Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lechler, Maria; Strandmann, Philip A.E. Pogge von; Jenkyns, Hugh C.; Prosser, Giacomo; Parente, Mariano

doi:10.1016/j.epsl.2015.09.052

Cited by 100 publications

(76 citation statements)

References 96 publications

(157 reference statements)

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“…Limited Li isotopic data are also consistent with lower weathering fluxes before the latest Cretaceous Period (e.g. [87]). Proxies for continental weathering and erosion are, thus, consistent with the hypothesis of increasing resource availability at the base of marine trophic pyramids over the last 80 Myr or so, helping to explain the persistence if not the initiation of predator-driven evolutionary trends among marine animals.…”

Section: Discussionsupporting

confidence: 60%

A bottom-up perspective on ecosystem change in Mesozoic oceans

Knoll

Follows

2016

Proc. R. Soc. B.

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Mesozoic and Early Cenozoic marine animals across multiple phyla record secular trends in morphology, environmental distribution, and inferred behaviour that are parsimoniously explained in terms of increased selection pressure from durophagous predators. Another systemic change in Mesozoic marine ecosystems, less widely appreciated than the first, may help to explain the observed animal record. Fossils, biomarker molecules, and molecular clocks indicate a major shift in phytoplankton composition, as mixotrophic dinoflagellates, coccolithophorids and, later, diatoms radiated across shelves. Models originally developed to probe the ecology and biogeography of modern phytoplankton enable us to evaluate the ecosystem consequences of these phytoplankton radiations. In particular, our models suggest that the radiation of mixotrophic dinoflagellates and the subsequent diversification of marine diatoms would have accelerated the transfer of primary production upward into larger size classes and higher trophic levels. Thus, phytoplankton evolution provides a mechanism capable of facilitating the observed evolutionary shift in Mesozoic marine animals.

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Section: Discussionsupporting

confidence: 60%

A bottom-up perspective on ecosystem change in Mesozoic oceans

Knoll

Follows

2016

Proc. R. Soc. B.

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“…Therefore, fossil shells of calcitic mollusks are probably not good targets for inferring the past Li isotope composition or temperature of the oceans, unless the reconstructions are limited to single species. As mollusks can constitute a significant component of bulk carbonates (Wilkinson, 1979), it is important to take them into account to understand the Li isotope composition of bulk carbonates (Lechler et al, 2015;Pogge von Strandmann et al, 2013), at least when these are fossiliferous. The δ 7 Li and Li/Ca values of aragonitic mollusks are similar to inorganic aragonite composition.…”

Section: Implications For Reconstructing Past Seawater Compositionmentioning

confidence: 99%

“…Furthermore, the residence time of Li in the ocean is about 1-3 Ma, and the marine Li isotopic composition (δ 7 Li = [( 7 Li/ 6 Li)/( 7 Li/ 6 Li) L-SVEC -1] ×1000; expressed in ‰) and concentration are spatially uniform (Angino and Billings 1966). Published Li isotope records in foraminifera (Hathorne and James, 2006;Misra and Froelich, 2012) and bulk carbonates (Lechler et al, 2015;Pogge von Strandmann et al, 2013;Pogge von Strandmann et al, 2017) are characterized by large (several per mil) δ 7 Li variations. These changes have been attributed to past changes in weathering congruency, intensity, or rates (Bouchez et al, 2013;Froelich and Misra, 2014;Li and West, 2014;Wanner et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

The Li isotope composition of marine biogenic carbonates: Patterns and mechanisms

Dellinger

West

Paris

et al. 2018

Geochimica et Cosmochimica Acta

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Little is known about the fractionation of Li isotopes during formation of biogenic carbonates, which form the most promising geological archives of past seawater composition.Here we investigated the Li isotope composition (δ 7 Li) and Li/Ca ratios of organisms that are abundant in the Phanerozoic record, mollusks (mostly bivalves), echinoderms, and brachiopods. The measured samples include (i) modern calcite and aragonite shells from variable species and natural environments (13 mollusk samples, 5 brachiopods and 3 echinoderms), and (ii) shells from organisms grown under controlled conditions at various temperatures. When possible, the mollusk shell ultrastructure was micro-sampled in order to assess intra-shell heterogeneity. In this paper, we systematically characterize the respective influence of mineralogy, temperature, and biological processes on the δ 7 Li and Li/Ca of these shells and compare with published data for other taxa (foraminifera and corals).Aragonitic mollusks have the lowest δ 7 Li, ranging from +16 to +22‰, echinoderms have constant δ 7 Li of about +24‰, brachiopods have δ 7 Li of +25 to +28‰, and finally calcitic mollusks have the largest range and highest δ 7 Li values, ranging from +25‰ to +40‰. Measured brachiopods have similar δ 7 Li compared to inorganic calcite precipitated from seawater (δ 7 Li of +27 to +29‰), indicating minimum influence of vital effects, as also observed for other isotope systems and making them a potentially viable proxy of past seawater composition. Calcitic mollusks, on the contrary, are not a good archive for seawater paleo-δ 7 Li because many samples have significantly higher δ 7 Li values than inorganic calcite and display large inter-species variability, which suggest large vital effects. In addition, we observe very large intra-shell variability, in particular for mixed calcitearagonite shells (over 20‰ variability), but also in mono-mineralic shells (up to 12‰ variability). Aragonitic bivalves have less variable δ 7 Li (7‰ variability) compared to calcitic mollusks, but with significantly lower δ 7 Li compared to inorganic aragonite, indicating the existence of vital effects. Bivalves grown at various temperatures show that temperature has only a minor influence on fractionation of Li isotopes during shell precipitation. Interestingly, we observe a strong correlation (R 2 =0.83) between the Li/Mg ratio in bivalve Mytilus edulis and temperature with potential implications for paleo-temperature reconstructions.Finally, we observe a negative correlation between the δ 7 Li and both the Li/Ca and Mg/Ca ratio of calcite mollusks, which we relate to biomineralization processes.

