ALBERT

Description: Core HU97048-007PC was recovered from the continental Labrador Sea slope at a water depth of 945 m, 250km seaward from the mouth of Cumberland Sound, and 400km north of Hudson Strait. Cumberland Sound is a structural trough partly floored by Cretaceous mudstones and Paleozoic carbonates. The record extends from 10 to 58 ka. On-board logging revealed a complex series of lithofacies, including buff-colored detrital carbonate-rich sediments [Heinrich (H)-events] frequently bracketed by black facies. We investigate the provenance of these facies using quantitative X-ray diffraction on drill-core samples from Paleozoic and Cretaceous bedrock from the SE Baffin Island Shelf, and on the〈2-mm sediment fraction in a transect of five cores from Cumberland Sound to the NW Labrador Sea. A sediment unmixing program was used to discriminate between sediment sources, which included dolomite-rich sediments from Baffin Bay, calcite-rich sediments from Hudson Strait and discrete sources from Cumberland Sound. Results indicated that the bulk of the sediment was derived from Cumberland Sound, but Baffin Bay contributed to sediments coeval with H-0 (Younger Dryas), whereas Hudson Strait was the source during H-events 1–4. Contributions from the Cretaceous outcrops within Cumberland Sound bracket H-events, thus both leading and lagging Hudson Strait-sourced H-events.

Description: Ecological and taxonomic study of the mollusk-rich fauna of the Golfe d’Arguin, North Mauritania, investigates the various environmental influences affecting this tropical shelf. The upwelling of nutrient-rich waters leads to a highly productive environment under tropical conditions. The resulting mixed carbonate-siliciclastic sediment contains a large portion of calcareous components produced by heterotrophic organisms— e.g., mollusks, foraminifers, worms, barnacles—that are reworked on the open shelf. On the basis of mollusk assemblages, six taphocoenoses are defined, all being characterized by a mixed fauna of tropical (e.g., Tellina densestriata), subtropical (e.g., Macoma cumana) and temperate (e.g., Spisula subtruncata) species. Differences between the assemblages are related to the medium—grain size ranging from mud to gravel—that results from local hydrodynamic conditions and water depth. Among carbonate grains, Donax burnupi shells are very abundant in the swellexposed, northern part of the Golfe d’Arguin and reflect the tropical to subtropical, high-energy, and high-nutrient waters. Mollusk assemblages are demonstrated to be a sensitive tool for deciphering complex environmental conditions in sedimentary archives.

Description: Volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km3 of ejecta as dense-rock equivalent; recurrence interval of ∼105 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cultural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833–850) correlates to the “AD860B” ash (A.D. 846–848) found in Greenland and northern Europe. These occurrences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ∼100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distributed proxy records, and volcanic hazard assessment.

Description: This article documents the addition of 229 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Acacia auriculiformis × Acacia mangium hybrid, Alabama argillacea, Anoplopoma fimbria, Aplochiton zebra, Brevicoryne brassicae, Bruguiera gymnorhiza, Bucorvus leadbeateri, Delphacodes detecta, Tumidagena minuta, Dictyostelium giganteum, Echinogammarus berilloni, Epimedium sagittatum, Fraxinus excelsior, Labeo chrysophekadion, Oncorhynchus clarki lewisi, Paratrechina longicornis, Phaeocystis antarctica, Pinus roxburghii and Potamilus capax. These loci were cross-tested on the following species: Acacia peregrinalis, Acacia crassicarpa, Bruguiera cylindrica, Delphacodes detecta, Tumidagena minuta, Dictyostelium macrocephalum, Dictyostelium discoideum, Dictyostelium purpureum, Dictyostelium mucoroides, Dictyostelium rosarium, Polysphondylium pallidum, Epimedium brevicornum, Epimedium koreanum, Epimedium pubescens, Epimedium wushanese and Fraxinus angustifolia.

