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

Abstract

The Miocene Climatic Optimum (MCO; similar to 16.9 to 14.7Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (O-18) and carbon (C-13) isotope records (5-12kyr time resolution) spanning the late early to middle Miocene interval (18 to 13Ma) 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 similar to 13.8Ma. 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 100kyr variability with 400kyr cyclicity additionally imprinted on C-13 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 similar to 3.4 to similar to 4km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (O-18 minima) and C-13 decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to C-13 maxima and O-18 minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.