Depleted dissolved organic carbon and distinct bacterial communities in the water column of a rapid-flushing coral reef ecosystem

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 5 (2011): 1374–1387, doi:10.1038/ismej.2011.12.Coral reefs are highly productive ecosystems bathed in unproductive, low-nutrient oceanic waters, where microbially-dominated food webs are supported largely by bacterioplankton recycling of dissolved compounds. Despite evidence that benthic reef organisms efficiently scavenge particulate organic matter and inorganic nutrients from advected oceanic waters, our understanding of the role of bacterioplankton and dissolved organic matter in the interaction between reefs and the surrounding ocean remains limited. Here we present the results of a four-year study conducted in a well-characterized coral reef ecosystem (Paopao Bay, Moorea, French Polynesia) where changes in bacterioplankton abundance and dissolved organic carbon (DOC) concentrations were quantified and bacterial community structure variation was examined along spatial gradients of the reef:ocean interface. Our results illustrate that the reef is consistently depleted in concentrations of both DOC and bacterioplankton relative to offshore waters (averaging 79 µmol L-1 DOC and 5.5 X 108 cells L-1 offshore and 68 µmol L-1 DOC and 3.1 X 108 cells L-1 over the reef, respectively) across a four year time period. In addition, using a suite of culture-independent measures of bacterial community structure, we found consistent differentiation of reef bacterioplankton communities from those offshore or in a nearby embayment across all taxonomic levels. Reef habitats were enriched in Gamma-, Delta-, and Beta-proteobacteria, Bacteriodetes, Actinobacteria and Firmicutes. Specific bacterial phylotypes, including members of the SAR11, SAR116, Flavobacteria, and Synechococcus clades, exhibited clear gradients in relative abundance among nearshore habitats. Our observations indicate that this reef system removes oceanic DOC and exerts selective pressures on bacterioplankton community structure on timescales approximating reef water residence times, observations which are notable both because fringing reefs do not exhibit long residence times (unlike those characteristic of atoll lagoons) and because oceanic DOC is generally recalcitrant to degradation by ambient microbial assemblages. Our findings thus have interesting implications for the role of oceanic DOM and bacterioplankton in the ecology and metabolism of reef ecosystems.This project was supported by the US National Science Foundation Moorea Coral Reef Long Term Ecological Research project (NSF OCE-0417412) through minigrants to CAC and NSF OCE-0927411 to CAC as well as the MIRADA-LTERs program (NSF DEB-0717390 to LAZ)

Lahar-Triggering Mechanisms and Hazard at Ruapehu Volcano, New Zealand

Late Holocene volcanic activity at Ruapehu has been characterizedby the generation of small (107 m3) lahars and repeated,small to medium (VEI 1-3) tephra-producing eruptions. The Onetapu Formation groupsall lahar deposits that accumulated during the last 2,000 years on the southeastern Ruapehu ring plain. The andesitic tephras are grouped within the Tufa Trig Formation and are intercalated within the laharic sequence. By correlating these two formations with new radiocarbon ages obtained on interbedded paleosols, we reconstruct a detailed volcanic history of Ruapehu for this period. Clast assemblages identified in the laharic sequences record thelithologies of synchronous tephras and rocks within the source region. These assemblages suggest a strong genetic link between the development of Crater Lake, the variation in eruptivestyles, and the production of lahars. Lahar-triggering mechanisms include: (1) flank collapse ofhydrothermally altered and unstable portions of the cone; (2) phreatic and phreatomagmatic eruptions favoring the generation of snow-rich slurries and hyperconcentrated stream flows; (3) suddenCrater Lake rim collapse, releasing large amounts of water inducing debris flows; and (4) eruptions that generate large volumes of tephra on snow-covered slopes, later remobilized by heavy rain. Two major lahars in the Onetapu sequence had a volume≥ 4 × 107 m3, roughly 1 to 2 orders of magnitude larger than the 1953event leading to the Tangiwai disaster (151 casualties). One of these lahars crossed over a lowinterfluve currently separating the Whangaehu River from a stream feeding the Tongariro River,sometime since peat accumulated between AD 1400 and AD 1660. A repetition of such a large-scaleevent would have devastating consequences on the infrastructure, economy and environment withinthe distal areas of the two catchments. The 1995–1996 eruptions were a timely reminder ofthe hazards posed by the volcano

Geochemical fingerprinting of Holocene tephras in the Willaumez Isthmus District of West New Britain, Papua New Guinea

Electron microprobe analyses were conducted on volcanic glasses extracted from Holocene tephra marker beds on the Willaumez isthmus in West New Britain, Papua New Guinea. These tephra beds are pivotal in the dating of a wide range of human artefacts and manuports found in the intervening buried soils, extending back over the last 40,000 years. Three major groups can be easily separated: W-K1 and 2; W-K3 and 4; and the Dakataua tephra. Of the remaining post-W-K4 tephras, most show slightly higher FeO and CaO and lower SiO2 contents than the W-K3 and 4 group, although there is some overlap. The combination of these geochemical data sets with the known stratigraphy and radiocarbon dates has helped resolve tephra correlation where these ashes become thin and less visually diagnostic or where pumice has been resorted and redeposited by the Kulu-Dulagi River.fals

Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist

Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3)

Spectral tunability of plasmonic scattering by silver nanodiscs near a reflector

The scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite-Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO2 on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of ∼54% in the near-infrared, near-bandgap 600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of ∼18%. Wavelength-angle resolved scattering measurements indicate an angular scattering range between 20° to 80° with maximum intensity of the scattered power in the 20° to 60° angular range.6 page(s