Dataset Information

Molecular fossils from phytoplankton reveal secular Pco₂ trend over the Phanerozoic.

ABSTRACT: Past changes in the atmospheric concentration of carbon dioxide (Pco₂) have had a major impact on earth system dynamics; yet, reconstructing secular trends of past Pco₂ remains a prevalent challenge in paleoclimate studies. The current long-term Pco₂ reconstructions rely largely on the compilation of many different proxies, often with discrepancies among proxies, particularly for periods older than 100 million years (Ma). Here, we reconstructed Phanerozoic Pco₂ from a single proxy: the stable carbon isotopic fractionation associated with photosynthesis (?_p) that increases as Pco₂ increases. This concept has been widely applied to alkenones, but here, we expand this concept both spatially and temporally by applying it to all marine phytoplankton via a diagenetic product of chlorophyll, phytane. We obtained data from 306 marine sediments and oils, which showed that ?_p ranges from 11 to 24‰, agreeing with the observed range of maximum fractionation of Rubisco (i.e., 25 to 28‰). The observed secular Pco₂ trend derived from phytane-based ?_p mirrors the available compilations of Pco₂ over the past 420 Ma, except for two periods in which our higher estimates agree with the warm climate during those time periods. Our record currently provides the longest secular trend in Pco₂ based on a single marine proxy, covering the past 500 Ma of Earth history.

SUBMITTER: Witkowski CR

PROVIDER: S-EPMC6261654 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Molecular fossils from phytoplankton reveal secular Pco2 trend over the Phanerozoic.

Witkowski Caitlyn R CR Weijers Johan W H JWH Blais Brian B Schouten Stefan S Sinninghe Damsté Jaap S JS

Science advances 20181128 11

Past changes in the atmospheric concentration of carbon dioxide (Pco2) have had a major impact on earth system dynamics; yet, reconstructing secular trends of past Pco2 remains a prevalent challenge in paleoclimate studies. The current long-term Pco2 reconstructions rely largely on the compilation of many different proxies, often with discrepancies among proxies, particularly for periods older than 100 million years (Ma). Here, we reconstruct ...[more]

PMID: 30498776

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Project description:Evidence is compiled to demonstrate a redox scale within Earth's photosynthesisers that correlates the specificity of their RuBisCO with organismal metabolic tolerance to anoxia, and ecological selection by dissolved O2/CO2 and nutrients. The Form 1B RuBisCO found in the chlorophyte green algae, has a poor selectivity between the two dissolved substrates, O2 and CO2, at the active site. This enzyme appears adapted to lower O2/CO2 ratios, or more "anoxic" conditions and therefore requires additional energetic or nutrient investment in a carbon concentrating mechanism (CCM) to boost the intracellular CO2/O2 ratio and maintain competitive carboxylation rates under increasingly high O2/CO2 conditions in the environment. By contrast the coccolithophores and diatoms evolved containing the more selective Rhodophyte Form 1D RuBisCO, better adapted to a higher O2/CO2 ratio, or more oxic conditions. This Form 1D RuBisCO requires lesser energetic or nutrient investment in a CCM to attain high carboxylation rates under environmentally high O2/CO2 ratios. Such a physiological relationship may underpin the succession of phytoplankton in the Phanerozoic oceans: the coccolithophores and diatoms took over the oceanic realm from the incumbent cyanobacteria and green algae when the upper ocean became persistently oxygenated, alkaline and more oligotrophic. The facultatively anaerobic green algae, able to tolerate the anoxic conditions of the water column and a periodically inundated soil, were better poised to adapt to the fluctuating anoxia associated with periods of submergence and emergence and transition onto the land. The induction of a CCM may exert a natural limit to the improvement of RuBisCO efficiency over Earth history. Rubisco specificity appears to adapt on the timescale of ?100 Myrs. So persistent elevation of CO2/O2 ratios in the intracellular environment around the enzyme, may induce a relaxation in RuBisCO selectivity for CO2 relative to O2. The most efficient RuBisCO for net carboxylation is likely to be found in CCM-lacking algae that have been exposed to hyperoxic conditions for at least 100 Myrs, such as intertidal brown seaweeds.

Project description:Objective:Tuberculosis (TB) is a major public health problem in China, and contriving a long-term forecast is a useful aid for better launching prevention initiatives. Regrettably, such a forecasting method with robust and accurate performance is still lacking. Here, we aim to investigate its potential of the error-trend-seasonal (ETS) framework through a series of comparative experiments to analyze and forecast its secular epidemic seasonality and trends of TB incidence in China. Methods:We collected the TB incidence data from January 1997 to August 2019, and then partitioning the data into eight different training and testing subsamples. Thereafter, we constructed the ETS and seasonal autoregressive integrated moving average (SARIMA) models based on the training subsamples, and multiple performance indices including the mean absolute deviation, mean absolute percentage error, root-mean-squared error, and mean error rate were adopted to assess their simulation and projection effects. Results:In the light of the above performance measures, the ETS models provided a pronounced improvement for the long-term seasonality and trend forecasting in TB incidence rate over the SARIMA models, be it in various training or testing subsets apart from the 48-step ahead forecasting. The descriptive results to the data revealed that TB incidence showed notable seasonal characteristics with predominant peaks of spring and early summer and began to be plunging at on average 3.722% per year since 2008. However, this rate reduced to 2.613% per year since 2015 and furthermore such a trend would be predicted to continue in years ahead. Conclusion:The ETS framework has the ability to conduct long-term forecasting for TB incidence, which may be beneficial for the long-term planning of the TB prevention and control. Additionally, considering the predicted dropping rate of TB morbidity, more particular strategies should be formulated to dramatically accelerate progress towards the goals of the End TB Strategy.

Dataset Information

Molecular fossils from phytoplankton reveal secular Pco₂ trend over the Phanerozoic.

Publications

Molecular fossils from phytoplankton reveal secular <i>P</i>co<sub>2</sub> trend over the Phanerozoic.

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