Abstract
The early Paleogene represents the most recent interval in Earth's history characterized by global greenhouse warmth on multi-million year timescales, yet our understanding of long-term climate and carbon cycle evolution in the low latitudes, and in particular the Indian Ocean, remains very poorly constrained. Here we present the first long-term sub-eccentricity-resolution stable isotope (δ13C and δ18O) and trace element (Mg/Ca and B/Ca) records spanning the late Paleocene–early Eocene (∼58–53 Ma) across a surface–deep hydrographic reconstruction of the northern Indian Ocean, resolving late Paleocene 405-kyr paced cyclicity and a portion of the PETM recovery. Our new records reveal a long-term warming of ∼4–5°C at all depths in the water column, with absolute surface ocean temperatures and magnitudes of warming comparable to the low latitude Pacific. As a result of warming, we observe a long-term increase in δ18Osw of the mixed layer, implying an increase in net evaporation. We also observe a collapse in the temperature gradient between mixed layer- and thermocline-dwelling species from ∼57–54 Ma, potentially due to either the development of a more homogeneous water column with a thicker mixed layer, or depth migration of the Morozovella in response to warming. Synchronous warming at both low and high latitudes, along with decreasing B/Ca ratios in planktic foraminifera indicating a decrease in ocean pH and/or increasing dissolved inorganic carbon, suggest that global climate was forced by rising atmospheric CO2 concentrations during this time.
Highlights
The early Paleogene has emerged as the subject of much interest as it represents the most recent interval in Earth’s history characterized by sustained global greenhouse warmth, and was punctuated by transient warming events termed “hyperther-mals”, which may represent the closest analogues for future anthropogenic climate change
This study focuses on creating sub-eccentricity-resolution trace element and stable isotope records spanning the late Paleocene– early Eocene (∼58–53 Ma) from a new splice developed between International Ocean Discovery Program (IODP) Site U1443 and
Paleocene–Eocene sediment cores characterized by higher sedimentation rates and greater stratigraphic completeness have been recovered from the Atlantic, Pacific and Southern oceans, IODP Site U1443 and Ocean Drilling Program (ODP) Site 758 were chosen to shed new light on the paleoclimatic and paleoceanographic evolution of the poorly studied low latitude Indian Ocean, to identify if the temperature and carbonate chemistry trends observed in contemporaneous records from the low latitude Atlantic and Pacific oceans are global in scale
Summary
The early Paleogene has emerged as the subject of much interest as it represents the most recent interval in Earth’s history characterized by sustained global greenhouse warmth, and was punctuated by transient warming events termed “hyperther-mals”, which may represent the closest analogues for future anthropogenic climate change. Paired foraminiferal Mg/Ca and B/Ca data have emerged as promising proxies for unraveling the coupled temperature and carbonate chemistry [related to pH and dissolved inorganic carbon (DIC)] characteristics of the portion of the water column inhabited by foraminifera (e.g., Penman et al, 2014; Babila et al, 2016) These proxies have been extensively and successfully applied to understand temperature and carbonate chemistry changes during Plio-Pleistocene glacial-interglacial cycles using extant planktic foraminiferal species, where the species-specific relationship between trace element data and seawater characteristics has been constrained by laboratory culture experiments (e.g., Evans et al, 2016a, 2016b; Haynes et al, 2019), sediment trap studies (e.g., Anand et al, 2003; Gray et al, 2018), and core-top analyses (e.g., Brown et al, 2011; Stainbank et al, 2019). In the past few years, significant advances have been made in our understanding of the evolution of these variables during the Cenozoic and how foraminiferal Mg/Ca and B/Ca proxy sensitivities would have responded to them (e.g., Lemarchand et al, 2002; Allen et al, 2011, 2012; Evans et al, 2016a, 2016b, 2018; Babila et al, 2018; Haynes et al, 2019; Zeebe and Tyrrell, 2019), extending the utility of these geochemical proxies back into the greenhouse world of the early Paleogene
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