Incidence of marine debris and its relationships with benthic features in Gray's Reef National Marine Sanctuary, Southeast USA

Gray's Reef National Marine Sanctuary (GRNMS) is an increasingly popular site for recreational fishing and diving in the South Atlantic Bight (SAB). As a result, there has been heightened concern about potential accumulation of marine debris and its consequent effects on sanctuary resources. Field surveys were conducted at GRNMS in 2004 and 2005 to provide a spatially comprehensive characterization of benthic communities and to quantify the distribution and abundance of marine debris in relation to bottom features. The spatial distribution of debris was concentrated in the center of the sanctuary and was most frequently associated with ledges rather than other bottom types. On ledges, the presence and abundance of debris was significantly related to observed boating activity and physiographic features including ledge height, ledge area, and percent cover of benthic organisms. The results from this study will aid managers in optimizing cleanup efforts and long-term monitoring of debris accumulation patterns at GRNMS and other hard bottom areas in the SAB.     

Nitrogen cycling in the German Bight (SE North Sea) — Clues from modelling stable nitrogen isotopes

Nitrogen isotope values (δ¹⁵N) of surface sediments in the German Bight of the North Sea exhibit a significant gradient from values of 5–6‰ of the open shelf sea to values above 11‰ in the German Bight. This signal has been attributed to high reactive N (N_r) loading enriched in ¹⁵N from rivers and the atmosphere. To better understand the processes that determine the intensity and spatial distribution of δ¹⁵N anomalies in surface sediments, and to explore their usefulness for reconstructions of pristine N-input from rivers, we modeled the cycling of the stable isotopes ¹⁴N and ¹⁵N in reactive nitrogen through the ecosystem of the central and southern North Sea (50.9–57.3°N, 3.4°W−9.2°E) for the year 1995. The 3D-ecosystem model ECOHAM amended with an isotope-tracking module was validated by δ¹⁵N data of surface sediments within the model domain. A typical marine value (δ¹⁵N_nitrate=5‰) was prescribed for nitrate advected into the model domain at the seaside boundaries, whereas δ¹⁵N_nitrate of river inputs were those measured bi-monthly over 1 year; δ¹⁵N values of atmospheric deposition were set to 6‰ and 7‰ for NO_x and NH_y, respectively. The simulated δ¹⁵N values of different nitrogen compounds in the German Bight strongly depend on the mass transfers in the ecosystem. These fluxes, summarized in a nitrogen budget for 1995, give an estimate of the impacts of hydrodynamical and hydrological boundary conditions, and internal biogeochemical transformations on the nitrogen budget of the bight.     

Stormwater plume detection by MODIS imagery in the southern California coastal ocean

Stormwater plumes in the southern California coastal ocean were detected by MODIS-Aqua satellite imagery and compared to ship-based data on surface salinity and fecal indicator bacterial (FIB) counts collected during the Bight'03 Regional Water Quality Program surveys in February–March of 2004 and 2005. MODIS imagery was processed using a combined near-infrared/shortwave-infrared (NIR-SWIR) atmospheric correction method, which substantially improved normalized water-leaving radiation (nLw) optical spectra in coastal waters with high turbidity. Plumes were detected using a minimum-distance supervised classification method based on nLw spectra averaged within the training areas, defined as circular zones of 1.5–5.0-km radii around field stations with a surface salinity of S < 32.0 (“plume”) and S > 33.0 (“ocean”). The plume optical signatures (i.e., the nLw differences between “plume” and “ocean”) were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into “plume” and “ocean” using two criteria: (1) “plume” included the stations with salinity below a certain threshold estimated from the maximum accuracy of plume detection; and (2) FIB counts in “plume” exceeded the California State Water Board standards. The salinity threshold between “plume” and “ocean” was estimated as 32.2. The total accuracy of plume detection in terms of surface salinity was not high (68% on average), seemingly because of imperfect correlation between plume salinity and ocean color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between ocean color and bacterial contamination. Nevertheless, satellite imagery was shown to be a useful tool for the estimation of the extent of potentially polluted plumes, which was hardly achievable by direct sampling methods (in particular, because the grids of ship-based stations covered only small parts of the plumes detected via synoptic MODIS imagery). In most southern California coastal areas, the zones of bacterial contamination were much smaller than the areas of turbid plumes; an exception was the plume of the Tijuana River, where the zone of bacterial contamination was comparable with the zone of plume detected by ocean color.     

Changing of the guards: Detrital zircon provenance tracking sedimentological reorganization of a post-Gondwanan rift margin

Understanding the development of sedimentary systems during continental rifting is important for tracking environmental change and lithospheric processes. Conceptual models have been developed for the sourcing, routing and facies architecture of sediments in rift-settings, driven in part by quantitative sediment tracking. Here, we present laser ablation split-stream detrital zircon U/Pb geochronology and Hf-isotopes for post-rift (Cretaceous-Paleogene) clastic sediments from Ocean Drilling Program (ODP) wells and Plio-Pleistocene palaeoshoreline material, from the southern margin of Australia. Provenance results are contextualized through comparison with well-characterized source regions and regional pre- and syn-rift sediment reservoirs to track changes associated with Australia-Antarctica separation during East Gondwana break-up. The provenance character of the post-rift sediments studied are distinct from pre-existing sediment reservoirs and demonstrate termination of previously stable sediment routing systems and a dominance of local basement of the Proterozoic Madura and Coompana provinces (~1.2 Ga and CHUR-like Hf-signatures; Moodini Supersuite) in offshore ODP wells. A composite post-rift Cretaceous?-Eocene sample in the easternmost well expresses characteristic Phanerozoic zircon age signatures associated with source regions in eastern Australia that are interpreted to reflect inversion in the Ceduna Sub-basin to the east. Detrital zircon signatures in Plio-Pleistocene palaeoshoreline sediment are also relatively distinct, indicating derivation from coastal erosion in the Leeuwin Complex (~0.5 and 0.7 Ga subchondritic grains) and Albany–Fraser Orogen (~1.2 Ga subchondritic grains) several hundred, to over a thousand kilometers to the west. Collectively, results highlight the fundamental geological processes associated with rifting that dramatically change the character of sediment provenance via (a) isolation of pre-existing primary and secondary sources of detritus, (b) development of new source regions in basin compartmentalized highs and localized fault scarps, and (c) establishment of marine and coastal currents that redefine clastic sediment transport.     

