Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

Abstract

The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate‐carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (δ18O) and carbon (δ13C) isotope records (5–12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic Ice Sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity, and X‐ray fluorescence (XRF) scanner‐derived carbonate records from IODP Sites U1335, U1336, U1337, and U1338 on a consistent, astronomically tuned timescale. Benthic isotope and XRF scanner‐derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on δ13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with >75% carbonate loss occurring at paleodepths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (δ18O minima) and δ13C decreases, implying that climate‐carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial‐interglacial pattern, where dissolution maxima correspond to δ13C maxima and δ18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

Closing an early Miocene astronomical gap with Southern Ocean δ18O and δ13C records: Implications for sea level change

“…Arrow indicates stratotype for oxygen isotope Zone Mi2a defined here at a level 116.341 mcd (Figure ) and an age of 14.82 Ma where the maximum δ 18 O value occurs. (b) As in Figure a showing δ 18 O records from Sites 1337 (blue) [ Kochhann et al ., ] and 1338 (red) [ Holbourn et al ., ]. We spliced the records at 15.5 Ma (see text).…”

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

“…2), indicating that ∼ 90 % of the variability in the MS record is caused by changes in the bulk sediment CaCO 3 content. Middle Miocene CaCO 3 records from nearby Site U1335 show negatively skewed cycle shapes and have been interpreted as a dissolution-dominated signal (Herbert, 1994;Kochhann et al, 2016). In contrast, cycle shapes in the CaCO 3 content record for the Oligocene-Miocene of Site U1334 are less skewed, suggesting that here CaCO 3 content was predominantly controlled by a combination of productivity and dissolution.…”

“…The independent evidence that we provide for using a lithological (proxy) record for the astronomical age calibration of marine sediments yields further support for similar astronomical tuning methods. Examples are the middle Miocene (Kochhann et al, 2016) and Eocene-Oligocene (Westerhold et al, 2015) records from the equatorial Pacific Ocean and the Oligocene-Miocene records from the South Atlantic Ocean . We note, however, that these records show variable ratios of productivity to dissolution as the main source of variance in the data.…”

“…These studies used lithological data, such as elemental estimates based on X-ray fluorescence (XRF) core scanning records, as the sole tuning signal. The records from both these sites are characterized by a clear expression of eccentricity, either resulting from productivity-dominated cycles (at Site 1264; Liebrand et al, 2016) or dissolution-dominated cycles (at Site U1335; Kochhann et al, 2016). The general phase relationships between the ∼ 110 kyr cycles and 405 kyr cycles (in the case of Site U1335) in lithologic records and the stable eccentricity solution for this interval (Laskar et al, 2011a, b), i.e.…”

“…The general phase relationships between the ∼ 110 kyr cycles and 405 kyr cycles (in the case of Site U1335) in lithologic records and the stable eccentricity solution for this interval (Laskar et al, 2011a, b), i.e. whether maxima in signal curve correspond to minima or maxima in the target curve, were straightforward to derive Kochhann et al, 2016). These broadscale phase relationships were in agreement with those previously derived using benthic foraminiferal δ 18 O and δ 13 C records (e.g.…”