Sulphur cycling in organic-rich marine sediments from a Scottish fjord   总被引：1，自引：0，他引：1  

SIMON H. BOTTRELL  ROBERT J.G. MORTIMER  IAN M. DAVIES†  S. MARTYN HARVEY‡  MICHAEL D. KROM 《Sedimentology》2009,56(4):1159-1173

In this study, the biogeochemical transformations of sulphur in organic‐rich marine sediments in a Scottish fjord are investigated by a combination of pore water and sediment geochemistry with sulphide diffusive gradient thin‐film probes and sulphate isotopic data (δ³⁴S and δ¹⁸O). Particular attention is paid to sulphur cycling in the upper sediment profile where sulphate reduction occurs but free sulphide is below the detection limits of conventional pore water geochemical analysis but quantifiable by sulphide diffusive gradient thin film. In the uppermost part of the sediment core, δ¹⁸O sulphate decreased from near‐sea water values to +7‰, indicating that anoxic sulphide oxidation dominated during this interval. Sulphate δ³⁴S remained unchanged as there was no net sulphate reduction (i.e. reduction was balanced by re‐oxidation). Below 4 cm depth, there was a slight increase in sulphate δ³⁴S from 20‰ to 23‰ associated with minor accumulation of iron sulphide. The δ¹⁸O of the sulphate also increased, to around +10‰ at 10 cm depth, as a result of the isotopic exchange of sulphate–oxygen with pore water and/or sulphur disproportionation reactions mediated during sulphur cycling. These processes continued to increase the δ¹⁸O of the sulphate to 14‰ at 20 cm depth with no further change in the δ³⁴S of the sulphate. Below 20 cm depth, free sulphide is detectable in pore waters and both the δ³⁴S of the sulphate and sulphide increase with depth with an offset controlled by kinetic fractionation during bacterial sulphate reduction. The δ³⁴S of the sedimentary organic fraction shifted towards lower, more bacteriogenic, values with depth in the profile, without any increase in the size of this sulphur pool. Thus, the organic sulphur fraction was open to interaction with bacteriogenic sulphide without the occurrence of net addition. Therefore, caution should be exercised when using sulphur isotopic compositions to infer simple net addition of bacteriogenic sulphide to the organic sulphur fraction.  相似文献   

Geomorphology of the Himalaya: A Climato-Tectonic Framework     

IAN E. WHITEHOUSE 《New Zealand geographer》1990,46(2):75-85

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A mineral magnetic study of Holocene sedimentation in Lough Catherine, Northern Ireland     

IAN SNOWBALL  ROY THOMPSON 《Boreas: An International Journal of Quaternary Research》1990,19(2):127-146

A suite of 6 m long Mackereth cores collected from Lough Catherine, Northern Ireland, form the basis of a study of sediment accumulation rates throughout the Holocene. A data set produced by measuring the magnetic susceptibility, artificially induced remanent magnetisations and density of the sediment was used to correlate the cores by means of a sequence slotting algorithm. The resulting sediment accumulation pattern was dated by reference to previous¹⁴C and palynological studies. The interpretation of the magnetic logs was complicated by the authigenic formation of the magnetic mineral greigite (Fe₃S₄) and by magnetite dissolution discovered during a period of low sediment accumulation between the end of the Lateglacial period (10,100¹⁴C years B.P.) and the elm decline (5,200 B.P.). More traditional methods of core analysis based on sediment density and also new palynological studies were used to correlate sections of the cores where the magnetic results were least amenable to core matching on account of low downcore variability and low accumulation rate. The accumulation rate, a direct indication of catchment denudation, has accelerated fivefold during the Holocene. The sediment accumulation rate has increased most dramatically since the elm decline at 5,200 B.P., reflecting the increasing degree of human disturbance.  相似文献   

Carbonate cementation of some Pleistocene temperate marine sediments     

IAN M. WEST 《Sedimentology》1973,20(2):229-249

Carbonate cementation of some carbonate and quartz sands in three raised beaches of temperate origins was investigated. The carbonate of the cements was found to have been derived from the dissolution of skeletal debris. The sandstones, so produced, now possess only low-magnesium calcite, but the original sediments, like adjacent modern beach and blown sands, probably contained low-magnesium calcite, aragonite and some high-magnesium calcite, all of skeletal origin. In meteoric water the dissolution has occurred of all carbonate within minute, tubulelike, volumes of sand. Concurrent deposition in adjacent volumes of sand of low-magnesium calcite formed cements that are irregularly nodular or uneven on a small scale. Aragonite within the minute nodules has been replaced paramorphically by low-magnesium calcite. Additional local carbonate cements were formed at later dates, around and within solution pipes.  相似文献   

AEOLIAN BEDFORMS—THEIR DEVELOPMENT AND ORIGINS     

IAN G. WILSON 《Sedimentology》1972,19(3-4):173-210

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Sensitivity of the Southern Hemisphere SemiannualOscillation in surface pressure to changes in surface boundary conditions     

DAVID J. WALLAND  IAN H. SIMMONDS 《地球，A辑:动力气象学与海洋学》1998,50(4):424-441

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Source,timing, frequency and flux of ice‐rafted detritus to the Northeast Atlantic margin, 30–12 ka: testing the Heinrich precursor hypothesis     

