The Tsesis oil spill impact on the pelagic ecosystem

On 26 October, 1977, the tanker Tsesis grounded in the Swedish archipelago, 65 km south of Stockholm (northern Baltic proper, 59°N, 18°E). The Tsesis carried 17575 t of No. 5 fuel oil. The total spill was estimated as being somewhat more than 1000 t, of which about 600–700 t were recovered, thus leaving about 300 t in the environment. The spill occurred only about 5 km east of the Askö Laboratory, a marine ecological station, which made a relatively fast sampling response possible. The effects on the pelagic ecosystem were studied for 1 month following the spill. Severe effects were recorded only in the immediate vicinity of the wreck where zooplankton biomass declined substantially during the first few days after the spill. Within 5 days the zooplankton biomass was re-established. Oil contamination of zooplankton was recorded for over 3 weeks. It is suggested that an increased phytoplankton biomass and primary production in the impacted area was due to decreased zooplankton grazing rates. Increased bacterial numbers and the oil degradation pattern indicated a rapid bacterial degradation of hydrocarbons in the water column. Sediment traps positioned in the area demonstrated the importance of sedimentation as a pathway for removal of oil from the water column. During the second week after the spill, 0.7% of sedimented material was petroleum hydrocarbons. Using sediment trap data, a total sedimentation of 30–60 t of oil was estimated in the impacted area (42 km²). This corresponds to 10–15% of the unrecovered oil.     

The ammonite fauna and genesis of a mid-Cretaceous siliceous oolite from the Alagoas Basin, Brazil

Acanthoceratid ammonites from near Maceió, in the State of Alagoas, provide evidence of a mid-Cretaceous marine incursion into the present onshore part of the Alagoas Basin. The ammonites Pseudocalycoceras sp. cf. P. harpax (Stoliczka, 1864) and Kamerunoceras sp. are assigned a late Cenomanian age. The rock is a siliceous oolite that occurs as derived nodules and fragments in late Cenozoic continental sediments. It is interpreted as an originally calcareous oolite formed in a near-shore, high-energy environment. Absence of primary cement suggests that silicification took place early in diagenesis. The silicified, and therefore more resistant material from the original Cenomanian sequence was reworked and redeposited with the Cenozoic sediments. The age, indicated by the ammonites, suggests that the original deposition was related to the global late Cenomanian—early Turonian sea-level rise.     

Coalification anomalies induced by fluid flow at the Variscan thrust front: A numerical model of the palaeotemperature field

Geologie en Mijnbouw -     

Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield

The Ljusdal Batholith (LjB) is a major component of the central Svecofennian Domain in Sweden. It is separated from the Bothnian Basin to the north by the 1.82–1.80 Ga crustal-scale Hassela Shear Zone (HSZ). The LjB has emplacement ages of 1.86–1.84 Ga, is mainly alkali-calcic, metaluminous, has _Nd values between − 0.3 and + 1.2 and was formed in a magmatic arc setting.

During the Svecokarelian orogeny the LjB was affected by at least three fold episodes. Large-scale folded screens of migmatised metasedimentary rocks occur in the eastern part of the batholith, and to the north of the HSZ, there is a 50 km wide diatexite belt. The Transition Belt (TrB), consisting of 1.88–1.85 Ga granitoids, is located at the northwestern extension of this belt. A calc-alkaline and peraluminous composition combined with negative _Nd values (− 1.7 to − 0.8) indicates a large proportion of metasediments in the source for these granitoids.

U–Pb SIMS data on zircon rims from migmatites and leucogranites to the north and east of LjB yield ages of 1.87–1.86 Ga, i.e. coeval with the granitoids of the LjB and the TrB. There is thus a close relationship between the LjB, the TrB and the migmatites in both space and time. Syn-migmatitic shearing along the HSZ indicates that a proto-HSZ was initiated already at c. 1.86 Ga, and the location of the proto-HSZ is inferred to be controlled by two older nuclei present in the lower parts of the crust. As crustal-scale shear zone systems are known to act as ascent pathways for sheet-like flow in active orogenies the TrB may represents accumulations of melts that were attracted and extracted by the proto-HSZ and intruded in a block that was not pervasively affected by subsequent shear along the HSZ.

An active continental margin setting for the LjB implies subduction at c. 1.86 Ga, and provides a heat source for both the migmatites and the TrB.

A later migmatisation at 1.82 Ga has been recorded to the south of the HSZ. Within the LjB the 1.82 Ga stromatic migmatites are folded by F₂ folds, and the fabric is truncated by 1.80 Ga pegmatites.     

