Paper No. 16-2
Presentation Time: 1:50 PM
COSMOGENIC RADIONUCLIDE EROSION RATES AND CHEMICAL DENUDATION RATES IN CUBA ARE NOT RELATED
BIERMAN, Paul R.1, SIBELLO HERNÁNDEZ, Rita Y.2, CAMPBELL, Mae Kate3, GARCÍA MOYA, Alejandro2, DETHIER, David P.4, BOLAÑOS ALVAREZ, Yoelvis2, MASSEY-BIERMAN, Marika Eden5, GUILLÉN ARRUEBARRENA, Aniel2, RACELA, Jason5, SCHMIDT, Amanda H.6, CARTAS AGUILA, Hector A.2, CORBETT, Lee B.3, ALONSO-HERNÁNDEZ, Carlos2, DIX, Monica7 and CAFFEE, Marc W.8, (1)Department of Geology, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405, (2)Centro de Estudios Ambientales de Cienfuegos, Apartado Postal 5, Cienfuegos, 59350, Cuba, (3)Department of Geology, The University of Vermont, 180 Colchester Ave., Burlington, VT 05405, (4)Dept. Geosciences, Williams College, 947 Main Street, Williamstown, MA 01267, (5)Williams College, Center for Environmental Studies/Geosciences, 59 Lab Campus Drive, Thompson Bio, Williamstown, MA 01267, (6)Geology, Oberlin College, Geology Department, Rm. 403, 52 W. Lorain St, Oberlin, OH 44074, (7)Geology, Oberlin College, 52 West Lorain Street, Oberlin, OH 44074-1044, (8)Department of Physics, Purdue University, 1396 Physics Bldg., West Lafayette, IN 47907
The rate at which the landscapes of the island of Cuba are changing over time is not well known. Understanding the flux of mass from the land to the sea is important because this flux has direct bearing on the health of marine ecosystems including fringing reefs which are important tourist destinations and thus economic assets for the island.
Here, we use both in situ cosmogenic radionuclide data and chemical analysis of river water to understand better how and where weathering occurs on the Cuban landscape. These data were collected in central Cuba (2018, n=26 samples) and western Cuba (2019, n=20 samples) by a joint Cuban/American team. We measured in situ 10-Be in quartz and meteoric 10-Be in grain coatings. We determined chemical denudation rates by measuring cations and anions in river water and estimating run-off from precipitation data and run-off coefficients.
Rates of erosion determined from in situ 10-Be concentrations (n= 33) range from <2 to ~80 m/My, are more varied in central than western Cuba, and do not correlate with chemical denudation rates overall or in either region. Chemical denudation rates (n = 45) range from 42 to 302 tons/(km^2 yr) in central Cuba and from 6 to 73 tons/(km^2 yr) in western Cuba. Chemical denudation rates and total dissolved solids are on average 5 times higher in central Cuba than western Cuba. River water is dominated by Mg, Ca, Na, K, and Si in both areas.
Because there is no relationship between dissolved load and cosmogenically determined erosion rates, we suspect that much of the weathering generating the solute load carried by rivers originates below the several meter depth to which most cosmic rays penetrate. Such deep weathering is consistent with soil-mantled hillslopes and channels deeply incised into weathered rock and saprolite. Deep chemical weathering implies that total denudation exceeds the radionuclide-based estimates. The discrepancy between cosmogenic-based background erosion rates and chemical denudation rates highlights the importance of considering chemical denudation when examining landscape change, particularly in lithologies subject to rapid and extensive chemical weathering.
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