title: Ocean dynamics, not dust, have controlled equatorial Pacific productivity over the past 500,000 years.
abstract: Biological productivity in the equatorial Pacific is relatively high compared with other low-latitude regimes, especially east of the dateline, where divergence driven by the trade winds brings nutrient-rich waters of the Equatorial Undercurrent to the surface. The equatorial Pacific is one of the three principal high-nutrient low-chlorophyll ocean regimes where biological utilization of nitrate and phosphate is limited, in part, by the availability of iron. Throughout most of the equatorial Pacific, upwelling of water from the Equatorial Undercurrent supplies far more dissolved iron than is delivered by dust, by as much as two orders of magnitude. Nevertheless, recent studies have inferred that the greater supply of dust during ice ages stimulated greater utilization of nutrients within the region of upwelling on the equator, thereby contributing to the sequestration of carbon in the ocean interior. Here we present proxy records for dust and for biological productivity over the past 500 ky at three sites spanning the breadth of the equatorial Pacific Ocean to test the dust fertilization hypothesis. Dust supply peaked under glacial conditions, consistent with previous studies, whereas proxies of export production exhibit maxima during ice age terminations. Temporal decoupling between dust supply and biological productivity indicates that other factors, likely involving ocean dynamics, played a greater role than dust in regulating equatorial Pacific productivity.
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964; Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027; winckler@ldeo.columbia.edu.
authors.forename: Gisela
authors.initials: G
authors.lastname: Winckler
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964; Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027;
authors.forename: Robert F
authors.initials: RF
authors.lastname: Anderson
authors.affiliation: Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland; Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland;
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Jaccard
authors.affiliation: Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843.
authors.forename: Franco
authors.initials: F
authors.lastname: Marcantonio
mesh_terms: D001106:Archaeology; D005075:Biological Evolution; D004391:Dust / Q000032:analysis*; D019015:Geologic Sediments / Q000032:analysis*; D008386:Marine Biology; D010140:Pacific Ocean; D010839:Phytoplankton; D012623:Seawater / Q000032:analysis*
chemical_list: D004391:Dust
keywords: carbon; climate change; eolian dust; export production; iron fertilization