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51.
The role of floating mucilage in the invasive spread of the benthic microalga Chrysophaeum taylorii
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Sarah Caronni Maria Anna Delaria Kirsten Heimann Giovanni Macri Augusto Navone Pieraugusto Panzalis Giulia Ceccherelli 《Marine Ecology》2016,37(4):867-876
Chrysophaeum taylorii Lewis & Bryan (Pelagophyceae) is a mucilage‐producing benthic microalga that has recently begun to spread in the Mediterranean Sea, where a range expansion is occurring. This paper presents the results of three field experiments that aimed to increase the knowledge on mucilage provision mechanisms for this benthic microalga and to evaluate the importance of mucilage in its range expansion. By means of two correlative field experiments (several years of data were considered to encompass the variability of mucilage cover) we found that, on the sea bottom, mucilage cover does not depend on epilithic cell density and that both its cover and settling are affected by water flow. We also tested the hypothesis that cells embedded in floating mucilage fall on the underlying substratum, where their abundance depends on water flow. To this aim, in the field we manipulated the presence of floating mucilaginous aggregates in cages with different levels of exposure to winds. The abundance of C. taylorii cells on the substratum under cages with mucilage was compared with that of two control treatments: cages without mucilage and mucilage in still water, in the field and lab, respectively. The results suggested that mucilage can represent an excellent strategy for the species to disperse, as C. taylorii cells fall from the floating mucilage and, if the water flow is unimportant, settle on hard substrata just underneath the cage. This study enriches the portfolio of knowledge of the dispersal strategies of microalgae and contributes to the understanding of the spread of invasive species. 相似文献
52.
Marie Méheust Ruediger Stein Kirsten Fahl Lars Max Jan-Rainer Riethdorf 《Geo-Marine Letters》2016,36(2):101-111
Due to its strong influence on heat and moisture exchange between the ocean and the atmosphere, sea ice is an essential component of the global climate system. In the context of its alarming decrease in terms of concentration, thickness and duration, understanding the processes controlling sea-ice variability and reconstructing paleo-sea-ice extent in polar regions have become of great interest for the scientific community. In this study, for the first time, IP25, a recently developed biomarker sea-ice proxy, was used for a high-resolution reconstruction of the sea-ice extent and its variability in the western North Pacific and western Bering Sea during the past 18,000 years. To identify mechanisms controlling the sea-ice variability, IP25 data were associated with published sea-surface temperature as well as diatom and biogenic opal data. The results indicate that a seasonal sea-ice cover existed during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas during warmer intervals (Bølling-Allerød and Holocene) reduced sea ice or ice-free conditions prevailed in the study area. The variability in sea-ice extent seems to be linked to climate anomalies and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea, especially the Alaskan Stream injection though the Aleutian passes. 相似文献
53.
Valentin R. Troll Frances M. Deegan Steffi Burchardt Kirsten Zaczek Juan‐Carlos Carracedo Fiona C. Meade Vicente Soler Mario Cachao Jorge Ferreira Abigail K. Barker 《Geology Today》2015,31(4):137-145
The origin of volcanism in the Canary Islands has been a matter of controversy for several decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of superheated mantle material. However, the debate has recently come to a conclusion following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which tell us about the age and growth history of the western‐most island of the archipelago. Light coloured, pumice‐like ‘floating rocks’ were found on the sea surface during the first days of the eruption and have been shown to contain fragments of pre‐island sedimentary strata. These sedimentary rock fragments were picked up by ascending magma and transported to the surface during the eruption, and remarkably retained specimens of pre‐island Upper Cretaceous to Pliocene calcareous nannofossils (e.g. coccolithophores). These marine microorganisms are well known biostratigraphical markers and now provide crucial evidence that the westernmost and youngest island in the Canaries is underlain by the youngest sediment relative to the other islands in the archipelago. This finding supports an age progression for the onset of volcanism at the individual islands of the archipeligo. Importantly, as fracture‐related volcanism is known to produce non‐systematic age‐distributions within volcanic alignments, the now‐confirmed age progression corroberates to the relative motion of the African plate over an underlying mantle plume or hotspot as the cause for the present‐day Canary volcanism. 相似文献
54.
Nilanjan Chatterjee Kirsten Nicolaysen 《Contributions to Mineralogy and Petrology》2012,163(5):789-806
The Kerguelen Plateau is a submarine, Cretaceous Large Igneous Province in the southern Indian Ocean. Drilling on Elan Bank,
a western salient of the Kerguelen Plateau, yielded a ~26 m section of fluvial conglomerate intercalated with basalt. Chemical
dating of monazite within garnet and matrix monazite in metapelitic clasts from the conglomerate indicates that high-grade
metamorphism of the pelitic protolith occurred between 785 ± 12 and 694 ± 18 Ma. A calculated P–T pseudosection indicates
that the observed core-to-inner rim compositional zoning in garnet is consistent with P/T decrease from 10.2 kb/760°C to 6.2 kb/560°C.
