Mediterranean outflow through the Strait of Gibraltar since 18,000 Years B.P.: Mineralogical and geochemical arguments

Data obtained from mineralogical and geochemical analyses of piston and gravity cores, recovered from an area off Lisbon (Portugal) to the Alboran Sea (Mediterranean), serve as a basis for better understanding the past 18,000 years of hydrological exchanges at Gibraltar. Tracers used in this study are smectite, kaolinite, Ta, Th, La. One of the primary sources of particles both into and out of the Mediterranean is the Guadalquivir River. These particles are transported back into the Atlantic in the Mediterranean outflow water, and deposited along the Iberian slope. No evidence for reversal of this outflow current was found in those cores, since 18,000 years B.P.     

Dating of Quaternary Sediments from Western Borneo, Using Optically Stimulated Luminescence

Optically Stimulated Luminescence (OSL) dates from five sites in western Kalimantan are compared with ¹⁴C and thermo-luminescence dates from other sediments in the region. There is now strong evidence that the Old Alluvium of Peninsular Malaysia is of late Pleistocene age and that it can be correlated with the White Sand Complexes of western Borneo. This contrasts with the late Pliocene to mid Pleistocene ages for Old Alluvium, based primarily on stratigraphic deductions, put forward by geoscientists examining the regional tin deposits. This study shows that the upper parts, at least, of the western Borneo White Sand Complexes were deposited mid-way through the last glaciation (76 ka), with extensive terminal Pleistocene re-deposition (11.2-9.8 ka) and at least two gully erosion events during the Holocene (5.8-3.8 ka and 0.48 ka).     

Impacts of a bottom trawling exclusion zone on Snow Crab abundance and fish harvester behavior in the Labrador Sea, Canada

The Hawke Box trawling exclusion zone off southern Labrador is a 8610 km² closed area implemented in 2003 to protect soft-shelled pre-recruit Snow Crab and juvenile cod from mortality imposed by shrimp trawling and other bottom-impact fisheries. This study utilizes survey, logbook, and observer data from the Snow Crab and Northern Shrimp fisheries to assess the effectiveness of the Hawke Box in protecting and possibly enhancing the Snow Crab resource off southern Labrador. The results indicate that the exclusion zone has failed to protect pre-recruit crabs largely due to a redistribution and intensification of directed Snow Crab effort inside the Box in the years following closure. This unexpected outcome resulted in a high level of fishery-induced mortality to pre-recruit crabs and masked any potential positive outcomes from the cessation of trawling. The shortcomings that contributed to the failure of this exclusion area are discussed in relation to the current state of knowledge on the effectiveness of marine protected areas in general as management tools for conserving aquatic resources.     

Si diffusion in zircon

Self-diffusion of Si under anhydrous conditions at 1 atm has been measured in natural zircon. The source of diffusant for experiments was a mixture of ZrO₂ and ³⁰Si-enriched SiO₂ in 1:1 molar proportions; experiments were run in crimped Pt capsules in 1-atm furnaces. ³⁰Si profiles were measured with both Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis with the resonant nuclear reaction ³⁰Si(p,γ)³¹P. For Si diffusion normal to c over the temperature range 1,350–1,550°C, we obtain an Arrhenius relation D = 5.8 exp(−702 ± 54 kJ mol⁻¹/RT) m² s⁻¹ for the NRA measurements, which agrees within uncertainty with an Arrhenius relation determined from the RBS measurements [62 exp(−738 ± 61 kJ mol⁻¹/RT) m² s⁻¹]. Diffusion of Si parallel to c appears slightly faster, but agrees within experimental uncertainty at most temperatures with diffusivities for Si normal to c. Diffusion of Si in zircon is similar to that of Ti, but about an order of magnitude faster than diffusion of Hf and two orders of magnitude faster than diffusion of U and Th. Si diffusion is, however, many orders of magnitude slower than oxygen diffusion under both dry and hydrothermal conditions, with the difference increasing with decreasing temperature because of the larger activation energy for Si diffusion. If we consider Hf as a proxy for Zr, given its similar charge and size, we can rank the diffusivities of the major constituents in zircon as follows: D _Zr < D _Si << D _{O, dry} < D _{O, ‘wet’}.     

Gravity measurements in Kenya

summary . A new catalogue of gravity data from Kenya has been prepared and is briefly described here. New Bouguer anomaly maps have also been compiled and a copy is included.     

