How dusty was the early Paleogene greenhouse world?

Author(s): Amaya, D. J.; Thomas, D. J.
Author Affiliation(s): Primary:
Texas A&M University, Department of Atmospheric Sciences, College Station, TX, United States
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Models and limited proxy data suggest that overall hydrologic cycling was more intense during the early Paleogene, resulting in higher precipitation in temperate and high latitudes likely with greater vegetative cover than in drier periods. The lower aridity in temperate and tropical regions would have resulted in diminished dust transport to the ocean basins at these latitudes. However, a more intense hydrological cycle likely resulted in increased drying of the arid-to-semi-arid subtropical regions that may have enhanced the size of the available subtropical dust source regions. Because the accumulation of dust in remote, pelagic sediments is controlled by aridity in the source regions as well as the gustiness of the transporting winds, we can test the zonal pattern of aridity (dust availability) by reconstructing dust accumulation records from a meridional swath of deep-sea sedimentary sections. The available drill sites in the South Pacific provide a useful transect from ∼60 to 30S over the study interval ∼70-30 Ma. We estimated 232Th-based dust fluxes at DSDP Site 596 from published 232Th concentration data and sediment mass accumulation rates, and generated new 232Th-based dust fluxes from IODP Sites U1369, 1370 and 1371. Dust fluxes recorded at Site 596 vary between ∼5 and 12 mg/cm2/kyr with no apparent temporal trend from 70 to 30 Ma. Fluxes recorded at Sites U1369, 1370 and 1371 generally decrease over the interval ∼65 to 50 Ma, but by ∼50 Ma these sites recorded similar values as Site 596 to the north. While the range of values recorded at the southern sites overlaps, there is a general gradient in dust flux decreasing from west to east, with Site U1371 recording the highest overall fluxes and Site U1369 recording the lowest fluxes. The west to east decrease in dust flux suggests that the primary source of eolian material to the southern Pacific basin was to the west. This source region likely was Australia. However, the magnitude of the 232Th-based dust fluxes at all of the sites is low, indicating that the hypothesized Australian dust source region was not very arid from ∼70 to 30 Ma.
Year of Publication: 2013
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
IPOD International Phase of Ocean Drilling
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; DSDP Site 596; Deep Sea Drilling Project; East Pacific; Expedition 329; Greenhouse effect; IODP Site U1369; IODP Site U1370; IODP Site U1371; IPOD; Integrated Ocean Drilling Program; Leg 91; Lower Paleogene; Pacific Ocean; Paleoclimatology; Paleogene; South Pacific; Southeast Pacific; Tertiary
Coordinates: S455751 S455751 W1631103 W1631103
S415107 S415107 W1530623 W1530623
S235113 S235111 W1653916 W1653917
Record ID: 2015080411
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