Reconstruction of the Eastern Equatorial Pacific circulation over the last 160 kyr using foraminiferal Nd isotopes

Abstract:

The deep Pacific holds the largest oceanic reservoir of carbon which interchanges with the atmosphere on climatologically important timescales. However, the history of Pacific deep and intermediate circulation, as well as its role in regulating atmospheric CO₂ concentration during glacial-interglacial cycles, is poorly constrained because of low sedimentation rates and local high productivity affecting nutrient-based water mass proxies preferentially in sluggish circulation regimes. We reconstruct water mass circulation changes in deep (ODP 846, 03°5.80′ S, 90°49.07′ W, 3296 m) and intermediate (ODP 1241, 05°50.57′N, 86°26.68′W, 2027 m) cores from the Eastern Equatorial Pacific (EEP) near Galapagos Island over the last 160,000 years using Nd isotopes on foraminiferal coatings allowing comparison with other paleocean proxy records (e.g. δ¹³C, Cd/Ca, CaCO₃%, Δ¹⁴C and δ¹¹B) during MIS 1-6. The deeper ODP 846 Nd isotope record shows little to no variability over major glacial-interglacial cycles, but significant radiogenic peaks during each deglaciation which coincide with benthic Cd/Ca and δ¹¹B peaks in Pacific cores in the same water mass. The intermediate-depth ODP 1241 Nd isotope record has relatively unradiogenic glacials and radiogenic interglacials. We propose that this Nd isotope record is monitoring changes in the amount of Southern Ocean-sourced intermediate water, propagated to the EEP during MIS 2 and 6, which is further supported by less carbonate dissolution and nutricline shoaling. Taken together, Nd isotopes of these two records allow the investigation of the Eastern Equatorial Pacific circulation and its association with nutrient and carbon cycling over time.