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Search Results: 1 - 10 of 117902 matches for " T. Tyrrell "
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The subtle effects of sea water acidification on the amphipod Gammarus locusta
C. Hauton, T. Tyrrell,J. Williams
Biogeosciences (BG) & Discussions (BGD) , 2009,
Abstract: We report an investigation of the effects of increases in pCO2 on the survival, growth and molecular physiology of the neritic amphipod Gammarus locusta which has a cosmopolitan distribution in estuaries. Amphipods were reared from juvenile to mature adult in laboratory microcosms at three different levels of pH in nominal range 8.1–7.6. Growth rate was estimated from weekly measures of body length. At sexual maturity the amphipods were sacrificed and assayed for changes in the expression of genes coding for a heat shock protein (hsp70 gene) and the metabolic enzyme glyceraldehyde-3-phosphate dehydrogenase (gapdh gene). The data show that the growth and survival of this species is not significantly impacted by a decrease in sea water pH of up to 0.5 units. Quantitative real-time PCR analysis indicated that there was no significant effect of growth in acidified sea water on the sustained expression of the hsp70 gene. There was a consistent and significant increase in the expression of the gapdh gene at a pH of ~7.5 which, when combined with observations from other workers, suggests that metabolic changes may occur in response to acidification. It is concluded that sensitive assays of tissue physiology and molecular biology should be routinely employed in future studies of the impacts of sea water acidification as subtle effects on the physiology and metabolism of coastal marine species may be overlooked in conventional gross "end-point" studies of organism growth or mortality.
The subtle effects of sea water acidification on the amphipod Gammarus locusta
C. Hauton,T. Tyrrell,J. Williams
Biogeosciences Discussions , 2009,
Abstract: We report an investigation of the effects of increases in pCO2 on the growth and molecular physiology of the neritic amphipod Gammarus locusta, which has a cosmopolitan distribution in estuaries. Amphipods were reared from juvenile to mature adult in laboratory microcosms at three different levels of pH in nominal range 8.1–7.6. Growth rate was estimated from weekly measures of body length. At sexual maturity the amphipods were sacrificed and assayed for changes in the expression of genes coding for a heat shock protein (hsp70 gene) and the metabolic enzyme glyceraldehyde-3-phosphate dehydrogenase (gapdh gene). The data show that the growth and survival rate of this species is not significantly impacted by a decrease in sea water pH of up to 0.5 units. Quantitative real-time PCR analysis indicated that there was no significant effect of growth in acidified sea water on the expression of the hsp70 gene. However, there was a consistent and significant increase in the expression of the gapdh gene at a pH of ~7.5 which indicated a possible disruption to oxidative metabolic processes. It was concluded that future predicted changes in sea water pH may have subtle effects on the physiology and metabolism of coastal and marine species which may be overlooked in studies of whole organism response.
Coccolithophores and calcite saturation state in the Baltic and Black Seas
T. Tyrrell, B. Schneider, A. Charalampopoulou,U. Riebesell
Biogeosciences (BG) & Discussions (BGD) , 2008,
Abstract: The Baltic and Black Seas are both brackish, that is to say both have salinities intermediate between freshwater and seawater. The coccolithophore Emiliania huxleyi is abundant in one, the Black Sea, but absent from the other, the Baltic Sea. Here we present summertime coccolithophore measurements confirming this difference, as well as data on the calcium carbonate saturation state of the Baltic Sea. We find that the Baltic Sea becomes undersaturated (or nearly so) in winter, with respect to both the aragonite and calcite mineral forms of CaCO3. Data for the Black Sea are more limited, but it appears to remain strongly supersaturated year-round. The absence of E. huxleyi from the Baltic Sea could therefore potentially be explained by dissolution of their coccoliths in winter, suggesting that minimum annual (wintertime) saturation states could be most important in determining future ocean acidification impacts. In addition to this potential importance of winter saturation state, alternative explanations are also possible, either related to differences in salinity or else to differences in silicate concentrations.
Contrasting effects of temperature and winter mixing on the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean
C. Dumousseaud,E. P. Achterberg,T. Tyrrell,A. Charalampopoulou
Biogeosciences Discussions , 2009,
Abstract: Future climate change due to the increase in atmospheric CO2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary productivity and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic Ocean for the period between 2005 and 2007. Monthly observations were made between the English Channel and the Bay of Biscay using a ship of opportunity program. During the colder winter of 2005/2006, the maximum depth of the mixed layer reached 500 m in the Bay of Biscay, whilst during the warmer (by 2.6±0.5°C) winter of 2006/2007 the mixed layer depth reached only 300 m. The inter-annual differences in late winter concentrations of nitrate (2.8±1.1 μmol l 1) and dissolved inorganic carbon (22±6 μmol l 1), with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO2 fluxes (ranging from +4.5 to 5.5 mmol m 2 d 1) showed an increased oceanic CO2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences.
Coccolithophores and calcite saturation state in the Baltic and Black Seas
T. Tyrrell,B. Schneider,A. Charalampopoulou,U. Riebesell
Biogeosciences Discussions , 2007,
Abstract: The Baltic and Black Seas are both brackish, that is to say both have salinities intermediate between freshwater and seawater. The coccolithophore Emiliania huxleyi is abundant in one, the Black Sea, but absent from the other, the Baltic Sea. Here we present summertime coccolithophore measurements confirming this difference, as well as data on the calcium carbonate saturation state of the Baltic Sea. We find that the Baltic Sea becomes undersaturated (or nearly so) in winter, with respect to both the aragonite and calcite mineral forms of CaCO3. Data for the Black Sea are more limited, but it appears to remain strongly supersaturated year-round. The absence of E. huxleyi from the Baltic Sea could therefore potentially be explained by dissolution of their coccoliths in winter, suggesting that minimum annual (wintertime) saturation states could be most important in determining future ocean acidification impacts. In addition to this potential importance of winter saturation state, alternative explanations are also possible, either related to differences in salinity or else to differences in silicate concentrations.
