Taking account of catchability in groundfish survey trawls: implications for estimating demersal fish biomass   总被引：1，自引：0，他引：1  

Fraser  Helen M.; Greenstreet  Simon P. R.; Piet  Gerjan J. 《ICES Journal of Marine Science》2007,64(9):1800-1819

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Variation in the abundance of sandeels Ammodytes marinus off southeast Scotland: an evaluation of area-closure fisheries management and stock abundance assessment methods     

Greenstreet  Simon P.R.; Armstrong  Eric; Mosegaard  Henrik; Jensen  Henrik; Gibb  Iain M.; Fraser  Helen M.; Scott  Beth E.; Holland  Gayle J.; Sharples  Jonathan 《ICES Journal of Marine Science》2006,63(8):1530-1550

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Re‐analysis of key evidence in the case for a hemispherically synchronous response to the Younger Dryas climatic event     

Helen Green  Jon Woodhead  John Hellstrom  Robyn Pickering  Russell Drysdale 《第四纪科学杂志》2013,28(1):8-12

A south‐east Australian speleothem stable isotope record displaying an apparent cooling synchronous with the northern hemisphere Younger Dryas climate event (12.9–11.7 ka) has significantly influenced scientific thinking on the climatic response of the southern hemisphere following the Last Glacial Maximum. This is one of very few records displaying such a response, and yet the cooling was inferred from substantial extrapolation between just three uranium‐series ages. Technological advances since then have produced major improvements in both the spatial resolution and the accuracy of uranium‐series geochronologies. Re‐analysis of this sample has yielded ages of 7.96 ± 0.36 to 7.69 ± 0.33 ka for the interval previously inferred to span the Younger Dryas, and reveals a substantial hiatus in deposition from 6.93 ± 0.64 to 1.83 ± 0.16 ka. These data not only refute the original evidence for an inter‐hemispheric synchroneity of the Younger Dryas but also reject any evidence for neoglacial conditions at 3 ka. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand     

Kathryn E. Collins  Catherine M. Febria  Helen J. Warburton  Hayley S. Devlin  Kristy L. Hogsden  Brandon C. Goeller 《新西兰海洋与淡水研究杂志》2019,53(2):182-200

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.  相似文献   

Mapping spatial variation in demersal fish species diversity and composition in the North Sea: accounting for species- and size-related catchability in survey trawls     

Fraser  Helen M.; Greenstreet  Simon P. R.; Fryer  Rob J.; Piet  Gerjan J. 《ICES Journal of Marine Science》2008,65(4):531-538

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Characterising the intermediate depth waters of the Pacific Ocean using δ13C and other geochemical tracers     

Helen C. Bostock  Bradley N. Opdyke  Michael J.M. Williams 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(7):847-859

Evidence from geochemical tracers (salinity, oxygen, silicate, nutrients, alkalinity, dissolved inorganic carbon (DIC), carbon isotopes (δ¹³C_DIC) and radiocarbon (Δ¹⁴C)) collected during the Pacific Ocean World Ocean Circulation Experiment (WOCE) voyages (P10, P15, P17 and P19) indicate there are three main water types at intermediate depths in the Pacific Ocean; North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Waters (EqPIW). We support previous suggestions of EqPIW as a separate equatorial intermediate depth water as it displays a distinct geochemical signature characterised by low salinity, low oxygen, high nutrients and low Δ¹⁴C (older radiocarbon). Using the geochemical properties of the different intermediate depth waters, we have mapped out their distribution in the main Pacific Basin.From the calculated pre-formed δ¹³C_air–sea conservative tracer, it is evident that EqPIW is a combination of AAIW parental waters, while quasi-conservative geochemical tracers, such as radiocarbon, also indicate mixing with old upwelling Pacific Deep Waters (PDW). The EqPIW also displays a latitudinal asymmetry in non-conservative geochemical tracers and can be further split into North (NEqPIW) and South (SEqPIW) separated at ～2°N. The reason for this asymmetry is caused by higher surface diatom production in the north driven by higher silicate concentrations.The δ¹³C signature measured in benthic foraminifera, Cibicidoides spp. (δ¹³C_Cib), from four core tops bathed in AAIW, SEqPIW and NPIW, reflects that of the overlying intermediate depth waters. The δ¹³C_Cib from these cores show similarities and variations down-core that highlight changes in mixing over the last 30,000 yr BP. The reduced offset between the δ¹³C_Cib of AAIW and SEqPIW during the last glacial indicates that AAIW might have had an increased influence in the eastern equatorial Pacific (EEP) region at this time. Additional intermediate depth cores and other paleo-geochemical proxies such as Cd/Ca and radiocarbon are required from the broader Pacific Ocean to further understand changes in intermediate depth water formation, circulation and mixing over glacial/interglacial cycles.  相似文献   

Temperature effects on the calcite skeletal composition of deep-water gorgonians (Isididae)     

Ronald E. Thresher  Nicholas C. Wilson  Helen Neil 《Geochimica et cosmochimica acta》2010,74(16):4655-515

