Variations in the Particulate Flux of 230Th and 231Pa and Paleoceanographic Applications of the 231Pa/230Th Ratio.

• Main Author: Yu, Ein-Fen
• Other Authors: WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
• Format: Text
• Language: English
• Published: 1994
• Subjects: Inorganic Chemistry; Physical Chemistry; Physical and Dynamic Oceanography; Geology; Geochemistry and Mineralogy; *PARTICULATES; *OCEANOGRAPHY; *THORIUM; *FRACTIONATION; *PROTACTINIUM; THERMAL PROPERTIES; REMOVAL; CORES; WATER; INTENSITY; THESES; SURFACES; ATLANTIC OCEAN; SALINITY; CIRCULATION; PRODUCTION RATE; ADVECTION; SEDIMENTS; GEOCHEMISTRY; DEEP OCEANS; TRAPS; NUCLIDES; CARBONATES; PARTICLE FLUX; *PALEOCEANOGRAPHIC; THERMOHALINE; HOLOCENE PERIOD; BIOGENIC; Indian; Southern Ocean
• Online Access: http://www.dtic.mil/docs/citations/ADA296961; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA296961

Fractionation between 230Th (t1/2=7.5 x 10(exp 4yr) and 231Pa (t1/2=3.2xl0(exp 4yr) is found widely within the oceans. This large scale fractionation was investigated in samples of sinking particulate matter collected with sediment traps and in deep-sea sediment cores. The compiled sediment trap results demonstrated that over most of the ocean, the flux of 230Th into the sediments balances approximately its production rate in the overlying water column, whereas 231Pa tends to migrate towards the margins or other regions of high particle flux. Thus the 231Pa/230Th ratio is sensitive to regional differences in the scavenging intensity. The thesis describes aspects of the large scale geochemical fractionation between the two elements within the Atlantic Ocean during the Holocene and the Last Glacial Maximum. A quantification of the influence on the fractionation of the two nuclides by advection resulting from the thermohaline circulation was made, and it is shown that almost half of the 231Pa production in the water column is exported from the Atlantic Ocean to the Southern Ocean. This export is important in the budget of 231Pa in deep-sea sediments of the Southern Ocean. This suggests that the variations in 231Pa/230Th ratio reflect variations not only in particle flux, but also in the intensity or pattern of the thermohaline circulation. Reconstruction of the 230Th-normalized biogenic opal and carbonate paleo-fluxes suggests no significant changes in surface production in the southern Indian Ocean between the Last Glacial Maximum and the Holocene period. jg p. 273 Sponsored in part by Grants NSF-OCE88-17836, NSF-OCE89-22707.