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111.
The 500 km2 of tidal flats at the Banc d'Arguin, Mauritania, are a wintering site for over 2 million shorebirds, making this one of the areas with the highest density of shorebirds in the world. In earlier studies, it was found that these huge numbers of birds are dependent on a rather low biomass of benthic animals. To explain this paradoxical situation, we hypothesized that the earlier assessments of biomass in late winter and early spring do not reflect a year-round situation. Benthic biomass may be high when the birds arrive in autumn to be subsequently grazed down in the course of winter. To test this hypothesis, we have determined benthic biomass in September 1988. The result has been compared with a biomass value obtained in February–April 1986 with the same methods and at the same stations. These two biomass values do not differ significantly; so our hypothesis has to be rejected. It has to be admitted, however, that our experimental design cannot discern between differences due to the year of sampling and those due to the season. 相似文献
112.
113.
Anke Schwarzenberger Sofie D’Hondt Wim Vyverman Eric von Elert 《Aquatic Sciences - Research Across Boundaries》2013,75(3):433-445
Lakes are well known for having a pattern of seasonal succession of phytoplankton and zooplankton. The succession of different taxa of phytoplankton results in a succession of zooplankton taxa, and within the genus Daphnia, into a succession of different genotypes (clones). One cause for this succession of Daphnia clones might be the production of digestive protease inhibitors by cyanobacteria, which usually bloom in summer. Here we report seasonal changes in the frequency and the abundance of Daphnia magna haplotypes in a eutrophic lake, which developed a chymotrypsin-inhibitor-producing cyanobacterial bloom in May. These seasonal changes were not related to changes of biotic and abiotic lake parameters. However, a very high content of chymotrypsin inhibitors was observed in May (but not in other months). This was assumed to have exerted a strong punctual selection pressure on the Daphnia population and on the direct targets of the protease inhibitors, i.e. the digestive chymotrypsins of Daphnia. Actually, D. magna from before and during the cyanobacterial bloom showed a different protease pattern on activity stained SDS-PAGE in comparison to clones from the month after the bloom. However, no difference in tolerance, measured as IC50 values, to inhibition by natural lake seston from May was found between the clones from before and after the bloom. Thus, the hypothesis that a seasonal adaptation of D. magna subpopulations from either April/May or June might have occurred could not be proven. This suggests that the Daphnia population investigated here is locally adapted to cyanobacterial protease inhibitors. 相似文献
114.
The key role of global solid‐Earth processes in preconditioning Greenland's glaciation since the Pliocene
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After >500 Ma of absence, major Northern Hemisphere glaciations appeared during the Plio‐Pleistocene, with Greenland leading other northern areas. Here, we propose that three major solid‐Earth processes underpinned build‐up of the Greenland ice‐sheet. First, a mantle‐plume pulse, responsible for the North Atlantic Igneous Province at ~60 Ma, regionally thinned the lithosphere. Younger plume pulses led to uplift, which accelerated at ~5 Ma, lifting the parts of the East Greenland margin closest to Iceland to elevations of more than 3 km above sea level. Second, plate‐tectonic reconstruction shows a ~6° northward component of Greenland motion relative to the mantle since ~60 Ma. Third, a concurrent northward rotation of the entire mantle and crust towards the pole, dubbed True Polar Wander (TPW), contributed an additional ~12° change in latitude. These global geodynamic processes preconditioned Greenland to sustain long‐term glaciation, emphasizing the role of solid‐Earth processes in driving long‐term global climatic transitions. 相似文献
115.
Elie Verleyen Dominic A. Hodgson Koen Sabbe Holger Cremer Steven D. Emslie John Gibson Brenda Hall Satoshi Imura Sakae Kudoh Gareth J. Marshall Andrew McMinn Martin Melles Louise Newman Donna Roberts Steve J. Roberts Shiv M. Singh Mieke Sterken Ines Tavernier Sergey Verkulich Evelien Van de Vyver Wim Van Nieuwenhuyze Bernd Wagner Wim Vyverman 《Earth》2011,104(4):199-212
We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5–9 ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1 ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2 ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere's Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today. 相似文献
116.