In an Early Cretaceous paleogeographic reconstruction, the Elan Bank drill site is located on a SSW continuation of the Eastern
Indian Tectonic Zone (EITZ), a 876–784 Ma, NNE–SSW metamorphic belt with sinistral shear zones in eastern India. The retrograde
P–T path of the Elan Bank metapelitic clast overlaps with that of the EITZ metapelite, and the Elan Bank monazite chemical
dates and previously determined 824–675 Ma U–Pb isotope monazite dates by the TIMS method are remarkably similar to the monazite
chemical dates from the EITZ metapelites and high-grade metamorphic rocks from the eastern margin of the Eastern Ghats Belt.
Based on the demonstrable affinity of metamorphic, geochronologic, and spatial data, this study concludes that the EITZ was
likely a continuous, ~1,800–km-long tectono-metamorphic belt in the Rodinia supercontinent stretching from eastern India through
the Eastern Ghats to the basement of Elan Bank and probably to the Rayner Complex of East Antarctica. 相似文献
55.
Kirsten Warrach-Sagi Thomas Schwitalla Volker Wulfmeyer Hans-Stefan Bauer 《Climate Dynamics》2013,41(3-4):755-774
The Weather Research and Forecast (WRF) model with its land surface model NOAH was set up and applied as regional climate model over Europe. It was forced with the latest ERA-interim reanalysis data from 1989 to 2008 and operated with 0.33° and 0.11° resolution. This study focuses on the verification of monthly and seasonal mean precipitation over Germany, where a high quality precipitation dataset of the German Weather Service is available. In particular, the precipitation is studied in the orographic terrain of southwestern Germany and the dry lowlands of northeastern Germany. In both regions precipitation data is very important for end users such as hydrologists and farmers. Both WRF simulations show a systematic positive precipitation bias not apparent in ERA-interim and an overestimation of wet day frequency. The downscaling experiment improved the annual cycle of the precipitation intensity, which is underestimated by ERA-interim. Normalized Taylor diagrams, i.e., those discarding the systematic bias by normalizing the quantities, demonstrate that downscaling with WRF provides a better spatial distribution than the ERA interim precipitation analyses in southwestern Germany and most of the whole of Germany but degrades the results for northeastern Germany. At the applied model resolution of 0.11°, WRF shows typical systematic errors of RCMs in orographic terrain such as the windward–lee effect. A convection permitting case study set up for summer 2007 improved the precipitation simulations with respect to the location of precipitation maxima in the mountainous regions and the spatial correlation of precipitation. This result indicates the high value of regional climate simulations on the convection-permitting scale. 相似文献
56.
Michael Steiger Kirsten Linnow Dorothee Ehrhardt Mandy Rohde 《Geochimica et cosmochimica acta》2011,75(12):3600-3626
We report new measurements of equilibrium relative humidities for stable and metastable hydration-dehydration equilibria involving several magnesium sulfates in the MgSO4·nH2O series. We also report a comprehensive thermodynamic treatment of the system including solution properties and experimental data from the published literature, i.e. solubilities, heat capacities and additional decomposition humidities. While for some magnesium sulfate hydrates solubility data in the binary system MgSO4-H2O are sparse, there is a reasonable database of solubility measurements of these hydrates in the ternary MgCl2-MgSO4-H2O and the quaternary reciprocal Na+-Mg2+-Cl−-SO42−-H2O systems. To make these data suitable for the determination of solubility products, we parameterized a Pitzer ion interaction model for the calculation of activity coefficients and water activities in mixed solutions of these systems and report the ion interaction parameters for the Na+-Mg2+-Cl−-SO42−-H2O system. The model predicted solubilities in the reciprocal system are in very good agreement with experimental data. Using all available experimental data and the solution model an updated phase diagram of the MgSO4-H2O system covering the whole temperature range from about 170 to 473 K is established. This treatment includes MgSO4·H2O (kieserite), MgSO4·4H2O (starkeyite), MgSO4·5H2O (pentahydrite), MgSO4·6H2O (hexahydrite), MgSO4·7H2O (epsomite) and MgSO4·11H2O (meridianiite). It is shown that only kieserite, hexahydrite, epsomite and meridianiite show fields of stable existence while starkeyite and pentahydrite are always metastable. Due to sluggish kinetics of kieserite formation, however, there is a rather extended field of metastable existence of starkeyite which makes this solid a major product in dehydration reactions. The model predicted behavior of the magnesium sulfates is in excellent agreement with observations reported in the literature under terrestrial temperature and relative humidity conditions. We also discuss the implications of the new phase diagram for sulfates on Mars. 相似文献
57.
