Heidelberg 2015 – wissenschaftliches Programm
UP 13.23: Poster
Donnerstag, 26. März 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.