Factors affecting the biokinetics of technetium (^95mTc) in marine macroalgae     

S. Topcuoǧlu  S.W. Fowler 《Marine environmental research》1984,12(1):25-43

Technetium (Tc) biokinetics were investigated in marine macroalgae using ^92mTc as tracer. Green and red algae accumulated Tc (VII) to a very low degree (CF ? 1–20); however, a much higher affinity for pertechnetate was found in some brown algal species (CF > 10³). Comparative tests with different species of brown algae revealed that technetium does not accumulate similarly in all species of this group. Moreover, no significant differences in radionuclide uptake were noted between brown algae exposed to Tc in either the IV or VII oxidation states. Bioaccumulation of technetium appears to be a metabolically controlled process since uptake did not occur in heat-killed individuals and both light and temperature significantly enhanced the accumulation of technetium in brown algae. Dissection of Sargassum vulgare following the uptake phase showed that the rapidly growing air bladder, leaf-like laterals and small branches contained higher Tc concentrations and retained a greater fraction of the radioactivity than the older, cylindrical main axis. Pertechnetate retention in two brown algae was found to be significantly different; their biological half-lives for Tc differed by an order of magnitude ($\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 19 and 196}\text{days}$). During depuration, loss took place more rapidly from the younger portions of the seaweed, as evidenced by the highest concentration and greatest fraction of Tc retained in the older, cylindrical main axis. Provided certain precautions are taken, brown algae such as Cystoseira compressa and S. vulgare would serve as good bioindicator organisms for the presence of Tc contamination in marine waters.  相似文献   

Central‐Auckland rainfall, 1853–2020: Sites histories and implications for developing a long‐term rainfall record     

Anthony M. Fowler 《New Zealand geographer》2021,77(1):16-31

Previous work related to central‐Auckland site Albert Park showed that sparse site histories for inner‐city weather stations can be usefully supplemented by mining searchable online historical archives (Papers Past, DigitalNZ), at least as far back as 1909. Assessment of potential is extended here back to 1853, within the context of developing a long‐term rainfall record for Auckland. Although late 19th century sources are thinner and of poorer quality, much useful information could be gleaned about the locations and exposures of early sites. Hypothesised implications for the rainfall record suggest that all early site data need to be adjusted upwards.  相似文献   

Tropical cyclone activity in nested regional and global grid-refined simulations     

Atsushi Hashimoto  James M. Done  Laura D. Fowler  Cindy L. Bruyère 《Climate Dynamics》2016,47(1-2):497-508

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Archaeomagnetic record from Modoc Rock Shelter,Illinois, for the time range of 6200–8900 B.P.     

W. Kean  S. Ahler  M. Fowler  D. Wolfman 《Geoarchaeology》1997,12(2):93-115

The Modoc Rock Shelter is located in Randolph County, Illinois at the base of the Mississippi River bluffs, and is documented as having human occupation from 9000 B.P. to as recently as 800 B.P. Two hundred twenty-eight archaeomagnetic samples were collected from 28 surface hearths in two different excavation areas. Pilot samples from each hearth were A.F. demagnetized to 100 mT to establish the optimum demagnetization level for all samples from a specific hearth. The magnetic directions for individual hearths after appropriate demagnetization have high precision with α-95 values between 2° and 4°. Independent inclination and declination records from the two excavations, which were correlated with conventional radiocarbon dates, overlap in time and show good correlation. The composite record shows a prominent eastward declination swing of 15° from 6500–7800 yr B.P., followed by a westward swing of equal magnitude from 8000–8900 yr B.P. The inclination record is less varied. This secular variation record correlates well with soft sediment records from lakes in the north-central United States and is perhaps the longest and oldest archaeomagnetic secular variation record from a single site in North America. © 1997 John Wiley & Sons, Inc.  相似文献   

Using regional climate model data to simulate historical and future river flows in northwest England   总被引：2，自引：0，他引：2  