Late-Variscan fluid migration at the Variscan thrust front of Eastern Belgium: numerical modelling of the palaeothermal and fluid flow field

Modelling of the palaeothermal field at the Variscan thrust front in eastern Belgium indicates significant temperature modifications by late-Variscan palaeofluids migrating from internal to peripheral parts of the orogen. A detailed set of calibration data (chlorite geothermometry, microthermometry, organic rank) gives evidence of temporary palaeotemperature variations at the Variscan thrust front obviously connected to the migration of hot, low saline palaeofluids. These thermal events likely enhanced organic maturation (vitrinite reflectance, conodont alteration) of Devonian and Carboniferous sediments, which accumulated long before the Variscan orogeny occurred. Numerical simulation (2D Finite Element method) of the palaeothermal field includes coupled heat transport by thermal conduction and fluid flow. Palaeothermal scenarios yield successive palaeotemperatures (200–300°C), which are indicated by the control data, due to relatively short-term fluid ascent along the detachment and the imbricate thrust front. The simulated flow velocities are up to tens of metre per year lasting several thousand years (non-steady-state solution). In the scenarios modelled, these thermal events occur in a realm of enhanced bulk temperatures due to elevated basal heat flow densities (90 mW m⁻²) and an additional burial depth of some kilometres. The simulated temperature enhancement due to fluids ascending at the Variscan thrust front is several tens degrees. The scenarios demonstrate long-distance fluid migration during or after deformation of the Palaeozoic basin and its effect on the palaeothermal field.     

Salinization problems in the NEGB: results from thermohaline simulations

The occurrence of salty waters close to the surface is a well-known problem in the North East German Basin. Previous numerical simulations showed that near-surface brine occurrences are due to the interaction of hydrostatic and thermally induced forces (mixed convection). The influence of hydraulic permeabilities and thermal conductivities on the observed patterns remained an open question. Based on a hydro-geochemical dataset, thermohaline simulations are carried out in order to quantify the impact of these physical parameters on brine migration. The results indicate that the salinity and temperature profiles are strongly controlled by hydraulic permeabilities and can locally be influenced by thermal conductivities.     

Spectra,variances and length scales in a marine stable boundary layer dominated by a low level jet

A flow situation over coastal waters of the Baltic Sea is studied. The boundary layer was characterized by stable stratification and the presence of a pronounced low level jet at very low height, 30–150 m, above the surface of the sea. The atmospheric surface layer was apparently extremely shallow; thus the non-dimensional wind gradients and temperature gradients derived from measurements at 8 m do not show adherence to Monin-Obukhov similarity, in sharp contrast to findings from the same site at similar stability conditions but with no low level jet. Instead these quantities are shown to be governed by scales characteristic of stable shear flow away from the surface. The height to the jet centre appears to be an important quantity. Thus, for the cases with the lowest jet height values (30–50 m), some turbulent characteristics of the flow (non-dimensional velocity standard deviations and the correlation between the longitudinal and vertical velocity) have values similar to those found for the zero pressure-gradient laboratory boundary layer over a flat plate (the so called canonical boundary layer) rather than the typical values found in atmospheric boundary-layer flow. It was inferred that the large scale fluctuations known as inactive turbulence, as well as gravity waves, were suppressed in this case.     

Analysis of the turbulence structure of a marine low-level jet

Four aircraft measurement sets made in late May 1989 within low level jets over the Baltic Sea have been analyzed to estimate the turbulence energy budget. It is concluded that the jets had the same origin as found in an earlier study from the same general area: inertial oscillation caused by frictional decoupling when relatively warm air flows out over much colder water.In order to combine budget estimates from the four flights to form a representative average, self-preservation similarity was assumed. When the terms were made nondimensional with the proper scale combination, the largest terms in all four runs were of order one, indicating that the scaling is physically sound.Three terms were found to dominate the turbulence energy budget: shear production, dissipation and pressure transport. The latter was obtained as remainder term, since local time rate of change and advection terms were found to be of negligible magnitude. Shear production was found in a narrow layer above the jet core and in a much deeper layer below it. The pressure transport term was a gain in this layer as well, helping to keep the layer below the jet well mixed. This is in agreement with results from aircraft measurements in the low level jet and monsoon boundary layer over the Arabian Sea.It is concluded that development of the inertial jet downwind of a coastline is of fundamental importance for exchange of momentum at the sea surface in conditions when relatively warm air is advected over cold water. The jet produces turbulence that promotes mixing in the lower layers, which sharpens the shear below the jet core, so that mixing becomes even more effective. Turbulence brought down to the surface by the pressure transport term is likely to be of the inactive type, which does not produce shear stress. Through the above-mentioned process it is, however, instrumental in promoting the mechanism that eventually produces active turbulence, the carrier of momentum.