Early Oligocene glaciation and productivity in the eastern equatorial Pacific: Insights into global carbon cycling

Abstract

The onset of sustained Antarctic glaciation across the Eocene‐Oligocene transition (EOT) marks a pivotal change in Earth's climate, but our understanding of this event, particularly the role of the carbon cycle, is limited. To help address this gap we present the following paleoceanographic proxy records from Ocean Drilling Program Site 1218 in the eastern equatorial Pacific (EEP): (1) stable isotope (δ18O and δ13C) records generated in epifaunal benthic foraminifera (Cibicidoides spp.) to improve (double the resolution) the previously published records; (2) δ18O and δ13C records measured on Oridorsalis umbonatus, a shallow infaunal species; and (3) a record of benthic foraminifera accumulation rate (BFAR). Our new isotope data sets confirm the existence at Site 1218 of a two‐step δ18O increase. They also lend support to the hypothesized existence of a late Eocene transient δ18O increase and early Oligocene Oi‐1a and Oi‐1b glacial maxima. Our record of BFAR indicates a transient (∼500 kyr) twofold to threefold peak relative to baseline Oligocene values associated with the onset of Antarctic glaciation that we attribute to enhanced biological export production in the EEP. This takes the same general form as the history of opal accumulation in the Southern Ocean, suggesting strong high‐to‐low‐latitude oceanic coupling. These findings appear to lend support to the idea that the EOT δ13C excursion is traceable to increased organic carbon (Corg) burial. Paradoxically, early Oligocene sediments in the EEP are extremely Corg‐poor, and proxy records of atmospheric pCO2 indicate a transient increase associated with the EOT.

Stratigraphic calibration of Oligocene–Miocene organic-walled dinoflagellate cysts from offshore Wilkes Land, East Antarctica, and a zonation proposal

“…At DSDP Site 511, the FO of Malvinia escutiana is correlative with the Oi-1 isotope excursion , thus occurring in the earliest Oligocene (e.g. Coxall and Wilson, 2011). On the basis of this calibration, we calibrate the base of Zone SODZ1 to the Oi-1 isotope excursion.…”

Bryozoan beds in northern Italy as a shallow-water expression of environmental changes during the Oligocene isotope event 1

“…In the eastern equatorial Pacific, the Eocene-Oligocene climate change did not trigger a major shift towards increased productivity, but there is evidence for a shortlived rise in productivity and export production associated to the onset of sustained Antarctic glaciation (Coxall and Wilson, 2011). The increase in benthic foraminifera accumulation rate in the eastern equatorial Pacific and coeval opal accumulation in the Southern Ocean suggest that there is a link between both sites (Coxall and Wilson, 2011), such as an intensification of thermohaline circulation as interpreted for the earliest Oligocene (Miller and Tucholke, 1983;Wright and Miller, 1993;Thomas et al, 2008;Cramer et al, 2009;Coxall and Wilson, 2011;Pusz et al, 2011).…”

“…Deep-sea records suggest an increase in ocean surface palaeoproductivity occurring coevally to the δ 18 O shift at the EOT, especially in the Southern Ocean but also in mid and low latitudes (DiesterHaass, 1996;Diester-Haass and Zahn, 1996;Salamy and Zachos, 1999;Diester-Haass and Zachos, 2003;Dunkley Jones et al, 2008;Wade and Pearson, 2008;Coxall and Wilson, 2011;Plancq et al, 2014;Villa et al, 2014). This change is characterized by an important increase in export production shown by an increase in accumulation rate of benthic and planktonic foraminifera, radiolarians, diatoms, fish debris, echinoderms, and ostracodes (Coxall and Pearson, 2007, and references therein).…”

“…Dashed part of the curves corresponds to a 50 cm thick interval not sampled because of severe drilling disturbance. Age model (5) is based on conversion to Site 1218 (Coxall and Wilson, 2011). Note that the prominent positive oxygen-isotope shift leading to the Oi-1 occurs at the base of magnetochron C13n, shortly before a prominent carbon-isotope shift.…”

“…The Oligocene isotope event 1 (Oi-1; Zachos et al, 1996;Katz et al, 2008;Miller et al, 2008Miller et al, , 2009), occurring at around 33.55 Ma, is characterized in deep-sea deposits by an up to 1‰ positive shift in δ 18 O. Despite advances made in recent years Miller et al, 2008Miller et al, , 2009Coxall and Wilson, 2011), little is known about the effect of the cooling associated to the Oi-1 in shallow-marine environments. On one hand, shallow-marine sedimentary records are incomplete in nature due to hiatuses and erosive processes.…”