Preprints
https://doi.org/10.5194/cp-2021-85
https://doi.org/10.5194/cp-2021-85

  27 Jul 2021

27 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal CP.

Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 ka

María H. Toyos1,2,3, Gisela Winckler4,5, Helge W. Arz6, Lester Lembke-Jene3, Carina B. Lange2,7,8, Gerhard Kuhn3, and Frank Lamy3 María H. Toyos et al.
  • 1Programa de Postgrados en Oceanografía, Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción, Chile
  • 2Centro de Investigación Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Universidad Austral de Chile, Valdivia, Chile
  • 3Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar und Meeresforschung, Bremerhaven, Germany
  • 4Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964
  • 5Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027
  • 6Leibniz-Institut für Ostseeforschung Warnemünde (IOW), Rostock-Warnemünde, Germany
  • 7Departamento de Oceanografía and Centro Oceanográfico COPAS Sur-Austral, Universidad de Concepción, Chile
  • 8Scripps Institution of Oceanography, La Jolla, California 92037

Abstract. Changes in Southern Ocean export production have broad biogeochemical and climatic implications. Specifically, iron fertilization likely increased subantarctic nutrient utilization and enhanced the efficiency of the biological pump during glacials. However, past export production in the subantarctic Southeast Pacific is poorly documented, and its connection to Fe fertilization, potentially related to Patagonian Ice Sheet dynamics is unknown. We report on biological productivity changes over the past 400 ka, based on a combination of 230Thxs-normalized and stratigraphy-based mass accumulation rates of biogenic barium, organic carbon, biogenic opal, and calcium carbonate as indicators of paleo-export production in a sediment core upstream of the Drake Passage. In addition, we use fluxes of iron and lithogenic material as proxies for terrigenous matter, and thus potential micronutrient supply. Stratigraphy-based mass accumulation rates are strongly influenced by bottom-current dynamics, which result in variable sediment focussing or winnowing at our site. Carbonate is virtually absent in the core, except during peak interglacial intervals of the Holocene, and Marine Isotope Stages (MIS) 5 and 11, likely caused by transient decreases in carbonate dissolution. All other proxies suggest that export production increased during most glacial periods, coinciding with high iron fluxes. Such augmented glacial iron fluxes at the core site were most likely derived from glaciogenic input from the Patagonian Ice Sheet promoting the growth of phytoplankton. Additionally, glacial export production peaks are also consistent with northward shifts of the Subantarctic and Polar Fronts, which positioned our site south of the Subantarctic Front and closer to silicic acid-rich waters of the Polar Frontal Zone, as well as a with a decrease in the diatom utilization of Si relative to nitrate under Fe-replete conditions. However, glacial export production near the Drake Passage was lower than in the Atlantic and Indian sectors of the Southern Ocean, which may relate to complete consumption of silicic acid in the study area. Our results underline the importance of micro-nutrient fertilization through lateral terrigenous input from South America rather than aeolian transport, and exemplify the role of frontal shifts and nutrient limitation for past productivity changes in the Pacific entrance to the Drake Passage.

María H. Toyos et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2021-85', G. Cortese, 17 Sep 2021
    • AC1: 'Reply on RC1', María H. Toyos, 20 Oct 2021
  • RC2: 'Comment on cp-2021-85', Louisa Bradtmiller, 22 Sep 2021
    • AC2: 'Reply on RC2', María H. Toyos, 20 Oct 2021

María H. Toyos et al.

María H. Toyos et al.

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Short summary
Past export production in the southeast Pacific and its link to Patagonian ice dynamics is unknown. We reconstruct biological productivity changes at the Pacific entrance to the Drake Passage, covering the past 400,000 years. We show that glacial-interglacial variability in export production responds to glaciogenic Fe supply from Patagonia and silica availability due to shifts in oceanic fronts whereas dust, as a source of lithogenic material, plays a minor role.