The Benthic B/Ca Record at Site 806: New Constraints on the Temperature of the West Pacific Warm Pool and the "El Padre" State in the Pliocene. Issue 10 (30th September 2020)

• Record Type: Journal Article
• Authors: White, S. M.; Ravelo, A. Christina
• Is Part Of: Paleoceanography and paleoclimatology. Volume 35:Issue 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-30
• Subjects: foraminifera -- Mg/Ca -- proxy -- Pliocene -- SST -- carbonate ion; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2019PA003812
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The West Pacific Warm Pool (WPWP)'s response to increased p CO2 during the Pliocene is a key model validation target. Different temperature proxies show different trends: The foraminiferal Mg/Ca sea surface temperature (SST) record shows Pliocene WPWP temperatures ~1.2°C cooler than today (Wara et al., 2005, https://doi.org/10.1126/science.1112596 ), whereas a TEX86 study finds a cooling trend and claims the Pliocene WPWP was warmer than today (Zhang et al., 2014, https://doi.org/10.1126/science.1246172 ). We focus on understanding biases in Mg/Ca data as the best way to constrain the temperature of the Pliocene WPWP. The strongest nonthermal controls on foraminiferal Mg/Ca are Mg/Ca of seawater and dissolution. Dissolution, which imparts a cool bias to Mg/Ca temperatures, depends on Δ[CO3 2− ], the difference from the carbonate ion concentration needed for calcite saturation. Thus, Pliocene proxy discrepancies might stem from varying Δ[CO3 2− ] over time. To constrain the effect of changing dissolution on the Mg/Ca data, we collected benthic foraminiferal B/Ca data (a proxy for Δ[CO3 2− ]) from the WPWP spanning 0–5.5 Ma. We find no long‐term trend in Δ[CO3 2− ], but variations above and below the threshold of foraminiferal dissolution yield an ~0.4°C cold bias when averaged over the middle to early Pliocene. Changes in seawater Mg/Ca create an ~0.6°C cold bias in the Pliocene Mg/Ca data. After accounting for these biases, we find that the Pliocene WPWP was ~0.1°C cooler than the late Holocene, ranging from −0.5°C to +0.5°C including all uncertainties. Our reconstruction shows a much lower east‐west temperature gradient in the Pliocene tropical Pacific than today, supporting a permanent El Niño‐like "El Padre" state. Key Points: Benthic foraminiferal B/Ca data from ODP 806 show no trend in deep sea [CO3 2− ], but variations yield an ~0.4°C cold bias in Mg/Ca Given bias from varying dissolution and seawater Mg/Ca, the Pliocene West Pacific Warm Pool was approximately the same temperature as the late Holocene The east‐west SST gradient in the tropical Pacific during the Pliocene was about half that of the late Holocene