A Cool, Nutrient-Enriched Eastern Equatorial Pacific During the Mid-Pleistocene Transition

• Published in: Geophysical Research Letters
• Main Authors: Robinson, Rebecca S., Jones, Colin A., Kelly, Roger P., Rafter, Patrick, Etourneau, Johan, Martínez, Philippe
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2019
• Subjects: Pacific; Southern Ocean
• Online Access: http://hdl.handle.net/10261/203742; https://doi.org/10.1029/2018GL081315

The emergence of high‐amplitude, low‐frequency glacial‐interglacial cycles during the mid‐Pleistocene climate transition (MPT; 800–1,200 ka) is associated with global cooling. In the eastern equatorial Pacific, sea surface temperatures cooled, and the upwelling‐induced cold tongue expanded significantlyduringtheMPT.Hereweusesedimentaryrecordsofiron,biogenicsilica,andnutrient‐nitrogen consumption to evaluate biogeochemical changes hypothesized to accompany the cold tongue expansion. Our results suggest that the eastern equatorial Pacific of the MPT hosted surface waters with higher nitrate contents and biogenic silica production relative to the last 600 ka. Increased production occurred despite low iron supply. We attribute this to enhanced upwelling and nutrient enrichment of thermocline waters, both likely related to the northward migration of Southern Ocean fronts. The return of these fronts to their southward positions after the MPT may be associated with stronger drawdown of nutrients and, potentially, atmospheric CO2 in the Southern Ocean. This work was supported in part by NSF‐MGG (1060779) and USSSAC postcruisesupportforLeg202toR.S.R. We thank P. Rumford and the IODP Core repository for providing samples and assistance with XRF core scanning; K. Kelley for analytical assistance; and Z. Kerrigan, J. Freedman, and A. Stahl for the help with sample preparation. New data will be archived at the NCEI Paleoceanography Data Repository. National Science Foundation (US)