An investigation of the relationship between bulk composition, inferred reaction progress and fluid-flow parameters for layered micaceous carbonates from Maine, USA

Reaction progress exhibited by multivariant assemblages in micaceous limestones can provide an excellent record of metamorphic fluid flow. However, it is necessary to understand the sensitivity of these assemblages to bulk‐composition parameters. Here, analysis of bulk composition on different scales and pseudosection construction are used to draw conclusions on relationships between bulk composition, fluid flow and reaction progress. Issues addressed include the effects of bulk composition on the mineralogical evolution of micaceous carbonates, the sensitivity of bulk composition to bulk‐composition sampling methods, the magnitude of cross‐layer fluid‐composition gradients, the potential for metasomatism to drive reaction progress, and the relative timing of reaction in adjacent layers. Pseudosections successfully represent observed mineral assemblages, constrain the position of reactions in T–X(CO₂) space, and allow assessment of the sensitivity of reaction position, inferred reaction progress and calculated fluid fluxes to uncertainties in bulk composition. The scale of bulk‐composition sampling affects bulk compositions, calculated modes, predicted mineral assemblages and calculated fluid compositions. Larger samples record an average of different lithological subdomains, while point‐count‐derived bulk compositions are subject to uncertainties related to the small number of sample points. The optimum bulk composition for pseudosection purposes probably lies between measured bulk compositions. Results suggest that reaction progress in some extensively reacted layers was driven by infiltration of H₂O‐rich fluid which flowed or diffused parallel to layering, perpendicular to layering in response to fluid‐composition gradients, and out of veins. Small variations in fluid composition across layering (ΔX(CO₂) < 0.02) were maintained by internal buffering by the mineral assemblages. Internal buffering must also have driven samples up a sequence of narrow low‐variance fields in T–X(CO₂) space, and so reaction in adjacent layers must have close to simultaneous. Metasomatic effects on reaction progress are likely to have been small, so long as the porosity was low.     

Trans-Atlantic responses of Calanus finmarchicus populations to basin-scale forcing associated with the North Atlantic Oscillation

Populations of the copepod species Calanus finmarchicus often dominate the springtime biomass and secondary production of shelf ecosystems throughout the North Atlantic Ocean. Recently, it has been hypothesised that interannual to interdecadal fluctuations observed in such populations are driven primarily by climate-associated changes in ocean circulation. Here, we compare evidence from the North Sea and Gulf of Maine/Western Scotian Shelf (GoM/WSS) linking fluctuations in C. finmarchicus abundance to changes in ocean circulation associated with the North Atlantic Oscillation (NAO). A particularly striking contrast emerges from this Trans-Atlantic comparison: whereas the North Sea C. finmarchicus population exhibits a negative correlation with the NAO index, the GoM/WSS population exhibits a more complex, positive association with the index. The physical processes underlying these contrasting population responses are discussed in the context of regional- to basin-scale circulation changes associated with the NAO.     

Use of submerged aquatic vegetation as habitat by young-of-the-year epibenthic fishes in shallow Maine nearshore waters

Epibenthic fishes were collected with daytime beam trawl tows (n = 1713) in three shallow (<10 m) habitats of submerged aquatic vegetation (SAV), Zostera marina (eelgrass), Laminaria longicruris (kelp), Phyllophora sp. (algae), and unvegetated sandy/mud areas. We divided the Maine coast into three broad zones based upon geological features and sampled over five consecutive years; during April–November 2000 in the mid coast, in 2001 and 2002 along the south coast and in 2003 and 2004 along the eastern Maine coast. We quantified habitat use by eight economically important fish species (Gadus morhua, Microgadus tomcod, Pollachius virens, Urophycis chuss, Urophycis tenuis, Osmerus mordax, Tautogolabrus adspersus, and Pseudopleuronectes americanus) and 10 other common epibenthic species (n = 18 571). We identified the physical and biological variables most important in discriminating between habitats with and without individual fish species. Logistic regression models based on nearshore habitat characteristics were developed to predict the distribution of these species along the three zones representing broad geological regions of the Maine coast. Logistic regression models correctly classified individual fish species 58.7–97.1% of the time based on the temporal and physical habitat variables (month, temperature, salinity, and depth) and the presence–absence of submerged aquatic vegetation (Zostera, Laminaria, or Phyllophora). Overall fish presence and economically important fish presence were correctly classified 61.1–79.8% and 66.0–73.6% of the time, respectively. The Maine shallow water fish community was composed primarily of young-of-the-year and juvenile fishes with all habitats functioning as facultative nursery areas. Presence of most fish species was positively associated with Zostera, Laminaria, and to a lesser extent, Phyllophora. This study provides direct evidence of shallow waters of the Gulf of Maine as critical facultative nursery habitat for juvenile G. morhua, M. tomcod, P. virens, U. tenuis, U. chuss, T. adspersus, O. mordax and P. americanus, and many ecologically important species.     

