Astronomical tunings of the Oligocene–Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle

Abstract

Abstract. Astronomical tuning of sediment sequences requires both unambiguous cycle pattern recognition in climate proxy records and astronomical solutions, as well as independent information about the phase relationship between these two. Here we present two different astronomically tuned age models for the Oligocene-Miocene transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning has on astronomically calibrated ages and the geologic timescale. These alternative age models (roughly from ∼ 22 to ∼ 24 Ma) are based on different tunings between proxy records and eccentricity: the first age model is based on an aligning CaCO 3 weight (wt%) to Earth's orbital eccentricity, and the second age model is based on a direct age calibration of benthic foraminiferal stable carbon isotope ratios (δ 13 C) to eccentricity. To independently test which tuned age model and associated tuning assumptions are in best agreement with independent ages based on tectonic plate-pair spreading rates, we assign the tuned ages to magnetostratigraphic reversals identified in deep-marine magnetic anomaly profiles. Subsequently, we compute tectonic plate-pair spreading rates based on the tuned ages. The resultant alternative spreading-rate histories indicate that the CaCO 3 tuned age model is most consistent with a conservative assumption of constant, or linearly changing, spreading rates. The CaCO 3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n-C7n.1r, which are not based on astronomical tuning in the latest iteration of the geologic timescale. Furthermore, it provides independent evidence that the relatively large (several 10 000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity constitute a real feature of the OligoceneMiocene climate system and carbon cycle. The age constraints from Site U1334 thus indicate that the delayed responses of the Oligocene-Miocene climate-cryosphere system and (marine) carbon cycle resulted from highly nonlinear feedbacks to astronomical forcing.

High-latitude biomes and rock weathering mediate climate–carbon cycle feedbacks on eccentricity timescales

“…Their overall in-phase behaviour at 100-kyr time scales is characterized by an average lag of δ 13 C compared to δ 18 O of 1.9 kyr (0.12 rad) in Interval I, and 2.5 kyr (0.16 rad) in Interval II. This small but noticeable phase lag of δ 13 C has been observed before 10,49,50 and explained by thẽ 65 kyr residence time of carbon in the ocean 9,51 . The large size of the ocean carbon reservoir, in combination with a non-linear climate response to precessional forcing, causes the response time of the carbon cycle to eccentricity to be several thousand years slower than that of the climate-cryosphere system.…”

“…All Sites that constitute the δ 13 C megasplice are included here (references in Fig. 1 ) and are complemented by additional orbital-resolution benthic isotope data from Sites 926 82 , 982 83 , 1264/1265 15 , 49 , U1334 50 , 84 , U1337 17 and U1338 6 , 85 (data as time-series in Supplementary Fig. 3 ).…”

A review of the importance of the Caribbean region in Oligo-Miocene low latitude planktonic foraminiferal biostratigraphy and the implications for modern biogeochronological schemes

“…A reassessment of the range charts from key biozonations has also been undertaken in order to determine whether certain bioevents were recognisable. A number of potential amendments to the low latitude biogeochronology of Wade et al (2011) have been suggested based upon the historical importance of certain bioevents, as well as updating the Miocene component to more recent magnetochronologies (Kochhann et al, 2016;Ogg et al, 2016;Drury et al, 2017;Beddow et al, 2018) and astronomically tuned records (Wilkens et al, 2017).…”

Astronomical Time Keeping of Earth History: An Invaluable Contribution of Scientific Ocean Drilling

“…This tuning has been confirmed at the ~400 kyr eccentricity level using sedimentary records from the Atlantic Ocean, including ODP Leg 177 (Billups et al, 2004), ODP Leg 154 (Pälike et al, 2006a), ODP Leg 208 (Liebrand et al, 2016), and IODP Expedition 342 (Van Peer et al, 2017). A more recent eccentricity-tuned record from the equatorial Pacific (IODP Expedition 320/321; Beddow et al, 2018) confirmed the accuracy of the numerical ages across the Oligocene-Miocene transition to the ~100 kyr eccentricity level.…”

“…ice sheet, preceding the transient cooling and "re-glaciation" of Antarctica across the Oligocene-Miocene climatic transition (OMT; 23 million years ago; Billups et al, 2004;Pälike et al, 2006b;Liebrand et al, 2016;Beddow et al, 2018).…”