Search

A paleoceanographic reconstruction of the southern Panama Basin for the last 23.000 years, based on the benthic foraminiferal analysis from the deep sea core ME0005A-24JC (0.01°N, 86.28°W, water depth 2941) is presented. Cluster and SHEBI (SHE Analysis for Biozone Identification) analyses performed on the benthic foraminiferal assemblages, evidence a faunal turnover in the early Holocene at 14 ky BP. Between 23 and 14 ky BP, Fursenkoina rotundata , Hoeglundina elegans , Globobulimina affinis , Globobulimina pacifica , Cibicidoides wuellerstorfi and Uvigerina hispidocostata were common. Conversely, from 14 ky to the present, the assemblage is represented by Chilostomella oolina , Laticarinina pauperata , and Uvigerina proboscidea . This faunal turnover suggests significant fluctuations in oxygen content at the sea floor and the organic matter (OM) influx, which could reflect: (1) fluctuations in the surface productivity related to the equatorial divergence and, (2) OM advection caused by the dynamic of the deep sea currents. Paleoproductivity estimates and benthic foraminiferal rates depict a general trend towards lower values since the Last Glacial Maximum (LGM) with a conspicuous change at 14 ky BP. Therefore, the paleoceanographic reconstructions of the ME0005A-24JC core suggest a transition from La Niña-like conditions during the LGM to El Niño-like conditions in the recent, as previously proposed for the Eastern Equatorial Pacific. Estimates of the paleo-intensity of deep sea currents based on the relative percentage abundance of the epifaunal foraminifera Cibicidoides wuellerstorfi suggest stronger deep sea currents on the Carnegie Ridge before 14 ky BP. [ABSTRACT FROM AUTHOR]

The purpose of this study is to show that seafloor hydrothermal venting in the open northeast Pacific Ocean has a marked impact on secondary biomass and production within the overlying water column. Specifically, we use net tows and concurrently measured acoustic backscatter data collected over six summers to examine the effects of hydrothermal venting from the Endeavour Segment of Juan de Fuca Ridge on macro-zooplankton biomass and production throughout the entire 2000 m depth range. Previous research shows that ontogenetic diapausing migrators and their predators from the upper ocean aggregate above the neutrally buoyant plumes in summer and resume feeding on plume and bottom upwelled particles, resulting in increased zooplankton reproductive output to the upper ocean. Within the limitations of our sampling methodology, net tows reveal a statistically significant exponential decline in total water-column biomass with increasing lateral distance from the vent fields. The acoustic backscatter data show a similar decline, but only below 800 m depth. Near-surface biomass was highly variable throughout the region, but values near vents consistently ranged higher than summer values found elsewhere in the offshore northeast Pacific. Water-column biomass was similar in magnitude above and below 800 m depth throughout the region. Because epiplume biomass can be advected a considerable distance from vent fields, biomass enhancement of the water column from hydrothermal venting may extend considerable distances to the west and northwest of the vent sites, in the prevailing directions of the subsurface flow. Based on the extensive acoustic Doppler current profiler (ADCP) data collected, and the strong correlation between zooplankton production derived from net sample biomass and acoustic backscatter intensity, we estimate that daily macro-zooplankton production in the upper 400 m of the water column within 10 km of the vent fields averages approximately 16% of photosynthetic primary production (the “ Z ratio”), whereas the total water-column zooplankton production averages 26% of surface primary production. Local grazing-rate estimates, metabolic constraints and other open-ocean studies suggest that the Z ratio should be no higher than 5%, which it is at off-axis background sites in the study region. This finding indicates that nutrient sources other than upper-ocean primary production fuel both upper- and deep-ocean zooplankton biomass and growth near the Endeavour Ridge hydrothermal vents. [ABSTRACT FROM AUTHOR]

In part I, equatorial Pacific Ocean temperature index SST3.4 was found to have segments during 1990–2014 showing a phase-locked annual signal and phase-locked signals of 2- or 3-year periods. Phase locking is to an inferred solar forcing of 1.0 cycle/yr. Here the study extends to the global ocean, from surface to 700 and 2000 m. The same phase-locking phenomena are found. The El Niño/La Niña effect diffuses into the world oceans with a delay of about two months. [ABSTRACT FROM AUTHOR]