H. J. Fowler  C. G. Kilsby 《Climatic change》2007,80(3-4):337-367

Daily rainfall and temperature data were extracted from the multi-ensemble HadRM3H regional climate model (RCM) integrations for control (1960–1990) and future (2070–2100) time-slices. This dynamically downscaled output was bias-corrected on observed mean statistics and used as input to hydrological models calibrated for eight catchments which are critical water resources in northwest England. Simulated daily flow distributions matched observed from Q₉₅ to Q₅, suggesting that RCM data can be used with some confidence to examine future changes in flow regime. Under the SRES A2 (UKCIP02 Medium-High) scenario, annual runoff is projected to increase slightly at high elevation catchments, but reduce by ~16% at lower elevations. Impacts on monthly flow distribution are significant, with summer reductions of 40–80% of 1961–90 mean flow, and winter increases of up to 20%. This changing seasonality has a large impact on low flows, with Q₉₅ projected to decrease in magnitude by 40–80% in summer months, with serious consequences for water abstractions and river ecology. In contrast, high flows (> Q₅) are projected to increase in magnitude by up to 25%, particularly at high elevation catchments, providing an increased risk of flooding during winter months. These changes will have implications for management of water resources and ecologically important areas under the EU Water Framework Directive.  相似文献   

Influence of chronic exposure to silver and mercury in the field on the bioaccumulation potential of the bivalve Macoma balthica     

Florence Boisson  Mark G.J. Hartl  Scott W. Fowler  Claude Amiard-Triquet   《Marine environmental research》1998,45(4-5)

In order to assess the adaptation to metals previously observed in the bioindicator organism, Macoma balthica, subjected to chronic contamination by silver and mercury in the French Loire estuary, the bioaccumulation potential of individual organisms originating from the contaminated Loire estuary and a relatively uncontaminated control estuary (Somme) was evaluated using both radiotracers and stable isotopes of Ag (80 μg Ag litre⁻¹) and Hg (100 μg Hg litre⁻¹). Clams from the contaminated estuary were more sensitive to Ag (LT₅₀ = 9d) than those originating from the Somme estuary (LT₅₀ > 15d), even though the former bioaccumulated Ag to a significantly lower degree. This is attributed to a consequence of the chronic stress induced by Ag while clams were living in their natural environment. Therefore, past history of trace metal contamination should be considered when evaluating the susceptibility of M. balthica to heavy metal exposure. Lower uptake rates obtained for Hg (during the initial uptake phase only) and for Ag in clams from the polluted estuary suggest the presence of an adaptive trait for survival in contaminated areas. However, the lower degree of bioconcentration observed for Ag was not sufficiently low to reduce the sensitivity of the organisms to Ag and allow them to resist the toxic stress. Clams that survived Ag or Hg exposure at LT₅₀ did not protect themselves against metal toxicity by accumulating a significantly lesser amount of these metals than clams which did not survive metal stress. The results suggest that the bioaccumulation potential of each individual was not a factor which can explain the survival ability of M. balthica exposed to chronic Ag and Hg contamination in estuaries. In this case, cellular, biochemical and genetic levels of adaptation are presumed to be of greater importance.  相似文献   

Evidence for cyanobacterial inputs and heterotrophic alteration of lipids in sinking particles in the Alboran Sea (SW Mediterranean)     

Jordi Dachs  Josep M. Bayona  Scott W. Fowler  Juan-Carlos Miquel  Joan Albaigs 《Marine Chemistry》1998,60(3-4)

The different sources of lipid compounds present in sinking particles collected in a sediment trap mooring deployed in the Alboran Sea (SW Mediterranean) were elucidated using the molecular marker concept. A significant contribution of cyanobacterial lipids was identified based on the occurrence of a series of 3- and 5-methylalkanes and dimethylalkanes. Further evidence of cyanobacterial inputs was obtained by principal component analysis of all data showing diploptene and n-alkanes in the range C₁₄–C₂₂ clustered together with those branched alkanes. The use of methyl and dimethyl alkanes to trace cyanobacterial sources in the water column is proposed with advantage to sterols which are usually masked by phytoplanktonic sterols. The sterol distribution indicates phytoplankton as a major source with a contribution from heterotrophic zooplanktonic. Both fossil and biogenic sources can be contributors to the large unresolved complex mixture (UCM) found in these samples.  相似文献   

