Wave-induced steady streaming,mass transport and net sediment transport in rough turbulent ocean bottom boundary layers

The interaction between two important mechanisms which causes streaming has been investigated by numerical simulations of the seabed boundary layer beneath both sinusoidal waves and Stokes second order waves, as well as horizontally uniform bottom boundary layers with asymmetric forcing. These two mechanisms are streaming caused by turbulence asymmetry in successive wave half-cycles (beneath asymmetric forcing), and streaming caused by the presence of a vertical wave velocity within the seabed boundary layer as earlier explained by Longuet-Higgins. The effect of wave asymmetry, wave length to water depth ratio, and bottom roughness have been investigated for realistic physical situations. The streaming induced sediment dynamics near the ocean bottom has been investigated; both the resulting suspended load and bedload are presented. Finally, the mass transport (wave-averaged Lagrangian velocity) has been studied for a range of wave conditions. The streaming velocities beneath sinusoidal waves (Longuet-Higgins streaming) is always in the direction of wave propagation, while the streaming velocities in horizontally uniform boundary layers with asymmetric forcing are always negative. Thus the effect of asymmetry in second order Stokes waves is either to reduce the streaming velocity in the direction of wave propagation, or, for long waves relative to the water depth, to induce a streaming velocity against the direction of wave propagation. It appears that the Longuet-Higgins streaming decreases as the wave length increases for a given water depth, and the effect of wave asymmetry can dominate, leading to a steady streaming against the wave propagation. Furthermore, the asymmetry of second order Stokes waves reduces the mass transport (wave-averaged Lagrangian velocity) as compared with sinusoidal waves. The boundary layer streaming leads to a wave-averaged transport of suspended sediments and bedload in the direction of wave propagation.     

A dynamic 2DH flocculation model for coastal domains

Ocean Dynamics - A dynamic two-dimensional depth-averaged (2DH) parameterization for flocculation of cohesive sediments is proposed based on the kinetic model by Winterwerp (J Hydraul Res...     

The role of biogenic structures on the biogeochemical functioning of mangrove constructed wetlands sediments - A mesocosm approach

Benthic metabolism (measured as CO₂ production) and carbon oxidation pathways were evaluated in 4 mangrove mesocosms subjected daily to seawater or 60% sewage in the absence or presence of mangrove trees and biogenic structures (pneumatophores and crab burrows). Total CO₂ emission from darkened sediments devoid of biogenic structures at pristine conditions was comparable during inundation (immersion) and air exposure (emersion), although increased 2-7 times in sewage contaminated mesocosms. Biogenic structures increased low tide carbon gas emissions at contaminated (30%) and particularly pristine conditions (60%). When sewage was loaded into the mesocosms under unvegetated and planted conditions, iron reduction was substituted by sulfate reduction and contribution of aerobic respiration to total metabolism remained above 50%. Our results clearly show impacts of sewage on the partitioning of electron acceptors in mangrove sediment and confirm the importance of biogenic structures for biogeochemical functioning but also on greenhouse gases emission.     

Spectral Irradiance, Phytoplankton Community Composition and Primary Productivity in a Salt Marsh Estuary, North Inlet, South Carolina, USA

We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m^?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l^?1 and a winter minimum of 1.4 μg chl a l^?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ^?1?h^?1 (32–803 mg C m^?3?day^?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m^?3?year^?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.     

Closed Circuit Television (CCTV) Earthquake Behaviour Coding Methodology: analysis of Christchurch Public Hospital video data from the 22 February Christchurch earthquake event

Earthquake epidemiological research indicates that the behavioural response influences the nature and severity of injuries sustained. However, there is no observational evidence of the actions individuals engage in during and immediately following earthquake shaking, and the context in which earthquake injuries and deaths are caused. Closed Circuit Television Earthquake Behaviour Coding Methodology has been developed as a tool to classify human behaviour during and immediately following earthquake shaking using real event video data. The coding methodology was applied to security video data captured during the 22 February 2011 M_w6.3 ‘Christchurch’ earthquake event from the Christchurch Public Hospital which experienced shaking intensity of MM9 lasting approximately 12–15 s. We applied this coding methodology to determine: demography, trans-event behavioural responses, post-event behavioural responses, influence of social context on behaviour, and influence of behaviour on injuries. A total of 213 individuals from 31 different camera views were analysed. Sixty-six per cent of the individuals were adult-aged females. The primary trans-event responses were to hold (26%) onto furniture, walls, and/or other people close to them and to look around (30%). No individuals were observed to perform all ‘Drop, Cover, Hold’ actions, the recommended action during strong earthquake shaking in New Zealand. Post-event behaviour included: running, walking, providing assistance, moving towards others, visual communication, and some individuals gave instructions. Social contextual behaviour varied depending on the role of the adult. There were no serious injuries linked to behaviour. The results of this initial study indicate the coding methodology can record the distribution of and variation in human behaviours. Therefore, objective observation of earthquake video data can provide a useful quantitative measure of human behaviour. Significantly, the process will enable researchers to look more closely at behaviours, as well as the social and physical contexts associated with injury risk during and immediately following earthquake shaking.     

