HR: 08:30h
AN: OS31C-03 INVITED    [Abstracts]
TI: Radiogenic and stable isotope variations accompanying continental weathering
AU: * Burton, K W
EM: burton@lmtg.obs-mip.fr
AF: Earth Sciences, The Open University Walton Hall, Milton Keynes, MK11 1JH, United Kingdom
AU: * Burton, K W
EM: burton@lmtg.obs-mip.fr
AF: LMTG, Universite Paul Sabatier, Toulouse, 31400, France
AU: Gannoun, A
EM: mouhcine.gannoun@earth.ox.ac.uk
AF: Earth Sciences, The Open University Walton Hall, Milton Keynes, MK11 1JH, United Kingdom
AU: Gannoun, A
EM: mouhcine.gannoun@earth.ox.ac.uk
AF: Earth Sciences, University of Oxford, Oxford, OX1 3PR, United Kingdom
AU: Georg, B
EM: Bastian.Georg@earth.ox.ac.uk
AF: Earth Sciences, University of Oxford, Oxford, OX1 3PR, United Kingdom
AU: Gislason, S R
EM: sigrg@raunvis.hi.is
AF: Institute of Geology, University of Iceland, Reykjavik, 101, Iceland
AU: James, R H
EM: r.h.james@open.ac.uk
AF: Earth Sciences, The Open University Walton Hall, Milton Keynes, MK11 1JH, United Kingdom
AU: Parkinson, I J
EM: i.j.parkinson@open.ac.uk
AF: Earth Sciences, The Open University Walton Hall, Milton Keynes, MK11 1JH, United Kingdom
AU: Pogge von Strandmann, P A
EM: P.poggevonStrandmann@bristol.ac.uk
AF: Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom
AU: Mokadem, F
EM: f.mokadem@open.ac.uk
AF: Earth Sciences, The Open University Walton Hall, Milton Keynes, MK11 1JH, United Kingdom
AB: Many natural isotope systems, both stable and radiogenic, are sensitive to variations in weathering processes, but the difficulty remains in distinguishing variations that result from weathering from those caused by differences in rock type. One approach that circumvents this problem is the study of monolithologic catchments, where variations in physical and chemical weathering rates, runoff, catchment age, vegetative and glacial cover can be related to river chemistry. This study presents an overview of our recent work on radiogenic and stable isotopes in rivers and estuaries from Iceland, draining basaltic terrains, where variations in glacial cover result in a wide range of weathering conditions. Each radiogenic and stable isotope system reveals complementary information on the nature of the weathering process, and the estuarine data indicates how this signal is transferred to the oceans. For the dissolved riverine phase, in the absence of variations in rock type, the principal controls on isotope variations accompanying weathering are; (i) For many radiogenic isotope systems, preferential (incongruent) weathering of specific mineral phases, where those phases possess a markedly different parent/daughter ratio, and hence radiogenic isotope composition; (ii) For many stable isotope systems, preferential removal of an isotope into secondary phases formed during weathering, leaves residual waters depleted in that isotope. Despite the wide range of isotope compositions in the dissolved load, for Iceland it is the nature of weathering of the suspended load in the estuarine environment that likely dominates the signal to the oceans. Moreover, both the flux and nature of the suspended load are highly dependent on riverine discharge, and hence climate change. These results clearly demonstrate that weathering processes can exert a significant influence on the riverine isotope signal to the oceans, and for some isotopes marine sedimentary archives will preserve a record of changes in weathering in response to climatic or tectonic change. The challenge remains in deconvolving the effects of weathering from those caused by variations in rock type, or a simple change in the weathering flux.
DE: 1030 Geochemical cycles (0330)
DE: 1039 Alteration and weathering processes (3617)
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4924 Geochemical tracers
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting