The geologic record of dust DANIEL R. MUHS GEOLOGY AND ENVIRONMENTAL CHANGE TEAM U.S. GEOLOGICAL SURVEY DENVER, COLORADO
Thanks to Art Bettis for organizing this session and with whom I've studied North America's loess deposits from the Arctic Ocean to the Gulf of Mexico
Geologic records of dust are found over much of the Earth s surface: Ice sheets Loess Lakes Soils Deep sea sediments
What are the sources of dust in the geologic record? Non-glacial sources of dust are most common in desert regions Dune fields (Grand Erg Oriental, Algeria/Tunisia) Dry washes (Algeria/Tunisia) Playas (Chott el Jered, Tunisia)
What are the sources of dust in the geologic record? Glaciers, such as those in the Alaska Range, are efficient rock grinders and produce abundant dust-sized particles Alaska Range Dust Dust Dust storm in the Delta River Valley, Alaska, July, 2004 Dust deposition on vegetation Delta River bed Boreal forest east of the Delta River
There can be both glacial and non-glacial dust: Taklimakan Desert, China Silt particle 1 production by glaciers Loess deposition on adjacent mountains 2 Fluvial transport of silts to basin 4 3 Eolian transport of silts enhanced by active dune sand
Because glaciers are efficient producers of silt, there was much more "rock flour" dust produced in the last glacial period The last glacial period, 25-10 ka Present interglacial period,10-0 ka
Ironically, some of the best archives of dust accumulation are in the remaining ice sheets: Greenland (Dye 3, Camp Century GRIP, NGRIP) Antarctica (Vostok, Dome C)
The Dome C, Antarctica record shows that dust deposition is cyclic, with much greater rates in glacial periods: -380-410 -440 Dust (µg /kg) Glacial Glacial Glacial Glacial Glacial Glacial d-d (o/oo) Glacial Glacial 1200 800 400 0 100 200 300 400 500 600 700 Age (ka) EPICA project members, 2004
RUSSIA CHINA Yellow Sea NORTH KOREA SOUTH KOREA Sea of Japan Dust from China is transported regularly to Korea and Japan; a record of this dust is found in lake sediments JAPAN NASA-MODIS, 2 April 2002
Flux of Chinese dust to Lake Biwa, Japan: also greater during glacial periods: Eolian quartz flux (g/cm 2 /10 3 yr) Normalized oxygen isotope composition 8 7 6 5 4-3 -2-1 0 1 2 Late last glacial Early last glacial 0 20 40 60 80 100 120 140 Age, in thousands of years before present Penultimate glacial (Martinson et al., 1987, QR; Xiao et al, 1997, QR)
East of Japan ~2000 km, the deep sea records similar cycles of dust: 0 Chinese loess S0 Dust flux in V21-146 (mg/cm 2 /ka) 0 200 400 600 Oxygen isotopes, V21-146 (o/oo) 6 5 4 3 L1 GLACIAL 100 S1 L2 GLACIAL Age (ka) 200 300 S2 L3 S3 GLACIAL L4 GLACIAL 400 S4 L5 GLACIAL 500 S5 Hovan et al., 1989, QR
The Pacific Ocean isn't the only one affected: transatlantic dust transport has been confirmed by a 45-year dust trap record by Joseph Prospero, U. of Miami: Greenland North America Atlantic Ocean Europe Dust Dust Dust Bahamas Dust Africa Hispaniola
Localities around the Atlantic where we have verified African dust additions to soils: NORTH AMERICA Florida Keys Jamaica Bermuda Bahamas Puerto Rico Barbados Canary Islands Mallorca AFRICA EUROPE SOUTH AMERICA
Which brings us to loess, covering approximately 10% of the Earth: Eurasia North America South America
Turkey Egypt Cyprus Syria Lebanon Israel Jordan In some regions, repeated low rates of dust flux over geologic timescales results in thick, but quite old loess deposits: Ruhama Badlands, Israel: OSL ages from Weider et al., 2008, J.Pl.Nutr.Soil Sci.. 14 ka 44 ka 68 ka 127 ka 172 ka Soil Soil Loess Soil Loess Soil Loess Soil Loess
~16 m In other regions, tens of meters of loess were deposited during the last glacial period alone Morrison, Illinois: glaciogenic loess from the Mississippi River ~40 m Loveland, Illinois: glaciogenic loess from the Missouri River
Much loess in North America came from rivers draining ice sheets, such as the Mississippi, Missouri, and Ohio: Mississippi Laurentide Ice Sheet Missouri River River Ohio River
However, loess in the Great Plains is non-glaciogenic: Great Plains loess is derived from volcaniclastic siltstones of the White River Group Badlands National Park, South Dakota
Nevertheless, Great Plains loess can have extraordinary thicknesses (47 m at Bignell Hill, Nebraska) Bignell Hill, Nebraska Eustis, Nebraska
Despite different origins, glacial and non-glacial loess deposits are about the same age, ~28,000 to 12,000 yr This suggests a common CLIMATE forcing, not supply-related NON-GLACIAL LOESS GLACIAL LOESS
CONCLUSIONS: The extraordinary situation of a dusty planet must have had profound effects on the global radiation balance, ocean fertilization, and soils and ecosystems There are geologic records of dust deposition in a wide variety of archives, spanning the geosphere, hydrosphere, cryosphere and pedosphere Ice core records, lake records, deep-sea records and loess records all indicate greatest dust deposition during glacial periods, especially the last glacial period Last-glacial loess records have the same age range, regardless of whether the loess is glacial or non-glacial This all suggests a very dusty, last-glacial planet, perhaps due to (a) stronger winds; (b) drier climates; (c) less vegetation and (d) a decreased intensity of the hydrologic cycle