Multi-proxy Analysis of Pleistocene Carbonate Fluctuations in the Eastern Equatorial Pacific

Abstract:

Uncertainties persist regarding calcium carbonate preservation and its controls within Eastern Equatorial Pacific (EEP) paleoceanographic analyses. Studies have used two indirect proxies from foraminifera tests to constrain and quantify fluctuations in CaCO₃: 1) coarse fraction (> 150 μm, %CF) and 2) fragmentation (% fragmented tests in sample). Whereas dilution by terrigenous matter and volcanic debris, changes in productivity, and dissolution all influence %CF measurements, fragmentation measurements are based on the percentage of broken foraminiferal tests, which directly correlates with dissolution. The EEP currently lacks longer timescale Pleistocene fragmentation records. We are developing a longer-timescale record of fragmentation and %CF measurements so that we may interpret potential changes in dominant CaCO₃ controls within the EEP. We are extending the work of Martin et al. (2002, EPSL) by analyzing Eastern Equatorial Pacific core CDH-36 (1.53° N, 86.79° W, 3225 m water depth), cored from the Carnegie Platform northwest of the Grijalva Ridge. This core was taken from the same site as core TR163-31B/P, and is close to the location of core V19-29. Core CDH-36 is 42.63 meters in length, with an approximate sedimentation rate of 7 cm/kyr. Therefore, we estimate the timescale of this core to extend from the present day to ~600 kyr, extending into the Pleistocene through Marine Isotope Stage (MIS) 14. We are generating a benthic Cibicidoides Wuellerstorfi d¹⁸O record, measured at 10 cm (~1.4 kyr resolution), throughout core CDH-36. We will combine this d¹⁸O record with fragmentation and %CF measurements which are also being measured every 10 cm throughout the core, with the goal of developing the longest existing fragmentation record within the EEP. Preliminary results for CDH-36 support studies which suggest that dissolution dominates early Pleistocene CaCO₃ fluctuations. By extending existing shorter EEP fragmentation records, we hope to better constrain CaCO₃ fluctuations over longer timescales. Additionally, the length of this record will allow us to extend fragmentation records to anomalous intervals such as MIS 11, and thus to explore the coupling between Pacific dissolution and carbon cycle changes during these intervals.