Detecting Past Climates

Detecting Past ClimatesTaking measurementsOnly recorded over last 150-200 yearsProxy data- reconstruct data using indirect evidence (ex: seafloor sediment, ice core samples, tree rings etc.)Paleoclimatology: study of ancient climatesSeafloor sedimentSurface organisms, die, sink become part of seafloor sedimentWhat we know:Certain organisms thrive in certain climatesDeeper the dig, farther back in time

Oxygen isotope analysisTwo oxygen isotope: O16 and O18; both are part of water molecules, O16 is lighter and more abundantWater with O16 evaporates more easily, thus more in O18 ocean water and more O16 in glacial ice during cold/glacial periods. More O16 in ocean water during warm periods Thus, when organisms use water when making shells, if theres more O18 the climate was warmer, more O16 the climate was cooler

Isotopically light means the ratio favors O16 Nonglacial (warm) period- more O16 evaporates, then rains and returns; so MORE O16 to O18 in ocean.Glacial (cool) period- evaporation but O16 doesnt return, stay in glacier, so MORE O18 in ocean

Constructed Temperature based on sea sediment layers and oxygen isotope analysis of organisms in the sedimentGlacial Ice coresDrill in glaciers (poles, mountains, etc) for core of iceWithin ice, bubbles of air (ancient atmosphere)Deeper the drill farther back in time (approximately 200,000 years back)Cores also include dust, pollen, ash, etc, deposited on the iceUse oxygen isotope to determine past tempMore O16 locked in the ice, cooler temp.

DendrochronologyTree rings- one ring = one yearWide ring = large growth (good conditions for that species)Use size/thickness of rings to infer precipitation and temperatureUseful up to about 1000 years for past climates

Other proxy dataFossilized plant pollen: biological activity gives clues to climate conditionsCoral reef: coral make limestone (CaCO3) so can use oxygen isotope analysis to examine climate conditions)Historical data: manuscripts, novels, historical records, art