Equatorial Pacific Export Production over the Middle Miocene Climate Transition

Abstract:

The Middle Miocene Climate Transition (MMCT) at ~13.8 Ma marks the point when Earth made its final transition to the icehouse conditions of the Pleistocene (see Tian et al., 2013). Prior to the MMCT, the Middle Miocene Climate Optimum (MCO) is characterized by relatively high levels of pCO₂ in the atmosphere (350-400 ppm; Foster et al., 2012). Across the MMCT, there is rapid cooling and a decrease in pCO₂ levels (down to 260-200 ppm; Foster et al., 2012). As present day atmospheric pCO₂ reaches levels similar to those in the MCO, understanding the sensitivity of the climate system to external forcing during times of high pCO₂ becomes even more crucial. Accordingly, a high resolution (<5 kyr) record of export production in the eastern equatorial Pacific at IODP Site U1337 was produced spanning 14.1-13.5 Ma using marine barite accumulation rates (BAR) following Paytan et el. (1993). This site is estimated to have been at ~3900 m depth at 15 Ma and was within the paleoequatorial band throughout the middle Miocene (Expedition 320/321 Scientists, 2010). The age model was created by Tian et al. (2013) from the spliced section by tuning the benthic δ¹⁸O from U1337 to the obliquity of the astronomical solution of Laskar et al. (2004). Using this age model, ~200 samples were selected from Site U1337 and a record of export production was constructed. BAR fluctuates dramatically across this interval, from peaks of over 20 mg/cm²·kyr to less than 1 mg/cm²·kyr. The results from this study are compared with previously published δ¹⁸O and δ¹³C records (Tian et al., 2013) from the same core at a similar temporal resolution. This data will give us valuable insight into controls on the carbon cycle, including relationships with orbital parameters over intervals of rapidly changing climate.