Effect of macrofaunal bioturbation on bacterial distribution in marine sandy sediments, with special reference to sulphur-oxidising bacteria     

Marisol Goi-Urriza  Xavier de Montaudouin  Rmy Guyoneaud  Guy Bachelet  Rutger de Wit 《Journal of Sea Research》1999,41(4):170

We have studied the impact of the bioturbating macrofauna, in particular the lugworm Arenicola marina and the bivalve Cerastoderma edule, on abundances and distribution patterns of total bacteria and of bacteria of selected functional groups in sandy intertidal sediments. The selected groups comprised the colourless sulphur-oxidising bacteria and the anoxygenic phototrophic bacteria, which are expected to occupy small zones at the oxygen–sulphide interface in stable (non-bioturbated) sediments. The presence of a wooden wreck buried in the sediment at 10 cm depth within a large area of intertidal sand flat colonised by lugworms provided a unique opportunity to confront field observations with laboratory simulations. The site with the wooden wreck, which was used as control site, was devoid of both A. marina and C. edule, while the composition of the rest of the zoobenthic community was rather similar to that of the surrounding area. In the field, the density of total bacteria was approximately one order of magnitude higher in the control site than in the natural (bioturbated) site. This can be explained by the higher contents of silt and clay particles (higher surface-area/volume ratio) and higher total organic-carbon contents found at the control site. It appears that the presence of macrofauna affects sedimentation processes, which indirectly influence bacterial dynamics. Samples from the control site have been incubated in the laboratory with A. marina and C. edule added (bioturbated core), while an unamended core served as a control. The laboratory experiments contrasted with the field observations, because it was found that total bacteria were actually higher in the deeper layers of the bioturbated core. Moreover, the populations were more homogeneous (less stratified) and colourless sulphur bacteria were on average less numerous in the bioturbated core. In general, laboratory incubations resulted in a decrease of total bacteria with a concomitant increase of colourless and phototrophic sulphur-oxidising bacteria and thus in modifications of the bacterial community structure. Hence, our results demonstrate that care must be taken in extrapolating results from laboratory experiments (e.g. mesocosm research) to field situations.  相似文献   

Aragonite depositional facies in a Late Ordovician calcite sea,Eastern Laurentia     

Noel P. James  Guy M. Narbonne  Alexis K. R. Armstrong 《Sedimentology》2020,67(7):3513-3532

The Black River (Upper Ordovician – Sandbian) and Trenton (Upper Ordovician – Katian) groups are traditionally interpreted as a deepening-upward succession deposited in a progressively subsiding Appalachian Basin margin that contained warm-water, marine, photozoan deposits that pass upward into cool-water, marine, heterozoan carbonates. This succession is customarily interpreted to reflect an incursion of cold, high-latitude ocean waters into the area. This view is herein confirmed for coeval carbonates in the northern part of the basin, particularly the St. Lawrence Platform. They are now well explained in this study on the basis of recent studies of cool-water carbonates and calcite–aragonite seas. Overall the succession is one of Sandbian photozoan ramp deposits succeeded by Katian heterozoan ramp carbonates that changed back to photozoan ramp deposits prior to the Hirnantian glaciation. The current interpretation, that deposition took place throughout a calcite sea time, seems at odds with this series of strata. Instead it is herein proposed that deposition took place during an aragonite sea time wherein calcite sea-like sediments accumulated under cold ocean-water temperatures. Such an interpretation is supported by recent experimental data that supports the importance of seawater temperature on CaCO₃ polymorph precipitation. If correct, this means that some of the evidence for calcite sea deposition through time brought about by global tectonics, should be re-evaluated to make sure it was not simply cool-water carbonate production.  相似文献   

Scientific detector workshop 2022 on-sky performance verification of near-infrared e−APD technology for wavefront sensing and demonstration of e−APD pixel performance to improve the sensitivity of large science focal planes     

Gert Finger  Frank Eisenhauer  Reinhard Genzel  Christopher Mandla  Ian Baker  Domingo Alvarez  Antonio Amorim  Wolfgang Brandner  Christophe Dupuy  Casey Deen  Derek Ives  Leander Mehrgan  Manfred Meyer  Karin Perraut  Guy Perrin  Jörg Stegmeier  Christian Straubmeier  Harald J. Weller  Vincent Isgar 《Astronomische Nachrichten》2023,344(8-9):e20230069

Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e⁻APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is m_k = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10⁻³ e⁻/s have been demonstrated with 1Kx1K e⁻APD arrays and 2Kx2K e⁻APD arrays have already been developed, the possibilities and adaptations of e⁻APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed.  相似文献