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The calcareous nannofossil assemblages from sediment core DS97-2P from the Reykjanes Ridge have been investigated to document oceanographic changes in surface water during the Holocene. The recorded variations in coccolithophore species assemblages and accumulation rates indicate that the region was subjected to rapid changes of surface water masses throughout the entire Holocene. Coccolithophore assemblages generally are of low species diversity and consist mainly of Emiliania huxleyi and Coccolithus pelagicus ssp. pelagicus. Two major events occurred at 8.5-7. ka and at 4.5- 3.5. ka, showing higher coccolith accumulation rates, suggesting that the influence of relatively warm Atlantic waters via the Irminger Current was strong in the investigated area. The coccolithophore assemblages have been compared with diatom, foraminifer and sedimentological records within the same core. These data, supported by a comparison with previously published proxy records, add credit to the hypothesis that Holocene changes did not occur uniformly across the North Atlantic. The results have highlighted the Holocene pattern in the North Atlantic, as a period influenced by strong regionalism with discrepancies in the hydrographical trends and in the distribution of the planktonic proxies. © 2010 Elsevier B.V.

The ecology and distribution in the Delta area (The Netherlands) are described for the echinoderm species Astropecten irregularis, Solaster papposus, Asterias rubens, Ophiotrix fragilis, Amphipholis squamata, Ophiura texturata, O. albida, O. affinis, Psammechinus miliaris, Echinocyamus pusillus, Spatangus purpureus, Echinocardium cordatum, and Thyonidium commune. A list is given of the species of echinoderms occurring in Dutch coastal waters.

40Ar/39Ar geochronology relies on magnetic sector mass spectrometers to determine relative isotopic abundances. Ongoing technological developments within noble gas mass spectrometers over the last decade have led to analysis of increasingly smaller samples and higher precision, but also result in more complex data correction and interpretation. We describe a new multi-collector noble gas spectrometer, the Isotopx NGX-600, that is configured to optimize 40Ar/39Ar measurements. The NGX-600 is equipped with 9 Faraday collectors and one ion counting electron multiplier. Each Faraday is equipped with Isotopx ATONA® amplifier technology, enabling measurements spanning a dynamic range of amplified beam current from below 10−16 A to above 10−9 A. The performance of the NGX-600 is evaluated using both a conventional Nier-type ion source, and a next generation low temperature ion source, which allows for trap current variation from 200 μA to 1000 μA. We have performed over 3000 analyses of atmospheric argon to: (1) assess optimal measurement and integration times for blanks, baselines, and air aliquots of various ion intensities, (2) quantify the sensitivity via measurements of first principles 40Ar/39Ar standards, (3) compare the sensitivity between the conventional and new low temperature Nier-type ion sources, and (4) evaluate corrections associated with inter-Faraday biases, instrumental mass bias, and Faraday-multiplier gain. In addition to optimization experiments, we report a comparative analysis of both single crystal fusion and incremental heating data from Quaternary volcanic rocks obtained using both the 5-collector Nu Instruments Noblesse and the NGX-600 spectrometers.

AbstractClimate change is currently one of the main driving forces behind changes in species distributions, and understanding the mechanisms that underpin macroecological patterns is necessary for a more predictive science. Warming sea water temperatures are expected to drive changes in ectothermic marine species ranges due to their thermal tolerance levels. Here, we develop a mechanistic tool to predict size‐ and season‐specific distributions based on the physiology of the species and the temperature and food conditions in the sea. The effects of climate conditions on physiological‐based habitat utilization was then examined for different size‐classes of two commercially important fish species in the North Sea, plaice, Pleuronectes platessa, and sole, Solea solea. The two species provide an attractive comparison as they differ in their physiology (e.g. preferred temperature range). Combining dynamic energy budget (DEB) models with the temperature and food conditions estimated by an ecosystem model (ERSEM), allowed spatial differences in potential growth (as a proxy for habitat quality) to be estimated for 2 years with contrasting temperature and food conditions. The resulting habitat quality maps were in broad agreement with observed ontogenetic and seasonal changes in distribution as well as with the recent changes in distribution which could be attributed to an increase in coastal temperatures. Our physiological‐based model provides a powerful tool to explore the effect of climate change on the spatio‐temporal fish dynamics, predict effects of local or broad‐scale environmental changes and provide a physiological basis for observed changes in species distributions.