The formation of ice sails     

A. C. Fowler  C. Mayer 《地球物理与天体物理流体动力学》2017,111(6):411-428

Debris-covered glaciers are prone to the formation of a number of supraglacial geomorphological features, and generally speaking, their upper surfaces are far from level surfaces. Some of these features are due to radiation screening or enhancing properties of the debris cover, but theoretical explanations of the consequent surface forms are in their infancy. In this paper we consider a theoretical model for the formation of “ice sails”, which are regularly spaced bare ice features which are found on debris-covered glaciers in the Karakoram.  相似文献   

Developing observational methods to drive future hydrological science: Can we make a start as a community?     

Keith Beven  Anita Asadullah  Paul Bates  Eleanor Blyth  Nick Chappell  Stewart Child  Hannah Cloke  Simon Dadson  Nick Everard  Hayley J. Fowler  Jim Freer  David M. Hannah  Kate Heppell  Joseph Holden  Rob Lamb  Huw Lewis  Gerald Morgan  Louise Parry  Thorsten Wagener 《水文研究》2020,34(3):868-873

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Time-series measurements of Th in water column and sediment trap samples from the northwestern Mediterranean Sea     

J. Kirk Cochran  Juan Carlos Miquel  Robert Armstrong  Scott W. Fowler  Pere Masqu  Beat Gasser  David Hirschberg  Jennifer Szlosek  Alessia M. Rodriguez y Baena  Elisabet Verdeny  Gillian M. Stewart 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1487-1501

Disequilibrium between ²³⁴Th and ²³⁸U in water column profiles has been used to estimate the settling flux of Th (and, by proxy, of particulate organic carbon); yet potentially major non-steady-state influences on ²³⁴Th profiles are often not able to be considered in estimations of flux. We have compared temporal series of ²³⁴Th distributions in the upper water column at both coastal and deep-water sites in the northwestern Mediterranean Sea to coeval sediment trap records at the same sites. We have used sediment trap records of ²³⁴Th fluxes to predict temporal changes in water column ²³⁴Th deficits and have compared the predicted deficits to those measured to determine whether the time-evolution of the two coincide. At the coastal site (327 m water depth), trends in the two estimates of water column ²³⁴Th deficits are in fairly close agreement over the 1-month deployment during the spring bloom in 1999. In contrast, the pattern of water column ²³⁴Th deficits is poorly predicted by sediment trap records at the deep-water site (DYFAMED, 2300 m water depth) in both 2003 and 2005. In particular, the transition from a mesotrophic to an oligotrophic system, clearly seen in trap fluxes, is not evident in water column ²³⁴Th profiles, which show high-frequency variability. Allowing trapping efficiencies to vary from 100% does not reconcile the differences between trap and water column deficit observations; we conclude that substantial lateral and vertical advective influences must be invoked to account for the differences.Advective influences are potentially greater on ²³⁴Th fluxes derived from water column deficits relative to those obtained from traps because the calculation of deficits in open-ocean settings is dominated by the magnitude of the “dissolved” ²³⁴Th fraction. For observed current velocities of 5–20 cm s⁻¹, in one radioactive mean-life of ²³⁴Th, the water column at the DYFAMED site can reflect ²³⁴Th scavenging produced tens to hundreds of kilometers away. In contrast, most of the ²³⁴Th flux collected in shallow sediment traps at the DFYFAMED site was in the fraction settling >200 m d⁻¹; in effect the sediment trap can integrate the ²³⁴Th flux over distances 40-fold less than water column ²³⁴Th distributions. In some sense, sediment trap and water column sampling for ²³⁴Th provide complementary pictures of ²³⁴Th export. However, because the two methods can be dominated by different processes and are subject to different biases, their comparison must be treated with caution.  相似文献