ALBERT

Description: Understanding how complex, highly variable sedimentary systems interact in time and space to release, transport and concentrate diamonds is the basis for successful exploration strategies for placer diamond deposits. De Beers’ and Namdeb's West Coast operations are widely involved in a variety of applied scientific research to unravel the complex interactions of Cainozoic fluvial, marine and aeolian systems that have contributed to the formation of the most spectacular gem diamond placer in the world. Geological models produced not only provide the basis for exploration target selection but also high-resolution orebody characterisation, a prerequisite for high confidence geostatistical evaluation, mining system design and mine planning. This paper draws on some of the many applied research projects that have contributed to De Beers’ and Namdeb's placer exploration success that continues to deliver new mineral resources on the West Coast. The history of the Orange River has, and continues to be intensively studied both on- and offshore as the principal conduit for diamond introduction to the continental margin. Use of the “Jago” submersible has introduced a new dimension to offshore sedimentological studies on the continental shelf through direct seafloor observation, which helped us to identify the latest deep-water offshore development—the late Pliocene/early Pleistocene Orange River fan-delta.

Description: Indices of β-diversity are of two major types, (1) those that measure among-plot variability in species composition independently of the position of individual plots on spatial or environmental gradients, and (2) those that measure the extent of change in species composition along predefined gradients, i.e. species turnover. Failure to recognize this distinction can lead to the inappropriate use of some β-diversity indices to measure species turnover. Several commonly-used indices of β-diversity are based on Whittaker's βW (βW = γ/α, where γ is the number of species in an entire study area and α is the number of species per plot within the study area). It is demonstrated that these indices do not take into account the distribution of species on spatial or environmental gradients, and should therefore not be used to measure species turnover. The terms ‘β-diversity’ and ‘species turnover’ should not be used interchangeably. Species turnover can be measured using matrices of compositional similarity and physical or environmental distances among pairs of study plots. The use of indices of β-diversity and similarity-distance curves is demonstrated using simulated data sets.

Description: The relationship between partial melting and granite intrusion in a classic Barrovian metamorphic terrane has been assessed. Thirteen samples were dated by SHRIMP U–Pb zircon geochronology from the island of Naxos, Greece, one of the Aegean metamorphic core complexes. The effect of partial melting during peak Barrovian metamorphism on Naxos is recorded by fine (〈30 mm) zircon overgrowths surrounding older cores in seven of nine samples of migmatite analyzed. The ages of these overgrowths suggest that partial melting commenced prior to 20.7 Ma. The timing of partial melting on Naxos also constrainsthe onset of extensional tectonism in the area to pre-20.7 Ma. The preservation of zircon overgrowth rims with distinctly different concordant ages, ranging from 20.7 to 16.8 Ma, both from different samples and from within the one handspecimen, suggests that zircon precipitation, associated with the partial melting process, was episodic over this age range on both local(cm) and regional (km) scales. Zircons from four granite intrusives were also dated and range in age from 15.4 to 11.3 Ma, with the main period of magmatic activity at ca. 12 Ma, clearly post-dating metamorphism. The sequence of partial melting, Barrovian metamorphism and magmatism in the Naxos metamorphic core complex can be related to a change from overall crustal shortening to extensional tectonism in the Aegean region, caused by post-collisional roll-back of the subducting African slab along the Hellenic trench system.

Description: Miocene exhumation of metamorphic rocks in the Aegean Sea is partly a consequence of post-orogenic extension. If the post-orogenic mechanism of exhumation is rather well understood, the earlier syn-orogenic Eocene exhumation is still largely enigmatic. Previous authors have argued in terms of extension or compression. New structural and petrological data on Sifnos and Syros islands show that exhumation of high pressure–low temperature (HP–LT) rocks involves crustal-scale extensional ductile shear zones during the Eocene. We observe a continuum of top-to-the-NE and -E ductile shear from the Eocene (in the blueschist facies) to the Miocene (in the greenschist facies). This deformation is distributed in the eclogites and blueschists, whereas it is rather localised along ductile shear zones in the greenschists. Eclogites, which are preserved only at the top of the structural pile, are exhumed with a ‘cold’ retrograde P–T path. In the lower part of the structural pile we observe a progressive retrogression of eclogites in blueschist then greenschist facies. This lower part of pile is subsequently exhumed with P–T paths showing a nearly isothermal decompression before cooling. P–T–t-deformation data suggest that the Cycladic blueschists are progressively exhumed by a continuum of accretion at the base of the orogenic wedge, and by a partly non-coaxial extensional deformation above, distributed during the syn-orogenic stage, then localised during the post-orogenic stage. We then compare the mechanism of syn-orogenic exhumation of Crete and the Cyclades and we discuss a simple geodynamic scenario for the Aegean domain and the external Hellenides which accounts for (1) the southward migration of the Hellenic trench and arc during the Cenozoic; (2) the P–T–t-deformation data for the Cycladic blueschists and the Phyllite–quartzite nappe; and (3) the transition from syn-orogenic to post-orogenic in the Cyclades.

