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241 results on '"Wallace, Malcolm W."'

8. Uncovering the Ediacaran phosphorus cycle

Author

Dodd, Matthew S., Shi, Wei, Li, Chao, Zhang, Zihu, Cheng, Meng, Gu, Haodong, Hardisty, Dalton S., Loyd, Sean J., Wallace, Malcolm W., vS. Hood, Ashleigh, Lamothe, Kelsey, Mills, Benjamin J. W., Poulton, Simon W., and Lyons, Timothy W.

Published
2023
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12. Contents

Author

Wallace, Malcolm W.

Published
1952

21. A lithium-isotope perspective on the evolution of carbon and silicon cycles

Author

Kalderon-Asael, Boriana, Katchinoff, Joachim A. R., Planavsky, Noah J., Hood, Ashleigh v. S., Dellinger, Mathieu, Bellefroid, Eric J., Jones, David S., Hofmann, Axel, Ossa, Frantz Ossa, Macdonald, Francis A., Wang, Chunjiang, Isson, Terry T., Murphy, Jack G., Higgins, John A., West, A. Joshua, and Wallace, Malcolm W.

Subjects
Lithium -- Chemical properties, Carbon cycle (Biogeochemistry) -- Natural history, Isotopes -- Chemical properties, Silicon -- Natural history -- Chemical properties, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

The evolution of the global carbon and silicon cycles is thought to have contributed to the long-term stability of Earth's climate.sup.1-3. Many questions remain, however, regarding the feedback mechanisms at play, and there are limited quantitative constraints on the sources and sinks of these elements in Earth's surface environments.sup.4-12. Here we argue that the lithium-isotope record can be used to track the processes controlling the long-term carbon and silicon cycles. By analysing more than 600 shallow-water marine carbonate samples from more than 100 stratigraphic units, we construct a new carbonate-based lithium-isotope record spanning the past 3 billion years. The data suggest an increase in the carbonate lithium-isotope values over time, which we propose was driven by long-term changes in the lithium-isotopic conditions of sea water, rather than by changes in the sedimentary alterations of older samples. Using a mass-balance modelling approach, we propose that the observed trend in lithium-isotope values reflects a transition from Precambrian carbon and silicon cycles to those characteristic of the modern. We speculate that this transition was linked to a gradual shift to a biologically controlled marine silicon cycle and the evolutionary radiation of land plants.sup.13,14. Analysis of shallow-water marine carbonate samples from 101 stratigraphic units allows construction of a record of lithium isotopes from the past 3 billion years, tracking the evolution of the global carbon and silicon cycles., Author(s): Boriana Kalderon-Asael [sup.1] , Joachim A. R. Katchinoff [sup.1] , Noah J. Planavsky [sup.1] , Ashleigh v. S. Hood [sup.2] , Mathieu Dellinger [sup.3] , Eric J. Bellefroid [sup.1] [...]

Published
2021
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46. Eocene to Oligocene terrestrial Southern Hemisphere cooling caused by declining 𝑝CO2

Author

Lauretano, Vittoria, Kennedy-asser, Alan T., Korasidis, Vera A., Wallace, Malcolm W., Valdes, Paul J., Lunt, Daniel J., Pancost, Richard D., and Naafs, B. David A.

Abstract

The greenhouse-to-icehouse climate transition from the Eocene into the Oligocene is well documented by sea surface temperature records from the southwest Pacific and Antarctic margin, which show evidence of pronounced long-term cooling. However, identification of a driving mechanism depends on a better understanding of whether this cooling was also present in terrestrial settings. Here, we present a semi-continuous terrestrial temperature record spanning from the middle Eocene to the early Oligocene (~41–33 million years ago), using bacterial molecular fossils (biomarkers) preserved in a sequence of southeast Australian lignites. Our results show that mean annual temperatures in southeast Australia gradually declined from ~27 °C (±4.7 °C) during the middle Eocene to ~22–24 °C (±4.7 °C) during the late Eocene, followed by a ~2.4 °C-step cooling across the Eocene/Oligocene boundary. This trend is comparable to other temperature records in the Southern Hemisphere, suggesting a common driving mechanism, likely pCO2. We corroborate these results with a suite of climate model simulations demonstrating that only simulations including a decline in pCO2 lead to a cooling in southeast Australia consistent with our proxy record. Our data form an important benchmark for testing climate model performance, sea–land interaction and climatic forcings at the onset of a major Antarctic glaciation.

Published
2021

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