stable isotopes, planktic foraminifera, porosity, East Equatorial Pacific

Global climate during the Pliocene (5.33-2.58 Ma) was similar or even warmer than today’s climate such that this period provides a potential analog on how future global climate change may look like. Although the Pliocene has been studied extensively, major gaps in our knowledge are still existing, specifically in the east Pacific. During the early Pliocene the east Pacific was likely warmer than today, the equatorial cold tongue did not exist yet and the Oxygen Minimum Zones (OMZ) may have been less intense or even absent. This overview attempts to look at the history of the OMZ in the east Pacific both on a long-term timescale, i.e. from the early Pliocene to after the onset of Northern Hemisphere Glaciation, and on a shorter, glacial-interglacial timescale. We reconstruct variability potentially related to the OMZ from several (I)ODP sites (Site U1338, Site 1236, Site 1241) using different foraminifera-based proxies. Changes in the stratification of the water column, related to upwelling intensity and ventilation, are reconstructed by temperature (Mg/Ca) and relative salinity (d¹⁸O_sw) analysed on Trilobatus sacculifer and Neogloboquadrina dutertrei representing different waterdepths. Nutrient utilization in the water column related to the upwelling of nutrients is reconstructed by nitrogen isotopes (d¹⁵N) determined on the shells of T. sacculifer and may be related to changes in the OMZ. Specific changes in the OMZ are reconstructed by the abundance of the planktic foraminifera Globorotaloides hexagonus and changes in the porosity of its shell showing a strong affinity with the OMZ. Our results suggest a strong control of changes in OMZ intensity by low-latitudinal insolation expressed by clear precession cyclicity in both the d¹⁵N and G. hexagonus records.