Heidelberg 2015 – scientific programme

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UP: Fachverband Umweltphysik

UP 13: Postersession Bodenkunde, Kryosphäre, Meßtechnik, Ozeanographie

UP 13.23: Poster

Thursday, March 26, 2015, 10:45–19:45, G/Foyer

Growth rates of ferromanganese crusts - O2 concentration in the deep Pacific during the LGM — •Freya Hemsing¹, Augusto Mangini¹, Christian Wirsig², and Norbert Frank¹ — ¹Institute of Environmental Physics, Heidelberg, Germany — ²Laboratory of Ion Beam Physics, ETH Zurich, Switzerland

In the last years several studies and hypotheses suggest climate driven variations of the O₂ concentration leading to potentially anoxic conditions in the Deep Water of the Pacific during glacial times like the Last Glacial Maximum (LGM). The growth of ferromanganese crusts is closely linked to the dissolved O₂ content in bottom waters. The crust VA13-2 from the Equatorial Pacific (146^∘ W, 9^∘ 25’ S, 4830 m) is analysed for a period covering the LGM. Due to the extremely slow growth rate of 10.30 ± 0.88 mm/Ma this only corresponds to about the upper 300 ± 10 µm. Four profiles were taken with a spatial resolution of 12.6 mm² and a depth resolution of 10 - 20 µm. The ²³⁰Th concentration of each layer was measured by thermal ionisation mass spectrometry. Applying ²³⁰Th excess dating and a constant flux model for ²³⁰Th, the temporal growth rate development was derived with a resolution of 500 a. The obtained temporal variations of the growth rate show a significant slowdown of the growth during the LGM. This implies a noticeable O₂ depletion of the Pacific Deep Water during the LGM. However, no growth stops and thus no anoxic conditions can be inferred with respect to the achieved resolution.