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Deep Ocean (deep + ocean)
Selected AbstractsRAPID SPECIATION AND ECOLOGICAL DIVERGENCE IN THE AMERICAN SEVEN-SPINED GOBIES (GOBIIDAE, GOBIOSOMATINI) INFERRED FROM A MOLECULAR PHYLOGENYEVOLUTION, Issue 7 2003Lukas Rüber Abstract., The American seven-spined gobies (Gobiidae, Gobiosomatini) are highly diverse both in morphology and ecology with many endemics in the Caribbean region. We have reconstructed a molecular phylogeny of 54 Gobio-somatini taxa (65 individuals) based on a 1646-bp region that includes the mitochondrial 12S rRNA, tRNA-Val, and 16S rRNA genes. Our results support the monophyly of the seven-spined gobies and are in agreement with the existence of two major groups within the tribe, the Gobiosoma group and the Microgobius group. However, they reject the monophyly of some of the Gobiosomatini genera. We use the molecular phylogeny to study the dynamics of speciation in the Gobiosomatini by testing for departures from the constant speciation rate model. We observe a burst of speciation in the early evolutionary history of the group and a subsequent slowdown. Our results show a split among clades into coastal-estuarian, deep ocean, and tropical reef habitats. Major habitat shifts account for the early significant acceleration in lineage splitting and speciation rate and the initial divergence of the main Gobiosomatini clades. We found that subsequent diversification is triggered by behavior and niche specializations at least in the reef-associated clades. Overall, our results confirm that the diversity of Gobiosomatini has arisen during episodes of adaptive radiation, and emphasize the importance of ecology in marine speciation. [source] Climate control on the long-term anomalous changes of zooplankton communities in the Northwestern MediterraneanGLOBAL CHANGE BIOLOGY, Issue 1 2008JUAN CARLOS MOLINERO Abstract In marine ecosystems, pelagic copepods, chaetognaths and jellyfish play a key role in matter and energy flow. While copepods support most food webs and the biological pump of carbon into the deep ocean, chaetognaths and jellyfish may affect the strength of the top-down control upon plankton communities. In this study, we show that the main events in the long-term variability of these functional groups in the Northwestern Mediterranean were tightly linked to changes of climate forcing of the North Atlantic sector. Large-scale climate forcing has altered the pelagic food-web dynamics through changes in biological interactions, competition and predation, leading to substantial changes manifested as bursts or collapses in zooplankton populations, and consequently to a major change ca. 1987. These events become more frequent in the 1980s and the early 1990s in the studied zooplankton functional groups suggesting a shift in the functioning of the pelagic ecosystem. The environmental modifications and the results reported here are therefore, indicators of a regime change pointing to a more regeneration-dominated system in the study area. We suggest a chain of mechanisms, whereby climate variation has modified the long-term dynamics of pelagic copepods, chaetognaths and jellyfish in the Ligurian Sea. [source] A Self-Consistent Bathymetric Mapping AlgorithmJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1-2 2007Chris Roman The achievable accuracy of bathymetric mapping in the deep ocean using robotic systems is most often limited by the available guidance or navigation information used to combine the measured sonar ranges during the map making process. This paper presents an algorithm designed to mitigate the affects of poor ground referenced navigation by applying the principles of map registration and pose filtering commonly used in simultaneous localization and mapping (SLAM) algorithms. The goal of the algorithm is to produce a self-consistent point cloud representation of the bottom terrain with errors that are on a scale similar to the sonar range resolution rather than any direct positioning measurement. The presented algorithm operates causally and utilizes sensor data that are common to instrumented underwater robotic vehicles used for mapping and scientific explorations. Real world results are shown for data taken on several expeditions with the JASON remotely operated vehicle (ROV). Comparisons are made between more standard mapping approaches and the proposed method is shown to significantly improve the map quality and reveal scene information that would have otherwise been obscured due to poor direct navigation information. © 2007 Wiley Periodicals, Inc. [source] Holocene bipolar climate seesaw: possible subtle evidence from the deep North East Atlantic Ocean?,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2010Mark A. Maslin Abstract The occurrence of a millennial-scale bipolar climate seesaw has been documented in detail for the last glacial period and Termination. There is, however, debate whether it occurs during interglacials and if it does what influence it could have on future climate. We present here new evidence from a North East Atlantic Ocean deep-sea core which supports the hypothesis for a Holocene bipolar climate seesaw. BENGAL Site 13078#16, from the Porcupine Abyssal Plain, is 4844,m deep and situated at the North Atlantic Deep Water and Antarctic Bottom Water (AABW) interface. Planktic foraminiferal fragment accumulation rate data at this site is an indicator of coarse carbonate dissolution, which is highly sensitive to the incursion of under-saturated AABW. Five dissolution peaks have been identified, which seem to occur approximately 500 a after each of the North Atlantic 'Bond' ice rafting pulses, suggesting a subsequent subtle shallowing of AABW. This indicates a possible lagged climatic link between North East Atlantic surface water conditions and AABW