Reconstruction of past bottom water conditions of the Peruvian Oxygen Minimum Zone (OMZ) for the last 22,000 years and the benthic foraminiferal response to (de)oxygenation
The Peruvian margin is characterised by a strong OMZ as result of enhanced surface primary productivity and sluggish ventilation of the subsurface waters. This present study investigated the potential changes in the structure and shape of the OMZ since the Last Glacial Maximum using downcore distributions of the benthic foraminiferal assemblages. The sediment cores considered in this study were recovered from the lower oxic-suboxic OMZ boundary. In addition, stratigraphic information from 31 sediment cores was compiled with a focus on the time intervals since the LGM. Erosional features together with gaps depict a prograding feature on the continental slope from south to north during the deglaciation. The recent oceanographic and sedimentological observations showed that tide-topography interactions result in non-linear internal waves which shape the continental slope by erosion and remobilization of the sediments. The compilation of downcore records and the northward expanding feature of the hiatus revealed that the tide-topography interactions have progressively evolved since the LGM. The oxygen quantification approach was validated using multiple regression analysis on three data sets of living calcareous benthic foraminiferal distributions and measured oxygen concentrations from 1 to 18°S. It was later followed by application of a transfer function to the four sediment cores. Estimated bottom water oxygen concentrations were low compared to modern values however the trend of decreasing oxygen levels during the Termination I and slight increase in the Holocene was consistent across all cores. The overall change in the bottom water oxygen levels from the LGM and the Holocene was reckoned to be 25 μmol/kg. Deoxygenation was observed as a gradual expansion of the northern OMZ boundary during the last deglaciation. Comparison of the bottom water oxygen estimates with other proxies from the region showed that the deoxygenation did not always co-occur with enhanced surface productivity.
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