Abstract: An inventory of Canada's marine renewable energy resources based on numerical modeling of the potential tidal, wave and wind energy has been published that identifies areas with maximum resource potential. However, the inventory does not consider the seabed geological conditions that will control the safe development of seabed installations and cable corridors. The Geological Survey of Canada (Natural Resources Canada) has therefore undertaken an assessment of seafloor geological characteristics and physical environmental parameters that will be encountered during any extensive deployment of marine renewable energy systems for the Pacific offshore of Canada. Here we present an overview of seabed characterization for key sites for each of the three energy types. Narrow passages exiting the Salish Sea near the Canadian boundary with the United States and northwards out of the Strait of Georgia provide very promising sites for tidal generation. Here, elliptical fields of very large subaqueous dunes, from 12 to 28m in height, present a significant challenge to site development. Along the exposed continental shelf of Vancouver Island focused wave-energy close to shore (40–60m water depth) offers significant energy potential, but any engineering systems would have to be founded on a seafloor made up of a mobile gravel lag and an extensive boulder pavement. A large wind farm proposed for the Pacific North Coast would be built on an extensive shallow bank that has active sediment transport and a large field of sand ridges that have developed within a macrotidal environment. A significant challenge is providing for a safe seafloor cable corridor of over 100km that crosses a large subaqueous dune field to connect to the electrical grid on the mainland. These examples show how geoscience has and will provide critical information to project proponents and regulators for the safe development of marine renewable energy. [Copyright &y& Elsevier]

Abstract: Coarse-grained ripples (CGRs) develop within the seafloor depression–sand ridge systems along the Shimizu coast, in the northwestern part of Suruga Bay facing the Pacific Ocean, central Japan. In this paper, we analyze data from high-resolution bathymetry, seafloor observation by an underwater video camera, and high-resolution seismic surveys and seafloor trenching of shallow strata, obtained between 2005 and 2007, to describe their geomorphological and sedimentological characteristics in detail, and to examine the formative processes and maintenance of the systems. In water depths of 5–30m, CGRs occur in seafloor depressions that are approximately 40–70cm deeper than the surrounding sandy seafloor. In many cases, the ripples develop in depressions between shore-normal sand ridges composed mainly of fine sand (<70cm high, 100–400m long) on a relatively narrow shelf. The alongshore width of the sand ridges is 10–100m, and that of the depressions is 10–150m. The CGRs (wavelength<3.5m, height<30cm) have almost shore-parallel crests with a symmetrical or slightly asymmetrical shape, suggesting wave-generated oscillating flows. The crests of the lager ripples are composed of gravel (maximum long axis: 5–8cm) and the troughs consist of fine to very fine sand. The CGR–depression–sand ridge systems develop widely during the passage of typhoons in the summer–autumn seasons. At the narrower shelf, the surface fine-grained sediments and the surface and subsurface coarse-grained sediments, which form the sand ridges and the CGRs respectively, are repeatedly eroded and redeposited during typhoon-related storms. In contrast, active sediments are currently limited to the surface fine deposits on the wider shelf areas. The sediments that make up the CGRs appear to be derived from both modern beach sediments and relict sediments. We postulate that the CGR–depression–sand ridge system appears to be controlled mainly by both seafloor erosion and offshore-directed sediment transport during storms, and these processes may depend on the shelf width. In fact, the sand ridges (covering the CGRs) that imply significant offshore-directed transport only develop on the narrower shelf. The distribution and seabed expression of the CGRs is constrained by the thickness and distribution of surface-covering sandy sediments, such as the sand ridges. This represents a new interpretation of the distribution of CGRs within seafloor depressions on the shelf of an active margin that receives a large supply of sandy and gravelly fluvial sediments, and differs from the processes seen on the sediment-starved shelves of passive margins. [Copyright &y& Elsevier]

