Evolution and variability of the Indian Ocean summer monsoon; evidence from the Western Arabian Sea Drilling Program

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doi: 10.1029/GM070p0447
Author(s): Prell, Warren L.; Murray, David W.; Clemens, Steven C.
Author Affiliation(s): Primary:
Brown University, Department of Geological Sciences, Providence, RI, United States
University of Michigan, United States
University of Wales College of Cardiff, United Kingdom
Bundesanstalt für Geowissenschaften und Rohstoffe, Federal Republic of Germany
Lamont-Doherty Geological Observatory of Columbia University, United States
NOAA Paleoclimatology Program, United States
Volume Title: Synthesis of results from scientific drilling in the Indian Ocean
Volume Author(s): Duncan, Robert A., editor; Rea, David K.; Kidd, Robert B.; von Rad, Ulrich; Weissel, Jeffrey K.
Source: Synthesis of results from scientific drilling in the Indian Ocean, edited by Robert A. Duncan, David K. Rea, Robert B. Kidd, Ulrich von Rad and Jeffrey K. Weissel. Geophysical Monograph, Vol.70, p.447-469. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0065-8448. ISBN: 978-1-118-66803-0 CODEN: GPMGAD
Note: In English with English summary. 112 refs.; illus., incl. sketch maps
Summary: General Circulation Model (GCM) experiments show that orbitally-induced increases in solar radiation significantly strengthen the monsoon winds and precipitation over southern Asia, but that surface boundary conditions (including sea surface temperature, albedo) associated with glacial phases weaken monsoon winds and precipitation. Experiments with full (modem elevations) and reduced plateau-mountain elevations reveal stronger winds and higher precipitation as mountain elevation increases. These results indicate that monsoon strength is equally sensitive to changes in solar radiation (on orbital time scales) and orographic changes (on longer time scales). They also indicate that global cooling cannot intensify the monsoon, so that the onset of the monsoon is most likely related to increased mountain elevation. Sediments in the northwest Arabian Sea exhibit characteristic fauna (radiolarians and foraminifers) that are endemic to areas of strong upwelling. In the Arabian Sea, intense seasonal upwelling is induced by the southwesterly monsoon winds. Miocene to Recent sediments from the northwest Arabian Sea show distinct geochemical and biological changes which suggest that monsoonal upwelling conditions (abundant nutrients and cold temperatures) were established near 8 Ma. Pelagic sediments deposited before 10.5 Ma contain nannofossils characteristic of warm waters and relatively low surface productivity. Opal-rich sediments, previously thought to reflect the initiation of the strong monsoon circulation, were deposited between 10.5 Ma and 8.0 Ma. However, the fauna in these sediments are not characteristic of the species associated with strong upwelling. Near 8 Ma, the relative abundance of endemic upwelling species increases and is interpreted to reflect the intensification and onset of the strong modern monsoon circulation. Terrestrial climate indicators from adjacent Pakistan are consistent with monsoon intensification at this time. The comparison of ODP sediment records and climate model simulations of monsoon circulation suggests that the combined effects of strong solar radiation and increased elevations (at least half of the modern orography) forced a strong monsoonal circulation about 8 Ma, which produced intense upwelling in the Arabian Sea and more seasonal climates over southern Asia.
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Albedo; Arabian Sea; Asia; Calcium carbonate; Cenozoic; China; Climate effects; Cooling; Far East; Foraminifera; Framework silicates; Himalayas; Indian Ocean; Invertebrata; Leg 117; Microfossils; Monsoons; Mountains; Nutrients; Ocean Drilling Program; Opal; Pelagic environment; Protista; Radiolaria; Silica minerals; Silicates; Solar activity; Solar radiation; Temperature; Uplifts; Upwelling; Western Arabian Sea; Xizang China
Coordinates: N160748 N182912 E0604438 E0572212
Record ID: 2007093174
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