Description: Sampling and Analyzing Method: Acarininid shells were cast in epoxy, ground to midsection and imaged by SEM to identify suitable, well-preserved domains for analysis. In situ d18O data were acquired in the WiscSIMS Laboratory at the Department of Geoscience, UW-Madison, using a CAMECA IMS-1280 large radius multicollector SIMS. (Kita et al., 2009; Valley and Kita, 2009). Depending on the size of the target, samples were analyzed with a 10 µm or 3 µm primary beam. Four consecutive measurements of UWC-3 calcite standard (d18O = 12.40 per mille Vienna standard mean ocean water; VSMOW; Kozdon et al., 2009) were performed before and after every set of typically 10 sample analyses.

Description: The middle Miocene climate transition (MMCT) is characterized by an abrupt 1‰ increase in benthic foraminiferal oxygen isotopes at ca. 13.8 Ma, marking expansion of the Antarctic Ice Sheet and transition of Earth's climate to a cooler, relatively stable glacial state. Also occurring during this period is a globally recognized positive carbon isotope excursion (16.9-13.5 Ma) in benthic and planktonic foraminifera with shorter carbon isotope maxima (CM) events, linking hypotheses for climate change at the time with the carbon cycle. In order to test whether export production in the eastern equatorial Pacific is related to the largest such event (CM6), coincident with Antarctic Ice Sheet expansion, a high-resolution (〈5 k.y.) record of export production at Integrated Ocean Drilling Program Site U1337 spanning the MMCT (14.02-13.43 Ma) was produced using marine pelagic barite mass accumulation rates. Export production is elevated with an extended period of more than double present-day values. These variations are not orbitally paced and provide evidence for a reorganization of nutrients supplied to the eastern equatorial Pacific in the Miocene and intensification of upwelling. If such changes are representative of the entire region, then this mechanism could sequester enough carbon to have a significant effect on atmospheric pCO2. However, continual delivery of nutrients to the surface waters of the eastern equatorial Pacific is required in order to sustain export production without depleting the surface ocean of limiting nutrients. This might be accomplished by a change in ocean circulation or a combination of other processes requiring further study.