HR: 11:05h
AN: PP52C-04    [Abstracts]
TI: Synchronous decadal to centennial scale variability in surface productivity off Peru and Indian Monsoon during the last millennium
AU: * Agnihotri, R
EM: ragnihotri@umassd.edu
AF: School for Marine Sciences and Technology, University of Massachusetts, Dartmouth, 706, Rodney French Blvd., New Bedford, MA 02744 United States
AU: Altabet, M A
EM: maltabet@umassd.edu
AF: School for Marine Sciences and Technology, University of Massachusetts, Dartmouth, 706, Rodney French Blvd., New Bedford, MA 02744 United States
AU: Herbert, T D
EM: Timothy_Herbert@Brown.EDU
AF: Dept. of Geological Sciences, Brown University, Box 1846, Brown University, Providnece, RI 02912 United States
AU: Tierney, J E
EM: jtierney@whoi.edu
AF: Geology and Geophysics Department, MS22 Woods Hole Oceanographic Institution , 360 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Donnelly, J P
EM: jdonnelly@whoi.edu
AF: Geology and Geophysics Department, MS22 Woods Hole Oceanographic Institution , 360 Woods Hole Road, Woods Hole, MA 02543 United States
AB: Indian Monsoon (IM) and ENSO are known to play pivotal roles in determining modern climatic variability and their past behavior is important for understanding underlying forcings and developing predictive models. Here we present ultra-high resolution proxy data of a sediment core W7706-40K (11°15'S, 77° 58'W; ~186 m) from the ENSO-sensitive Peru margin. X-radiographs of the core showed the presence of fine laminations throughout. A suite of major and minor elements were measured using scanning XRF at 0.4mm depth and ~0.7 year temporal resolutions. Among major elements, Ti and Fe show strong covariance with darker grayscale index. Mainly of continental origin, both are diluted by biogenic materials produced by upwelling induced surface productivity. Therefore, the Ti and Fe record is a likely negative index of surface productivity with Ti/Fe further used as an aeolian source indicator on this dry margin. Though Fe is redox sensitive, the presence of laminations indicate that changes in bottom water O2 was not a major factor in determining sediment Fe content. This Peru margin productivity record for the last ~1300 yrs is compared with a contemporaneous high-resolution (6-7 years) varve thickness data (a positive index of IM) from the Pakistan margin. Both paleo-records show a remarkable similarity at decadal to centennial time scales suggesting common forcings. Both IM intensity and surface productivity at Peru margin appear to be at a minimum at ~300 and 550 yr BP i.e. during the Maunder and Sp”rer minima of solar activity (compositely termed as Little Ice Age). The Medieval warm period from ~1100 to 600 yr BP, in contrast, has relatively more intense IM and Peru productivity. Our results are consistent with climate models and modern instrumental data showing co-occurrence of ENSO with substantially diminished Peru productivity and IM intensity in sub-decadal time scale. Spectral analyses of the both Ti and Fe data reveal dominant cycles of ~550, 300, 220, 110 and 90 years; the majority of which are known to be of solar origin. Ti/Fe ratio and thus aeolian source appears to be sensitive to the shorter ENSO cycles perhaps due to changes in coastal wind intensity or aridity. Periodogram of Ti/Fe ratio reveals significant cycles of 6.8 and 3.6 years. A detailed interpretation of our data in concert with other contemporaneous marine and continental paleo-records revealing ENSO forcing of the climate will be presented.
DE: 4522 ENSO (4922)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4922 El Nino (4522)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005