Mesozoic sedimentation rates in the Western Canada Basin as indicators of the time and place of tectonic activity

Abstract The Mesozoic stratigraphy of the westernmost part of the Western Canada Basin is used to estimate sedimentation and relative crustal subsidence rates in the region between 49^oN and 60^oN, immediately to the east of the disturbed belt. Average rates of subsidence varied from zero to 120 m/Myr, with prominent maxima occurring three times during the Mesozoic. The first occurred during the Tithonian, when rates rose to 100 m/Myr; the second during the Albian to early Santonian, when rates rose to 120 m/Myr in the north and to 70 m/Myr in the south, with subsidence occurring earlier in the north than in the south. The third period of rapid subsidence occurred during the Campanian and Maastrichtian, with rates rising to 120 m/Myr in the southern part of the basin. During non-peak periods, average rates of subsidence ranged from 3.5 m/Myr to 35 m/Myr in the Triassic, from zero to 20 m/Myr in the Jurassic and from zero to 30 m/Myr in the Cretaceous.
Tectonic loading of the lithosphere is considered to be the most probable cause for all three of these periods of rapid subsidence. The three separate episodes are correlated with the separate arrivals of accreted terranes; the first in north-east Oregon and central west Idaho during the Late Jurassic, the second in the central Yukon during the late Early Cretaceous and the third in south-east British Columbia during the Late Cretaceous.     

Simulation of currents, ice melting, and vertical mixing in the Barents Sea using a 3-D baroclinic model

A baroclinic. 3-D model is described. It is adapted to the Barents Sea and includes thermodynamics and atmospheric input. The freezing and melting of ice is allowed for in the model. The main task of the study is to look at the development of the ice cover, the vertical mixing, and the vertical and horizontal density gradients.
Despite simple approximations in the air temperature input, realistic ice-cover is produced in the model area during simulation of a "freezing period" (winter). This intermediate result is briefly discussed and also forms the start of a "melting period" simulation (spring/summer). Atmospheric input data (wind, air pressure, and heat flux) from the spring and summer 1983 is used, and details about vertical mixing, temperature, and salinity are discussed. The simulation results demonstrate the temporal variation of the thermocline depth, the variation of the ice cover, and the horizontal changes of density. The conclusion is that despite often simplified input, the model seems to produce a physical picture characteristic of the Barents Sea.     

Dynamics of plankton growth in the Barents Sea: model studies

1-D and 3-D models of plankton production in the Barents Sea are described and a few simulations presented. The 1-D model has two compartments for phytoplankton (diatoms and P. pouchelii) , three for limiting nutrients (nitrate, ammonia and silicic acid), and one compartment called "sinking phytoplankton". This model is coupled to a submodel of the important herbivores in the area and calculates the vertical distribution in a water column. Simulations with the 3-D model indicate a total annual primary production of 90-120g C m⁻² yr⁻¹ in Atlantic Water and 20-50g C m⁻² yr⁻¹ in Arctic Water, depending on the persistence of the ice cover during the summer.
The 3-D model takes current velocities, vertical mixing, ice cover, and temperature from a 3-D hydrodynamical model. Input data are atmospheric wind, solar radiation, and sensible as well as latent heat flux for the year 1983. The model produces a dynamic picture of the spatial distribution of phytoplankton throughout the spring and summer. Integrated primary production from March to July indicates that the most productive area is Spitsbcrgenbanken and the western entrance to the Barents Sea. i.e. on the northern slope of Tromsøflaket.     

The Effects of Small Amounts of H2O, CO2 and Na2O on the Partial Melting of Spinel Lherzolite in the System CaO-MgO-Al2O3-SiO2 {+/-} H2O {+/-} CO2 {+/-} Na2O at 1{middle dot}1 GPa

The effects of small amounts of H₂O (<4 wt % in the melt)on the multiply saturated partial melting of spinel lherzolitein the system CaO–MgO–Al₂O₃–SiO₂ ±Na₂O ± CO₂ have been determined at 1·1 GPa inthe piston-cylinder apparatus. Electron microprobe analysisand Fourier transform infrared spectroscopy were used to analysethe experimental products. The effects of H₂O are to decreasethe melting temperature by 45°C per wt % H₂O in the melt,to increase the Al₂O₃ of the melts, decrease MgO and CaO, andleave SiO₂ approximately constant, with melts changing fromolivine- to quartz-normative. The effects of CO₂ are insignificantat zero H₂O, but become noticeable as H₂O increases, tendingto counteract the H₂O. The interaction between H₂O and CO₂ causesthe solubility of CO₂ at vapour saturation to increase withincreasing H₂O, for small amounts of H₂O. Neglect of the influenceof CO₂ in some previous studies on the hydrous partial meltingof natural peridotite may explain apparent inconsistencies betweenthe results. The effect of small amounts of H₂O on multiplysaturated melt compositions at 1·1 GPa is similar tothat of K₂O, i.e. increasing H₂O or K₂O leads to quartz-normativecompositions, but increasing Na₂O produces an almost oppositetrend, towards nepheline-normative compositions. KEY WORDS: H₂O; CO₂; FTIR; hydrous partial melting; mantle melting; spinel lherzolite; system CaO–MgO–Al₂O₃–SiO₂ ± H₂O ± CO₂ ± Na₂O     

Riverine influence determines nearshore heterogeneity of nutrient (C,N, P) content and stoichiometry in the KwaZulu-Natal Bight,South Africa

Riverine influences on nearshore oceanic habitats often have detrimental consequences leading to algal blooms and hypoxia. In oligo- to mesotrophic systems, however, nutrient delivery via rivers may stimulate production and even be a vital source of nutrients, as may nutrient supplements from upwelling. We investigated the nutrient content (C, N, P) and stoichiometry of sediment, and several pelagic, benthopelagic and benthic species in the KwaZulu-Natal (KZN) Bight, a narrow shelf area on the south-east coast of South Africa, bordering the Agulhas Current. Three suggested nutrient sources to the bight are the Thukela River in the central region of the bight, upwelling in the northern part and a semi-permanent eddy (Durban Eddy) in the southern part. Elemental content of the various groups studied showed significantly higher values for most groups at the site near the Thukela River. C:P and N:P were highest in the southern part of the bight, and lowest near the Thukela Mouth or at Richards Bay in the north, indicating the latter were the P-richer sites. Sediment organic matter showed lowest elemental content, as expected, and zooplankton stoichiometry was highest compared to all other biotic groups. Environmental heterogeneity played a greater role in organismal C, N and P content and stoichiometry compared to phylogeny, with the exception of the differences in C:P and N:P of zooplankton. From this bight-wide study, the higher elemental content and lower ratios at the Thukela Mouth site supported previous findings of the importance of coastal nutrient sources to the bight ecosystem. Reductions in river flow for water use in the catchment areas may therefore have negative consequences for the productivity of the entire ecosystem.