Enumerating Segmented Patterns in Compositions and Encoding by Restricted Permutations
Sergey Kitaev,Tyrrell B. McAllister,T. Kyle Petersen
Mathematics , 2005,
Abstract: A composition of a nonnegative integer (n) is a sequence of positive integers whose sum is (n). A composition is palindromic if it is unchanged when its terms are read in reverse order. We provide a generating function for the number of occurrences of arbitrary segmented partially ordered patterns among compositions of (n) with a prescribed number of parts. These patterns generalize the notions of rises, drops, and levels studied in the literature. We also obtain results enumerating parts with given sizes and locations among compositions and palindromic compositions with a given number of parts. Our results are motivated by "encoding by restricted permutations," a relatively undeveloped method that provides a language for describing many combinatorial objects. We conclude with some examples demonstrating bijections between restricted permutations and other objects.
Carbon and nutrient mixed layer dynamics in the Norwegian Sea
H. S. Findlay, T. Tyrrell, R. G. J. Bellerby, A. Merico,I. Skjelvan
Biogeosciences (BG) & Discussions (BGD) , 2008,
Abstract: A coupled carbon-ecosystem model is compared to recent data from Ocean Weather Station M (66° N, 02° E) and used as a tool to investigate nutrient and carbon processes within the Norwegian Sea. Nitrate is consumed by phytoplankton in the surface layers over the summer; however the data show that silicate does not become rapidly limiting for diatoms, in contrast to the model prediction and in contrast to data from other temperate locations. The model estimates atmosphere-ocean CO2 flux to be 37 g C m 2 yr 1. The seasonal cycle of the carbonate system at OWS M resembles the cycles suggested by data from other high-latitude ocean locations. The seasonal cycles of calcite saturation state and [CO32-] are similar in the model and in data at OWS M: values range from ~3 and ~120 μmol kg 1 respectively in winter, to ~4 and ~170 μmol kg 1 respectively in summer. The model and data provide further evidence (supporting previous modelling work) that the summer is a time of high saturation state within the annual cycle at high-latitude locations. This is also the time of year that coccolithophore blooms occur at high latitudes.
Contrasting effects of temperature and winter mixing on the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean
C. Dumousseaud, E. P. Achterberg, T. Tyrrell, A. Charalampopoulou, U. Schuster, M. Hartman,D. J. Hydes
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Future climate change as a result of increasing atmospheric CO2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary production and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic Ocean for the period between 2005 and 2007. Monthly observations were made between the English Channel and the Bay of Biscay using a ship of opportunity program. During the colder winter of 2005/2006, the maximum depth of the mixed layer reached up to 650 m in the Bay of Biscay, whilst during the warmer (by 2.6 ± 0.5 °C) winter of 2006/2007 the mixed layer depth reached only 300 m. The inter-annual differences in late winter concentrations of nitrate (2.8 ± 1.1 μmol l 1) and dissolved inorganic carbon (22 ± 6 μmol kg 1, with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the chlorophyll α-fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO2 fluxes (ranging from +3.7 to 4.8 mmol m 2 d 1) showed an increased oceanic CO2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences.
Carbon and nutrient mixed layer dynamics in the Norwegian Sea
H. S. Findlay,T. Tyrrell,R. G. J. Bellerby,A. Merico
Biogeosciences Discussions , 2007,
Abstract: A coupled carbon-ecosystem model is compared to recent data from Ocean Weather Ship M (66° N, 02° E) and used to investigate nutrient and carbon processes within the Norwegian Sea. Nitrate is consumed by phytoplankton in the surface layers over the summer; however the data show that silicate does not become rapidly limiting for diatoms, in contrast to the model prediction and in contrast to data from other temperate locations. The model estimates atmosphere-ocean CO2 flux to be 37 g C m 2 yr 1. A detailed comparison of the carbonate system at other ocean locations reveals that although coccolithophore blooms occur at OWS M, they are not as prevalent here as other areas. The seasonal cycles of calcite saturation state and [CO32 ] are similar in the model and in data: values range from ~3 and ~120 μmol kg 1 respectively in winter, to ~4 and ~170 μmol kg 1 respectively in summer. The timing of coccolithophore blooms within the year therefore coincides with a time of high calcite saturation state, as predicted by previous modelling work.
Biologically Inspired Intercellular Slot Synchronization
Alexander Tyrrell,Gunther Auer
EURASIP Journal on Wireless Communications and Networking , 2009, DOI: 10.1155/2009/854087
Abstract: The present article develops a decentralized interbase station slot synchronization algorithm suitable for cellular mobile communication systems. The proposed cellular firefly synchronization (CelFSync) algorithm is derived from the theory of pulse-coupled oscillators, common to describe synchronization phenomena in biological systems, such as the spontaneous synchronization of fireflies. In order to maintain synchronization among base stations (BSs), even when there is no direct link between adjacent BSs, some selected user terminals (UTs) participate in the network synchronization process. Synchronization emerges by exchanging two distinct synchronization words, one transmitted by BSs and the other by active UTs, without any a priori assumption on the initial timing misalignments of BSs and UTs. In large-scale networks with inter-BS site distances up to a few kilometers, propagation delays severely affect the attainable timing accuracy of CelFSync. We show that by an appropriate combination of CelFSync with the timing advance procedure, which aligns uplink transmission of UTs to arrive simultaneously at the BS, a timing accuracy within a fraction of the inter-BS propagation delay is retained.
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