HR: 17:15h
AN: PP34A-06    [Abstracts]
TI: Seawater Li and d7Li: Proxies for Silicate Weathering?
AU: James, R H
EM: R.H.James@open.ac.uk
AF: Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AU: * Hathorne, E C
EM: E.C.Hathorne@open.ac.uk
AF: Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AU: Kisakurek, B
EM: B.Kisakurek@open.ac.uk
AF: Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AU: Harris, N B
EM: N.B.W.Harris@open.ac.uk
AF: Centre for Earth, Planetary, Space and Astronomical Research, The Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AB: This paper presents (i) the first systematic survey of lithium and its isotopes in the dissolved load and suspended and bed sediments of Himalayan rivers, and (ii) multi-species records of the Li/Ca ratio and Li isotopic composition of planktonic foraminifera from the Pacific and Atlantic oceans for the past 18 Ma. Modelling of the dissolved composition of Himalayan rivers indicates that most of the dissolved Li is derived from silicates even in carbonate-dominated catchments. Moreover, fractionation of Li isotopes between the dissolved and suspended load is lower at low altitiude where weathering is more intense. These data thus suggest that riverine Li fluxes largely reflect silicate weathering rates, while riverine δ⁷Li varies with weathering intensity. Given this information, and that the hydrothermal flux of Li into the oceans and the flux of Li removed from the oceans during low-temperature uptake by marine basalts and sediments have not changed significantly since 18 Ma and using published data for changing seawater calcium concentration, we can therefore interpret our planktonic foraminiferal Li/Ca and δ⁷Li records in terms of global average river δ⁷Li and Li fluxes. These records suggest that both silicate weathering rates and weathering intensity decreased between 16 and ~6Ma which may have been responsible for putative increases in levels of atmospheric CO₂. In contrast, silicate weathering rates and weathering intensity appear to have increased since ~6Ma despite global cooling and apparently little variation in atmospheric CO₂.
DE: 1030 Geochemical cycles (0330)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005