Study of radionuclides, lead and lead isotope ratios in Scottish sea loch sediments

This research involved the study of sediment cores from Loch Etive, Loch Long, Loch Goil and Loch Fyne with the aims of investigating the geochemistry of natural, and manmade radionuclides and heavy metals within the sea loch environment. The main aims of the research were to determine accumulation rates and the extent of mixing within these sediments and to assess the fluxes, sources and temporal variations in input of pollutant heavy metals to these environments. In recent years it has been suggested that Pb is mobile in sea loch sediments which questions the validity of applying ²¹⁰Pb dating in this environment. This has important implications with respect to interpreting sediment cores to assess temporal trends of pollutant inputs and investigating the rates of physical and biogeochemical processes that are taking place in the coastal environment. Hence, one of the aims of this research was to determine whether Pb was mobile in these sediments. The ²⁰⁶Pb/²⁰⁷Pb isotope ratio can potentially be used to determine the extent of pollutant Pb input from leaded petrol to the environment and a further objective of the work was to investigate the isotopic signature of pollutant Pb in the sediment. Concentration of ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³⁸U, ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am in the sediments were analysed using gamm a spectroscopy and the heavy metals, Pb, Zn and Cu were determined using X-ray Fluorescence. Stable Pb isotope ratios were determined using Inductively coupled plasma Mass spectrometry. The results obtained indicated that Pb is not subject to diagenetic mobility in these sediments and that ²¹⁰Pb profiles can be used to determine sedimentation rates for most of the sediment cores. lt was not possible to determine accumulation rates for the two cores from Loch Fyne by ²¹⁰Pb dating, and in this case the sedimentation rate was assessed by correlating the maximum concentration of ¹³⁷Cs in the sediments with the maximum ¹³⁷Cs discharge from Sellafield, BNFL's reprocessing plant located on the Cumbrian coast. The flux of ²¹⁰Pb to the lochs varied significantly suggesting that there has been sediment focusing of fine and/or organic rich material to the deeper sites, resulting in an enhanced flux of ²¹⁰Pb to these sediments. Sellafield waste radionuclides also provided useful chronologies by relating sediment maximum concentrations to maxima in the discharges. ¹³⁷Cs was observed to be subject to diffusive movement, invalidating the use of its total depth of penetration as a chronological indicator. The temporal trends of pollutant metal input agreed well with known historical trends and the Pb isotope profiles indicated that the onset of deposition from pollutant Pb from petrol occurred in the late 1920's. The maximum input of Pb from petrol peaked in the early 1980's and since then there has been a decrease in this input. The two sea lochs which were closest to the industrial centre of Glasgow exhibited a large anthropogenic pollutant input, confirming that these sediments have been highly perturbed by human activities, either directly as a result of sludge dumping or due to changes in land use (eg. road construction, deforestation, etc.) in the catchment. All the sea lochs reflected a change in the supply of material to the sediments over the last eighty years, indicating that increased anthropogenic activity has had an effect on these environments

Processes controlling the geochemical composition of the South China Sea sediments during the last climatic cycle

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 257 (2008): 240-246, doi:10.1016/j.chemgeo.2008.10.002.Sediments of the upper 28.2 meters of Ocean Drilling Program (ODP) Site 1145 from the northern South China Sea (SCS) were analyzed for their geochemical composition. Most of the major and trace elements exhibit significant fluctuations at glacial-interglacial scales, implying a close relation with regional and global climate change. Al-normalized elemental ratios can be subdivided into three principal components (PC). PC1 (e.g., Ca/Al, Ba/Al, Sr/Al) displays significant glacial-interglacial variation and is related to paleoproductivity in the northern SCS. PC2 (e.g., K/Al, Mg/Al, Rb/Al) is associated with the degree of chemical weathering in the source regions and shows little glacial-interglacial variation. PC3 (e.g., Ti/Al, Zr/Al) reflects the relative contribution of coarse- and fine-grained materials in the terrigenous components of the SCS sediments, likely associated with changes in sea level and monsoon-induced fluvial input. Spectral analyses indicate that paleoproductivity (i.e., Ba/Al) in the South China Sea lags Hulu/Sanbao speleothem δ18O record (a indicator of annual average meteoric precipitation) by 102° and Indian summer monsoon (multi-proxy stack) by 23° at the precession band, indicating a close relationship with the Indian summer monsoon. However, the chemical weathering degree in the source area (PC2) is not sensitive to monsoon-related changes at the precession band during the last climatic cycle.This study was supported by the NSFC to Y.B. Sun and the US NSF to D.W. Oppo (OCE 0502960) and S.C. Clemens (OCE 0352215)

Lower export production during glacial periods in the equatorial Pacific derived from (231Pa/230Th)xs,0 measurements in deep-sea sediments