Abstract: Understanding if and how particles are laterally transported before final deposition is crucial for accurately reconstructing paleoceanographic conditions from pelagic sediments. We use digital seismic reflection data from the AMAT03 site survey cruise for IODP EXP 320/321 to investigate the Neogene and Quaternary pelagic sedimentation across the eastern-‐central equatorial Pacific (110–130°W). Spatially continuous stratigraphy was derived from five latitudinal seismic transects between the Clipperton and Galapagos Fracture Zones, revealing evidence of widespread sediment redistribution increasing towards the western part of this region. A large-scale anomaly in sediment thickness in the northwestern part of the surveyed area suggests that sediment focusing and/or bottom-current induced resedimentation has been occurring in the central Pacific on timescales of millions of years. The relatively confined character of this anomaly does not support a longitudinally continuous focusing of sediments on the equator, as has been suggested to occur during the Pleistocene glacial stages. [Copyright &y& Elsevier]

Abstract: This study uses the amplitudes of bottom-side reflected shear waves to constrain the morphology and dynamics of subducted oceanic lithosphere beneath northwestern Pacific subduction zones. Across Honshu arc, the 410- and 660-km seismic discontinuities are detected at the respective depths of 395±5 and 685±5km within the Wadati–Benioff zone. Their topographies are negatively correlated along slab dip, showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone. The base of the upper mantle shows broad depressions as well as localized zones of shallow/average depths beneath Korea and northeast China. The 15+km peak-to-peak topography west of the Wadati–Benioff zones suggests that the stagnant part of the subducted Pacific plate is not as flat as previously suggested. Eastward slab ‘pile-up’ is also possible at the base of the upper mantle. Across southern Kuril arc, the shear wave reflection coefficients of major olivine phase boundaries fall below 5% within the Wadati–Benioff zone. The apparent reflection gaps and the spatial connection between a strong reflector at ~900km depth may imply 1) possible compositional variations at the top and bottom of the transition zone and 2) substantial mass/heat flux across the 660-km seismic discontinuity. We also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths. The depths and strengths of these reflectors are highly variable between Honshu and southern Kuril islands. [Copyright &y& Elsevier]

Abstract: We present a new multi-proxy reconstruction of sea-surface properties spanning the last 140 ka in the IMAGES Core MD02-2529 located in the eastern tropical Pacific Ocean off Costa Rica. Spectral analysis of the records allowed us to examine the ecological imprints of orbital changes on planktic foraminiferal and coccolithophore assemblages and on the pattern of primary production in the Eastern Equatorial Pacific, north of the Equatorial upwelling. Independent productivity reconstructions based on phyto- and zooplankton assemblages show a coherent pattern dominated by orbital precession, which appears to have control productivity changes recorded in the studied core over the last glacial–interglacial cycle. The proposed mechanism of this control invokes an atmospheric forcing associated with equatorial insolation maxima in spring and fall with a period of ∼20 ka. Faunal evidence for a stronger upper-ocean mixing with enhanced nutrient supply to the euphotic zone suggests a more vigorous local atmospheric circulation and associated enlargement of the Costa Rica Dome that influenced the core site at times of May insolation maxima. The last two terminations in the studied record are associated with conspicuous changes in planktic assemblages which require additional nutrient-delivery mechanisms to amplify the precession forcing. Our faunal and stable isotope data are in favour of the previously postulated nutrient advection via the Southern Ocean “tunnelling” operating during deglaciations. [Copyright &y& Elsevier]

