Late Quaternary sea‐level change and evolution of Belfast Lough,Northern Ireland: new offshore evidence and implications for sea‐level reconstruction     

Ruth M. K. Plets  S. Louise Callard  J. Andrew G. Cooper  Joseph T. Kelley  Daniel F. Belknap  Robin J. Edwards  Antony J. Long  Rory J. Quinn  Derek W. T. Jackson 《第四纪科学杂志》2019,34(4-5):285-298

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions.  相似文献   

Use of Sonication for Enhanced Sampling of Attached Microbes from Groundwater Systems     

Murray Close  Phil Abraham  Judith Webber  Eliza Cowey  Bronwyn Humphries  Graham Fenwick  Simon Howard  Kimberly Huynh  Travis Grace  Pierre-Yves Dupont  Louise Weaver 《Ground water》2020,58(6):901-912

The vast majority of microorganisms in aquifers live as biofilms on sediment surfaces, which presents significant challenges for sampling as only the suspended microbes will be sampled through normal pumping. The use of a down-well low frequency sonicator has been suggested as a method of detaching microbes from the biofilm and allowing rapid sampling of this community. We developed a portable, easy to use, low-frequency electric sonicator and evaluated its performance for a range of well depths (tested up to 42 m below ground level) and casing types. Three sonicators were characterized in laboratory experiments using a 1 m long tank filled with pea gravel. These included a commercially available pneumatic sonicator, a rotating flexible shaft sonicator, and the prototype electric sonicator. The electric sonicator detached between 56 and 74% of microbes grown on gravel-containing biobags at distances ranging between 2 and 50 cm from the sonicator. The field testing comprises of a total of 55 sampling events from 48 wells located in 4 regions throughout New Zealand. Pre- and post-sonication samples showed an average 33 times increase in bacterial counts. Microbial sequence data showed that the same classes are present in pre- and post-sonicated samples and only slight differences were seen in the proportions present. The sampling process was rapid and the significant increases in bacterial counts mean that microbial samples can be quickly obtained from wells, which permits more detailed analysis than previously possible.  相似文献   

Pattern,style and timing of British–Irish Ice Sheet advance and retreat over the last 45 000 years: evidence from NW Scotland and the adjacent continental shelf     

Tom Bradwell  Derek Fabel  Chris D. Clark  Richard C. Chiverrell  David Small  Rachel K. Smedley  Margot H. Saher  Steven G. Moreton  Dayton Dove  S. Louise Callard  Geoff A. T. Duller  Alicia Medialdea  Mark D. Bateman  Matthew J. Burke  Neil McDonald  Sean Gilgannon  Sally Morgan  David H. Roberts  Colm ó Cofaigh 《第四纪科学杂志》2021,36(5):871-933

