Global change across the Oligocene-Miocene transition: High-resolution stable isotope records from IODP Site U1334 (equatorial Pacific Ocean)

Abstract

The Oligocene-Miocene transition (OMT) (~23 Ma) is interpreted as a transient global cooling event, associated with a large-scale Antarctic ice sheet expansion. Here we present a 2.23 Myr long high-resolution (~3 kyr) benthic foraminiferal oxygen and carbon isotope (δ 18 O and δ 13 C) record from Integrated Ocean Drilling Program Site U1334 (eastern equatorial Pacific Ocean), covering the interval from 21.91 to 24.14 Ma. To date, five other high-resolution benthic foraminiferal stable isotope stratigraphies across this time interval have been published, showing a~1‰ increase in benthic foraminiferal δ 18 O across the OMT. However, these records are still few and spatially limited and no clear understanding exists of the global versus local imprints. We show that trends and the amplitudes of change are similar at Site U1334 as in other high-resolution stable isotope records, suggesting that these represent global deep water signals. We create a benthic foraminiferal stable isotope stack across the OMT by combining Site U1334 with records from ODP Sites 926, 929, 1090, 1264, and 1218 to best approximate the global signal. We find that isotopic gradients between sites indicate interbasinal and intrabasinal variabilities in deep water masses and, in particular, note an offset between the equatorial Atlantic and the equatorial Pacific, suggesting that a distinct temperature gradient was present during the OMT between these deep water masses at low latitudes. A convergence in the δ 18 O values between infaunal and epifaunal species occurs between 22.8 and 23.2 Ma, associated with the maximum δ 18 O excursion at the OMT, suggesting climatic changes associated with the OMT had an effect on interspecies offsets of benthic foraminifera. Our data indicate a maximum glacioeustatic sea level change of 50 m across the OMT.

Evolution of the early Antarctic ice ages

“…These intervals are contemporaneous with 405-ky eccentricity maxima during ∼2.4-My eccentricity maxima, specifically 405-ky Cycles 73, 68, 57, and 49. Thus, although the OMT deserves its status as a major transient Cenozoic event (1,20) because it is a prominent but transient glacial episode that abruptly terminates Late Oligocene warming, the amplitude of ice age cycles observed as the climate system emerges from peak glacial OMT conditions is not unique in the Oligo-Miocene. In fact, this recovery phase of the OMT is one of four Oligo-Miocene intervals characterized by particularly high-amplitude ∼110-ky oscillations between glacial and interglacial Antarctic conditions (Fig.…”

A comparison of two astronomical tuning approaches for the Oligocene-Miocene Transition from Pacific Ocean Site U1334 and implications for the carbon cycle

“…3). These 221 frequencies broadly correspond to those found in the benthic δ 18 O and δ 13 C depth 222 series at 0.15 cycles/m and 0.65 cycles/m [Beddow et al, 2016]. Smaller spectral 223 peaks are present in the CaCO 3 content record at 1.83 cycles/m and 2.8 cycles/m (Fig.…”

“…3). After the boundary, both δ 18 O and δ 13 C values show higher amplitude variability, and 216 a shift towards more positive values [Beddow et al, 2016]. 217 218…”

“…We use AnalySeries [Paillard et al, 1996] to conduct spectral analyses on the benthic 169 foraminiferal δ 13 C and δ 18 O and the CaCO 3 datasets in the depth domain, on the 170 magnetostratigraphic age model [Beddow et al, 2016], and on both astronomically 171 tuned age model options presented here. Prior to analysis, the data were re-sampled 172…”

“…This 164 magnetostratigraphic age model yields an initial duration of ~21.9 to 24.1 Ma for the 165 study interval (Fig. 3) [Channell et al, 2013;Beddow et al, 2016]. 166 167…”