Description: Protein synthesis is fundamental to all living organisms and it has been studied intensively and at varying levels of complexity. This chapter provides a comprehensive review of research on protein synthesis in fish, examines data to produce simple models describing protein synthesis in terms of key variables, and provides explanations for variations from expected or predicted rates of protein synthesis. The underlying there is to integrate information at the organismal level. A variety of methods for measuring protein synthesis have been used and comparison suggest they give similar results for fish. Major influences on protein synthesis are species, life-history stage, temperature, feeding, and nutrition. The effects of other factors such as pollutants, anoxia, salinity, and hormones have also been investigated. In growing fish between 20 and 50% of energy expenditure is associated with protein synthesis. Protein synthesis is, therefore, a major energy-demanding process in fish that is influenced by many environmental and biotic factors.

Description: A synopsis of results from two sediment trap moorings deployed at the mid- and outer slope (water depths 1450 and 3660 m, respectively) of the Goban Spur (N.E. Atlantic Margin) is presented. Fluxes increase with trap deployment depth; below 1000 m resuspended and advected material contributes increasingly to bulk flux. Fluxes of dry weight, POC and diatoms in the traps 400 m above bottom (mab) are smaller than those recorded at the sediment surface due to lateral fluxes in the benthic nepheloid layer. These near-bottom fluxes are larger at shallower water depths. 231Pa/230Th ratios in sedimenting material suggest that boundary scavenging is not significant at the Goban Spur. Fluxes of 210Pb in the intermediate and deep traps are comparable to the 210Pb supply rate at this site. At the outer slope, sediment 210Pb fluxes are similar to those measured in the traps 400 mab; at the mid-slope they are a factor of 2 higher, once again indicating large near-bottom lateral particle input. Based on POC-normalised biomarkers in sedimenting material, we followed changes in the quality of sedimenting material with differing trap depth and on seasonal and event-related time scales. In spring fresh, diatom-dominated sedimentation occurs, with progressive degradation of POC with time (to winter) and depth (from 600 to 3220 m). Deeper traps are distinguished on the basis of opal and aluminium fluxes that are dominant in lateral input. A storm event during late September 1993 was clearly reflected in the δ15N isotope ratio of sedimenting material, with a time lag of 2–3 weeks. Diatom and opal fluxes were elevated in this storm-related signal, and its biomarker composition in the 600-m trap was similar to that during spring. An estimate made of upward nitrate flux (new production) at the shelf break and at the outer slope indicated a 2-fold higher new (export) production at the shelf break. Particulate organic carbon export from the shelf break to below the depth of maximal seasonal mixing ranges between 3 and 9% of primary production.

Description: Porewater fluxes into or out of the sediments in aquatic systems are frequently estimated using Fick's First Law. This assumes that diffusive processes control the transport of nutrients. As a corollary, advection, bioturbation and chemical processes are assumed not to be significant. Through a series of sediment core incubations, this paper seeks to quantify the uncertainties involved in such assumptions. Duplicate sediment cores were collected from 28 sites along the Swan–Canning Estuary, returned to the laboratory and incubated under oxic or anoxic conditions. Porewater nutrient concentrations, sediment porosity and initial nutrient concentrations in the overlying water were measured. These parameters were used to estimate the expected nutrient fluxes via Fick's First Law. The estimated fluxes were then compared with measured fluxes of nutrients out of the sediments over the incubation period. Severe bioturbation occurred in several of the anoxic treatments, resulting in large releases of nutrients into the overlying water. Aside from these bioturbated cores, phosphate and ammonium fluxes under anoxic conditions are well predicted by Fick's First Law. Nitrate fluxes are predicted well under oxic conditions. For coarse sediments (D10 averaging 0·3 mm) and under redox conditions favourable for nutrient release, Fick's First Law predicted close to 100% of the observed fluxes. For finer grain sediments (D10 〈 0·01 mm), Fick's First Law overestimated the observed flux by up to 40%. Under unfavourable oxygen conditions, chemical retardation processes are likely to dominate fluxes, and the error associated with using Fick's First Law is increased. These results confirm the usefulness of using Fick's First Law for a baseline estimate of nutrient fluxes under favourable redox conditions. Much greater care must be taken when using Fick's First Law to estimate nutrient fluxes under unfavourable redox conditions, or under conditions when bioturbation is likely to be severe.