AbstractPolar bears (Ursus maritimus) are exposed to high concentrations of mercury because they are apex predators in the Arctic ecosystem. Although mercury is a potent neurotoxic heavy metal, it is not known whether current exposures are of neurotoxicological concern to polar bears. We tested the hypotheses that polar bears accumulate levels of mercury in their brains that exceed the estimated lowest observable adverse effect level (20 μg/g dry wt) for mammalian wildlife and that such exposures are associated with subtle neurological damage, as determined by measuring neurochemical biomarkers previously shown to be disrupted by mercury in other high‐trophic wildlife. Brain stem (medulla oblongata) tissues from 82 polar bears subsistence hunted in East Greenland were studied. Despite surprisingly low levels of mercury in the brain stem region (total mercury = 0.36 ±0.12 μg/g dry wt), a significant negative correlation was measured between N‐methyl‐D‐aspartate (NMDA) receptor levels and both total mercury (r = —0.34, p < 0.01) and methylmercury (r = —0.89, p < 0.05). No relationships were observed among mercury, selenium, and several other neurochemical biomarkers (dopamine‐2, gamma‐aminobutyric acid type A, muscarinic cholinergic, and nicotinic cholinergic receptors; cholinesterase and monoamine oxidase enzymes). These data show that East Greenland polar bears do not accumulate high levels of mercury in their brain stems. However, decreased levels of NMDA receptors could be one of the most sensitive indicators of mercury's subclinical and early effects.

The Ensemble Kalman filter (EnKF) has been applied to a 1-D complex ecosystem model coupled with a hydrodynamic model of the Ligurian Sea. In order to improve the performance of the EnKF, an ensemble subsampling strategy has been used to better represent the covariance matrices and a pre-analysis step for correcting the non-normality of the members distribution has been implemented. Twin experiments have been realized to assess the performance of the developed tool and a real data assimilation experiment has been conducted to hindcast the ecosystem at the Dyfamed site during the year 2000. Finally the performance of the EnKF has been compared with a Singular Evolutive Extended Kalman (SEEK) filter with a fixed basis. We conclude that, on one hand, there is a benefit in using the subsampling strategy and the lognormal transformation with the EnKF, and on the other hand, this filter presents better performance than the fixed basis version of the SEEK filter. However, it also incurs a large computational cost.

The link between anthropogenic nutrient loads and the magnitude and extent of diatom and Phaeocystis colony blooms in the Southern Bight of the North Sea was explored with the complex ecosystem model MIRO. The model was adapted for resolving the changing nutrient loads, the complex biology of the bloom species and the tight coupling between the benthic and pelagic compartments that characterise this shallow coastal shelf sea ecosystem. State variables included the main inorganic nutrients (nitrate [NO3], ammonium [NH 4], phosphate [PO4] and dissolved silica [DSi]), 3 groups of phytoplankton with different trophic fates (diatoms, nanophytoflagellates and Phaeocystis colonies), 2 zooplankton groups (copepods and microzooplankton), bacteria, and 5 classes of detrital organic matter with different biodegradability. The capability of the MIRO model to properly simulate the observed SW-NE gradient in nutrient enrichment and the seasonal cycle of inorganic and organic C and nutrients, phytoplankton, bacteria and zooplankton in the eastern English Channel and Southern Bight of the North Sea is demonstrated by running the model for the period from 1989 to 1999. The MIRO code was implemented in a simplified multi-box representation of the hydrodynamic regime. These model runs give the first general view of the seasonal dynamics of Phaeocystis colony blooms and nutrient cycling within the domain. C, N and P budget calculations show that (1) the coastal ecosystem has a low nutrient retention and elimination capacity, (2) trophic efficiency of the planktonic system is low, and (3) both are modulated by meteorological forcing.