PaleoceanographyPaleoceanography

The StartThe Start►HMS Challenger HMS Challenger

1700s—info about 1700s—info about sed distributionsed distribution

► Piston corer (1940’s) Piston corer (1940’s) showed CaCO3showed CaCO3

►Ocean environment Ocean environment variedvaried

► Challenged notion of Challenged notion of unchanging oceansunchanging oceans

►C. Emiliani (1950s) founded science of C. Emiliani (1950s) founded science of paleoceanographypaleoceanography Studied SST changes from CaCO3 O2 Studied SST changes from CaCO3 O2

isotopesisotopes

► Sed record extends Sed record extends to 180 myto 180 my

Cenozoic Cenozoic PlExampleate MotionsPlExampleate Motions

► Warm water forams Warm water forams decrease at about 4 m.y.decrease at about 4 m.y.

► Diatoms more abundantDiatoms more abundant► Warm water Pacific/Atl Warm water Pacific/Atl

communication ceasescommunication ceases► Pacific is colderPacific is colder► May initiate glaciationMay initiate glaciation

Vostok Ice Core RecordVostok Ice Core Record

ProxiesProxies►Can’t measure ancient oceansCan’t measure ancient oceans►Use proxies=substitutes in seds, iceUse proxies=substitutes in seds, ice

Marine organisms bestMarine organisms best►Ecological preferencesEcological preferences

Temp, pressure, salinity, etc.Temp, pressure, salinity, etc.

Sea Surface TemperaturesSea Surface Temperatures► See cycles in sea See cycles in sea

temperature recordtemperature record► Related to Related to

Milankovitch CyclesMilankovitch Cycles Changes in Earth’s Changes in Earth’s

orbitorbit►Doesn’t explain Doesn’t explain

everythingeverything

Oxygen Isotope ProxyOxygen Isotope Proxy► Use calcium carbonate Use calcium carbonate

planktonic foramsplanktonic forams► Lower T = high Lower T = high

O18/O16 ratioO18/O16 ratio Ratio depends on speciesRatio depends on species Seawater evaporation, Seawater evaporation,

light O16 removedlight O16 removed Precipitation= heavier Precipitation= heavier

O18O18 Both processes deplete Both processes deplete

oceanic O16 oceanic O16

Oxygen Isotope ContinuedOxygen Isotope Continued►Must remove ice volumeMust remove ice volume►Use benthic foramsUse benthic forams►Subtract benthic delta 18O from Subtract benthic delta 18O from

planktonicplanktonic

Other ProxiesOther Proxies► Mg/Ca ratios-planktonic foramsMg/Ca ratios-planktonic forams

Vary with TVary with T Does not vary with ice volumeDoes not vary with ice volume

► Problem, most carbonate sed Problem, most carbonate sed below CCDbelow CCD Poorly preserved foramsPoorly preserved forams

► Ocean circulationOcean circulation Use cadmium proxyUse cadmium proxy Older waters = more nutrientsOlder waters = more nutrients Surface water lower cadium Surface water lower cadium

concentrationconcentration Cadmiu/calcium ratio in foram Cadmiu/calcium ratio in foram

= cadmium/calcium ratios in = cadmium/calcium ratios in seawaterseawater

Last 400K cadmium/calcium Last 400K cadmium/calcium ratios higher in seds during ratios higher in seds during glacialsglacials

More nutrients, less NADWMore nutrients, less NADW

Carbon Isotope ProxyCarbon Isotope Proxy► Carbon occurs as Carbon occurs as

12C&C1312C&C13► Photosynthesis favors 12CPhotosynthesis favors 12C

Organic matter enriched in Organic matter enriched in 12C, depleted 13C12C, depleted 13C

► Nutrient poor Nutrient poor waters=higher 13C/12C waters=higher 13C/12C like N. Atlanticlike N. Atlantic Pacific lower ratiosPacific lower ratios

► Glacial times = lower Glacial times = lower ratios in N. Atlantic = less ratios in N. Atlantic = less NADWNADW

Gas HydratesGas Hydrates► Large negative changes in Large negative changes in

delta 13C at delta 13C at Paleocene/Eocene boundaryPaleocene/Eocene boundary

► High latitude surface High latitude surface temperates 5-7oC highertemperates 5-7oC higher 30-40% benthic forams 30-40% benthic forams

extinctextinct► Cause, great infusion of 12C—Cause, great infusion of 12C—

gas hydratesgas hydrates Methane has negative Methane has negative

delta13Cdelta13C Lead to greenhouse effectLead to greenhouse effect

► Quaternary CO2 levels not as Quaternary CO2 levels not as high as presenthigh as present

► Need to study sediments to Need to study sediments to predict futurepredict future

Carbonate SystemCarbonate System► Track CCD changesTrack CCD changes

Sediment below CCD=20% or less carbonateSediment below CCD=20% or less carbonate►Glacial times CCD deeper in Pacific/Indian Glacial times CCD deeper in Pacific/Indian

OceansOceans More CO3 in deep waterMore CO3 in deep water

►Less CO2 in atmosphereLess CO2 in atmosphere►Or more bacterial respirationOr more bacterial respiration

H2O+CO2+CaCO3-Ca2+HCO3-H2O+CO2+CaCO3-Ca2+HCO3-►Also, increased biological productivity, decreases Also, increased biological productivity, decreases

atmospheric CO2atmospheric CO2 Opposite in AtlanticOpposite in Atlantic