ANNA I. HAAPANIEMI  JAMES D. SCOURSE  VICTORIA L. PECK  HILARY KENNEDY  PAUL KENNEDY  SIDNEY R. HEMMING  MARK F. A. FURZE  ANNA J. PIEŃKOWSKI  WILLIAM E. N. AUSTIN  JOHN WALDEN  EMILIE WADSWORTH  IAN R. HALL 《Boreas: An International Journal of Quaternary Research》2010,39(3):576-591

Haapaniemi, A.I., Scourse, J.D., Peck, V.L., Kennedy, H., Kennedy, P., Hemming, S.R., Furze, M.F.A., Pieńkowski, A.J., Austin, W.E.N., Walden, J., Wadsworth, E. & Hall, I.R. 2010: Source, timing, frequency and flux of ice‐rafted detritus to the Northeast Atlantic margin, 30–12 ka: testing the Heinrich precursor hypothesis. Boreas, Vol. 39, pp. 576–591. 10.1111/j.1502‐3885.2010.00141.x. ISSN 0300‐9483. Increased fluxes of ice‐rafted detritus (IRD) from European ice sheets have been documented some 1000–1500 years before the arrival of Laurentide Ice Sheet (LIS)‐sourced IRD during Heinrich (H) events. These early fluxes have become known as ‘precursor events’, and it has been suggested that they have mechanistic significance in the propagation of H events. Here we present a re‐analysis of one of the main cores used to generate the precursor concept, OMEX‐2K from the Goban Spur covering the last 30 ka, in order to identify whether the British–Irish Ice Sheet (BIIS) IRD fluxes occur only as precursors before H layers. IRD characterization and planktonic foraminiferal δ¹⁸O measurements constrained by a new age model have enabled the generation of a continuous record of IRD sources, timing, frequency and flux, and of local contemporary hydrographic conditions. The evidence indicates that BIIS IRD precursors are not uniquely, or mechanistically, linked to H events, but are part of the pervasive millennial‐scale cyclicity. Our results support an LIS source for the IRD comprising H layers, but the ambient glacial sections are dominated by assemblages typical of the Irish Sea Ice Stream. Light isotope excursions associated with H events are interpreted as resulting from the melting of the BIIS, with ice‐sheet destabilization attributed to eustatic jumps generated by LIS discharge during H events. This positive‐feedback mechanism probably caused similar responses in all circum‐Atlantic ice‐sheet margins, and the resulting gross freshwater flux contributed to the perturbation of the Atlantic Meridional Overturning Circulation during H events.  相似文献   

Interglacial intensity in the North Atlantic over the last 800 000 years: investigating the complexity of the mid‐Brunhes Event     

IAN CANDY  ERIN L. MCCLYMONT 《第四纪科学杂志》2013,28(4):343-348

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Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments     

JOHAN STRIBERGER  SVANTE BJÖRCK  ÓLAFUR INGÓLFSSON  KURT H. KJÆR  IAN SNOWBALL  CINTIA B. UVO 《Boreas: An International Journal of Quaternary Research》2011,40(1):28-45

Striberger, J., Björck, S., Ingólfsson, Ó., Kjær, K. H., Snowball, I. & Uvo, C. B. 2010: Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments. Boreas, 10.1111/j.1502‐3885.2010.00153.x. ISSN 0300‐9483. Properties of varved sediments from Lake Lögurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajökull, an outlet glacier of the Vatnajökull icecap, were examined. A varve chronology, which covers the period AD 1262–2005, was constructed from visual observations, high‐resolution images, X‐ray density and geochemical properties determined from X‐radiography and X‐ray fluorescence scanning. Independent dating provided by ¹³⁷Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark‐coloured seasonal laminae, formed mainly of coarser suspended matter from the non‐glacial river Grímsá, is positively correlated (r=0.70) with winter precipitation, and our 743‐year‐long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light‐coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jökulsáí Fljótsdal, increased significantly during the AD 1972 surge of Eyjabakkajökull. As a consequence of the surge, the ice‐dammed Lake Háöldulón formed and recurrently drained and delivered significant amounts of rock flour to Lake Lögurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light‐coloured laminae in the sediment record, we suggest that Eyjabakkajökull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.  相似文献   

Reconstructions of western Ross Sea palaeo-ice-stream grounding zones from high-resolution acoustic stratigraphy     

IAN M. HOWAT  EUGENE W. DOMACK 《Boreas: An International Journal of Quaternary Research》2003,32(1):56-75

This study analyses acoustic profiles of two mid-shelf troughs, the JOIDES Basin and Pennell Trough in the western Ross Sea, Antarctica. These troughs are subglacial erosion features formed by repeated advance of streaming ice onto the Ross Sea continental shelf. Sediment wedge formations, interpreted to have been deposited at the most seaward grounding zone during the Last Glacial Maximum (LGM), are observed within the mid-shelf region of these troughs. By correlating high-resolution acoustic profiles with core samples, we resolve the stratigraphy of these wedge formations to assess the relationships between bathymetry, subglacial sediment distribution and palaeo-ice-stream configuration. The grounding zone wedge geometries were controlled by the pre-existing topography. The JOIDES and Pennell Troughs were only partially infilled during the LGM. Axial diamict progradation from the landward margin of the troughs indicates enhanced flow (debris supply) along the axis of ice flow. Differences in grounding zone geometries indicate a decrease in basal debris deposition and/or supply during ice recession. The lack of a recessional ice-shelf facies indicates that either the ice shelf was absent during retreat, or that there was no melt-out of basal debris.  相似文献