Abstract: Seafloor bathymetry north of the Galápagos microplate in the Eastern Pacific Ocean contains evidence for a sequence of short-lived rifts cross-cutting abyssal hills adjacent to the East Pacific Rise. These secondary rifts are sub-parallel to the Incipient Rift that marks the current triple junction at 2°40′N and are nearly perpendicular to the direction of opening between the Cocos and Nazca plates. Secondary rifts likely initiated from the EPR by lithospheric cracking. Eventually, their activity stopped and they were carried away from the triple junction as part of the Cocos plate. We developed and analyzed numerical models of rift interaction to understand the evolution of rift configuration in this area. By varying the geometry and locations of rifts, we constrain the factors that have led to the location and orientation of secondary rifts at the northern Galápagos Triple Junction. Interaction between secondary rifts and the Cocos-Nazca Rift results in ~10° clockwise rotation of the secondary rift propagation direction, as observed. Furthermore, if a rift has become detached from the East Pacific Rise, a zone of reduced tension is present ahead of the rift tip, prohibiting its connection to the East Pacific Rise. Two zones of tensile stress enhancement develop along the East Pacific Rise next to the detached rift and control where new cracks are likely to form. Although the magnitude of tensile stress enhancement is controlled by the gap between the detached rift and the East Pacific Rise, whether the new rift forms north or south of the detached rift is controlled by position of the Cocos-Nazca Rift. Therefore, the sequence of ancient rifts found northeast of the current triple junction at 2°40′N represents the natural consequence of rift disconnection events and their position records the kinematic history of the gap between the East Pacific Rise and the Cocos-Nazca Rift. [Copyright &y& Elsevier]

Abstract: Video analysis of a whale-fall discovered in the northeast Pacific Ocean, off Vancouver Island at a depth of 1288m during ROV diving operations has identified 26 taxa of deep-sea benthic organisms inhabiting the seafloor immediately surrounding remnants of the whale skeleton. A photo-mosaic derived from high-definition video provides a quantitative visual record of the present condition of the site, the species richness, and substrate preference. Only the skull and caudal vertebrae remains of this large whale skeleton are estimated to have been approximately 16.5m in length. Most organisms identified near the whale-fall are common benthic deep-sea fauna, typical of this water depth and seafloor composition. Much of this species richness comes from sessile suspension feeding cnidarians attached to the numerous glacial dropstones found throughout the area rather than the presence of the whale skeleton. Seep and bone specialists are rare (4 taxa) and may be, in part, a remnant population from a sulphophilic stage of whale-fall decomposition. Evidence of past colonization by Osedax sp. is visible on the remaining bones and we conclude that rapid degradation of the missing bones has occurred at this site as has been observed at whale-falls off central California in Monterey Canyon. [Copyright &y& Elsevier]

Abstract: Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields. [Copyright &y& Elsevier]

Abstract: Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal–upper abyssal (1500–2000m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~1500m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time. At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms. The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers (“Strangelove Ocean Model”) or to the collapse of the biotic pump (“Living Ocean Model”). [Copyright &y& Elsevier]

Abstract: In addition to the atmosphere, the oceans play important roles in the excitation of the Chandler wobble. The contributions made by the Pacific Ocean, the Indian Ocean and the Atlantic Ocean from 1980 to 2005 to the excitation of the Chandler wobble are first and systematically researched by taking advantage of the data of the current velocity field and ocean floor pressure provided by the marine circulation model of the Estimating the Circulation and Climate of the Ocean (ECCO). Studies show that the contributions of the three oceans to the excitation of the Chandler wobble are different from one another: the excitation energy of the Pacific Ocean makes up about 22.2% of the observational excitation energy, the largest one among the three oceans, that of the Indian Ocean accounts for about 12.7% and that of the Atlantic Ocean amounts to about 7.1%, the smallest among the three great oceans. The remarkable increase in the excitation energy of the Chandler wobble by the Pacific Ocean may be possibly due to the effect of the strong ENSO event which occurred from 1982 to 1983. [Copyright &y& Elsevier]

Whale falls provide abundant but relatively ephemeral, sulphide-rich habitat islands on the deep-sea floor. To explore life-history adaptations to whale-fall habitats, we examined the reproductive biology of Idas washingtonia, a bathymodiolin mussel occurring in abundance on sunken whale skeletons in the deep northeast Pacific Ocean. Analysis of the reproductive biology of I. washingtonia demonstrates strong evidence of protandric hermaphroditism. Developing males were recognised in individuals as small as 1.7mm shell length and spermatogenesis continued until ∼7mm length. At >6.5mm, males were generally spent and the first previtellogenic oocytes were observed. Although developing females were found as small as 4.5mm shell length, most well-developed females were >6mm shell length. Overall, females only formed ∼12% of the population. As with other modiolid bivalves, fecundity was high and the egg size <50μm, indicative of planktotrophic development. The occurrence of protandric hermaphroditism, high fecundity and planktotrophic dispersal may be an adaptation to the ephemeral nature of their habitat. The success of this adaptation is shown by the rapid colonisation of whale falls even though these may have been severely reduced in abundance since the peak of commercial whaling activity in the 20th century. [Copyright &y& Elsevier]

