Modeling of mesoscale coupled ocean–atmosphere interaction and its feedback to ocean in the western Arabian Sea     

Hyodae Seo  Raghu Murtugudde  Markus Jochum  Arthur J. Miller 《Ocean Modelling》2008,25(3-4):120-131

Observations of the western Arabian Sea over the last decade have revealed a rich filamentary eddy structure, with large horizontal SST gradients in the ocean, developing in response to the southwest monsoon winds. This summertime oceanic condition triggers an intense mesoscale coupled interaction, whose overall influence on the longer-term properties of this ocean remains uncertain. In this study, a high-resolution regional coupled model is employed to explore this feedback effect on the long-term dynamical and thermodynamical structure of the ocean.The observed relationship between the near-surface winds and mesoscale SSTs generate Ekman pumping velocities at the scale of the cold filaments, whose magnitude is the order of 1 m/day in both the model and observations. This additional Ekman-driven velocity, induced by the wind-eddy interaction, accounts for approximately 10–20% of oceanic vertical velocity of the cold filaments. This implies that Ekman pumping arising from the mesoscale coupled feedback makes a non-trivial contribution to the vertical structure of the upper ocean and the evolution of mesoscale eddies, with obvious implications for marine ecosystem and biogeochemical variability.Furthermore, SST features associated with cold filaments substantially reduce the latent heat loss. The long-term latent heat flux change due to eddies in the model is approximately 10–15 W/m² over the cold filaments, which is consistent with previous estimates based on short-term in situ measurements. Given the shallow mixed layer, this additional surface heat flux warms the cold filament at the rate of 0.3–0.4 °C/month over a season with strong eddy activity, and 0.1–0.2 °C/month over the 12-year mean, rendering overall low-frequency modulation of SST feasible. This long-term mixed layer heating by the surface flux is approximately ±10% of the lateral heat flux by the eddies, yet it can be comparable to the vertical heat flux. Potential dynamic and thermodynamic impacts of this observed air–sea interaction on the monsoons and regional climate are yet to be quantified given the strong correlation between the Somalia upwelling SST and the Indian summer monsoons.  相似文献   

Origin,distribution, and alteration of asphalts at Chapopote Knoll,Southern Gulf of Mexico     

Markus Brüning  Heiko Sahling  Ian R. MacDonald  Feng Ding  Gerhard Bohrmann 《Marine and Petroleum Geology》2010

Following the discovery of asphalt volcanism in the Campeche Knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at Chapopote. The novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water. The released petroleum forms characteristic flow structures at the seafloor with surfaces that are ‘ropy’ or ‘rough’ similar to magmatic lava flows. The surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles. Consequently, the heavy petroleum forms the observed asphalt deposit and solidifies. Detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations: e.g. volume reduction leading to the formation of visible cracks in the asphalt surface, followed by fragmentation of the entire deposit. While relatively fresh asphalt samples were gooey and sticky, older, fragmented pieces were found to be brittle without residual stickiness. Furthermore, there is evidence for petroleum seepage from below the asphalt deposits, leading to local up-doming and, sometimes, to whip-shaped extrusions. Extensive mapping by TV-guided tools of Chapopote Asphalt Volcano indicates that the main asphalt deposits occur at the south-western rim that borders a central, crater-like depression. The most recent asphalt deposit at Chapopote is the main asphalt field covering an area of ∼2000 m². Asphalt volcanism is distinct from oil and gas seepage previously described in the Gulf of Mexico and elsewhere because it is characterized by episodic intrusions of semi-solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief. As Chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism.  相似文献   

Towards sustainable fisheries subsidies: Entering a new round of reform under the Common Fisheries Policy     

