Increased Dust Flux and Decreased Productivity in the Central Equatorial Pacific during the Last Glacial Maximum

Abstract:

Because the nutrients upwelled in the Central Equatorial Pacific are primarily sourced from the Southern Ocean, changes in paleoproductivity can reflect the ocean’s dynamical response to paleoclimate change. To reconstruct the productivity in the Central Equatorial Pacific, we will present new opal flux, ²³¹Pa/²³⁰Th, and foram-bound δ¹⁵N records, along with dust flux data, from six cores from the Line Islands (160˚W, 0-7˚N) at two time slices: the Modern (0-10,000 years before present) and the LGM (17,000-27,000 years before present). We observe a latitude-dependent decrease in both opal flux and ²³¹Pa/²³⁰Th during the LGM, with the strongest response at the equator and almost no change at the more northerly cores. These data are indicative of decreased surface productivity, despite contemporaneous increases in dust fluxes and, potentially, iron deposition. Furthermore, relatively constant δ¹⁵N of planktic foraminifera across the two time slices imply that nutrient utilization did not increase in the Central Equatorial Pacific during the LGM. Decreased productivity coupled with static nutrient utilization suggests that the overall nutrient concentration in upwelling waters may have decreased. Lower nutrient concentrations in waters feeding the low latitudes are consistent with recent evidence for higher nutrient utilization at high latitudes, and this coupling provides further evidence for the feedback between polar and tropical climate change.