Abstract: Ever since the discovery that the mid-ocean ridge axis deepens at most axial discontinuities, there has been vigorous debate about whether ridge axis depth and shape reflect magma supply. Here we report evidence, from one of the most thoroughly studied ridge discontinuities on a fast-spreading mid-ocean ridge, that volcanic eruption effusion rates have been low relative to nearby segment centers throughout its two million year history. This pattern of low volcanic effusion rates is inferred from the fields of constructional volcanic mounds on the seafloor which are much more abundant in the off-axis discordant zone of the East Pacific Rise (EPR) 9°N Overlapping Spreading Centers (OSC) than on typical EPR seafloor. Detailed seafloor mapping in 2007 shows that these mound fields consist of concentrations of large pillow mounds that formed within the current OSC basin and ridge tips, rather than off-axis. Pillow lava, erupted at approximately an order of magnitude lower effusion rate than lobate or sheet flows, primarily builds mounds on the seafloor. Crustal thickness, a proxy for long-term magma supply, does not decrease in spite of the decreased lava effusion rates implied by widespread pillow eruptions. To resolve the problem of achieving the same magma emplacement rate with lower effusion rates, without violating our observations by requiring drastically increased eruption frequency or unreasonably long eruption durations, we propose that eruptions occur across the entire OSC basin. The current configuration of mid-crustal melt sills within the OSC as resolved by multichannel seismic reflection surveys have neither the correct location nor appropriate size to deliver magma to these eruptive vents in the OSC basin via vertically propagating dikes. Instead, we propose that magma delivery to eruptions occurs via laterally propagating dikes from robust mid-crustal melt sills outside of the overlap zone. [Copyright &y& Elsevier]

Abstract: The combination of fluid inclusion analyses and microfossil analyses is an excellent method to study the preservation process of deep sub-seafloor microorganisms. By studying fluid inclusions in the same mineral phases as microfossils, it is possible to reconstruct the conditions that prevailed when the microorganisms where entombed and to put them in a geological and environmental context. This study has been performed on carbonate and gypsum veins in drilled basalt samples from three seamounts belonging to the Emperor Seamounts in the Pacific Ocean: Detroit, Nintoku and Koko Seamounts. The study show that variations in salt composition (MgCl2, NaCl, KCl and CaCl2) and salinity (2.1 and 10.5eq. wt% NaCl) of the hydrothermal fluids do not have an influence on the occurrence of microfossils throughout the samples. The microorganisms were trapped and entombed at minimum temperatures of ∼130°C which implies that the microorganisms could have existed at temperatures of ∼130°C for shorter periods of time. The microorganisms were entrapped at shallow-marine to submarine conditions and the entrapment of the microorganisms occurred relatively late compared to the volcanic activity. [Copyright &y& Elsevier]

