David W. Szymanski

Galapagos‐OIB signature in southern Central America: Mantle refertilization by arc–hot spot interaction

[1] Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America (central Costa Rica and Panama) have isotopic and trace element compositions with an ocean island basalt (OIB) affinity, similar to the Galapagos-OIB lavas (e.g., Ba/La 10, 206Pb/204Pb > 18.8). Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene ∼6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas similar to the Galapagos hot spot. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hot spot tracks (the Seamount Province and the Cocos/Coiba Ridge) at the Middle American Trench. The higher Pb isotopic ratios, relatively lower Sr and Nd isotopic ratios, and enriched incompatible-element signature of central Costa Rican magmas can be explained by arc–hot spot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridge (Central Galapagos Domain). Geological and geochemical evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hot spot tracks, which started to collide with the margin ∼8 Ma ago. The Galapagos hot spot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

Determination of Trace Elemental Concentrations in Document Papers for Forensic Comparison Using Inductively Coupled Plasma–Mass Spectrometry

Abstract:  With improvements in manufacturing procedures, comparing physical characteristics of paper samples may not offer sufficient discrimination among different vendors. In this work, the potential to differentiate paper samples based on trace element concentrations was investigated. Paper samples from two different vendors were microwave‐digested and trace element concentrations (Mg, Al, Mn, Fe, Sr, Y, Ba, Ce, and Nd) were determined using inductively coupled plasma–mass spectrometry. Differences in concentration were assessed statistically using two‐way ANOVA and Tukey’s honestly significant differences test. Elemental concentrations were shown to be consistent across a single sheet as well as within a single ream of paper for each vendor. Reams from vendor A were differentiated based on Al and Ba concentration while reams from vendor B were differentiated based on Mg, Mn, and Sr concentrations. Paper was differentiated according to vendor based on significant differences in Ba, Sr, Ce, and Nd concentrations.

Characterization of undigested particulate material following microwave digestion of recycled document papers

Abstract:  Recycled document paper was microwave digested in a solution of HNO3 and H2O2 prior to analysis by inductively coupled plasma mass spectrometry (ICP‐MS) to determine the trace elemental concentrations within the paper. Undigested particulate material was observed and subsequently characterized as a mixture of kaolin (clay) and TiO2 by Fourier transform infrared spectroscopy and X‐ray diffraction spectroscopy. The effect of the particulate material on the elemental concentrations was then investigated. Paper samples were completely digested in hydrofluoric acid (HF) and element concentrations determined in the HF and HNO3/H2O digests were statistically compared using Student’s t‐test (95% confidence limit). Statistical differences in element concentrations between the two digests were observed for only four elements and there was no evidence of element adsorption by the particulate material. Hence, the HNO3/H2O2 digestion proved sufficient to digest paper for ICP‐MS analysis, eliminating the need to use the hazardous and corrosive HF matrix.

Speaking Out or Staying Quiet on Climate Change: Broadcast Meteorologists Influenced by the Need to Be Pithy, Popular and Politically Cautious

Broadcast meteorologists are in a position to convey knowledge about climate change to the public. These media professionals make deliberate choices about what information to omit or present to their audiences. Interviews with broadcast meteorologists revealed a wide range of attitudes about conveying climate science to their viewers. Three significant concerns emerged from conversations with participants: on-air time constraints are non-negotiable, pressure to be a “popular” personality is constant, and there is an enduring apprehension about taking a position associated with a perceived controversial topic or political viewpoint. Discomfort with these constraints affects the content choices of broadcast meteorologists who might otherwise take a stand representing the scientific consensus on climate change.

A Picture is Worth a Thousand Words: Commentary of Broadcast Meteorologists on the Visual Presentation of Climate Change

Broadcast meteorologists are trusted by the general public to convey knowledge on climate change and they make choices about what information to present to their viewing audiences. Interviews with broadcast meteorologists revealed a wide range in their knowledge base and confidence in conveying climate science to their audiences. However, all interviewees agreed that visual images are an essential means for communicating with their viewers. Three major themes emerged from interviews with participants: visual imagery is important, dramatic images are powerful motivators, and the new visual presentation technologies have great value.