Céline Déandreis Christian Pagé Pascale Braconnot Lars Bärring Edoardo Bucchignani Wim Som de Cerff Ronald Hutjes Sylvie Joussaume Constantin Mares Serge Planton Maarten Plieger 《Climatic change》2014,125(3-4):333-347
Future climate evolution is of primary importance for the societal, economical, political orientations and decision-making. It explains the increasing use of climate projections as input for quantitative impact studies, assessing vulnerability and defining adaptation strategies in different sectors. Here we analyse 17 national and representative use cases so as to identify the diversity of the demand for climate information depending on user profiles as well as the best practices, methods and tools that are needed to answer the different requests. A particular emphasis is put on the workflow that allows to translate climate data into suitable impact data, the way to deal with the different sources of uncertainty and to provide a suited product to users. We identified three complementary tools to close the gap between climate scientists and user needs: an efficient interface between users and providers; an optimized methodology to handle user requests and a portal to facilitate access to data and elaborated products. We detail in the paper how these three tools can limit the intervention of experts, educate users, and lead to the production of useful information. This work provides the basis on which the ENES (European Network for Earth System Modelling) Portal Interface for the Climate Impact Communities is built. 相似文献
117.
We estimated the influence of planktonic and benthic grazing on phytoplankton in the strongly tidal, river-dominated northern San Francisco Estuary using data from an intensive study of the low salinity foodweb in 2006–2008 supplemented with long-term monitoring data. A drop in chlorophyll concentration in 1987 had previously been linked to grazing by the introduced clam Potamocorbula amurensis, but numerous changes in the estuary may be linked to the continued low chlorophyll. We asked whether phytoplankton continued to be suppressed by grazing and what proportion of the grazing was by benthic bivalves. A mass balance of phytoplankton biomass included estimates of primary production and grazing by microzooplankton, mesozooplankton, and clams. Grazing persistently exceeded net phytoplankton growth especially for larger cells, and grazing by microzooplankton often exceeded that by clams. A subsidy of phytoplankton from other regions roughly balanced the excess of grazing over growth. Thus, the influence of bivalve grazing on phytoplankton biomass can be understood only in the context of limits on phytoplankton growth, total grazing, and transport. 相似文献
118.
Lukas Jonkers Furu Mienis Wim Boer Ian R. Hall Geert-Jan A. Brummer 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(8):1027-1038
North Atlantic sediment drifts are valuable archives for paleoceanographic reconstructions spanning various timescales. However, the short-term dynamics of such systems are poorly known, and this impinges on our ability to quantitatively reconstruct past change. Here we describe a high-resolution 319-day time-series of hydrodynamics and near-bottom (4 m) particulate matter flux variability at a 2600 m deep site with an extremely high sediment accumulation rate on the southern Gardar Drift in the North Atlantic. We compare our findings with the actual deposits at the site. The total annual particle flux amounted to ~360 g m?2 yr?1, varied from ~0.15 to >5.0 g m?2 day?1 and displayed strong seasonal compositional changes, with the highest proportion of fresh biogenic matter arriving after the spring bloom in June and July. Flux variability also depended on the changing input of lithogenic matter that had been (re)suspended for a longer time (decades). Active focussing of material from both sources is required to account for the composition and the magnitude of the total flux, which exceed observations elsewhere by an order of magnitude. The enhanced focussing or increased delivery appeared to be positively related to current velocity. The intercepted annual particle flux accounted for only 60% of the sediment accumulation rate of 600±20 g m?2 yr?1 (0.20±0.07 cm yr?1), indicating higher intra- and inter-annual variability of both the biogenic and lithogenic fluxes and/or advection of additional sediment closer to the seafloor (i.e. <4 m). This temporal variability in the composition and amount of material deposited highlights intra-annual changes in the flux of lithogenic material, but also underscores the importance of (reworked) sediment focussing and seasonality of the biogenic flux. All should be taken into account in the interpretation of the paleorecord from such depositional settings. 相似文献
119.
Wim Brouw 《Astrophysics and Space Science》2001,278(1-2):205-208
The next generation radio telescope being planned is the Square Kilometer Array (SKA): an international project which is currently
in the research and development phase. Australia is one of the partner countries in the SKA consortium; here I describe some
of the SKA research being undertaken in Australia.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
120.
Wim Z. Hoek 《《幕》》2008,31(2):226-229
The Last Glacial-Interglacial Transition is one of the most intensively studied periods in Earth History. The rapid climate and environmental changes that occurred during the transition can be used to test ideas about the functioning of our climate system. The stratigraphy of this period has been thoroughly investigated and, in particular, the recently proposed event stratigraphy for the Last Glacial-Interglacial Transition based on the Greenland ice core records serves as a tool for synchronisation of records from the ice, marine and terrestrial environment. 相似文献