Till Markus 《Marine Policy》2010

On 22 April 2009 the European Commission published its ‘Green Paper on the Reform of the Common Fisheries Policy’. The Green Paper points out a contradiction in policy, noting on one hand that public financial support to the Community's fisheries sector is substantial, but on the other hand such support is often incompatible with other Common Fisheries Policy (CFP) objectives, particularly the need to reduce overcapacities. Providing an analytical framework to better understand the effects of subsidies as well as an overview of existing funding schemes under the CFP, this article aims at answering some of the questions posed by the European Commission within its Green Paper. Answers are based on two ideas: the exploitation of marine capture resources ultimately depends on the level of available fish stocks and that a large share of subsidies fuels the race to fish by inducing investment incentives for the fisheries sector. Policies that have ignored this tend to encourage inefficient and unsustainable fishing as well as the misallocation of public funds. Although support schemes under the CFP have changed in recent years, some problematic support schemes persist. A future reform will have to continue the course taken towards sustainable and efficient approaches to supporting the fisheries industry.  相似文献   

Widespread rocky reef occurrence in the central English Channel and the implications for predictive habitat mapping   总被引：1，自引：1，他引：0  

Markus Diesing  Roger Coggan  Koen Vanstaen 《Estuarine, Coastal and Shelf Science》2009,83(4):647-658

Reefs are one of the marine habitats listed in Annex I of the European Union's Habitats Directive, which aims to establish a coherent European ecological network of Special Areas of Conservation. EU Member States are required to prepare and propose a national list of sites for evaluation under the scheme, but currently the occurrence of reefs in the United Kingdom's nearshore and offshore areas is not well documented. Here we report on our search for rocky reefs in the central English Channel, which unexpectedly revealed an extensive reef system covering an area of 1100 km². Prior to our work, it was generally perceived that the seabed in this area comprised mostly gravel, with a few isolated rock outcrops.Our approach to determining the location, extent and character of these reefs incorporated broad, medium and fine-scale analyses over a 3200 km² area of seabed, using single- and multi-beam acoustic data, ground-truthed by underwater video and stills imagery. A benthic terrain model was developed in ArcGIS to map topographic features at the broad and medium scales. Biotope assignments were made at the fine scale through detailed analysis of video footage obtained from 30 sampling stations. The study area has a complex geological history and lies at the centre of a major bedload-parting zone. Together, these strongly influence the seabed character and the distribution of biotopes. An integrated assessment of the physical and biological features was used to map the study area to level 4 of the EUNIS habitat classification system.Similar physical conditions exist in other areas of the UK continental shelf, raising the prospect of predicting where other rocky reef systems might occur. In the absence of a co-ordinated national seabed survey programme, such predictions, coupled with interpretation of existing single-beam bathymetry data, can help prioritise areas where limited survey resources could be most effectively deployed.  相似文献   

Seasonal and depth-related dynamics of prokaryotes and viruses in surface and deep waters of the northwestern Mediterranean Sea     

Christian Winter  Marie-Emmanuelle Kerros  Markus G. Weinbauer   《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1972-1982

The study site located in the northwestern Mediterranean Sea was visited nine times in 2005–2006 to collect water samples from the epi- (5 m), meso- (200, 600 m), and bathypelagic (1000, 2000 m) zone. Total abundance of prokaryotes and viruses was determined by flow cytometry (FCM). Prokaryotic abundance in the epi-, meso-, and bathypelagic varied between 0.9 and 15.9×10⁵, 0.6 and 2.1×10⁵, and 0.3 and 1.3×10⁵ ml⁻¹, respectively. Variation of viral abundance in the epi-, meso-, and bathypelagic was between 1.2 and 57.5×10⁶, 0.5 and 3.5×10⁶, and 0.4 and 1.3×10⁶ ml⁻¹, respectively. The fraction of low (LNA) and high (HNA) nucleic acid prokaryotes averaged 42.9% and 57.1% throughout the water column and did not differ between depth layers. Throughout the water column the fraction of low, medium, and high fluorescent viruses (Vir-LF, Vir-MF, Vir-HF) averaged 66.3%, 30.2%, and 3.5%. Vir-LF and Vir-MF did not differ between depth layers; however, Vir-HF showed a preference for surface waters. The fraction of LNA cells decreased in the epi- and increased in the bathypelagic with decreasing stratification. The fraction of Vir-LF viruses increased in the epipelagic and decreased in the bathypelagic with increasing prokaryotic abundance. Also, the relationship between viral abundance and the bacterial community was different in surface and deep waters. The data suggest that different mechanisms of interaction between viruses and their prokaryotic hosts prevail at the surface and in deep waters.  相似文献   

