603-pp17 - Small perturbations to the hydrological cycle...

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1 Kelly Robinson Geological Oceanography Spring 2008 Small perturbations to the hydrological cycle cause large changes in global climate & ocean circulation Image credit: NASA/JPL http://www.nasastockphotography.com Carlson et al. 2007 PNAS Geochemical proxies of North American freshwater routing during the Younger Dryas cold event Globigerina bulloides Neogloboquadrina pachyderma Image credit: Mary W. Silver, UC Santa Cruz Questions • What role does freshwater play in forcing abrupt climate change? • Did eastward routing with an increase freshwater flux into the St. Lawrence River cause the Younger Dryas (YD) cold event? Methods • Mg/Ca, U/Ca, 87 Sr/ 86 Sr & δ 18 O used as tracers of – Increase in Mg/Ca Æ decrease in SST – Increase U/Ca Æ increase flux of oxygenated, particulate-rich riverine water into estuary – Increase 87 Sr/ 86 Sr Æ Weathering of old bedrock – Depletion of δ 18 O Æ decrease in salinity Atmospheric-ocean coupling Image credits: Al ey, R.B. 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19: 213-226; Marika Hol and http://www.asp.ucar.edu/col oquium/2000/Lectures/hol and.html Pleistocene temperature variability North Atlantic Meridional Overturning Circulation YD winters in northern Europe 26-28°C colder than today Lake Agassiz before & after catastrophic flood • 9500 km 3 of water released to the N. Atlantic Broecker 2003 Science 300(6):1519-1522
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2 Precambrian Paleozoic Mesozoic Cenozoic 12.5 kyr BP ice margin Pre-YD drainage area YD drainage area End YD ice margin Drainage of St. Lawrence Basin doubled 1.35 x 10 6 km 2 Æ 3.13 x 10 6 km 2 a) Dinoflagellate cyst SST reconstruction Younger Dryas Canadian freshwater sources have δ 18 O of (-25 ‰) Æ freshwater flux into estuary would result in deplete δ 18 O values Aburpt 0.32 decrease in δ 13 C indicates increased flux of 12 C-enriched freshwater run-off
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This note was uploaded on 02/10/2012 for the course MAS 603 taught by Professor Haywick during the Fall '11 term at S. Alabama.

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603-pp17 - Small perturbations to the hydrological cycle...

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