| 1. |
- Murphy, Melissa J., et al.
(författare)
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Li Isotope Behaviour in the Low Salinity Zone During Estuarine Mixing
- 2014
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Ingår i: Procedia Earth and Planetary Science. - : Elsevier BV. - 1878-5220. ; 10, s. 204-207
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Tidskriftsartikel (refereegranskat)abstract
- During mixing of river water and seawater, changes in water chemistry can affect the behaviour of elements in estuaries, and consequently may alter their input into the oceans. In order to evaluate this, lithium (Li) concentrations and isotope compositions of estuarine waters from the Kalix and Råne River estuaries (Northern Sweden) have been determined. The waters span δ7Li values of +21.7 to +30.4 ‰, with the lowest values found within the shallowest samples with the lowest salinities. Dissolved Li concentrations show near conservative behaviour with increasing salinity; however their δ7Li isotopic compositions may be explained by either conservative mixing with an intermediate salinity Bothnian Bay end member; or non-conservative behaviour, with excess Li added to solution during mixing. The non-conservative behaviour of Li might be ascribed to cation exchange processes with suspended riverine particles or weathering during mixing with seawater within the low salinity zones of the Kalix and Råne River estuaries.The existence of non-conservative mixing of Li in estuarine environments suggests that the Li isotopic riverine input signature could be modified within estuaries, which may affect the marine and palaeo-marine budgets. Hence, this has important implications for the estimation of the fluvial Li flux into the oceans
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| 2. |
- Sproson, Adam D., et al.
(författare)
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Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations
- 2022
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X. ; 577
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Tidskriftsartikel (refereegranskat)abstract
- The Ordovician (∼487 to 443 Ma) ended with the formation of extensive Southern Hemisphere ice sheets, known as the Hirnantian glaciation, and the second largest mass extinction in Earth History. It was followed by the Silurian (∼443 to 419 Ma), one of the most climatically unstable periods of the Phanerozoic as evidenced by several large scale (>5‰) carbon isotope (δ13C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187Os/188Os) and lithium (δ7Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ13C excursions. Osmium and Li isotope records resemble those previously recorded for the Hirnantian glaciation suggesting a similar causal mechanism. When combined with a new dynamic carbon-osmium-lithium biogeochemical model we suggest that astronomical forcing of the marine organic carbon cycle, as opposed to a decline in volcanic arc degassing or the rise of early land plants, resulted in drawdown of atmospheric CO2, triggering continental scale glaciation, intense global cooling and eustatic sea-level lows recognised in the geological record. Lower atmospheric pCO2 and temperatures during the Hirnantian and Silurian glaciations suppressed CO2 removal by silicate weathering, driving 187Os/188Os and δ7Li variability, supporting the existence of climate-regulating feedbacks.
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