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SUMMARY:Deglacial Meridional Overturning changes inferred from sedimentary
  231Pa/230Th records from the North Atlantic - Jeanne Gherardi Scao\, Bjer
 knes Centre for Climate Research
DTSTART:20090210T163000Z
DTEND:20090210T173000Z
UID:TALK15287@talks.cam.ac.uk
CONTACT:Alex Piotrowski
DESCRIPTION:Comparison of sediment 231Pa/230Th profiles obtained at five s
 ites\nfrom the western and eastern North Atlantic between 1710m and 4550m\
 nwater depth provides new insights into the evolution of the mode of\ndeep
  water formation during the last deglaciation and the changes in\nthe rate
  of the Atlantic meridional overturning circulation during\nthe last 20\,0
 00 years. 231Pa/230Th measured in upper Holocene\nsediments indicates slow
  deep water renewal rates above ~2500m and\nfaster rates below\, consisten
 t with our understanding of modern\ncirculation. In contrast\, during the 
 Last Glacial Maximum (LGM)\, the\nformation of Glacial North Atlantic Inte
 rmediate Water (GNAIW) drove\na rapid overturning circulation to a depth o
 f at least ~3000m depth\,\nwhile deep water renewal rates were significant
 ly slower than today\nbelow ~4000m. At the onset of Heinrich event 1 (H1)\
 , the rate of the\noverturning circulation declined at all depths. GNAIW s
 hoaled above\n3000m while its rate of formation significantly decreased bu
 t did not\ntotally stop. During the Bølling-Allerød (BA) that followed\,
  the rate\nof meridional overturning further decreased above 2000m but inc
 reased\nbelow. Our results suggest for the first time that ocean circulati
 on\nduring that period was quite distinct from the modern circulation\nmod
 e\, with comparatively higher renewal rates above 3\,000m and lower\nrenew
 al rates below\, in a pattern similar to the LGM but less\naccentuated. Th
 e rate of the meridional overturning during the\nYounger Dryas (YD) was ve
 ry similar to that of the BA down to 2\,000 m\nbut slightly slower below.\
 n\nThe coherence of these results and the absence of a clear signal that\n
 could suggest a control by particle flux or composition further\nsupport t
 he interpretation of 231Pa/230Th in Atlantic sediments as a\npaleocirculat
 ion proxy\, and provide new insight into the depth of\nwater column integr
 ation for the 231Pa/230Th sediment signal.\n
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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