Hafnium isotopic variations in East Atlantic intraplate volcanism

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), 176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (176Hf/177Hfm up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over >10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed "C" mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMUlike endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has "C"-like isotope compositions and is believed to represent subducted, =1 Ga

Symbiont Diversity of Zooxanthellae (Symbiodinium Spp.) In Porities Astreoides and Montastraea Cavernosa from a Reciprocal Transplant in the Lower Florida Keys

In recent years, coral reefs worldwide have suffered high mortality rates due to coral bleaching, a phenomenon contributing to a 40% decrease in coral cover in the Florida Keys since the 1997/98 El Niño event. In the Florida Keys, coral from inshore reefs are known to be more thermotolerant than their conspecifics from offshore reefs but the mechanism behind this difference is unclear. In this study we conducted a two-year, reciprocal transplant of Porites astreoides and Montastraea cavernosa from an inshore and offshore reef in the lower Florida Keys to determine if changes in the dominant symbiotic algae (Symbiodinium spp.) could explain variation in holobiont tolerance as well as to assess the possibility of acclimatization to a changing stress regime. Increased complexity and diversity was demonstrated in the composition of Symbiodinium spp. from both coral species collected at the offshore reef when compared to conspecifics collected inshore. As a result of this complexity, the offshore reef samples displayed higher numbers of transitions of zooxanthellae subclade types between seasons, while inshore fragments demonstrated more stability and may explain previously measured thermotolerance. Additionally, the known thermotolerant subclade type D1 was associated with one M. cavernosa fragment from the inshore reef. When fragments were transplanted, compositional patterns of Symbiodinium spp. were retained from site of collection, indicating a lack of acclimatization to a new environment over the lengthy two-year experiment. These results demonstrate variability in the dominant Symbiodinium spp. of P. astreoides and M. cavernosa conspecifics from inshore and offshore reefs in the lower Florida Keys and point to possible patterns in holobiont thermotolerance. This variability may be key to the continued persistence of these species in the face of climate change, but future studies are needed to determine the mechanisms and range in which these subclade types withstand thermal stress

Lipid biomarkers in Symbiodinium dinoflagellates : new indicators of thermal stress

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Coral Reefs 32 (2013): 923-934, doi:10.1007/s00338-013-1076-3.Lipid content and fatty acid profiles of corals and their dinoflagellate endosymbionts are known to vary in response to high temperature stress. To better understand the heat stress response in these symbionts, we investigated cultures of Symbiodinium goreauii type C1 and Symbiodinium clade subtype D1 grown under a range of temperatures and durations. The predominant lipids produced by Symbiodinium are palmitic (C16) and stearic (C18) saturated fatty acids and their unsaturated analogs, docosahexaenoic (C22:6, n-3) polyunsaturated fatty acid (PUFA), and a variety of sterols. The relative amount of unsaturated acids within the C18 fatty acids in Symbiodinium tissue decreases in response to thermal stress. Prolonged exposure to high temperature also causes a decrease in abundance of fatty acids relative to sterols. These shifts in fatty acids and sterols are common to both types C1 and D1, but the apparent thermal threshold of lipid changes is lower for type C1. This work indicates that ratios among free fatty acids and sterols in Symbiodinium can be used as sensitive indicators of thermal stress. If the Symbdionium lipid stress response is unchanged in hospite, the algal heat stress biomarkers we have identified could be measured to detect thermal stress within the coral holobiont.. These results provide new insights into the potential role of lipids in the overall Symbiodinium thermal stress response.This research was supported by Award No. USA 00002 to K. Hughen made by King Abdullah University of Science and Technology (KAUST).2014-12-0

The CRESST Experiment: Recent Results and Prospects

The CRESST experiment seeks hypothetical WIMP particles that could account for the bulk of dark matter in the Universe. The detectors are cryogenic calorimeters in which WIMPs would scatter elastically on nuclei, releasing phonons. The first phase of the experiment has successfully deployed several 262 g sapphire devices in the Gran Sasso underground laboratories. A main source of background has been identified as microscopic mechanical fracturing of the crystals, and has been eliminated, improving the background rate by up to three orders of magnitude at low energies, leaving a rate close to one count per day per kg and per keV above 10 keV recoil energy. This background now appears to be dominated by radioactivity, and future CRESST scintillating calorimeters which simultaneously measure light and phonons will allow rejection of a great part of it.Comment: To appear in the proceedings of the CAPP2000 Conference, Verbier, Switzerland, July, 2000 (eds J. Garcia-Bellido, R. Durrer, and M. Shaposhnikov

The CRESST Dark Matter Search

We present first competitive results on WIMP dark matter using the phonon-light-detection technique. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils. The observed count rate in the neutron band is compatible with the rate expected from neutron background. CRESST is presently being upgraded with a 66 channel SQUID readout system, a neutron shield and a muon veto system. This results in a significant improvement in sensitivity.Comment: 6 pages, 3 figures, to be published in the proceedings of the 5th International Workshop on the Identification and Detection of Dark Matter IDM 2004, Edinburgh, Sept. 2004, World Scientifi