HR: 1340h
AN: GP53B-1223    [Abstracts]
TI: Sedimentology, geochemistry and rock magnetic properties of beach sands in Galapagos Islands - implications for nesting marine turtles
AU: * Perez-Cruz, L
EM: perezcruz@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Circuito Exterior Cd. S/N Universitaria. Coyoacan, Mexico, DF 04510, Mexico
AU: Urrutia-Fucugauchi, J
EM: juf@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Circuito Exterior Cd. S/N Universitaria. Coyoacan, Mexico, DF 04510, Mexico
AU: Vazquez-Gutierrez, F
EM: felipe@icmyl.unam.mx
AF: Instituto de Ciencias del Mar y Limnologia, UNAM, Circuito Exterior de Cd. Universitaria S/N Coyoacan, Mexico, DF 04510, Mexico
AU: Carranza-Edwards, A
EM: carranza@icmyl.unam.mx
AF: Instituto de Ciencias del Mar y Limnologia, UNAM, Circuito Exterior de Cd. Universitaria S/N Coyoacan, Mexico, DF 04510, Mexico
AB: Marine turtles are well known for their navigation ability in the open ocean and fidelity to nesting beaches. Green turtle adult females migrate from foraging areas to island nesting beaches, traveling hundreds or thousands of kilometers each way. The marine turtle breeding in the Galapagos Islands is the Green Sea Turtle (Chelonia mydas agassisi); fairly common throughout the islands but with nesting sites located at Las Bachas (Santa Cruz), Barahona and Quinta Playa (Isabela), Salinas (Baltra), Gardner Bay (Espaņola) and Bartolomé Islet. In order to characterize and to identify the geochemical signature of nesting marine turtle beaches in Galapagos Islands, sedimentological, geochemical and rock magnetic parameters are used. A total of one hundred and twenty sand samples were collected in four beaches to relate compositional characteristics between equivalent areas, these are: Las Bachas, Salinas, Barahona and Quinta Playa. Grain size is evaluated using laser particle analysis (Model Coulter LS 230). Bulk ICP-MS geochemical analysis is performed, following trace elements are analyzed: Al, V, Cr, Co, Ni, Cu, Zn, Cd, Ba, Pb, Fe, Mn, K, Na, Mg, Sr, Ca and Hg; and low-field magnetic susceptibility is measured in all samples at low and high frequencies. Granulometric analysis showed that Barahona and Quinta Playa are characterized for fine grained sands. In contrast, Salinas and Las Bachas exhibit medium to coarse sands. Trace metals concentrations and magnetic susceptibility show different distribution patterns in the beach sands. Calcium is the most abundant element in the samples. In particular, Co, K, and Na show similar concentrations in the four beaches. Las Bachas beach shows highest concentrations of Pb and Hg (maximum values 101.1 and 118.5 mg/kg, respectively), we suggest that the enrichment corresponds to an anthropogenic signal. Salinas beach samples show high concentrations of Fe, V, Cr, Zn, Mn and the highest values of magnetic susceptibility (maximum 932 10-6 SI), we propose, a human activity influence less evident than in Bachas beach that could overlap the contribution of continent source. Quinta Playa sands show the maximum concentration of calcium and also high concentration of Fe and Mg, and relatively high values of magnetic susceptibility. Ca results from marine biogenic carbonates (mainly coral reefs). Barahona also show high concentrations in calcium that could be correlated with the presence of biogenous source around the beach.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1065 Major and trace element geochemistry
DE: 1512 Environmental magnetism
DE: 4835 Marine inorganic chemistry (1050)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting