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321.
Mercury dynamics in sulfide-rich sediments: Geochemical influence on contaminant mobilization within the Penobscot River estuary, Maine, USA 总被引:1,自引:0,他引:1
Research concerning the fate and biogeochemical cycling of mercury (Hg) within coastal ecosystems has suggested that microbially mediated diagenetic processes control Hg mobilization and that ligands with strong affinity for Hg, such as dissolved inorganic sulfide (S(-II)) and dissolved organic matter (DOM), control Hg partitioning between the dissolved and particulate phases. We have studied total Hg cycling in the sediments of the Penobscot River estuary using a combination of equilibrium porewater samplers and kinetic modeling. The Penobscot estuary has been subject to Hg contamination from multiple industries including a recently closed chlor-alkali production facility. The Hg concentration within the estuary surface sediments ranges from 1.25 to 27.5 nmol Hg g−1 sediment and displays an association with sediment organic matter and a concentration maximum within 3 cm of the sediment-water interface (SWI). Porewater profiles for the Penobscot estuary are divisible into three kinetically discrete intervals with respect to Hg dynamics. Beginning at depth in the sediment and moving upward toward the SWI we have defined: (1) a zone of net Hg solubilization at depth, with a zero-order net Hg production rate , (2) a zone of net Hg consumption within the zone dominated by FeS(s) precipitation with , and (3) a zone of net diffusive transfer within the vicinity of the SWI. Zone 1 is characterized by dissolved S(-II) concentrations ranging from 400 to 500 μM. Equilibrium modeling in this zone suggests that inorganic S(-II) plays the dominant role in both mobilization of sediment-bound Hg and complexation of dissolved Hg. In zone 2, FeS(s) precipitation occurs concomitant with Hg consumption. Net transfer within zone 3 is consistent with the potential for ligand-mediated Hg efflux across the SWI. S(-II)-mediated Hg mobilization at depth in Penobscot estuary sediments suggests a broadening of the depth interval over which biogeochemical Hg cycling must be examined. Our results also show that, while estuary sediments act as a net sink for particulate Hg inputs, they may also function for a considerable time interval as a source of dissolved Hg. 相似文献
322.
Anna Stevenson Jamie Pearce Tony Blakely Vivienne Ivory Karen Witten 《New Zealand geographer》2009,65(3):211-221
Over the past two decades, there has been a resurgence of interest into place‐based influences on health. Researchers have identified that various characteristics of neighbourhoods exert an influence on the health outcomes and behaviours of local residents. Understanding the processes linking places to health provides considerable potential for a range of policy interventions. We review the New Zealand‐based neighbourhoods and health research. Consideration is given to the types of neighbourhood characteristics, as well the range of health outcomes that have been studied. Finally, we suggest some priorities for further research into the mechanisms underpinning neighbourhood influences on health in New Zealand. 相似文献
323.
High‐resolution gravity cores and box cores from the North Icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foraminiferal data. Results from two outer shelf cores covering the last 13.6 k 14C yr BP are presented in this paper. The sediments accumulated in north–south trending basins on each side of the Kolbeinsey Ridge at water depths of ca. 400 m. Sedimentation rates up to 1.5 m kyr−1 are observed during the Late‐glacial and Holocene. The Vedde and Saksunarvatn tephras are present in the cores as well as the Hekla 1104. A new tephra, KOL‐GS‐2, has been identified and dated to 13.4 k 14C yr BP, and another tephra, geochemically identical to the Borrobol Tephra, has been found at the same level. At present, the oceanographic Polar Front is located on the North Icelandic shelf, which experiences sharp oceanographic surface boundaries between the cold East Icelandic Current and the warmer Irminger Current. Past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the Polar Front. The area was deglaciated before ca. 14 kyr BP, but there is evidence of ice rafting up to the end of the GS‐1 (Greenland Stadial 1, Younger Dryas) period, increasing again towards the end of the Holocene. Foraminiferal studies show a relatively strong GS‐2 (pre‐13 kyr BP) palaeo‐Irminger Current, followed by severe cooling and then by unstable conditions during the remainder of the GI‐1 (Greenland Interstadial 1, Bølling–Allerød) and GS‐1 (Younger Dryas). Another cooling event occurred during the Preboreal before the Holocene current system was established at about 9 kyr BP. After a climatic optimum between 9 and 6 kyr BP the climate began to deteriorate and fluctuate. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
324.
Dennis J. Geist Karen S. Harpp Terry R. Naumann Michael Poland William W. Chadwick Minard Hall Erika Rader 《Bulletin of Volcanology》2008,70(6):655-673
Sierra Negra volcano began erupting on 22 October 2005, after a repose of 26 years. A plume of ash and steam more than 13 km
high accompanied the initial phase of the eruption and was quickly followed by a ~2-km-long curtain of lava fountains. The
eruptive fissure opened inside the north rim of the caldera, on the opposite side of the caldera from an active fault system
that experienced an mb 4.6 earthquake and ~84 cm of uplift on 16 April 2005. The main products of the eruption were an `a`a flow that ponded in
the caldera and clastigenic lavas that flowed down the north flank. The `a`a flow grew in an unusual way. Once it had established
most of its aerial extent, the interior of the flow was fed via a perched lava pond, causing inflation of the `a`a. This pressurized
fluid interior then fed pahoehoe breakouts along the margins of the flow, many of which were subsequently overridden by `a`a,
as the crust slowly spread from the center of the pond and tumbled over the pahoehoe. The curtain of lava fountains coalesced
with time, and by day 4, only one vent was erupting. The effusion rate slowed from day 7 until the eruption’s end two days
later on 30 October. Although the caldera floor had inflated by ~5 m since 1992, and the rate of inflation had accelerated
since 2003, there was no transient deformation in the hours or days before the eruption. During the 8 days of the eruption,
GPS and InSAR data show that the caldera floor deflated ~5 m, and the volcano contracted horizontally ~6 m. The total eruptive
volume is estimated as being ~150×106 m3. The opening-phase tephra is more evolved than the eruptive products that followed. The compositional variation of tephra
and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2.1 km beneath the
caldera floor. 相似文献
325.
Cholwek Gary Bonde John Li Xing Richards Carl Yin Karen 《Marine Geophysical Researches》2000,21(5):409-421
To categorize spawning and nursery habitat for lake trout in Minnesota's near shore waters of Lake Superior, data was collected with a single beam echo sounder coupled with a RoxAnn bottom classification sensor. Test areas representative of the different bottom surficial substrates were sampled. The collected data consisted of acoustic signals which showed both depth and substrate type. The location of the signals was tagged in real-time with a DGPS. All data was imported into a GIS database. To better interpret the output signal from the RoxAnn, several pattern classifiers were developed by multivariate statistical method. From the data a detailed and accurate map of lake bed bathymetry and surficial substrate types was produced. This map will be of great value to fishery and other natural resource managers. 相似文献
326.
Harvey C. Perkins Michael Mackay Deborah Levy Malcolm Campbell Nick Taylor Raewyn Hills Karen Johnston 《New Zealand geographer》2019,75(3):140-151
We discuss case studies of three South Island small towns: Ashburton, Timaru and Oamaru and their wider local authority jurisdictions, focusing on how local stakeholders are defining the issues facing these places and identifying, prioritising and investing in regeneration initiatives, sometimes with the support of central government and other external agencies. Our key finding is that small‐town regeneration is complex, demands a long‐term local collaborative approach, and significant investment in skills, information sharing and programme development, some of which needs to be provided by external, central government, agencies. 相似文献
327.
Peter Jenniskens Jason Utas Qing‐Zhu Yin Robert D. Matson Marc Fries J. Andreas Howell Dwayne Free Jim Albers Hadrien Devillepoix Phil Bland Aaron Miller Robert Verish Laurence A. J. Garvie Michael E. Zolensky Karen Ziegler Matthew E. Sanborn Kenneth L. Verosub Douglas J. Rowland Daniel R. Ostrowski Kathryn Bryson Matthias Laubenstein Qin Zhou Qiu‐Li Li Xian‐Hua Li Yu Liu Guo‐Qiang Tang Kees Welten Marc W. Caffee Matthias M. M. Meier Amy A. Plant Colin Maden Henner Busemann Mikael Granvik 《Meteoritics & planetary science》2019,54(4):699-720
It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν6 resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance. 相似文献
328.
Russell D. Frew Paul F. Dennis Karen J. Heywood Michael P. Meredith Steven M. Boswell 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12)
The ratio of oxygen-18 to oxygen-16 (expressed as per mille deviations from Vienna Standard Mean Ocean Water, δ18O) is reported for seawater samples collected from seven full-depth CTD casts in the northern North Atlantic between 20° and 41°W, 52° and 60°N. Water masses in the study region are distinguished by their δ18O composition, as are the processes involved in their formation. The isotopically heaviest surface waters occur in the eastern region where values of δ18O and salinity (S) lie on an evaporation–precipitation line with slope of 0.6 in δ18O–S space. Surface isotopic values become progressively lighter to the west of the region due to the addition of 18O-depleted precipitation. This appears to be mainly the meteoric water outflow from the Arctic rather than local precipitation. Surface samples near the southwest of the survey area (close to the Charlie Gibbs Fracture Zone) show a deviation in δ18O–S space from the precipitation mixing line due to the influence of sea ice meltwater. We speculate that this is the effect of the sea ice meltwater efflux from the Labrador Sea. Subpolar Mode Water (SPMW) is modified en route to the Labrador Sea where it forms Labrador Sea Water (LSW). LSW lies to the right (saline) side of the precipitation mixing line, indicating that there is a positive net sea ice formation from its source waters. We estimate that a sea ice deficit of ≈250 km3 is incorporated annually into LSW. This ice forms further north from the Labrador Sea, but its effect is transferred to the Labrador Sea via, e.g. the East Greenland Current. East Greenland Current waters are relatively fresh due to dilution with a large amount of meteoric water, but also contain waters that have had a significant amount of sea ice formed from them. The Northeast Atlantic Deep Water (NEADW, δ18O=0.22‰) and Northwest Atlantic Bottom Waters (NWABW, δ18O=0.13‰) are isotopically distinct reflecting different formation and mixing processes. NEADW lies on the North Atlantic precipitation mixing line in δ18O–salinity space, whereas NWABW lies between NEADW and LSW on δ18O–salinity plots. The offset of NWABW relative to the North Atlantic precipitation mixing line is partially due to entrainment of LSW by the Denmark Strait overflow water during its overflow of the Denmark Strait sill. In the eastern basin, lower deep water (LDW, modified Antarctic bottom water) is identified as far north as 55°N. This LDW has δ18O of 0.13‰, making it quite distinct from NEADW. It is also warmer than NWABW, despite having a similar isotopic composition to this latter water mass. 相似文献
329.
Michael McFaul Karen Lynn Traugh Grant D. Smith William Doering Christian J. Zier 《Geoarchaeology》1994,9(5):345-374
Soil-sediment records and radiometric dating allow the development of environmental histories of three South Platte River alluvial terraces in the vicinity of Kersey, Colorado. These advocate a correlation with Holocene glacial records for the Colorado Front Range (Benedict, 1981, 1985). The archaeological potential of the Kersey fill, the Kuner strath, and the Hardin fill depends upon their age and sediment context. The oldest and most extensive terrace is the Kersey fill. The position of cultural components on the Kersey terrace implies an association of older Paleoindian sites (11,500–10,000 B.P.) with channel banks and bars on the terrace, younger Paleoindian sites (<10,000 B.P.) with terrace margins near the river, and Archaic and younger sites with eolian deposits on the terrace. An association of Clovis components with both Kersey alluvium and adjacent eolian dune fields indicates that eolian deposition began prior to 11,000 B.P. and that sediment availability influenced early Holocene eolian deposition. Examination of 150 cores and 75 backhoe test units along an 8-km study corridor demonstrates that Paleoindian sites are not as abundant on the Kersey terrace as previous researchers have proposed. Although the incision of the Kuner strath began earlier than 9600 B.P., we propose that its greatest potential is to yield cultural components that postdate ca. 7250 B.P. In turn, the Hardin fill may yield cultural components dating to the Kuner abandonment (ca. 6380 B.P.). However, Hardin sediment and soil records recommend that this fill terrace's highest potential is to yield in situ cultural components dating from ca. 1900 to 120 B.P. © 1994 John Wiley & Sons, Inc. 相似文献
330.
Numerical simulation of upwelling currents in pockmarks,and data from the Inner Oslofjord,Norway 总被引:5,自引:3,他引:2
The deflection of oceanic or tidal currents into pockmarks has been studied by both general three-dimensional computational
fluid dynamics simulations and acoustic measurements in a number of pockmarks in the Inner Oslofjord, Norway. The modeling
demonstrates upstream convergence of flow lines, followed by upwelling over the pockmark. This upwelling is an effect of deflected
regional currents, not of expulsion of fluids or gas from the seafloor, and is sufficiently strong to prevent the settling
of fine particles. The field measurements, although noisy at low vertical velocities, are consistent with the hypothesis of
upwelling. The reduction in sedimentation rate inferred over the pockmarks (relative to that of the flat surrounding seabed)
can explain the maintenance, or even deepening of pockmarks in the absence of fluid or gas seepage. The current pattern may
also have consequences for the marine biology of pockmarks. 相似文献