production in the Southern Ocean during the Holocene. This provides the first tentative evidence that there was a Holocene bipolar climate seesaw and that the deep ocean was involved. This study also suggests that extremely sensitive locations need to be sought as the Holocene bipolar climate seesaw seems to be very subtle compared with its glacial counterparts. Copyright © 2009 John Wiley & Sons, Ltd. [source] Turbulence energetics in stably stratified geophysical flows: Strong and weak mixing regimesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 633 2008S. S. Zilitinkevich Abstract Traditionally, turbulence energetics is characterised by turbulent kinetic energy (TKE) and modelled using solely the TKE budget equation. In stable stratification, TKE is generated by the velocity shear and expended through viscous dissipation and work against buoyancy forces. The effect of stratification is characterised by the ratio of the buoyancy gradient to squared shear, called the Richardson number, Ri. It is widely believed that at Ri exceeding a critical value, Ric, local shear cannot maintain turbulence, and the flow becomes laminar. We revise this concept by extending the energy analysis to turbulent potential and total energies (TPE, and TTE = TKE + TPE), consider their budget equations, and conclude that TTE is a conservative parameter maintained by shear in any stratification. Hence there is no ,energetics Ric', in contrast to the hydrodynamic-instability threshold, Ric,instability, whose typical values vary from 0.25 to 1. We demonstrate that this interval, 0.25 < Ri < 1, separates two different turbulent regimes: strong mixing and weak mixing rather than the turbulent and the laminar regimes, as the classical concept states. This explains persistent occurrence of turbulence in the free atmosphere and deep ocean at Ri , 1, clarifies the principal difference between turbulent boundary layers and free flows, and provides the basis for improving operational turbulence closure models. Copyright © 2008 Royal Meteorological Society [source] Bacteria in the cold deep-sea benthic boundary layer and sediment,water interface of the NE AtlanticFEMS MICROBIOLOGY ECOLOGY, Issue 2 2000Carol Turley Abstract This is a short review of the current understanding of the role of microorganisms in the biogeochemistry in the deep-sea benthic boundary layer (BBL) and sediment,water interface (SWI) of the NE Atlantic, the gaps in our knowledge and some suggestions of future directions. The BBL is the layer of water, often tens of meters thick, adjacent to the sea bed and with homogenous properties of temperature and salinity, which sometimes contains resuspended detrital particles. The SWI is the bioreactive interface between the water column and the upper 1 cm of sediment and can include a large layer of detrital material composed of aggregates that have sedimented from the upper mixed layer of the ocean. This material is biologically transformed, over a wide range of time scales, eventually forming the sedimentary record. To understand the microbial ecology of deep-sea bacteria, we need to appreciate the food supply in the upper ocean, its packaging, passage and transformation during the delivery to the sea bed, the seasonality of variability of the supply and the environmental conditions under which the deep-sea bacteria grow. We also need to put into a microbial context recent geochemical findings of vast reservoirs of intrinsically labile organic material sorped onto sediments. These may well become desorped, and once again available to microorganisms, during resuspension events caused by deep ocean currents. As biotechnologists apply their tools in the deep oceans in search of unique bacteria, an increasing knowledge and understanding of the natural processes undertaken and environmental conditions experienced by deep-sea bacteria will facilitate this exploitation. [source] Earth's magnetic field: ocean current contributions to vertical profiles in deep oceansGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001F. E. M. (Ted) Lilley SUMMARY The Earth's main magnetic field, arising in the core, should, in the ocean, have a well-defined uniform gradient with depth. Superimposed upon this uniform gradient may be magnetic signals due to a variety of sources. These include crustal magnetization, the transient fluctuations arising external to the Earth and causing secondary induced fields within it; and, the focus of the present paper, magnetic signals arising from the motional induction of seawater moving in the steady main magnetic field of Earth. There are circumstances where theory predicts such motionally-induced magnetic fields to be of order 102 nT, and to vary with depth in a way which is directly related to the velocity profile. Exploratory soundings of the magnetic field with depth have been made in the oceans around Australia, both to test these predictions, and to investigate the practicability of measuring such profiles. The magnetic field parameter observed has been that of the ,total field', which should sense the component of the ocean velocity which lies in the magnetic meridian. The magnetometer has been lowered by cable from a ship and also operated free-fall to the seafloor (and return). The observations appear both to confirm the theoretical gradient of the main field where there is no ocean current and, where ocean currents exist, to give evidence of their profiles resolved in the direction of magnetic north. In particular, observations taken in an eddy of the East Australian Current show the correct contrast in sign for north and south flowing streams. [source] Five hundred pages on the unknown shallows of the deep oceans.MARINE ECOLOGY, Issue 2 2009Fisheries & Conservation, Seamounts: Ecology No abstract is available for this article. [source] | |||||||||||||