Description: North Atlantic climate is very sensitive to overturning in the Greenland-Iceland-Norwegian (GIN) Seas, overflow of deep water into the North Atlantic via the Greenland-Iceland-Scotland Ridge, and compensating northward flow of warm surface water. Physical models suggest that, in the absence of such overturning, oceanic heat transport to the Northern Hemisphere is reduced by as much as 50%, open North Atlantic sea-surface temperatures are as much as 6 °C lower, and the winter sea-ice limit migrates as far south as 45°N. Although simulations of the equilibrium climate state for the Last Glacial Maximum (LGM) suggest the absence of GIN Seas overflow, tests of these model results have been hampered by ambiguity in sedimentary proxies. Here we present a bottom-water neodymium (Nd) isotope record from the Rockall Trough to investigate changes in the sources of circulating waters over the past 43 k.y. Today and throughout most of the Holocene, water from the GIN Seas, along with water from the North Atlantic Current (NAC) entrained during overflow, sets the bottom-water Nd isotope composition of the Rockall Trough to ∼–10. Our results suggest the persistence of this scenario back into the LGM and beyond to mid-Marine Isotope Stage 3. Periodic radiogenic excursions punctuate the record at times of meltwater events, implying either continued GIN Seas overflow without NAC entrainment, or millennial-scale interruptions in the overflow and shoaling of Southern Source Water. We conclude that overflow was at least intermittently present during the LGM, if not continuous, and that the GIN Seas have remained a source of deep water to the North Atlantic during the last glacial cycle.

Description: We present a new three-dimensional (3-D) P-wave velocity model for the upper-crustal structure beneath the Strait of Georgia, southwestern British Columbia based on non-linear tomographic inversion of wide-angle seismic refraction data. Our study, part of the Georgia Basin Geohazards Initiative (GBGI) is primarily aimed at mapping the depth of the Cenozoic sedimentary basin and delineating the near-surface crustal faults associated with recent seismic activities (e.g. M = 4.6 in 1997 and M = 5.0 in 1975) in the region. Joint inversion of first-arrival traveltimes from the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS) and the 2002 Georgia Basin experiment provides a high-resolution velocity model of the subsurface to a depth of ???7 km. In the southcentral Georgia Basin, sedimentary rocks of the Cretaceous Nanaimo Group and early Tertiary rocks have seismic velocities between 3.0 and 5.5 km s-1. The basin thickness increases from north to south with a maximum thickness of 7 (??1) km (depth to velocities of 5.5 km s-1) at the southeast end of the strait. The underlying basement rocks, probably representing the Wrangellia terrane, have velocities of 5.5-6.5 km-1 with considerable lateral variation. Our tomographic model reveals that the Strait of Georgia is underlain by a fault-bounded block within the central Georgia Basin. It also shows a correlation between microearthquakes and areas of rapid change in basin thickness. The 1997/1975 earthquakes are located near a northeast-trending hinge line where the thicknesses of sedimentary rocks increase rapidly to the southeast. Given its association with instrumentally recorded, moderate sized earthquakes, we infer that the hinge region is cored by an active fault that we informally name the Gabriola Island fault. A northwest-trending, southwest dipping velocity discontinuity along the eastern side of Vancouver Island correlates spatially with the surface expression of the Outer Island fault. The Outer Island fault as mapped in our seismic tomography model is a thrust fault that projects directly into the Lummi Island fault, suggesting that they are related structures forming a fault system that is continuous for nearly 90 km. Together, these inferred thrust faults may account for at least a portion of the basement uplift at the San Juan Islands. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Description: Sediment samples were obtained from areas of diffuse hydrothermal venting along the seabed in the Tonga sector of the Tonga-Kermadec Arc, southwest Pacific Ocean. Sediments from Volcano 1 and Volcano 19 were analyzed by X-ray diffraction (XRD) and found to be composed primarily of the iron oxyhydroxide mineral, two-line ferrihydrite. XRD also suggested the possible presence of minor amounts of more ordered iron (hydr)oxides (including six-line ferrihydrite, goethite/lepidocrocite and magnetite) in the biogenic iron oxides (BIOS) from Volcano 1; however, Mössbauer spectroscopy failed to detect any mineral phases more crystalline than two-line ferrihydrite. The minerals were precipitated on the surfaces of abundant filamentous microbial structures. Morphologically, some of these structures were similar in appearance to the known iron-oxidizing genus Mariprofundus spp., suggesting that the sediments are composed of biogenic iron oxides. At Volcano 19, an areally extensive, active vent field, the microbial cells appeared to be responsible for the formation of cohesive chimney-like structures of iron oxyhydroxide, 2–3 m in height, whereas at Volcano 1, an older vent field, no chimney-like structures were apparent. Iron reduction of the sediment material (i.e. BIOS) by Shewanella putrefaciens CN32 was measured, in vitro, as the ratio of [total Fe(II)]:[total Fe]. From this parameter, reduction rates were calculated for Volcano 1 BIOS (0.0521 day−1), Volcano 19 BIOS (0.0473 day−1), and hydrous ferric oxide, a synthetic two-line ferrihydrite (0.0224 day−1). Sediments from both BIOS sites were more easily reduced than synthetic ferrihydrite, which suggests that the decrease in effective surface area of the minerals within the sediments (due to the presence of the organic component) does not inhibit subsequent microbial reduction. These results indicate that natural, marine BIOS are easily reduced in the presence of dissimilatory iron-reducing bacteria, and that the use of common synthetic iron minerals to model their reduction may lead to a significant underestimation of their biological reactivity.

