Publications by authors named "Sandra Kirtland Turner"

4 Publications

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Past climates inform our future.

Science 2020 11;370(6517)

Department of Oceanography, Texas A&M University, College Station, TX, USA.

As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change. Here, we review the relevancy of paleoclimate information for climate prediction and discuss the prospects for emerging methodologies to further insights gained from past climates. Advances in proxy methods and interpretations pave the way for the use of past climates for model evaluation-a practice that we argue should be widely adopted.
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http://dx.doi.org/10.1126/science.aay3701DOI Listing
November 2020

Constraints on the onset duration of the Paleocene-Eocene Thermal Maximum.

Philos Trans A Math Phys Eng Sci 2018 Oct;376(2130)

Department of Earth Sciences, University of California, Riverside, CA 92521, USA

The Paleocene-Eocene Thermal Maximum (PETM, approx. 56 Ma) provides a test case for investigating how the Earth system responds to rapid greenhouse gas-driven warming. However, current rates of carbon emissions are approximately 10 Pg C yr, whereas those proposed for the PETM span orders of magnitude-from ≪1 Pg C yr to greater than the anthropogenic rate. Emissions rate estimates for the PETM are hampered by uncertainty over the total mass of PETM carbon released as well as the PETM onset duration. Here, I review constraints on the onset duration of the carbon isotope excursion (CIE) that is characteristic of the event with a focus on carbon cycle model-based attempts that forgo the need for a traditional sedimentary age model. I also review and compare existing PETM carbon input scenarios employing the Earth system model cGENIE and suggest another possibility-that abrupt input of an isotopically depleted carbon source combined with elevated volcanic outgassing over a longer interval can together account for key features of the PETM CIE.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.
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http://dx.doi.org/10.1098/rsta.2017.0082DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127381PMC
October 2018

A probabilistic assessment of the rapidity of PETM onset.

Nat Commun 2017 08 25;8(1):353. Epub 2017 Aug 25.

Department of Earth Sciences, University of California, Riverside, Riverside, CA, 92506, USA.

Knowledge of the onset duration of the Paleocene-Eocene Thermal Maximum-the largest known greenhouse-gas-driven global warming event of the Cenozoic-is central to drawing inferences for future climate change. Single-foraminifera measurements of the associated carbon isotope excursion from Maud Rise (South Atlantic Ocean) are controversial, as they seem to indicate geologically instantaneous carbon release and anomalously long ocean mixing. Here, we fundamentally reinterpret this record and extract the likely PETM onset duration. First, we employ an Earth system model to illustrate how the response of ocean circulation to warming does not support the interpretation of instantaneous carbon release. Instead, we use a novel sediment-mixing model to show how changes in the relative population sizes of calcareous plankton, combined with sediment mixing, can explain the observations. Furthermore, for any plausible PETM onset duration and sampling methodology, we place a probability on not sampling an intermediate, syn-excursion isotopic value. Assuming mixed-layer carbonate production continued at Maud Rise, we deduce the PETM onset was likely <5 kyr.Single-foraminifera measurements of the PETM carbon isotope excursion from Maud Rise have been interpreted as indicating geologically instantaneous carbon release. Here, the authors explain these records using an Earth system model and a sediment-mixing model and extract the likely PETM onset duration.
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http://dx.doi.org/10.1038/s41467-017-00292-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5572461PMC
August 2017

Stringent response processes suppress DNA damage sensitivity caused by deficiency in full-length translation initiation factor 2 or PriA helicase.

Mol Microbiol 2014 Apr 28;92(1):28-46. Epub 2014 Feb 28.

Department of Biochemistry and Molecular & Cellular Biology, Georgetown University Medical Center, Box 571455, 3900 Reservoir Rd. NW, Washington, DC, 20057-1455, USA.

When Escherichia coli grows in the presence of DNA-damaging agents such as methyl methanesulphonate (MMS), absence of the full-length form of Translation Initiation Factor 2 (IF2-1) or deficiency in helicase activity of replication restart protein PriA leads to a considerable loss of viability. MMS sensitivity of these mutants was contingent on the stringent response alarmone (p)ppGpp being at low levels. While zero levels (ppGpp°) greatly aggravated sensitivity, high levels promoted resistance. Moreover, M+ mutations, which suppress amino acid auxotrophy of ppGpp° strains and which have been found to map to RNA polymerase subunits, largely restored resistance to IF2-1- and PriA helicase-deficient mutants. The truncated forms IF2-2/3 played a key part in inducing especially severe negative effects in ppGpp° cells when restart function priB was knocked out, causing loss of viability and severe cell filamentation, indicative of SOS induction. Even a strain with the wild-type infB allele exhibited significant filamentation and MMS sensitivity in this background whereas mutations that prevent expression of IF2-2/3 essentially eliminated filamentation and largely restored MMS resistance. The results suggest different influences of IF2-1 and IF2-2/3 on the replication restart system depending on (p)ppGpp levels, each having the capacity to maximize survival under differing growth conditions.
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http://dx.doi.org/10.1111/mmi.12538DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4008491PMC
April 2014