Cenozoic evolution of deep ocean temperature from clumped isotope thermometry

Abstract

Characterizing past climate states is crucial for understanding the future consequences of ongoing greenhouse gas emissions. Here, we revisit the benchmark time series for deep ocean temperature across the past 65 million years using clumped isotope thermometry. Our temperature estimates from the deep Atlantic Ocean are overall much warmer compared with oxygen isotope–based reconstructions, highlighting the likely influence of changes in deep ocean pH and/or seawater oxygen isotope composition on classical oxygen isotope records of the Cenozoic. In addition, our data reveal previously unrecognized large swings in deep ocean temperature during early Eocene acute greenhouse warmth. Our results call for a reassessment of the Cenozoic history of ocean temperatures to achieve a more accurate understanding of the nature of climatic responses to tectonic events and variable greenhouse forcing.

Temperature Dependence of Clumped Isotopes (∆47) in Aragonite

“…The ∼1.5°C difference in reconstructed temperature between the calibrations in the low temperature range (<30°C) may seem trivial and requires the complete A. islandica data set (N = 278; see Figure 3) to resolve. However, in paleoclimate reconstructions (e.g., Agterhuis et al, 2022;de Winter, Müller et al, 2021;de Winter et al, 2017;Meckler et al, 2022;Petersen et al, 2016;Vickers, Fernandez, et al, 2020), this temperature offset may have significant consequences. A ∼1.5°C cold bias in temperature reconstructions may lead to a significant underestimation of climate sensitivity to CO 2 forcing, biasing the physical science basis for informing policymakers about future climate change (e.g., Dennis et al, 2013;IPCC, 2021;Modestou et al, 2020;Tierney et al, 2020;Westerhold et al, 2020).…”

Cenozoic Antarctic Peninsula Temperatures and Glacial Erosion Signals From a Multi‐Proxy Biomarker Study

“…However, mismatches between deep ocean δ 18 O and pCO 2 have been noted, with Oligocene warmth presenting a conundrum (O'Brien et al, 2020). Progress on separating deep ocean temperature and ice volume variables, using Mg/Ca (Lear et al, 2000(Lear et al, , 2015 and later using clumped isotope paleothermometry, found warm deep ocean temperatures persist longer than thought, with temperatures of 5°C-10°C recorded across the Oligocene and Miocene (Meckler et al, 2022). Antarctic temperature reconstructions are vital to understand local climate-cryosphere coupling; however, accessing sedimentary archives remains challenging (e.g., McKay et al, 2022).…”

Temperature dependence of clumped isotopes (∆47) in aragonite

“…However, our highly temperature-controlled A. islandica datapoints reveal that, despite uncertainty on formation temperature, the Meinicke et al (2021) The ∼1.5°C difference in reconstructed temperature between the calibrations in the low temperature range (<30°C) may seem trivial and requires the complete A. islandica data set (N = 278; see Figure 3) to resolve. However, in paleoclimate reconstructions (e.g., Agterhuis et al, 2022;de Winter, Müller et al, 2021;de Winter et al, 2017;Meckler et al, 2022;Petersen et al, 2016;Vickers, Fernandez, et al, 2020), this temperature offset may have significant consequences. A ∼1.5°C cold bias in temperature reconstructions may lead to a significant underestimation of climate sensitivity to CO 2 forcing, biasing the physical science basis for informing policymakers about future climate change (e.g., Dennis et al, 2013;IPCC, 2021;Modestou et al, 2020;Tierney et al, 2020;Westerhold et al, 2020).…”

“…The latter represents an improvement over the often-used oxygen isotope paleothermometer (δ 18 O), which requires knowledge of the oxygen isotope composition of the precipitation fluid (δ 18 O w ; e.g., Epstein et al, 1953;Kim & O'Neil, 1997). The clumped isotope method has many applications, notably to reconstruct absolute temperature variability throughout Earth's history (e.g., Agterhuis et al, 2022;de Winter, Müller et al, 2021;Meckler et al, 2022;Henkes et al, 2018;Rodríguez-Sanz et al, 2017;Vickers, Lengger, et al, 2020).…”