Kelly L. Kirsten Thomas Kasper Hayley C. Cawthra Paul Strobel Lynne J. Quick Michael E. Meadows Torsten Haberzettl 《第四纪科学杂志》2020,35(4):572-581
We present a diatom record from a well-dated 15.25 m composite sedimentary core from Verlorenvlei, a shallow coastal lake on the west coast of South Africa. We show that fluctuations in the diatom record occur in response to changes in sea level, ocean–atmosphere interactions and latitudinal shifts in the wind belts. During the early to mid-Holocene, the system primarily responds to sea level changes. A marine community that favours high nutrients is evident, particularly during 9200–8000, 7420–7000 and 6200–5600 cal a bp , corroborating periods of Benguela upwelling linked to fluctuations in the southeast trade winds. Increases in bioproductivity (%TOC, C/N) and fresher-water diatoms are associated with wetter conditions over the region and the northward migration of the southern westerly wind belt, most notably between 8000 and 7500 cal a bp and over the last 700 years. The latter trends are concomitant with changes in the extent of Antarctic sea ice and availability of moisture in southern South America. During the late Holocene, as sea levels stabilised to modern levels, climate variability is more strongly evident. The body of evidence further reveals the sensitivity of the region to high-latitude atmospheric mechanisms, but also showcases the significance of the southeast trade winds. 相似文献
58.
A high‐resolution record of Holocene climate and vegetation dynamics from the southern Cape coast of South Africa: pollen and microcharcoal evidence from Eilandvlei
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59.
Natural waters often contain complex mixtures of unknown contaminants potentially posing a threat to marine communities through chemical interactions. Here, acute effects of the photosystem II-inhibiting herbicides diuron, tebuthiuron, atrazine, simazine, and hexazinone, herbicide breakdown products (desethyl-atrazine (DEA) and 3,4-dichloroaniline (3,4-DCA)) and binary mixtures, were investigated using three tropical benthic microalgae; Navicula sp. and Cylindrotheca closterium (Ochrophyta) and Nephroselmis pyriformis (Chlorophyta), and one standard test species, Phaeodactylum tricornutum (Ochrophyta), in a high-throughput Maxi-Imaging-PAM bioassay (Maxi-IPAM). The order of toxicity was; diuron > hexazinone > tebuthiuron > atrazine > simazine > DEA > 3,4-DCA for all species. The tropical green alga N. pyriformis was up to 10-fold more sensitive than the diatoms tested here and reported for coral symbionts, and is recommended as a standard tropical test species for future research. All binary mixtures exhibited additive toxicity, and the use of herbicide equivalents (HEq) is therefore recommended in order to incorporate total-maximum-load measures for environmental regulatory purposes. 相似文献
60.
Dynamic adjustment of training sets (‘moving-window’ reconstruction) by using transfer functions in paleolimnology—a new approach 总被引:1,自引:0,他引:1
Thomas Hübener Mirko Dreßler Anja Schwarz Kirsten Langner Sven Adler 《Journal of Paleolimnology》2008,40(1):79-95
This paper presents a new method (moving-windows) that optimizes diatom-based paleolimnological reconstructions of past environmental
conditions from supra-regional training sets. The moving-window method identifies the best number of nearest neighbours (window
size) from a merged supra-regional EDDI and local (MV) training set (n = 429) for each fossil diatom assemblage and the best type of transfer function (ML, WA-PLS) based on the error statistic
of each transfer function (highest cross-validated R
2, lowest cross-validated average bias, maximum bias and RMSEP). At first we evaluated the moving-window approach by comparing
measured TP-values with inferred TP-values using both the moving-window approach and the WA-PLS method. The relative errors
of the moving-window approach were not significantly different for 208 samples that had an error <15 μg/l TP using the WA-PLS
method. However, for the remaining 221 samples with errors >>15 μg/l TP using the WA-PLS method, the moving window approach
significantly reduced the relative error of the inferred TP levels. Secondly, the moving- window approach was used to reconstruct
epilimnetic total phosphorous (TP) for Lake Dudinghausen, Lake Rugensee, Lake Tiefer See and Lake Drewitzer See (Northern
Germany) using both the supra-regional EDDI training set and a local training set from Northern Germany (MV training set).
The moving-window inferred TP-levels of the four study lakes were compared with published reconstructed TP-values and with
inferred TP-values based on the local MV training set. Overall, the moving-window and the published TP-trends agree well with
each other. However, the moving-window reconstructions generally indicated lower TP-levels throughout the past ∼5,000 to 12,000 years,
including past maxima. Thus, the moving-window method seems to generate more realistic absolute TP levels due to the optimized
window size (highest number of modern analogues, best error statistics). The identification of more realistic absolute historic
TP-values is important for the validation of reference conditions for inland waters. This study also demonstrates that a robust
local training set may, similar to moving-window training sets, also lead to reliable reconstructions, if the geological settings
of the local training set lakes and the study lakes are similar. 相似文献