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Paleoceanography Paleoceanography

Paleoceanography

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Paleoceanography. The Start. HMS Challenger 1700s—info about sed distribution Piston corer (1940’s) showed CaCO3 Ocean environment varied Challenged notion of unchanging oceans. C. Emiliani (1950s) founded science of paleoceanography Studied SST changes from CaCO3 O2 isotopes. - PowerPoint PPT Presentation

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Page 1: Paleoceanography

PaleoceanographyPaleoceanography

Page 2: Paleoceanography

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

Page 3: Paleoceanography

►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

Page 4: Paleoceanography

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

Page 5: Paleoceanography

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

Page 6: Paleoceanography

Vostok Ice Core RecordVostok Ice Core Record

Page 7: Paleoceanography

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.

Page 8: Paleoceanography

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

Page 9: Paleoceanography

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

Page 10: Paleoceanography

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

Page 11: Paleoceanography

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

Page 12: Paleoceanography

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

Page 13: Paleoceanography

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

Page 14: Paleoceanography

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