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Title: Chemical weathering in an icehouse world : the record from soils and lakes
Author: Keech, Andrew R.
ISNI:       0000 0004 2720 226X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2011
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Chemical weathering of silicate rocks removes carbon dioxide from the atmosphere at a rate roughly proportional to its atmospheric abundance. This negative feedback mechanism is widely believed to have kept the Earth's climate within habitable bounds since life emerged several billion years ago. However, the presence of continental ice sheets (an 'icehouse' world, such as at the present day) may weaken the feedback mechanism or even change its sign. In order to test this hypothesis, samples were collected from two soil chronosequences in Scotland and Wyoming and from lake sediments in California. The behaviour of several radiogenic (strontium (Sr) and neodymium (Nd) and stable (molybdenum (Mo), copper (Cu) and zinc (Zn) isotope systems during weathering were then investigated. The composition of Sr released from silicate minerals in soils deposited since the last deglaciation (~20 ka) was observed to change from relatively radiogenic to relatively unradiogenic compositions with increasing soil age. This finding can, in part, explain the observed glacial-interglacial variability in Sr isotope composition of runoff from the Sierra Nevada over the past 150 ka as recorded in lake sediments. Such glacial-interglacial variation in the continental Sr flux to the oceans would alleviate existing problems with the marine Sr budget according to previous modelling and would support the hypothesis that the nature of feedback between climate (and atmospheric CO2 levels) and weathering changes as the Earth moves between greenhouse and icehouse conditions. Mo, Cu and Zn isotopes were shown to be fractionated by various biogeochemical processes in soils from Glen Feshie and the Wind River Mountains, Wyoming. The heavy isotopic composition of dissolved riverine Mo and Zn was shown to be related to incongruent weathering processes, perhaps related to soil age, whereas Cu appeared to weather congruently. Fractionation by vegetation and the role of organic matter within soils was also shown to be important in controlling the isotopic composition, concentration and distribution of Mo, Cu and Zn.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available