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Paleoceanography

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.

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Paleoceanography

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  1. Paleoceanography

  2. The Start • HMS Challenger 1700s—info about sed distribution • Piston corer (1940’s) showed CaCO3 • Ocean environment varied • Challenged notion of unchanging oceans

  3. C. Emiliani (1950s) founded science of paleoceanography • Studied SST changes from CaCO3 O2 isotopes

  4. Sed record extends to 180 my

  5. Cenozoic PlExampleate Motions • Warm water forams decrease at about 4 m.y. • Diatoms more abundant • Warm water Pacific/Atl communication ceases • Pacific is colder • May initiate glaciation

  6. Vostok Ice Core Record

  7. Proxies • Can’t measure ancient oceans • Use proxies=substitutes in seds, ice • Marine organisms best • Ecological preferences • Temp, pressure, salinity, etc.

  8. Sea Surface Temperatures • See cycles in sea temperature record • Related to Milankovitch Cycles • Changes in Earth’s orbit • Doesn’t explain everything

  9. Oxygen Isotope Proxy • Use calcium carbonate planktonic forams • Lower T = high O18/O16 ratio • Ratio depends on species • Seawater evaporation, light O16 removed • Precipitation= heavier O18 • Both processes deplete oceanic O16

  10. Oxygen Isotope Continued • Must remove ice volume • Use benthic forams • Subtract benthic delta 18O from planktonic

  11. Other Proxies • Mg/Ca ratios-planktonic forams • Vary with T • Does not vary with ice volume • Problem, most carbonate sed below CCD • Poorly preserved forams • Ocean circulation • Use cadmium proxy • Older waters = more nutrients • Surface water lower cadium concentration • Cadmiu/calcium ratio in foram = cadmium/calcium ratios in seawater • Last 400K cadmium/calcium ratios higher in seds during glacials • More nutrients, less NADW

  12. Carbon Isotope Proxy • Carbon occurs as 12C&C13 • Photosynthesis favors 12C • Organic matter enriched in 12C, depleted 13C • Nutrient poor waters=higher 13C/12C like N. Atlantic • Pacific lower ratios • Glacial times = lower ratios in N. Atlantic = less NADW

  13. Gas Hydrates • Large negative changes in delta 13C at Paleocene/Eocene boundary • High latitude surface temperates 5-7oC higher • 30-40% benthic forams extinct • Cause, great infusion of 12C—gas hydrates • Methane has negative delta13C • Lead to greenhouse effect • Quaternary CO2 levels not as high as present • Need to study sediments to predict future

  14. Carbonate System • Track CCD changes • Sediment below CCD=20% or less carbonate • Glacial times CCD deeper in Pacific/Indian Oceans • More CO3 in deep water • Less CO2 in atmosphere • Or more bacterial respiration • H2O+CO2+CaCO3-Ca2+HCO3- • Also, increased biological productivity, decreases atmospheric CO2 • Opposite in Atlantic

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