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“…In brief, the model uses Li formulations from previous work (Pogge von Strandmann et al, 2013;Lechler et al, 2015), with an added temperature dependence on the Li sink with a sensitivity of -0.15 ‰/K (Li and West, 2014), and links the weathering flux to that calculated by the carbon cycle model (based on GEOCARB III). Existing climate models suggest that pCO 2 needed to halve to ~8 PAL (present atmospheric level) to trigger the Hirnantian glaciation (Pohl et al, 2016).…”

Section: Figurementioning

confidence: 99%

“…The Hirnantian has been compared to Cenozoic glaciations (Ghienne et al, 2014), where both periods are now characterised by increasing δ 7 Li values (Misra and Froelich, 2012). The positive δ 7 Li excursion during the Hirnantian cooling event also compares well to negative δ 7 Li excursions during warming events (Pogge von Strandmann et al, 2013;Lechler et al, 2015). Overall, therefore, this study shows that if a tectonic-driven climate control (degassing) can push the climate system out of balance, a temperature-dependent feedback via silicate weathering will eventually stabilise the climate.…”

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confidence: 99%

Global climate stabilisation by chemical weathering during the Hirnantian glaciation

Strandmann¹,

Desrochers²,

Murphy³

et al. 2017

Geochem. Persp. Let.

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Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled "weathering thermostat" has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (δ 7 Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma). We find a positive δ 7 Li excursion, suggestive of a silicate weathering decline. Using a coupled lithium-carbon model, we show that initiation of the glaciation was likely caused by declining CO 2 degassing, which triggered abrupt global cooling, and much lower weathering rates. This lower CO 2 drawdown during the glaciation allowed climatic recovery and deglaciation. Combined, the data and model provide support from the geological record for the operation of the weathering thermostat. LetterThe recovery and stabilisation of Earth's climate system from perturbations is central to the continued survival of life. Chemical weathering of continental silicate rocks driving marine carbonate precipitation is the Earth's primary longterm mechanism for removal of atmospheric CO 2 (Berner, 2003 feedback control on weathering rates (i.e. greater temperatures cause higher weathering rates, removing more CO 2 ) would result in a climate-stabilising mechanism. This "weathering thermostat" has long been postulated and assumed in models (Colbourn et al., 2015). However, direct evidence for weathering rate changes in response to climate perturbations has been harder to pin down in the geological record.The Late Ordovician Hirnantian (~445 Ma) records the second largest mass extinction in Earth history. This was likely caused by rapidly decreasing temperatures, culminating in an ice-sheet over Gondwana (Elrick et al., 2013). As such, similarities exist between the Hirnantian and the Late Cenozoic glaciations (Ghienne et al., 2014). The behaviour of atmospheric CO 2 is of particular interest, because of the potential role of declining CO 2 in initiating the glaciation and of increasing CO 2 in terminating it (Vandenbroucke et al., 2010). Either or both could have involved changes in silicate weathering rates (Berner, 2003). The combination of changes in weathering rates and pCO 2 also resulted in a global positive δ 13 C excursion (HICE) (Lenton et al., 2012;Ghienne et al., 2014). Osmium isotopes have suggested a decline in weathering during the glacial maximum (Finlay et al., 2010). However, Os mainly traces weathering provenance, rather than weathering rates or processes. Lithium isotopes are the only tracer available whose behaviour is solely controlled by silicate weathering processes, and therefore give a unique insight into CO 2 drawdown and climate-stabilisation.Lithium isotopes (δ 7 Li) are not fractionated by biological processes (Pogge von Strandmann et al., 2016), and are not affected by carbon...

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Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Cited by 100 publications

References 96 publications

A bottom-up perspective on ecosystem change in Mesozoic oceans

A bottom-up perspective on ecosystem change in Mesozoic oceans

The Li isotope composition of marine biogenic carbonates: Patterns and mechanisms

Global climate stabilisation by chemical weathering during the Hirnantian glaciation

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