Predicting the future response of ice sheets to climate warming and rising global sea level is important but difficult. This is especially so when fast-flowing glaciers or ice streams, buffered by ice shelves, are grounded on beds below sea level. What happens when these ice shelves are removed? And how do the ice stream and the surrounding ice sheet respond to the abruptly altered boundary conditions? To address these questions and others we present new geological, geomorphological, geophysical and geochronological data from the ice-stream-dominated NW sector of the last British–Irish Ice Sheet (BIIS). The study area covers around 45 000 km² of NW Scotland and the surrounding continental shelf. Alongside seabed geomorphological mapping and Quaternary sediment analysis, we use a suite of over 100 new absolute ages (including cosmogenic-nuclide exposure ages, optically stimulated luminescence ages and radiocarbon dates) collected from onshore and offshore, to build a sector-wide ice-sheet reconstruction combining all available evidence with Bayesian chronosequence modelling. Using this information we present a detailed assessment of ice-sheet advance/retreat history, and the glaciological connections between different areas of the NW BIIS sector, at different times during the last glacial cycle. The results show a highly dynamic, partly marine, partly terrestrial, ice-sheet sector undergoing large size variations in response to sub-millennial-scale climatic (Dansgaard–Oeschger) cycles over the last 45 000 years. Superimposed on these trends we identify internally driven instabilities, operating at higher frequency, conditioned by local topographic factors, tidewater dynamics and glaciological feedbacks during deglaciation. Specifically, our new evidence indicates extensive marine-terminating ice-sheet glaciation of the NW BIIS sector during Greenland Stadials 12 to 9 – prior to the main ‘Late Weichselian’ ice-sheet glaciation. After a period of restricted glaciation, in Greenland Interstadials 8 to 6, we find good evidence for rapid renewed ice-sheet build-up in NW Scotland, with the Minch ice-stream terminus reaching the continental shelf edge in Greenland Stadial 5, perhaps only briefly. Deglaciation of the NW sector took place in numerous stages. Several grounding-zone wedges and moraines on the mid- and inner continental shelf attest to significant stabilizations of the ice-sheet grounding line, or ice margin, during overall retreat in Greenland Stadials 3 and 2, and to the development of ice shelves. NW Lewis was the first substantial present-day land area to deglaciate, in the first half of Greenland Stadial 3 at a time of globally reduced sea-level c. 26 kabp , followed by Cape Wrath at c. 24 kabp. The topographic confinement of the Minch straits probably promoted ice-shelf development in early Greenland Stadial 2, providing the ice stream with additional support and buffering it somewhat from external drivers. However, c. 20–19 kabp , as the grounding-line migrated into shoreward deepening water, coinciding with a marked change in marine geology and bed strength, the ice stream became unstable. We find that, once underway, grounding-line retreat proceeded in an uninterrupted fashion with the rapid loss of fronting ice shelves – first in the west, then the east troughs – before eventual glacier stabilization at fjord mouths in NW Scotland by ~17 kabp. Around the same time, ~19–17 kabp , ice-sheet lobes readvanced into the East Minch – possibly a glaciological response to the marine-instability-triggered loss of adjacent ice stream (and/or ice shelf) support in the Minch trough. An independent ice cap on Lewis also experienced margin oscillations during mid-Greenland Stadial 2, with an ice-accumulation centre in West Lewis existing into the latter part of Heinrich Stadial 1. Final ice-sheet deglaciation of NW mainland Scotland was punctuated by at least one other coherent readvance at c. 15.5 kabp , before significant ice-mass losses thereafter. At the glacial termination, c. 14.5 kabp , glaciers fed outwash sediment to now-abandoned coastal deltas in NW mainland Scotland around the time of global Meltwater Pulse 1A. Overall, this work on the BIIS NW sector reconstructs a highly dynamic ice-sheet oscillating in extent and volume for much of the last 45 000 years. Periods of expansive ice-sheet glaciation dominated by ice-streaming were interspersed with periods of much more restricted ice-cap or tidewater/fjordic glaciation. Finally, this work indicates that the role of ice streams in ice-sheet evolution is complex but mechanistically important throughout the lifetime of an ice sheet – with ice streams contributing to the regulation of ice-sheet health but also to the acceleration of ice-sheet demise via marine ice-sheet instabilities.  相似文献   

Social and environmental vulnerability in Southeast Brazil associated with the South Atlantic Convergence Zone     

da Fonseca Aguiar  Louise  Cataldi  Marcio 《Natural Hazards》2021,108(3):2423-2453

Natural Hazards - A landslide is a geomorphological hazard with significant ecological and economic damages. The present study aimed to identify landslide-prone areas in Farizi watershed via the...  相似文献   

An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples          下载免费PDF全文

Louise Alexander  Joshua F. Snape  Katherine H. Joy  Hilary Downes  Ian A. Crawford 《Meteoritics & planetary science》2016,51(9):1654-1677

Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.  相似文献   

Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations     

Louise Nuijens  Kerry Emanuel  Hirohiko Masunaga  Tristan L’Ecuyer 《Surveys in Geophysics》2017,38(6):1257-1282

Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions.  相似文献   

Pliocene and late Pleistocene (MIS 5e) decapod crustaceans from Santa Maria Island (Azores Archipelago: Central Atlantic): systematics,palaeoecology and palaeobiogeography     

Matúš Hyžný  Carlos S. Melo  Ricardo S. Ramalho  Ricardo Cordeiro  Patrícia Madeira  Lara Baptista  A. Cristina Rebelo  Cynthia Gómez  Alfred Uchman  Markes E. Johnson  Björn Berning  Sérgio P. Ávila 《第四纪科学杂志》2021,36(1):91-109

The presence of decapod crustaceans in the Pliocene and Pleistocene (MIS 5e) fossil record of Santa Maria Island (Azores Archipelago) is herein reviewed. Our study raises the number of fossil decapods from this island from one species to 10 taxa (three for the Pliocene and seven for the Last Interglacial). Four of these 10 taxa are reported for the first time in the fossil record, worldwide. A new species of a mud shrimp is also described (Upogebia azorensis n. sp.). Our study suggests that the Plio–Pleistocene decapod assemblages of the Azores did not differ significantly from modern ones, being dominated by species that are today widespread across the Webbnesia ecoregion, the Mediterranean Sea, and the eastern Atlantic shores, including the Azores. As far as can be judged from the limited fossil record, apparently no tropical crab species with a Cabo Verdean/Senegalese provenance reached the Azores during windows of opportunity associated with Glacial Termination 2 or with the initial setting of the Last Interglacial period. This contribution increases the total number of marine taxa reported for the Pliocene and Pleistocene outcrops of Santa Maria Island to 218 and 155, respectively, highlighting the scientific relevance of its palaeontological heritage.  相似文献   

Improving Properties of Sealing Layers Made of Till by Adding Green Liquor Dregs to Reduce Oxidation of Sulfidic Mine Waste     

Maria Mäkitalo  Josef Mácsik  Christian Maurice  Björn Öhlander 《Geotechnical and Geological Engineering》2015,33(4):1047-1054

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A multi‐storage groundwater concept for the SWAT model to emphasize nonlinear groundwater dynamics in lowland catchments          下载免费PDF全文

Matthias Pfannerstill  Björn Guse  Nicola Fohrer 《水文研究》2014,28(22):5599-5612

Hydrological models are useful tools to analyze present and future conditions of water quantity and quality. The integrated modelling of water and nutrients needs an adequate representation of the different discharge components. In common with many lowlands, groundwater contribution to the discharge in the North German lowlands is a key factor for a reasonable representation of the water balance, especially in low flow periods. Several studies revealed that the widely used Soil and Water Assessment Tool (SWAT) model performs poorly for low flow periods. This paper deals with the extension of the groundwater module of the SWAT model to enhance low flow representation. The current two‐storage concept of SWAT was further developed to a three‐storage concept. This was realized due to modification of the groundwater module by splitting the active groundwater storage into a fast and a slow contributing aquifer. The results of this study show that the groundwater module with three storages leads to a good prediction of the overall discharge especially for the recession limbs and the low flow periods. The improved performance is reflected in the signature measures for the mid‐segment (percent bias ?2.4% vs ?15.9%) and the low segment (percent bias 14.8% vs 46.8%) of the flow duration curve. The three‐storage groundwater module is more process oriented than the original version due to the introduction of a fast and a slow groundwater flow component. The three‐storage version includes a modular approach, because groundwater storages can be activated or deactivated independently for subbasin and hydrological response unit level. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Reply to comment on ‘Up‐scaling potential impacts on water flows from agricultural water interventions: opportunities and trade‐offs in the Osman Sagar catchment,Musi sub‐basin,India’. Hydrological Processes 27: 3905–3921 by Bouma et al.,          下载免费PDF全文

Kaushal K. Garg  Suhas P. Wani  Jennie Barron  Louise Karlberg  Johan Rockstrom 《水文研究》2014,28(8):3352-3355

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