183-2 Reactive Iron Geochemistry along a South Atlantic Transect: Implications for iron delivery and ocean productivity

Session: Recent Advances and New Voices in Marine and Coastal Geoscience (Posters)

Poster Booth No.: 33

Presenting Author:

Therra Wilbrandt

Authors:

Wilbrandt, Therra¹, Gilhooly, William P.², Lowery, Christopher Michael³, Borrelli, Chiara⁴, Kaplan, Michael R.⁵

(1) Indiana University Indianapolis, Indianapolis, IN, USA, (2) Indiana University Indianapolis, Indianapolis, IN, USA, (3) University of Texas, Institute for Geophysics, Austin, TX, USA, (4) University of Rochester, Dept. Earth and Environmental Sciences, Rochester, NY, USA, (5) LDEO of Columbia University, 209 Geochemistry Building, Palisades, NY, USA,

Abstract:

International Ocean Discovery Program (IODP) Expeditions 390 and 393 drilled seafloor sediment cores from five locations within the south Atlantic Gyre. The sites were aligned along a transect at ~30°S on the western side of the Mid-Atlantic Ridge. Sediments collected ranged in age from about 6.6 Ma (U1559) nearest to the spreading center to about 61.2 Ma (U1556) furthest from the ridge. This study focuses on the distribution of reactive iron minerals that include iron carbonates (e.g., siderite), iron oxides (e.g., ferrihydrite), magnetite, and iron sulfides (acid volatile sulfides and pyrite). The relative distribution of reactive iron can provide information about iron delivery to the central gyre and its potential influence on marine primary productivity. Gyres are typically nutrient-poor, low productivity regions, that do not deliver an abundance of nutrients and organic matter to the ocean floor. However, iron, a limiting nutrient for marine life, could be transported with wind-blown dust carrying bioavailable iron minerals such as ferrihydrite. The iron in oxides, carbonates, magnetite, and sulfides were sequentially extracted using wet chemical procedures from sediments collected at sites U1560, U1558, U1583, U1559, and U1556.Initial results indicate that crystalline iron oxides are the dominant iron species across all sites in the South Atlantic Transect beginning in the Miocene and peaking in the Plio-Pliestocene. Magnetite was the next most abundant form of iron and had peaks through the different sites also during the Miocene. Iron carbonates and sulfides were at trace to negligible amounts through all time periods in all five sites. The increase in bioavailable iron coincides with the southern hemispheric glaciation and the global drawdown in atmospheric CO₂ concentrations through the Pleistocene. An expansion of arid regions and intensified wind belts during glaciation potentially contributed to elevated iron delivery.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11021

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