Processing and attenuation of noise in deep seismic-reflection data from the Gulf of Maine

The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24–34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle.     

厦门海洋垃圾防治与管理实践及启示

海洋垃圾污染问题已经成为国际社会重点关注的环境问题,也是我国海洋环境治理的重要组成部分。文章从协调机制、日常监测、预测预报、风险评估、国际合作、宣传教育方面总结和分析了厦门市海洋垃圾污染防治与管理实践和经验,针对国内当前在海洋垃圾防治与管理实践中存在的问题,在厦门模式的基础上,提出了加强立法建设、关注源头控制、开展日常监测和预报、建立评价体系、拓展合作交流、强化宣传教育等方面的措施建议,为我国其他沿海地方海洋垃圾污染防治与管理提供参考。     

Diagnosis of trace Pb in domestic wells,Upper Gloucester Catchment,Maine, USA

Dissolved Pb in 32 wells associated with corroding submersible pumps is examined within a rural water district after almost 20 years (1984–2002). Groundwater Pb ranged from 0.4–24.9 μg L⁻¹ after 24 h pump flushing. Preliminary geochemistry and representative borehole lithology examinations were extrapolated by Markov chain modeling. The first-order geostatistical realizations of glacial sediments coupled with the Monte Carlo Metropolis-Hasting method suggest that elevated trace Pb persists in sand and gravel units, and continues at least to 40 m depth in the catchment. The ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb isotope compositions of groundwater Pb were decisive in discriminating the importance of leached Pb from submersible pump materials among geogenic sources.     

Major ice sheet response in eastern New England to a cold North Atlantic region, ca. 16-15 cal ka BP

A large ice sheet still covered almost all of Maine and eastern New England until ca. 15 cal ka BP, reaching south of 45 °S, despite rising summer insolation intensity and major ice recession elsewhere outside the North Atlantic region. Furthermore, the well-studied moraine belt along eastern coastal Maine, including the prominent Pineo Ridge delta/moraine complex and Pond Ridge moraine, indicates repeated readvances and stillstands between ca. 16 and 15 cal ka BP. This moraine belt reflects a considerable ice sheet response over eastern North America during this time period, coeval with the latter half of the European Oldest Dryas period. Moraine deposition was concurrent with reduction or elimination of North Atlantic meridional overturning, starting with the earlier onset of peak IRD and Heinrich Event 1 (HE-1). The existing ¹⁴C chronology suggests that the coastal moraine belt and the persistence of the ice sheet until ∼ 15 cal ka BP was a response to the severe cooling of the North Atlantic region after ∼ 17 cal ka BP.     

Turbulence avoidance and the wind-driven transport of plankton in the surface Ekman layer

Observations of turbulence avoidance in zooplankton are compared to estimates of the wind-driven turbulence in the upper ocean. Plankton that avoid wind-driven turbulence by moving deeper are no longer transported by the wind-driven Ekman currents near the surface because they are no longer near the surface. Here, a threshold level of turbulence that triggers an avoidance response is estimated, and is used to infer the wind speed and water column stratification conditions that would lead to zooplankton leaving the Ekman layer. Turbulence avoidance is argued to lead to near-shore retention in wind-driven upwelling systems, and to a reduction of the delivery of zooplankton to Georges Bank from the deeper waters of the Gulf of Maine.     

UPWELLING AND SEDIMENTATION DYNAMICS Ⅲ: COINCIDENCE OF UPWELLING AREAS WITH MUD PATCHES IN NORTH HEMISPHERE SHELF SEAS

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Organic matter production of American lobsters (Homarus americanus) during impoundment in Maine,United States

Lobster impoundments are dammed coastal embayments utilised to hold American lobsters (Homarus americanus) before shipping to market. The impacts of lobster impoundments on the environment have not been previously studied. Here, the digestive functioning of American lobsters was examined to assess the quantity and quality (TVS, total volatile solids) of lobster faeces produced under the temperatures and feeding regimens these animals were subjected to during the impoundment period. Overall it was determined that quantity and quality of faeces did not differ among the experimental temperatures (5, 10, and 15°C), and that animals fed every 1–2 days produced greater quantity and quality of faeces than those fed every 3–18 days, or those animals fed less than every 18 days. As a first estimate of organic matter production in active lobster impoundments, it was calculated that a typical lobster impoundment produced 0.79 ± 0.35 (average ± 1 SD) g TVS m^‐2 day^‐1 during the impoundment period, equivalent to 3.11 ± 0.60% of the total weight of lobsters stocked into the impoundment. This level of organic matter production is below the level produced by other aquaculture operations, and that at which benthic impacts might be expected.