Functional composition, but not richness, affected the performance of sessile suspension-feeding assemblages     

Nelson Valdivia  Kate L. de la Haye  Stuart R. Jenkins  Susan A. Kimmance  Richard C. Thompson  Markus Molis 《Journal of Sea Research》2009,61(4):216-221

The efficiency by which communities capture limiting resources may be related to the number of species or functional types competing therein. This is because species use different resources (i.e. complementarity effect) or because species-rich communities include species with extreme functional traits (positive selection effect). We conducted two manipulative studies to separate the effects of functional richness and functional identity on the feeding efficiency (i.e. filtration rate) of suspension-feeding invertebrates growing on vertical surfaces. In addition, one experiment tested whether the density of organisms influences the effect of functional diversity. Monocultures and complete mixtures of functional types were fed with a solution of microalgae of different sizes (6 μm–40 μm). Experiments conducted at two locations, Helgoland and Plymouth, showed that functional identity had far larger effects on filtration rate than richness. Mixtures did not outperform the average monoculture or the best-performing monoculture and this pattern was independent on density. The high efficiency of one of the functional types in consuming most microalgae could have minimised the resource complementarity. The loss or gain of particular species may therefore have a stronger impact on the functioning of epibenthic communities than richness per se.  相似文献   

Validation of the three-dimensional ECOHAM model in the German Bight for 2004 including population dynamics of Pseudocalanus elongatus     

Christoph Stegert  Andreas Moll  Markus Kreus   《Journal of Sea Research》2009,62(1):1-15

A three-dimensional ecosystem model for the North Sea which includes competition between Pseudocalanus elongatus and the rest of the zooplankton biomass was applied to describe the seasonal cycle of zooplankton in 2003–2004. The paper presents the comparison of simulated stage-resolved abundances with copepod counts at several stations in the German Bight during the GLOBEC-Germany project from February to October 2004. A validation of influential state variables gives confidence that the model is able to calculate reliably the stage development and abundances of P. elongatus as well as the range of bulk zooplankton biomass, and thus the ratio of population biomass to total biomass. In the German Bight, the population is below 20% in spring. The ratio increases up to 50% during summer. The number of generations was estimated from peaks in egg abundance to about 4–8 generations of P. elongatus in the southern North Sea. A mean of four generations per year were estimated in the central North Sea, six to eight generations northwest of the Dogger Bank (tails end) and five generations in the German Bight.  相似文献   

Effects of different closures for thickness diffusivity     

Carsten Eden  Markus Jochum  Gokhan Danabasoglu 《Ocean Modelling》2009,26(1-2):47-59

The effects of spatial variations of the thickness diffusivity (K) appropriate to the parameterisation of [Gent, P.R. and McWilliams, J.C., 1990. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr., 20, 150–155.] are assessed in a coarse resolution global ocean general circulation model. Simulations using three closures yielding different lateral and/or vertical variations in K are compared with a simulation using a constant value. Although the effects of changing K are in general small and all simulations remain biased compared to observations, we find systematic local sensitivities of the simulated circulation on K. In particular, increasing K near the surface in the tropical ocean lifts the depth of the equatorial thermocline, the strength of the Antarctic Circumpolar Current decreases while the subpolar and subtropical gyre transports in the North Atlantic increase by increasing K locally. We also find that the lateral and vertical structure of K given by a recently proposed closure reduces the negative temperature biases in the western North Atlantic by adjusting the pathways of the Gulf Stream and the North Atlantic Current to a more realistic position.  相似文献