Description: The atmospheric deposition of both macronutrients and micronutrients plays an important role in driving primary productivity, particularly in the low-latitude ocean. We report aerosol major ion measurements for five ship-based sampling campaigns in the western Pacific from similar to 25 degrees N to 20 degrees S and compare the results with those from Atlantic meridional transects (similar to 50 degrees N to 50 degrees S) with aerosols collected and analyzed in the same laboratory, allowing full incomparability. We discuss sources of the main nutrient species (nitrogen (N), phosphorus (P), and iron (Fe)) in the aerosols and their stoichiometry. Striking north-south gradients are evident over both basins with the Northern Hemisphere more impacted by terrestrial dust sources and anthropogenic emissions and the North Atlantic apparently more impacted than the North Pacific. We estimate the atmospheric supply rates of these nutrients and the potential impact of the atmospheric deposition on the tropical western Pacific. Our results suggest that the atmospheric deposition is P deficient relative to the needs of the resident phytoplankton. These findings suggest that atmospheric supply of N, Fe, and P increases primary productivity utilizing some of the residual excess phosphorus (P*) in the surface waters to compensate for aerosol P deficiency. Regional primary productivity is further enhanced via the stimulation of nitrogen fixation fuelled by the residual atmospheric iron and P*. Our stoichiometric calculations reveal that a P* of 0.1 mu mol L-1 can offset the P deficiency in atmospheric supply for many months. This study suggests that atmospheric deposition may sustain similar to 10% of primary production in both the western tropical Pacific.

Description: Linear, hummocky pillow mound volcanism dominates at slow and intermediate spreading rate mid-ocean ridges. Volcanic hummocks are thought to be formed by low effusion rates or as a result of flow focussing during effusive fissure style eruptions in which the initial dike intercepts the seafloor and erupts along its entire length. In this study, high-resolution autonomous underwater vehicle (AUV) bathymetry is used to accurately map the extents of four historical fissure eruptions of the Juan de Fuca and Gorda ridges: on the North Gorda, North Cleft, and CoAxial ridge segments. The four mapped eruptions take the form of pillow mounds, which are similar in both lithology and dimension to hummocks on the Mid-Atlantic Ridge. Pillow mounds may be isolated, or coalesce to form composite mounds, aligned as ridges or as clustered groups. In three of the four mapped sites, the eruptions were discontinuous along their lengths, with pillow mounds and composite mounds commonly separated by areas of older seafloor. This style of discontinuous eruption is inconsistent with typical en echelon fissure eruptions and is probably due to a mildly overpressured, fingering dike intersecting the seafloor along parts of its length.