The COPAS’08 expedition to the Patagonian Shelf: Physical and environmental conditions during the 2008 coccolithophore bloom

Here we present observations of the hydrography of the Patagonian Shelf, shelf break and offshore waters, with reference to the environmental conditions present during the period of peak coccolithophore abundance. Analysis of a hydrographic dataset collected in December 2008 (austral spring/summer), as part of the Coccolithophores of the Patagonian Shelf (COPAS) research cruise, identified 5 distinct surface water masses in the region between 37°S and 55°S. These water masses, identified through salinity gradients, displayed varying mixed layer depths, macronutrient inventories and chlorophyll-a fluorescence. Subantarctic Shelf Water (SSW), located to the north of the Falkland Islands and extending north along the shelf break, was also host to a large coccolithophore bloom. The similarities between the distribution of calcite, as seen in remote sensing data, and SSW indicate that the coccolithophore bloom encountered conditions conducive to bloom development within this water mass. Analysis of chemical and environmental data also collected during the COPAS cruise revealed that many of the commonly cited conditions for coccolithophore bloom development were present within SSW (e.g. low N:P ratio, high N:Si ratio, shallow mixed layer depth). In the other water masses present on the Patagonian Shelf greater variability in these same parameters may explain the more diffuse concentration of calcite, and the smaller size of possible coccolithophore blooms. The distribution of SSW is strongly influenced by the latitudinal variation in shelf break frontal width, which varies from 20 to 200 km, and consequently strong hydrographic controls underlie the position of the coccolithophore bloom during austral summer.     

SeaWiFS satellite monitoring of oil spill impact on primary production in the Galápagos Marine Reserve

Near daily satellite monitoring of ocean colour using sea viewing wide angle of field viewing sensor (SeaWiFS) allowed the oceanic and near coastal chlorophyll-a distributions to be followed across the Galápagos Marine Reserve (GMR) from space. In the aftermath of the Jessica spill early indications suggested that, compared to the three preceding years 1998-2000, local chlorophyll concentrations over January 2001 were elevated across the Galápagos Marine Reserve [Biological Impacts of the Jessica Oil Spill on the Galápagos Environment: Preliminary Report. Charles Darwin Foundation, Puerto Ayora, Galápagos, Ecuador, 2001]. At the time of the spill the central and eastern extent of the archipelago was experiencing a spatially extensive moderate bloom event (0.5-2.5 mgm(-3) chl-a) extending over the central islands, including the source of the spill and areas of known impact such as the islands of Santa Fé, eastern Santa Cruz and Floreana directly in the advection path.Further investigation shows that chlorophyll across the affected regions of western San Cristóbal, Santa Fé, southeast Santa Cruz, eastern Floreana and eastern Isabela declined in the week directly following the spill event, yet rose in the successive month to levels analogous to preceding years. Although there may have been a localised effect of the spill upon near coast phytoplankton primary production in the short term, the observed variance in the weeks following the spill was not significant in comparison to the normal high variation between years and within the El Ni?o/Southern Oscillation signal.     

Anomalous gradient winds in the subtropical jet stream and interpretations of forecast failures

Summary Dramatic examples of forecast failures in global models of moderate resolution (i.e., T106) have been shown to occur during periods of the negative phase of the Pacific/North American (PNA) pattern in the Northern Hemisphere winter. Specifically, in these periods forecast skills at 500hPa as measured by the standard anomaly correlation index dropped to rather low values by days 4 and 5 of the forecasts. This paper examines systematically some of the factors that may have contributed to the failure of these model forecasts.In particular, strong winds approaching intensities on the order of 100ms^–1 south of Japan at the 200hPa level were degraded by the initialization and data assimilation procedures of the models. These observed winds were found to be supergradient in nature and representative of the anomalous solution of the gradient wind equation. Procedures such as the multivariate optimum interpolation (with its geostrophic constraints) and the normal-mode initialization including several vertical modes apparently were factors that led to the degradation of these strong winds in the initial model states. In this paper, an analysis of these factors is presented, and it is shown that uninitialized analyses (with no constraints) based on a simple successive correction procedure can retain the strong winds evident in the observations. Forecasts thus performed appear to retain wave trains, a characteristic feature of negative PNA initial states, leading to a significant improvement in forecast skill.     

Benthic diatom community response to environmental variables and metal concentrations in a contaminated bay adjacent to Casey Station, Antarctica

This study examined the effects of anthropogenic contaminants and environmental variables on the composition of benthic diatom communities within a contaminated bay adjacent to an abandoned waste disposal site in Antarctica. The combination of geographical, environmental and chemical data included in the study explained all of the variation observed within the diatom communities. The chemical data, particularly metal concentrations, explained 45.9% of variation in the diatom communities, once the effects of grain-size and spatial structure had been excluded. Of the metals, tin explained the greatest proportion of variation in the diatom communities (28%). Tin was very highly correlated (R2>0.95) with several other variables (copper, iron, lead, and sum of metals), all of which explained similarly high proportions of total variation. Grain-size data explained 23% of variation once the effects of spatial structure and the chemical data had been excluded. The pure spatial component explained only 1.8% of the total variance. The study demonstrates that much of the compositional variability observed in the bay can be explained by concentrations of metal contaminants.     

The lateral distribution of extensive air showers produced by cosmic rays above 10 eV as measured by water- erenkov detectors

Measurements of the lateral distribution function (ldf) of Extensive Air Showers (EAS) as recorded by the array of water- erenkov detectors at Haverah Park are described, and accurate experimental parameterizations expressing the mean ldf for 2 × 10¹⁷ < E < 4 × 10¹⁸ eV, 50 < r < 700 m, and θ < 45° are given. An extrapolation of these relations to the regime E ≥ 10¹⁹ eV and r > 700 m is described: extrapolation in this energy domain appears valid, and an approximate correction term is given for the larger core distances. The results of recent Monte Carlo simulations of shower development and detector behavior are compared to the parameterized ldf. The agreement is good increasing confidence that these simulations may be trusted as design tools for the Auger project, a proposed ‘next generation’ detector system.     

THE EXPANSION METHOD: IMPLICATIONS FOR GEOGRAPHIC RESEARCH*

Geographic phenomena and our models of them are closely linked to the spatial-temporal contexts in which they are observed. The expansion method is a procedure that incorporates contextual effects into mathematical models. More importantly, it is the basis for a movement by some geographers away from the classical spatial science paradigm. The evolving paradigm associated with the expansion method represents a reformulation of the way in which geographers think about and use models, and is consistent with a more realistic perspective on the nature of geographic inquiry.