Lethal and sublethal effects of short term acute doses of Kuwait Crude Oil and a dispersant Corexit 9527 on bay scallops, Argopecten irradians (Lamarck) and two predators at different temperatures

Investigations of short term acute exposure of bay scallops, Argopecten irradians and two scallop predators, the oyster drill Urosalpinx cinerea and the common starfish Asterias forbesi, to oil, dispersant, and oil-dispersant mixtures (Kuwait Crude Oil and Corexit 9527) suggested that predator and prey have different lethal susceptibilities. Scallops were most sensitive to dispersant and dispersant mixed with oil, starfish were only sensitive to dispersant while the oyster drill seemed unaffected even though all were exposed to dilutions of identically prepared stock solutions. Scallops were least susceptible during winter months and most susceptible at summer temperatures. Treatment had less effect on predators than on scallops at summer temperatures. Sublethal concentrations of dispersant and oil-dispersant mixtures diminished the behavioural ability of scallops to recognise drills and starfish. The degree of effect increased with temperature. Predator detection of prey at the same concentrations was more complex. The feeding response or posturing reflex of starfish was significantly slowed by all treatments. In contrast, drills were unaffected in their recognition of scallop effluent in a choice chamber after treatment.     

Late Quaternary ice age climates of tropical Australasia: Interpretations and reconstructions

Paleoecological and paleogeographical evidence is used to mold a framework from which the basic parameters of the late Quaternary glacial-age climate of tropical Australasia can be inferred. The theory of physical circulations, a knowledge of present tropical circulation patterns, and a study of anomalous and extreme events in the present era are used to reemphasize the view of a less pluvial tropical and subtropical zone at that time. Cooler sea-surface temperature, cooler trades, and the effect of the then exposed land areas are indicated as instrumental in producing drier conditions. Tropical areas west of Cape York Peninsula and Torres Strait were subject to fewer tropical disturbances and were similar to the present tropical savannah of the northern interior of Australia. Such effects would exist even without shifts in major climatic zones, although they are shown to be consistent with an equatorward shift of the westerlies brought about by the increased pole to equator temperature gradient. Paleoenvironmental evidence from the New Guinea Highlands and southeastern Australia suggests that their climates were anomalous. Substantial data of the glacial period in New Guinea show snow lines to be 1000 to 1500 m lower than at present which matches a 6 to 8°C lowering of temperature in highland New Guinea. The deep-sea cores of the CLIMAP Project suggest a mere 2°C cooling of the surrounding tropical oceans. It is shown that it is highly unlikely that an upper-level decrease in temperature of 6 to 8°C could be maintained while the surface cools by only 2°C. It is suggested that either the temperature of the tropical oceans of the western Pacific were overestimated by CLIMAP or that cold air incursions from higher latitudes (for which some analogs exist today) were sufficiently frequent to allow the maintenance of a snow line well below the freezing level of the ancient ambient tropical atmosphere. It is shown that in southeastern Australia considerable evidence of aridity cannot be explained by merely displacing the westerlies more equatorward. To account for the aridity, a new circulation pattern is proposed. Noting that there is CLIMAP evidence of preferred equatorward extension of sea ice, a pattern is postulated that displays only small seasonal change and is characterized by an enhanced Indian Ocean trough, marked ridging at eastern Australian longitudes, and a further trough in the western Tasman. Such a basic flow is consistent with (i) a low rainfall over southeastern Australia, (ii) frequent cold outbreak conditions favorable for the maintenance of the New Guinea glaciers, and (iii) considerable precipitation to nourish the ice caps of Tasmania and the Australian and New Zeland Alps.     

Metropolitan growth and the mobility and immobility of skilled and creative couples across the life course

The human capital and creative class hypotheses argue that the agglomeration of skilled and creative people is key to economic growth. Migration is assumed to play an important role in forming these agglomerations. However, the results of this study indicate that while younger cohorts of skilled and creative individuals are highly mobile, skilled and creative couples are highly immobile. This research hypothesizes that it is these relatively immobile skilled and creative couples that are behind the link between urban growth and concentrations of skill and creativity. Indeed, this analysis finds a strong empirical link between concentrations of skilled couples, but not creative class couples, and economic growth. Public policies designed to increase the size of the skilled population should be directed at retaining younger cohorts long enough for them to develop the local networks upon which spillover effects rely.