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 10-20 cm/kyr

Microscope view of rinsed seafloor sediment

Archer D.E., 1996

Marine paleothermometers

• Foraminiferal abundance

• Sediment chemistry (Alkenones)

• Coral chemistry– δ18O, Sr/Ca

• Chemistry of foraminifera– δ18O, Mg/Ca

Oxygen Isotopes

• For every 500 water molecules in the sea, one bears the heavy isotope 18O

• In a variety of earth substances, the ratio of heavy oxygen atoms (18O) to light oxygen atoms (16O) varies from this 1/500 ratio by several percent

• For example, marine CaCO3 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