We test for and calibrate a proxy for ocean temperature based on the skeletal composition of the widely distributed, deep-sea gorgonians in the family Isididae (bamboo corals), through use of three complementary methods: a short-term comparison of element/Ca ratios to a four-year temperature record, a long-term comparison with oceanographic records spanning forty years, and a geographic comparison of Isidids collected at sites ranging from the tropics to Antarctica. The assays consistently support a temperature-dependency for Mg/Ca ratios and suggest S/Ca is indirectly affected by temperature, but indicate little or no effect of temperature on P/Ca and Sr/Ca. The consensus relationship between Mg/Ca and temperature for Isidid calcite from the comparisons with the temperature time-series is T = −0.505 + 0.048 Mg/Ca, where T is in °C, Mg/Ca is in mmol/mol, and the applicable range is 3-6 °C. The results of the geographic assay, though imprecise, suggest the applicable range extends to temperatures below freezing. The scatter of data points around the regression of temperature and Mg/Ca is wide in all assays. This could reflect the effect of factors other than temperature on Mg/Ca ratios, but is also likely to reflect limitations of the field data, the effects of assumed constant growth rates in the corals and instrumental analytical error. The combined effects of micro-scale variability in growth rates and wide confidence intervals for each data point suggests that environmental reconstruction from Isidid internode calcite from sparse data or at time scales less than decades be done with caution. Comparisons within and among colonies do not indicate strong vital effects on ontogenetic variability in the corals, other than possibly close to the central pore of the coral. However, similar Mg/Ca ratios for Isidids from Antarctic and more temperate regions suggest adaptation to local conditions and hence a role for physiology at higher taxonomic levels, at least. Taxonomically higher level vital effects are also suggested by large differences between gorgonian families in their regressions between Mg/Ca and temperature, by Mg/Ca ratios that overlap over a wide temperature and habitat range, and for a non-linear relationship between temperature and the slope of the Mg/Ca-temperature relationship across the order.  相似文献   

Bacterial and eukaryotic intact polar lipids in the eastern subtropical South Pacific: Water-column distribution, planktonic sources, and fatty acid composition     

Benjamin A.S. Van Mooy  Helen F. Fredricks 《Geochimica et cosmochimica acta》2010,74(22):6499-6516

Fatty acids are generally the most abundant lipid molecules in plankton, and thus play a central role in the cycling of organic matter in the upper ocean. These fatty acids are primarily derived from intact polar diacylglycerolipids (IP-DAGs), which compose cell membranes in plankton. The molecular diversity of IP-DAGs in the upper ocean remains to be fully characterized, and the advent of high performance liquid chromatography/electrospray ionization-mass spectrometry (HPLC/ESI-MS) approaches have now provided the opportunity to readily analyze IP-DAGs from marine planktonic communities. We used HPLC/ESI-MS to determine the concentrations of three classes of phospholipids (phosphatidlyglycerol (PG), phosphatidylethanolamine (PE), and phosphatidylcholine (PC)), three classes of betaine lipids (diacylglyceryl trimethylhomoserine (DGTS), diacylglyceryl hydroxymethyl-trimethyl-β-alanine (DGTA), and diacylglyceryl carboxyhydroxymethylcholine (DGCC)), and three classes of glycolipids (monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol (SQDG)) in plankton filtered (>0.2 μm) from seawater collected within the euphotic zone of the eastern South Pacific. The distributions of these IP-DAGs along the cruise transect provided important new insights on their tentative planktonic sources. Complementary data from our cruise, a principle components analysis of our IP-DAG concentrations, observed fatty acid compositions of IP-DAG classes and published IP-DAG distributions in pure cultures of plankton suggest that heterotrophic bacteria were the dominant sources of PG and PE, while MGDG and SQDG originated primarily from Prochlorophytes. The origins of the other classes of IP-DAGs were less clear, although it is likely that PC, DGTS, DGTA, and DGCC were derived primarily from eukaryotic phytoplankton. The molecular distributions of fatty acids attached to the different classes of IP-DAGs were generally distinct from one another, and suggest that reported distributions of total fatty acids (as analyzed by gas chromatography) in the literature should be regarded as homogenized mixtures of distinct molecular pools of fatty acids.  相似文献   

Incised palaeo-channels of the late Middle Pleistocene Thames: age,origins and implications for fluvial palaeogeography and sea-level reconstruction in the southern North Sea basin     

Helen M. Roe  Richard C. Preece 《Quaternary Science Reviews》2011,30(19-20):2498-2519

Multidisciplinary investigations of the infills of steeply-incised buried channels on the coast of Essex, England, provide important insights into late Middle Pleistocene climate and sea-level change and have a direct bearing on the differentiation of MIS 11 and MIS 9 in terrestrial records. New data are presented from Rochford and Burnham-on-Crouch where remnants of two substantial palaeo-channels filled with interglacial sediment can be directly related to the terrace stratigraphy of the Thames. The sediments in both channels accumulated in an estuarine environment early in an interglacial when mixed oak forest was becoming established. Lithological evidence suggests that the interglacial beds post-date the brackish-water infill of an older palaeo-channel ascribed to the Hoxnian and correlated with part of MIS 11, and pre-date terrace gravels (Barling Gravel) ascribed to MIS 8. An MIS 9 attribution is supported by molluscan biostratigraphy, palaeo-salinity and amino-acid racemization data. The relative sea-level record in this area thus includes evidence for two major marine transgressions during MIS 11 and MIS 9, with local maxima of >10 m O.D. Both are associated with sediments that show ‘Hoxnian’ palynological affinities. The wider significance of these findings, and of an intermediate phase of pronounced fluvial incision during MIS 10, is discussed.  相似文献   

Serum transferrin polymorphism in grey trout,Cynoscion regalis,from the lower Rappahannock River     

Helen A. Russell  Jackson E. Jeffrey 《Estuaries and Coasts》1979,2(4):269-270

Serum transferrin distribution was studied in grey trout, Cynoscion regalis, obtained from the lower Rappahannock River of Virginia. Three phenotypes were observed, representing two codominant alleles at a single gene locus. The distribution of the phenotypes, designated as Tf A, Tf B, and Tf AB, did not differ significantly from that predicted by Hardy-Weinberg analysis.  相似文献