Cenozoic sea-level and cryospheric evolution from deep-sea geochemical and continental margin records

Abstract

<p>Cenozoic (past ~66 Myr) sea-level history reflects temperature changes and cryospheric evolution of the Earth from essentially ice-free conditions in the Early Eocene to bipolar ice sheets in the Quaternary. We derived a global mean sea level (GMSL) estimate for the Cenozoic using a new astronomically calibrated Pacific benthic foraminiferal δ<sup>18</sup>O splice from published records and a 2 Myr-smoothed Pacific bottom water temperature record based on published benthic foraminiferal Mg/Ca data. Our GMSL estimates are similar to sea-level estimates derived from “backstripping” (progressively accounting for compaction, loading and thermal subsidence) of cores from the mid-Atlantic U.S. continental margin. Peak global warmth, elevated GMSL, high CO<sub>2</sub>, and largely ice-free conditions occurred during the Early Eocene “Hothouse.” During the Middle-Late Eocene “Cool Greenhouse,” small ice sheets associated with lower atmospheric CO<sub>2</sub> drove sea-level changes. Continental-scale ice sheets began in the Oligocene “Icehouse” (ca. 34 Ma), a permanent East Antarctic ice sheet began in the middle Middle Miocene (ca. 12.8 Ma), and full, bipolar glaciation began in the Quaternary (ca. 2.55 Ma). The Last Glacial Maximum (20-27 ka) was the largest lowering of GMSL (~130 m) of the Mesozoic-Cenozoic and GMSL rise during last deglaciation (ca. 19-10 ka) exceeded 40-45 mm/yr.  Sea-level rise progressively slowed from 10 ka to 2 ka and was then at stillstand until late 19<sup>th</sup> to early 20<sup>th</sup> century when rates began to rise. Despite large uncertainties in proxies, our study reaffirms that throughout the Cenozoic, high long-term (10<sup>7</sup>-year scale) CO<sub>2</sub> was associated with warm climates and high sea levels.  However, sea level-change was dominated by periodic, astronomically controlled (10’s kyr-Myr scale) Milankovitch variations superimposed upon longer-term changes driven by CO<sub>2</sub>.</p>

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