Emily Pope (SNM): Earth’s deep water cycle

Torsdag den 22. oktober har foreningen fornøjelsen af oplæg af Emily Pope ved Statens Naturhistoriske Museum, som har dedikeret sin forskning til at karakterisere Jordens udviklng gennem tid med henblik på geologiske processer og biologiske udvikling ved brug af geokemiske metoder.

Der serveres pizza og forfriskninger efter mødet

The Earth’s hydrosphere is an open system in which water enters through meteorite impacts and is lost through hydrogen escape, and continuously fluxes between the major reservoirs of the oceans, mantle, continents, cryosphere and biosphere. These fluxes are controlled by independent geological and astronomical processes, and thus are not in steady state over Earth history, meaning that the size of any given reservoir of water within Earth’s hydrosphere has likely fluctuated significantly over geologic time.

The implications of such non-steady state water exchange between reservoirs and space are large. For example, subduction of water from the ocean into the mantle may play a significant role in facilitating plate tectonics. If oceans were significantly larger or smaller on early Earth, this would affect the surface albedo and climate, the timing of continental emergence, and with it a source of nutrients for Earth’s nascent biosphere.

As products of seawater-rock alteration are preferentially enriched in the light hydrogen isotope (H) over the heavier isotope (D, called deuterium), continuous sequestration of water from oceans over geologic time by continental growth, large-scale glaciation events, biologically mediated hydrogen escape to space, and subduction of water that is chemically bound in alteration minerals of the ocean crust should result in a measurable change in the hydrogen isotope composition of seawater over time.

Oceanic serpentinites and hydrous silicate minerals that are formed in subduction-related volcanic and hydrothermal environments obtain their hydrogen isotope composition from seawater-derived fluids, and thus may be used to calculate secular variation in the hydrogen isotope composition of seawater.

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