Abstract: Direct seismic measurements of the thickening of oceanic lithosphere away from the spreading axis are rare due to the remoteness of mid ocean ridges. On the East Pacific Rise, at 17°S, there were two long-term broadband ocean bottom seismometer deployments, the MELT and GLIMPSE experiments. These arrays spanned young Pacific plate seafloor ranging in age from 0 to 8 Ma. Combining these two data sets, we describe the increase in Rayleigh wave phase velocities for 16–100 s period as function of distance from the ridge with two parameterizations: an arbitrary function of seafloor age and a simple polynomial function of age on the Pacific and Nazca plates. Although resolution analysis shows that 10 to 15 independent pieces of information about the age variation of phase velocity on the Pacific plate can be resolved at periods of ≤50 s, the three parameter polynomial model fits the data almost as well, indicating a simple pattern of the evolution of structure with age. To compare our observations to the predictions for the conductive cooling of the lithosphere, we convert a thermal half-space cooling model to shear velocity using anharmonic and anelastic contributions. The patterns in the velocities are not consistent with simple conductive cooling. The conductive cooling model under predicts the changes in phase velocity with age observed in the 20 to 78 s period range. We observe significant changes in shear velocity in the asthenosphere at depths greater than conductive cooling should extend. The asthenospheric low velocity zone is asymmetric, dipping to the west with the lowest velocities beneath the Pacific plate west of the spreading center. The conductive cooling model also over predicts the shear velocities in the lithosphere by ~0.2 km/s. These anomalies indicate that more complicated mantle flow and significant mantle heterogeneities such as melt are required. [Copyright &y& Elsevier]

Abstract: The CaCO3 content of marine sediments in many regions of the ocean has varied systematically with climate throughout the late-Pleistocene glacial cycles. Both biological productivity and carbonate preservation have been proposed to be the master variable regulating this variability. We have evaluated the preserved flux of CaCO3 in cores from the central equatorial Pacific Ocean (∼140°W) using the 230Th-normalization technique. Neither barite fluxes nor 10Be/230Th ratios, both geochemical proxies for export production, correlate with CaCO3 fluxes, indicating that productivity is not the principal factor controlling CaCO3 accumulation in these sediments. Preserved fluxes of CaCO3 in central equatorial Pacific sediments correlate in time with the benchmark CaCO3 record from the Cape Basin (South Atlantic Ocean), supporting the view that changes in ocean chemistry (carbonate ion concentration) have controlled the pattern of CaCO3 preservation and accumulation at these sites. Modern CaCO3 preservation in equatorial Pacific sediments has dropped to levels nearly as low as those experienced at any time in the late Pleistocene. Similar changes occurred at the end of each of the late-Pleistocene interglacial periods, from which we infer that ocean carbonate chemistry has already undergone changes that are expected to precede the transition into the next ice age. However, during the late Pleistocene, the time interval between the decrease in CaCO3 preservation and the end of the interglacial has varied substantially from one interglacial to another (from ∼2000 to ∼15,000 years), so the late-Holocene decrease in CaCO3 preservation cannot be used to predict the end of the Holocene interglacial period. [Copyright &y& Elsevier]

Abstract: A postglacial sea-level record reconstructed through the study of 25 cores and 10 grab samples obtained from the siliciclastic-dominated northern South China Sea continental shelf between Hong Kong and Dongsha is presented. The seven sedimentary facies recognized are: [(1)] Pleistocene overconsolidated mud facies affected by palaeosol development due to sub-aerial exposure during the Last Glacial Maximum (LGM), [(2)] bioclastic sandy gravel facies occurring at a present-day seabed depth exceeding 120m, [(3)] LGM bioclastic beach-dune sand facies at a present-day seabed depth between 110 and 120m, [(4)] postglacial siliciclastic beach-dune sand facies formed during at least two episodes of sea-level stillstands at present-day seabed depths between 80 and 90m, and 30 and 50m, respectively, [(5)] postglacial transgressive sand facies of Late Pleistocene to Early Holocene age: radiocarbon dating shows that this facies was deposited in two stages before and after the 8200 calendar yr BP cold event, [(6)] postglacial sand and gravel-dominated facies with acoustic turbidity at a present-day seabed depth of about 50m, [(7)] postglacial mud facies. Based on the radiocarbon ages obtained from samples located above and below the Holocene–Pleistocene hiatus in the two innermost shelf cores, and large variations of atmospheric radiocarbon concentration found during the last glacial period in a submerged stalagmite from the Bahamas (Beck et al., 2001. Science 292, 2453–2458), ages exceeding 8200 calendar yr BP are likely to represent minimum values. Ages postdating this limit, which are less affected by variations of atmospheric radiocarbon concentration, indicate the presence of a post-8200 calendar yr BP cold event meltwater pulse caused by eustatic sea-level rise from approximately 40m below present to the present level by about 6000 calendar yr BP. Inaccuracies of the pre-8200 calendar yr BP radiocarbon ages may be attributed to large variations of atmospheric Δ14C during the postglacial period with greenhouse gases released from the sub-aerially exposed continental shelf probably accounting for a significant proportion. [Copyright &y& Elsevier]

