3.3.4. Ocean Sediments
Billions of tonnes of sediment accumulate in the ocean basins every year, and this may be indicative of climate conditions near the ocean surface or on the adjacent continents. Sediments are composed of both biogenic (organic) and terrigenous (inorganic) materials. The biogenic component includes the remnants of planktonic (surface ocean-dwelling) and benthic (deep-water- or sea floor-dwelling) organisms which provide a record of past climate and oceanic circulation. Such records may reveal information about past surface water temperatures, salinity, dissolved oxygen and nutrient availability. By contrast, the nature and abundance of terrigenous materials provides information about continental humidity-aridity variations, and the intensities and directions of winds. Ocean sediment records have been used to reconstruct palaeoclimate changes over a range of time scales, from thousands of years to millions and even tens of millions of years in the past.