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Oceanic Circulation (oceanic + circulation)
Selected AbstractsArchaeal diversity and a gene for ammonia oxidation are coupled to oceanic circulationENVIRONMENTAL MICROBIOLOGY, Issue 4 2009Pierre E. Galand Summary Evidence of microbial zonation in the open ocean is rapidly accumulating, but while the distribution of communities is often described according to depth, the other physical factors structuring microbial diversity and function remain poorly understood. Here we identify three different water masses in the North Water (eastern Canadian Arctic), defined by distinct temperature and salinity characteristics, and show that they contained distinct archaeal communities. Moreover, we found that one of the water masses contained an increased abundance of the archaeal alpha-subunit of the ammonia monooxygenase gene (amoA) and accounted for 70% of the amoA gene detected overall. This indicates likely differences in putative biogeochemical capacities among different water masses. The ensemble of our results strongly suggest that the widely accepted view of depth stratification did not explain microbial diversity, but rather that parent water masses provide the framework for predicting communities and potential microbial function in an Arctic marine system. Our results emphasize that microbial distributions are strongly influenced by oceanic circulation, implying that shifting currents and water mass boundaries resulting from climate change may well impact patterns of microbial diversity by displacing whole biomes from their historic distributions. This relocation could have the potential to establish a substantially different geography of microbial-driven biogeochemical processes and associated oceanic production. [source] Ecological effects of regime shifts in the Bering Sea and eastern North Pacific OceanFISH AND FISHERIES, Issue 2 2002Ashleen J Benson Abstract Large-scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability,from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects. [source] Potential changes in skipjack tuna (Katsuwonus pelamis) habitat from a global warming scenario: modelling approach and preliminary resultsFISHERIES OCEANOGRAPHY, Issue 4-5 2003Harilaos Loukos Abstract Recent studies suggest a reduction of primary production in the tropical oceans because of changes in oceanic circulation under global warming conditions caused by increasing atmospheric CO2 concentration. This might affect the productivity of medium and higher trophic levels with potential consequences on marine resources such as tropical tuna. Here we combine the projections of up-to-date climate and ocean biogeochemical models with recent concepts of representation of fish habitat based on prey abundance and ambient temperature to gain some insight into the impact of climate change on skipjack tuna (Katsuwonus pelamis), the species that dominates present-day tuna catch. For a world with doubled atmospheric CO2 concentration, our results suggest significant large-scale changes of skipjack habitat in the equatorial Pacific. East of the date line, conditions could be improved by an extension of the present favourable habitat zones of the western equatorial Pacific, a feature reminiscent of warming conditions associated with El Niño events. Despite its simplicity and the associated underlying hypothesis, this first simulation is used to stress future research directions and key issues for modelling developments associated to global change. [source] Sedimentary and faunal events revealed by a revised correlation of post-glacial Hirnantian (Late Ordovician) strata in the Welsh Basin, UKGEOLOGICAL JOURNAL, Issue 3 2009Jeremy R. Davies Abstract The discovery of a previously unrecognized unconformity and of new faunas in the type Llandovery area underpins a revised correlation of Hirnantian strata in mid Wales. This has revealed the sedimentary and faunal events which affected the Lower Palaeozoic Welsh Basin during the global rise in sea level that followed the end-Ordovician glacial maximum and has allowed their interpretation in the context of local and global influences. In peri-basinal shelfal settings the onset of post-glacial deepening is recorded by an unfossiliferous, transgressive shoreface sequence (Cwm Clyd Sandstone and Garth House formations) which rests unconformably on Rawtheyan rocks, deformed during an episode of pre-Hirnantian tectonism. In the deep water facies of the basin centre, this same sequence boundary is now recognized as the contact between fine-grained, re-sedimented mudstones and an underlying regressive sequence of turbidite sandstones and conglomerates; it is at a level lower than previously cited and calls into question the established lithostratigraphy. In younger Hirnantian strata, graptolites associated with the newly recognized Ystradwalter Member (Chwefri Formation) demonstrate that this distal shelf unit correlates with the persculptus graptolite-bearing Mottled Mudstone Member of the basinal succession. Together these members record an important macrofaunal recolonization of the Welsh Basin and mark a key event in the post-glacial transgression. Further deepening saw the establishment of a stratified water column and the imposition of anoxic bottom water conditions across the basin floor. These post-glacial Hirnantian events are consistent with the re-establishment of connections between a silled Welsh Basin and the open Iapetus Ocean. However, a comparison with other areas suggests that each event records a separate deepening episode within a pulsed glacio-eustatic transgression, while also reflecting changes in post-glacial climate and patterns of oceanic circulation and associated biotic flux. British Geological Survey © NERC 2009. All rights reserved. [source] Thermodynamic optimization of global circulation and climateINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2005Adrian Bejan Abstract The constructal law of generation of flow structure is used to predict the main features of global circulation and climate. The flow structure is the atmospheric and oceanic circulation. This feature is modelled as convection loops, and added to the earth model as a heat engine heated by the Sun and cooled by the background. It is shown that the dissipation of the power produced by the earth engine can be maximized by selecting the proper balance between the hot and cold zones of the Earth, and by optimizing the thermal conductance of the circulation loops. The optimized features agree with the main characteristics of global circulation and climate. The robustness of these predictions, and the place of the constructal law as a self-standing principle in thermodynamics, are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Stable genetic polymorphism in heterogeneous environments: balance between asymmetrical dispersal and selection in the acorn barnacleJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2006D. VÉLIZ Abstract Elucidating the processes responsible for maintaining polymorphism at ecologically relevant genes is intimately related to understanding the interplay between selection imposed by habitat heterogeneity and a species' capacity for dispersal in the face of environmental constraints. In this paper, we used a model-based approach to solve equilibria of balanced polymorphism, given values of fitness and larval dispersal among different habitats in the acorn barnacle Semibalanus balanoides from the Gulf of St Lawrence. Our results showed that allele frequencies observed at both MPI* and GPI* loci represented stable equilibria, given empirical estimates of fitness values, and that considerably more larvae dispersed from one region (north) to the other (south) than vice versa. Dispersal conditions were predicted to be similar for the maintenance of polymorphism at both loci. Moreover, the values of asymmetrical dispersal required by the model to reach stable equilibria were compatible with empirical estimates of larval dispersal and oceanic circulation documented in this system. Overall, this study illustrated the usefulness of a modified and computable version of Bulmer's model (1972) in order to test hypotheses of balanced polymorphism resulting from interactions between spatial selection and asymmetrical dispersal. [source] | |||||||||||||