Archives of global climate change contained in ocean sediments

Ocean sediments as continuous climate archives Sediments consist of terrigenous material + organic rain + rain of calcite/silicate shells Sedimentary rain not derived from rocks is produced primarily by marine organisms (shells and excrement) Sedimentation rates range from almost nil to cm/kyr

Microscope view of rinsed seafloor sediment

Archer D.E., 1996

Marine paleothermometers Foraminiferal abundance Sediment chemistry (Alkenones) Coral chemistry –δ 18 O, Sr/Ca Chemistry of foraminifera –δ 18 O, Mg/Ca

Oxygen Isotopes For every 500 water molecules in the sea, one bears the heavy isotope 18 O In a variety of earth substances, the ratio of heavy oxygen atoms ( 18 O) to light oxygen atoms ( 16 O) varies from this 1/500 ratio by several percent For example, marine CaCO 3 has ~4% more heavy oxygen than seawater, while Antarctic snow has ~4% less heavy oxygen than seawater From “The Glacial World According to Wally”, 2002

Bemis et al., 1998

Data from Lea et al., (2000) presented in Wally