Description: A systematic intercomparison of three realistic eddy-permitting models of the North Atlantic circulation has been performed. The models use different concepts for the discretization of the vertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma) coordinates, respectively. Although these models were integrated under nearly identical conditions, the resulting large-scale model circulations show substantial differences. The results demonstrate that the large-scale thermohaline circulation is very sensitive to the model representation of certain localised processes, in particular to the amount and water mass properties of the overflow across the Greenland–Scotland region, to the amount of mixing within a few hundred kilometers south of the sills, and to several other processes at small or sub-grid scales. The different behaviour of the three models can to a large extent be explained as a consequence of the different model representation of these processes.

Description: The accurate dating of fossil coral reefs is of prime importance in determining the timing of deglaciation events and thus understanding the mechanisms driving glacial–interglacial cycles. So far, the most useful coral reef records of past sea level changes are those related to the last deglaciation and the Last Interglacial period. U/Th ages for older isotopic stages are more limited, due to the scarcity of datable material, reflecting diagenetic alteration. Most data are from emergent parts of reefs and reef terraces in active subduction zones where relative sea level records may be biased by variations in rates of tectonic uplift. New constraints on sea level changes over the past 300 000 yr are based on high-precision U-series age measurements of successive reef units on Mururoa. These have been cored in four continuous 300-m-long drill holes with seaward inclinations of 30 to 45° on the northeastern rim of the atoll. Past sea level positions have been calculated from the radiometric ages of corals by correcting the present depth of subsurface horizons both for thermal subsidence and for depositional palaeodepth. The location of this atoll at a considerable distance from former ice sheets (‘far field’) minimises the influence of glacio–isostatic rebound. Prominent units formed during four periods of relative sea level highstands, including the Holocene and stages 5 (∼125 ka), 7 (∼212 ka) and 9 (∼332 ka). These are primarily composed of coralgal frameworks that grew in very shallow water. Three periods of relative low stand correspond to stages 2 (∼17–23 ka), 4 (∼60 ka) and 8 (∼270 ka) during which small reefs developed in association with large bioclastic accumulations. Good agreement with the timing of sea level changes based on oxygen isotope measurements in deep-sea cores is noted for most of the dated reef units. We report here the first accurate coral record of the Last Glacial Maximum in the Pacific, 135–143 m below the present sea surface, suggesting that sea level may have been lower than expected during this period.

Description: A method for combining ground-based passive microwave radiometer retrievals of integrated liquid water (LWP), radar reflectivity profiles (Z), and statistics of a cloud model is proposed for deriving cloud liquid water profiles (LWC). A dynamic cloud model is used to determine Z–LWC relations and their errors as functions of height above cloud base. The cloud model is also used to develop an LWP algorithm based on simulations of brightness temperatures of a 20–30-GHz radiometer. For the retrieval of LWC, the radar determined Z profile, the passive microwave retrieved LWP, and a model climatology are combined by an inverse error covariance weighting method. Model studies indicate that LWC retrievals with this method result in rms errors that are about 10%–20% smaller in comparison to a conventional LWC algorithm, which constrains the LWC profile exactly to the measured LWP. According to the new algorithm, errors in the range of 30%–60% are to be anticipated when profiling LWC. The algorithm is applied to a time series measurement of a stratocumulus layer at GKSS in Geesthacht, Germany. The GKSS 95-GHz cloud radar, a 20–30-GHz microwave radiometer, and a laser ceilometer were collocated within a 5-m radius and operated continuously during the measurement period. The laser ceilometer was used to confirm the presence of drizzle-sized drops.