A bottom-up view of modern and past ocean chemistry
with Dr. Derek Vance, Professor of Geochemistry in the Department of Earth Science at ETH Zürich and President of the European Association of Geochemistry.
The secular evolution of ocean biogeochemistry, as recorded in the authigenic and biogenic fractions of sediments, provides one of our main records of environmental change through Earth history. The importance of such records lies in what they tell us about how the surface environment responds to changes in the operation of major Earth System controls: e.g., volcanic inputs of material to the surface Earth, chemical weathering, photosynthesis and other microbial activity, sedimentation. The use of such records requires a robust understanding of the important processes controlling the chemistry of the water column itself and how water column chemical and isotope signatures are transferred to sediment.
The modern view of ocean chemistry puts a strong emphasis on: (1) supply of material to the dissolved pool in the upper ocean, via rivers and aerosols; (2) packaging into particulate material – uptake into cells, incorporation into tests, shells and frustules, sorption onto surfaces; (3) transfer of this particulate material downwards; (4) return to the dissolved pool in the deep ocean via regeneration, dissolution and desorption. In this presentation I will show that, on its own, this view of ocean chemistry leads to imbalanced budgets for many elements and isotope systems. It is becoming increasingly apparent that early diagenetic reactions within sediment, transfer to pore waters, and fluxes back to the water column, are essential to chemical and isotope balances. These processes are also crucial to how water column signatures are imprinted on sedimentary records, including their interpretation in paleoceanography. The talk will illustrate these ideas using examples of elements on which established and emerging paleoceanographic proxies are based.
The Earth Science Colloquium Series, sponsored by Lamont-Doherty Earth Observatory and Columbia University Department of Earth and Environmental Sciences (DEES), provides a lively forum for discussing a wide variety of topics within the Earth sciences and related fields. Colloquia are attended by the full range of scientific and technical staff at LDEO. Colloquium attendance is required of all pre-orals DEES graduate students. The Colloquium Series supports the Lamont Seminar Diversity Initiative.