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Wanzhang Wang

Institution: University of Bremen
Office: GEO 4120
Phone: +49 421 218 - 65338
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Other webpage(s): Wanzhang's FB5 web page

 

Wanzhang Wang

PhD Project

Potential of magnetofossil abundance, morphology and alteration records as proxies for glacial oxygen depletion and carbon trapping in the deep North Pacific

The proposed Ph.D. thesis project engages into timely research issues around the potential role of the deep North Pacific Ocean as major ice age carbon trap. Glacial atmospheric carbon sequestration may have been enabled by slow-down or stagnation of bottom water circulation, which lead to a consumption and depletion of dissolved oxygen and preservation of dissolved and particulate organic carbon in the water column and surface sediment. Suboxic and sulfidic conditions in abyssal clays and pelagic oozes are known to consume iron oxides like magnetite for organic carbon remineralization. Changes in sedimentary nutrient and oxygen intake also modify the living conditions and population densities of benthic bacteria species. It is therefore promising to study the composition and preservation of bacterial magnetofossils that exist in large numbers in all North Pacific sediments, even in sub-lysoclinal abyssal basins.

The envisaged research issues require diversified experimental methods. In order to establish a stratigraphic core network, we will combine magnetostratigraphy (reversals and relative paleointensity) with cyclostratigraphy (physical and magnetic property logs, XRF element logs, color scans), and, where available, isotope stratigraphy (δ18O, δ13C, δ15N) to determine age, accumulation rate and water mass boundaries. The numerical unmixing of bacterial, detrital and authigenic magnetic fractions will be based both on detailed hysteresis (FORC analysis) and more rapid remanence methods (ARM and IRM acquisition, S* ratios of Usui et al., 2017). For mineral magnetic aspects (e.g. oxidation or sulfidization state), I will apply thermomagnetic methods (low-T/high-T cycling/demagnetization). Fossile magnetosome morphotype counts from TEM images will be needed for calibration and validation of the rock magnetic quantification methods.

In the overall objective of to constrain the spatial, depth and time intervals of glacial respiratory carbon storage and oxygen depletion in the deep North Pacific Ocean over the past ~ 1 Mill years, we aim to develop and test the paleoenvironmental proxy information carried by biogenic magnetite accumulation, alteration state and morphotype distribution:

  1. We depart by methodological investigations demonstrating the validity of (bio)magnetic unmixing methods in various sediment lithologies (abyssal clay, foram-nannofossil ooze) throughout exemplary glacial-interglacial resp. reduction-oxidation cycles.
  2. We then draw and analyze links of magnetosome abundance and shape speciation to complementary (geochemical, stable isotope, micropaleontological) paleoceanographic proxy records to establish evidence-based interpretation schemes.
  3. This will finally permit to compare a network of isochronic magnetofossil-based proxy records from major NW and NE Pacific basins and their dividing ranges (Shatsky and Hess Rise, Emperor Seamount Chain) to eventually constrain the lateral and vertical extent of particulate and dissolved organic matter pools over glacial periods.

Thesis Committee

Prof. Dr. Tilo von Dobeneck University of Bremen, MARUM - Center for Marine Environmental Sciences
Prof. Dr. Ralf Tiedemann Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Bremerhaven
Dr. Janna Just University of Bremen; Faculty of Geosciences
Prof. Dr. Michael Winklhofer University of Oldenburg, Institute for Biology and Environmental Sciences