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 19 (2004): PA4023, doi:10.1029/2003PA000994.The (231Pa/230Th)xs,0 records obtained from two cores from the western (MD97-2138; 1°25′S, 146°24′E, 1900 m) and eastern (Ocean Drilling Program Leg 138 Site 849, 0°11.59′N, 110°31.18′W, 3851 m) equatorial Pacific display similar variability over the last 85,000 years, i.e., from isotopic stages 1 to 5a, with systematically higher values during the Holocene, isotopic stage 3, and isotopic stage 5a, and lower values, approaching the production rate ratio of the two isotopes (0.093), during the colder periods corresponding to isotopic stages 2 and 4. We have also measured the 230Th-normalized biogenic preserved and terrigenous fluxes, as well as major and trace elements concentrations, in both cores. The (231Pa/230Th)xs,0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial Pacific during glacial periods. The (231Pa/230Th)xs,0 variations in the western equatorial Pacific also seem to be controlled by productivity (carbonate and/or opal). The generally high (231Pa/230Th)xs,0 ratios (>0.093) of the profile could be due to opal and/or MnO2 in the sinking particles. The profiles of (231Pa/230Th)xs,0 and 230Th-normalized fluxes indicate a decrease in exported carbonate, and possibly opal, during isotopic stages 2 and 4 in MD97-2138. Using 230Th-normalized flux, we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability.SP funding for this research was provided by grants from the French Minister of Research and a EURODOC grant of the Re´gion Rhoˆne-Alpes (SAFIR-980065327). SP also gratefully acknowledges the financial support of the WHOI Geology and Geophysics Dept. This work was also supported by a CNRS-NSF grant (SP and KWWS). The contribution of JFM to this study was supported in part by the US NSF and by WHOI OCCI and Mellon awards

Is pore water oxygen content decoupled from productivity on the California Margin? Trace element results from Ocean Drilling Program Hole 1017E, San Lucia slope, California

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95250/1/palo1223.pd

Ecological Role of Submarine Canyons and Need for Canyon Conservation: A Review

Submarine canyons are major geomorphic features of continental margins around the world. Several recent multidisciplinary projects focused on the study of canyons have considerably increased our understanding of their ecological role, the goods, and services they provide to human populations, and the impacts that human activities have on their overall ecological condition. Pressures from human activities include fishing, dumping of land-based mine tailings, and oil and gas extraction. Moreover, hydrodynamic processes of canyons enhance the down-canyon transport of litter. The effects of climate change may modify the intensity of currents. This potential hydrographic change is predicted to impact the structure and functioning of canyon communities as well as affect nutrient supply to the deep-ocean ecosystem. This review not only identifies the ecological status of canyons, and current and future issues for canyon conservation, but also highlights the need for a better understanding of anthropogenic impacts on canyon ecosystems and proposes other research required to inform management measures to protect canyon ecosystemsVersión del edito

A new vision of ocean biogeochemistry after a decade of the Joint Global Ocean Flux Study (JGOFS)

The Joint Global Ocean Flux Study (JGOFS) has completed a decade of intensive process and time-series studies on the regional and temporal dynamics of biogeochemical processes in five diverse ocean basins. Its field program also included a global survey of dissolved inorganic carbon (DIC) in the ocean, including estimates of the exchange of carbon dioxide (CO2) between the ocean and the atmosphere, in cooperation with the World Ocean Circulation Experiment (WOCE). This report describes the principal achievements of JGOFS in ocean observations, technology development and modelling. The study has produced a comprehensive and high-quality database of measurements of ocean biogeochemical properties. Data on temporal and spatial changes in primary production and CO2 exchange, the dynamics of of marine food webs, and the availability of micronutrients have yielded new insights into what governs ocean productivity, carbon cycling and export into the deep ocean, the set of processes collectively known as the "biological pump." With large-scale, high-quality data sets for the partial pressure of CO2 in surface waters as well for other DIC parameters in the ocean and trace gases in the atmosphere, reliable estimates, maps and simulations of air-sea gas flux, anthropogenic carbon and inorganic carbon export are now available. JGOFS scientists have also obtained new insights into the export flux of particulate and dissolved organic carbon (POC and DOG), the variations that occur in the ratio of elements in organic matter, and the utilization and remineralization of organic matter as it falls through the ocean interior to the sediments. JGOFS scientists have amassed long-term data on temporal variability in the exchange of CO2 between the ocean and atmosphere, ecosystem dynamics, and carbon export in the oligotrophic subtropical gyres. They have documented strong links between these variables and large-scale climate patterns such as the El Nino-Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO). An increase in the abundance of organisms that fix free nitrogen (N-2) and a shift in nutrient limitation from nitrogen to phosphorus in the subtropical North Pacific provide evidence of the effects of a decade of strong El Ninos on ecosystem structure and nutrient dynamics. High-quality data sets, including ocean-color observations from satellites, have helped modellers make great strides in their ability to simulate the biogeochemical and physical constraints on the ocean carbon cycle and to extend their results from the local to the regional and global scales. Ocean carbon-cycle models, when coupled to atmospheric and terrestrial models, will make it possible in the future to predict ways in which land and ocean ecosystems might respond to changes in climate