Unusual features of the distribution of Radon-222 in the bottom waters of the continental slope of the Mid-Atlantic Bight: Hydrodynamic implications

²²²Rn was measured in the near-bottom waters of the continental slope of the Mid-Atlantic Bight. Separate measurements of the ²²²Rn supported by dissolved ²²⁶Ra allowed the excess ²²²Rn that is derived from the underlying sediments to be distinguished. Measurements of production of ²²²Rn by the sediments were used to calculate fluxes of ²²²Rn from sediments that would be expected as a result of molecular diffusion. On the upper slope and on the lower slope excess ²²²Rn standing crops were, respectively, greater than and consistent with fluxes of radon from sediments by molecular diffusion as are typical of most ocean environments. On the middle slope, however, observed excess ²²²Rn concentrations and standing crops were significantly lower than what would be expected from the calculated fluxes from the underlying sediments. This unusual feature of low radon concentrations on the middle slope is referred to as the low-radon zone (LRZ). This LRZ was always present over several years and seasons, but was variable in intensity (excess-radon concentration and standing crop) and in location on the slope. Low concentrations of suspended particulate matter and low current velocities observed by others in the same region are consistent with low mixing as a possible cause of the LRZ. Radon profile shapes and recent work by others on near bottom mixing due to interactions between topography and internal waves, however, suggest that high mixing due to internal waves is a more likely cause of the LRZ.     

大连湾赤潮生物──赤潮异弯藻

于１９８５，１９８６和１９８７三年的夏季在辽宁大连湾采集赤潮生物──赤潮异弯藻，以相差显微镜和扫描电镜进行了形态观察和分类研究；同时述及其分类沿革及至今仍存在的争议，结合本种在大连湾的生态特点简要地综述了其在世界上的分布，生理宗，昼夜垂直移动，营养摄取以及细胞分裂周期和种群繁殖等。结果表明，在温带近海夏，秋季潮异弯藻的生长率最高，冬季休眠于海底；温度是限制其复苏的主要因子。本种昼夜都能摄取营养，生     

Seasonal variation in the molt status of an oceanic copepod

The timing of diapause, or suppressed development, in the dominant California Current copepod Calanus pacificus was examined in two ways. Diapause timing was inferred from changes in the abundance of deep, diapausing C. pacificus over a full year at a station off southern California, USA. Jaw phase and ecdysteroid content, indicators of molt cycle status in C. pacificus, were also examined to determine if shifts toward early molt phases, as are observed in diapausing Calanus, were also found among surface C. pacificus during periods when the abundance of deep, diapausing C. pacificus was increasing. The abundance of diapausing C. pacificus in deep water increased from June to mid-October, then declined from October to March. The percentage of surface-living C. pacificus CV with postmolt jaws, the earliest jaw phase, was significantly higher from June to mid-October than at other times. The ecdysteroid content of surface-living C. pacificus CV was also significantly lower during June to mid-October than during late October to May. Both of these changes indicate a shift to earlier molt phases in surface-living C. pacificus CV during periods of onset of diapause. However, the molt status of surface CV was variable from June to mid-October, suggesting that preparation for diapause was spatially or temporally heterogeneous. Hypotheses about environmental cues that induce diapause were evaluated, although the effect of cues on possibly sensitive stages could not be considered. The abundance of diapausing C. pacificus increased during a period of warm upper water column temperature and generally high and declining photoperiod; however, evaluation of the cues inducing diapause was inconclusive.     

Tasman Geosyncline greenstones and ophiolites

Palaeozoic greenstones lying at the base of stratigraphic sequences or in fault blocks in the Tasman Geosyncline are compared with the Penrose Conference definnition of an ophiolite by using tabulated petrological, structural, and metallogenic data. Of 45 occurrences, only 9 are recognizably ophiolites: 4 are in rift zones adjoining Precambrian continental crust at the ends of the geosyncline; and away from the margins, in that part of the geosyncline most typically of West Pacific‐type, only 5 of the 33 greenstone occurrences are recognizably ophiolites. Ophiolites are rare in the Tasman Geosyncline, in contrast to several Atlantic‐type geosynclines. This may be a characteristic of West Pacific‐type geosynclines in general.

Alpine‐type serpentinites are rather common in the Tasman Geosyncline. The metallogeny of some shows affinities with ophiolites, suggesting a common origin as oceanic crust. Their relative abundance suggests that West Pacific‐type geosynclines, such as the Tasman Geosyncline, may have developed on oceanic crust of unusual composition. Alternatively, it may reflect differences of deformation style between Atlantic‐ and West Pacific‐type geosynclines.

The term ophiolite has been used uncritically in plate tectonic analyses of the Tasman Geosyncline, calling in question the objectivity of these analyses. If objectivity is to be maintained, some indication should be given of the quality of the data used in plate tectonic analyses.