Abstract: Bottom sediments collected in the Northwest (NW) Pacific Ocean in 1997 were analysed for 90Sr, 137Cs, 239, 240Pu and 241Am contents to determine their distribution patterns, inventories and sources. Enhanced inventories of 239,240Pu and 241Am were observed in the latitudinal belts of 10–20°N and 30–40°N, which correspond to major areas of local (tropospheric) and global (stratospheric) fallout (with a contribution from local fallout), respectively. The sediment inventory of 239,240Pu near the Bikini Atoll exceeded its overlying water inventory, however, in the mid-latitudes, more than 70% of 239,240Pu still remains in the water column. 241Am inventories in sediments exceeded that of the water column for the entire NW Pacific Ocean. Higher 137Cs and 90Sr sediment inventories in the latitudinal belt of 30–40°N are due to global fallout, and they account for about 10% and less than 5% of the water column inventories, respectively. The observed activity ratios of 137Cs/90Sr, 238Pu/239,240Pu and 241Am/239,240Pu in sediment were at some stations higher than the global fallout ratios due to contributions from local fallout and due to specific processes in the water column. Two end-member mixing model based on the 240Pu/239Pu atom ratios observed in global and local fallout yielded ∼60% contribution of the local fallout in the bottom sediments near the Bikini Atoll. The upward decrease in the 240Pu/239Pu atom ratios in the sediment column indicates a decrease in the contribution of local fallout to the Pu inventory with time. 241Am and 241Pu dating of sediment layers was utilized to explain a hiatus in sediment accumulation in the deep seafloor. [Copyright &y& Elsevier]

Abstract: Vigtorniella flokati, a new species of polychaete worm associated with decaying whale remains, is described. Three separate V. flokati populations were sampled using submersibles: two associated with implanted gray whale carcasses in the San Diego Trough (1240m depth) and the Santa Cruz Basin (1670m) off California, and one from sperm whale and balaeanopterid bones implanted on the slope of Oahu, Hawaii at 1000m. Extraordinarily large numbers of live specimens were observed and videotaped in situ using submersibles in the San Diego Trough and the Santa Cruz Basin. The populations on the carcass implanted for 4 months in San Diego Trough, and on the bones implanted for 2 years off Oahu, were composed only of small sized individuals (including juveniles). V. flokati most closely resembles the poorly known V. zaikai Kiseleva, 1992, described from the Black Sea. Forty-six morphological characters were used in a phylogenetic analysis of selected nereidiform polychaetes. The resulting most-parsimonious trees indicate sister taxon status between V. flokati and V. zaikai, and that this clade is sister to the putatively ancient polychaete clade Chrysopetalidae. Whale falls, which are intense point sources of organic enrichment at the deep-sea floor, pass through three successional stages. V. flokati appears to colonize the middle, “enrichment opportunist” stage, inhabiting organic-rich bones and sediments ∼4–24 months after carcass arrival. V. flokati exhibits remarkable behavior, clinging posteriorly to whale bones or nearby sediments to form a writhing carpet at densities exceeding 8000m-2. Its extraordinary abundance on whale falls, and apparent absence from other habitats, suggests it to be a whale-fall specialist. The precise feeding mechanism of the worm remains unknown, but we hypothesize that it may utilize dissolved organic carbon derived from the organic-rich setting of whale falls. The widespread occurrence of V. flokati on ephemeral, food-rich habitat islands in the Pacific suggests life-history strategies analogous to those for hydrothermal-vent and cold-seep species. [Copyright &y& Elsevier]

Provides information on a study on visible detrital aggregates formed between July and December at an abyssal station in the northeastern Pacific. Methods used; Results; Comparison of the results with the data available on chemical composition and respiration associated with detrital materials in other deep-sea area of the World Ocean.