Cornelia Winguth

Global decline in ocean ventilation, oxygenation, and productivity during the Paleocene-Eocene Thermal Maximum: Implications for the benthic extinction

The prominent global warming event at the Paleocene-Eocene boundary (55 Ma), referred to as the Paleocene-Eocene Thermal Maximum (PETM), was characterized by rapid temperature increase and changes in the global carbon cycle in

Simulating Permian–Triassic oceanic anoxia distribution: Implications for species extinction and recovery

The biggest mass extinction in the Phanerozoic, at the end of the Permian, has been associ- ated with oceanic changes, but the exact dynamics are still debated. Intensifi ed stratifi cation, widespread anoxia, chemocline excursions, and large-scale ocean overturn events have all been invoked as contributors to the extinction. In this study the effects of possible changes in environmental conditions, such as an increase in nutrient input or dust fl uxes into the ocean or an intensifi cation of the biological pump, on Permian-Triassic ocean chemistry are inves- tigated. Series of sensitivity experiments were performed with a fully coupled climate-carbon cycle model. None of the forcings alone generates extensive low-oxygen conditions in the deep sea. These are only simulated by an intense eutrophication in combination with an enhanced biological pump, but still confi ned to the central Panthalassic, Tethys, and the eastern Boreal Oceans. Our fi ndings support the conclusions from a recent geochemical study of a Japanese deep Panthalassa section, that around the Permian-Triassic boundary, the oxygen minimum zone expanded considerably, while the deep Panthalassa remained ventilated. The warming- induced increase in low-oxygen conditions within the water column aggravated adverse exist- ing conditions and likely contributed to the extinction peak. Upwelling of toxic water was probably regionally confi ned and hence not the main cause for the end-Permian marine and terrestrial mass extinction. Widespread deep-sea anoxia, generated by a strong increase in weathering and the related enhanced nutrient input into the oceans, is probably closely linked to the delayed recovery of species in the Early Triassic.

Groundwater flow beneath Late Weichselian glacier ice in Nordfjord, Norway

Basal water pressure and water flow patterns are significant factors in controlling the behavior of an ice sheet, because they influence ice-sheet thickness, stability and extent. Water produced by basal melting may infiltrate the subsurface, or occur as sheet or channelized flow at the ice/bed interface. We examine subglacial groundwater conditions along a flowline of the Scandinavian ice sheet through Nordfjord, in the western fjords region of southern Norway, using a steady-state, two- dimensional groundwater-flow model. Meltwater input to the groundwater model is calculated by a two-dimensional, time-dependent, thermomechanically coupled ice-flow model oriented along the same flowline. Model results show that the subglacial sediments could not have transmitted all the meltwater out of the fjord during times of ice advance and when the ice sheet was at its maximum position at the edge of the continental shelf. In order for pore-water pressures to remain below the overburden pressure of the overlying ice, other paths of subglacial drainage are necessary to remove excess water. During times of retreat, the subglacial aquifer is incapable of transmitting all the meltwater that was probably generated. Pulses of meltwater reaching the bed could explain non- climatically driven margin readvances during the overall retreat phase.