Die entwicklungsprobleme im “nordkalottgebiet” Schwedens Development problems in the northernmost parts of Sweden Les problèmes de développement dans la région suédoise de la “calotte du nord”

Sweden's high economic and social standard has been gained through a hard past and present structural rationalization process in the economy. This process has had the regional consequence that Norrland and especially its northernmost parts have met with considerable difficulties in maintaining services and full employment. A large number of farmers and forest workers migrated southward. Swedish location policy after 1965 aims at creating one or two growth poles in northern Norrland; Luleå and its neighbouring towns of Piteå and Boden appear to have good prerequisites. However, Umeå has the strongest population increase, a result of the newly established university which has developed very rapidly. It appears that the growth potentials in northern Norrland are greatest on the coast. Long distances, a widely spread population, and a bad urban structure with too many small communities and no big expansive ones make the inland of northern Norrland the greatest regional-political problem in Sweden.     

Paleoceanographic evolution of the SW Svalbard margin (76°N) since 20,000 C yr BP

Two cores from the southwestern shelf and slope of Storfjorden, Svalbard, taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera, oxygen isotopes, and ice-rafted debris. The results show that over the last 20,000 yr, Atlantic water has been continuously present on the southwestern Svalbard shelf. However, from 15,000 to 10,000 ¹⁴C yr BP, comprising the Heinrich event H1 interval, the Bølling-Allerød interstades and the Younger Dryas stade, it flowed as a subsurface water mass below a layer of polar surface water. In the benthic environment, the shift to interglacial conditions occurred at 10,000 ¹⁴C yr BP. Due to the presence of a thin upper layer of polar water, surface conditions remained cold until ca. 9000 ¹⁴C yr BP, when the warm Atlantic water finally appeared at the surface. Neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of Atlantic water. Its warm core was merely submerged below the cold polar surface water.     

Inherited basement canyons: Impact on sediment distribution in the North Atlantic

Studies of basement‐bounded canyons in West Greenland show that these were long‐lasting features that extended inland for several hundreds of kilometres, acting as prominent sediment conduits sourcing the Albian–Palaeocene Nuussuaq Basin during several phases of basin evolution. The Ilulissat Icefjord canyon was the major conduit for sediment into the basin and provenance data indicate that it had a huge catchment area that extended to East Greenland. The Uparuaqqusuitsut canyon was also an important conduit for sediment in the northern part of the basin. It is suggested that the initial canyon formation occurred during uplift events in the Late Triassic and Late Jurassic when the deeply weathered basement surface formed during Early–Middle Triassic time was eroded. The recognition of these canyons as long‐lasting sediment conduits have huge implications for understanding the sediment distribution, source‐to‐sink studies and the palaeogeography of the North Atlantic basins.     

Comparison of linear and nonlinear shallow wave water equations applied to tsunami waves over the China Sea

This paper discusses the applications of linear and nonlinear shallow water wave equations in practical tsunami simulations. We verify which hydrodynamic theory would be most appropriate for different ocean depths. The linear and nonlinear shallow water wave equations in describing tsunami wave propagation are compared for the China Sea. There is a critical zone between 400 and 500 m depth for employing linear and nonlinear models. Furthermore, the bottom frictional term exerts a noticeable influence on the propagation of the nonlinear waves in shallow water. We also apply different models based on these characteristics for forecasting potential seismogenic tsunamis along the Chinese coast. Our results indicate that tsunami waves can be modeled with linear theory with enough accuracy in South China Sea, but the nonlinear terms should not be neglected in the eastern China Sea region.