Showing papers by "David W. Lea published in 2008"
University of Cambridge1, Centre national de la recherche scientifique2, University of Kiel3, University of California, Santa Cruz4, National Oceanography Centre5, University of Barcelona6, UPRRP College of Natural Sciences7, Lamont–Doherty Earth Observatory8, Australian National University9, University of South Florida St. Petersburg10, University of Bremen11, Eckerd College12, Open University13, Japan Agency for Marine-Earth Science and Technology14, Oregon State University15, University of California, Santa Barbara16, University of Colorado Boulder17, Autonomous University of Barcelona18, University of Bristol19, PetroChina20, Rutgers University21, University of California, Davis22, Kōchi University23, University of Southern California24, University of South Carolina25
TL;DR: In this article, an interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg /Ca ratios worldwide.
Abstract: An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to 6 mmol/mol) were circulated with a dissolution protocol for analysis. Participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories. Statistical analysis was performed in accordance with the International Standardization Organization standard 5725, which is based on the analysis of variance (ANOVA) technique. Repeatability (RSDr%), an indicator of intralaboratory precision, for Mg/Ca determinations in solutions after centrifuging increased with decreasing Mg/Ca, ranging from 0.78% at Mg/Ca = 5.56 mmol/mol to 1.15% at Mg/Ca = 0.79 mmol/mol. Reproducibility (RSDR%), an indicator of the interlaboratory method precision, for Mg/Ca determinations in centrifuged solutions was noticeably worse than repeatability, ranging from 4.5% at Mg/Ca = 5.56 mmol/mol to 8.7% at Mg/Ca = 0.79 mmol/mol. Results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility. Additionally, the study confirmed the suitability of these solid standards as reference materials for foraminiferal Mg/Ca (and Sr/Ca) determinations, provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases.
196 citations
TL;DR: A 3-ma benthic foraminifer Mg/Ca record of Southern Ocean temperatures across the middle Miocene climate transition reveals ∼2 ± 2°C cooling (14.2-13.8 Ma), indicating that ∼70% of the increase relates to ice growth.
Abstract: [1] Relative contributions of ice volume and temperature change to the global ∼1‰ δ18O increase at ∼14 Ma are required for understanding feedbacks involved in this major Cenozoic climate transition. A 3-ma benthic foraminifer Mg/Ca record of Southern Ocean temperatures across the middle Miocene climate transition reveals ∼2 ± 2°C cooling (14.2–13.8 Ma), indicating that ∼70% of the increase relates to ice growth. Seawater δ18O, calculated from Mg/Ca and δ18O, suggests that at ∼15 Ma Antarctica's cryosphere entered an interval of apparent eccentricity-paced expansion. Glaciations increased in intensity, revealing a central role for internal climate feedbacks. Comparison of ice volume and ocean temperature records with inferred pCO2 levels indicates that middle Miocene cryosphere expansion commenced during an interval of Southern Ocean warmth and low atmospheric pCO2. The Antarctic system appears sensitive to changes in heat/moisture supply when atmospheric pCO2 was low, suggesting the importance of internal feedbacks in this climate transition.
187 citations
TL;DR: This paper examined the implications of adjusting available equatorial Pacific SST records based on Mg/Ca paleothermometry to account for the inferred past variations of seawater Mg and Ca.
92 citations
TL;DR: In this paper, the results of carbon-13, oxygen-18 and thermal labeling experiments conducted under high (HL) and low light (LL) regimes that vary symbiont photosynthetic activity were presented.
42 citations
TL;DR: Analysis of contemporary factors coupled with analyses of morphological variability holds promise for addressing the functional roles of mussel height and width and what proportion of phenotypic variability can be attributed to environmental factors.
Abstract: A mussel's shell records its history of growth. We investigated variability in the size and shape of mussel shells of Mytilus californianus Conrad (1837) to test the hypothesis that the mussel shell provides information on the contemporary condition of the mussel. Two factors were associated with shape: an epithelial discoloration and the Sr/Ca in the shell nacre. Sr/Ca data distinguished the mussel populations as did a discriminate analysis that included the trace metal ratios; Sr/Ca, Mg/Ca, Mn/ Ca, Ag/Ca, Cd/Ca, Ba/Ca, and Pb/Ca. Size varied independently of shape and was not associated with the two factors. However, a null model that describes the morphological variability in height and width suggests that mussel size also plays a central role in partitioning phenotypic variability. These analyses of contemporary factors coupled with analyses of morphological variability holds promise for addressing the functional roles of mussel height and width and what proportion of phenotypic variability can be attributed to environmental factors.
6 citations