Glacial rapid variability in deep-water temperature and δO from the Western Mediterranean Sea

Deep-water temperatures (DWTs) from the Western Mediterranean Sea are reconstructed for the last 50 ka based on the analysis of Mg/Ca ratios in benthic foraminifera from core MD95-2043 collected in the Alboran Sea. The exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the Dansgaard–Oeschger (D–O) rapid climatic variability. The applicability of Mg/Ca thermometry in the Western Mediterranean Deep-Water mass (WMDW) is first tested by the analysis of different benthic species in a collection of Mediterranean core tops. The results indicate the need of a readjustment of the existing Cibicidoides spp. calibrations in order to reconstruct present Western Mediterranean DWT values (12.7 °C). Different physiological effects in the Mg uptake between the C. pachydermus living in different regions could account for this offset in the Mediterranean samples. Consequently, the obtained DWT record still has many uncertainties in absolute terms but trends provide valuable information on past changes in WMDW conditions. The DWT record shows significant oscillations in relation to the D–O cycles, colder values occurred during the time of D–O stadials and warmer ones during D–O interstadials. Surprisingly, the coldest DWTs occurred during the time of Heinrich Event 4 (HE4) and not during the Last Glacial Maximum (LGM) when DWTs were mostly warm. These and other particular features of the DWT reconstruction mimic changes in the vegetation from the Eastern Mediterranean indicating the control of the Mediterranean climate on the DWT record. Paired analyses of Mg/Ca and δ¹⁸Occ (calcite δ¹⁸O) provide the opportunity to reconstruct deep-water δ¹⁸O (δ¹⁸Odw) and past salinities and hence changes in past WMDW density. Due to the large error associated with these calculations, they can only be discussed in terms of relative changes between different intervals. The results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early Holocene in relation to the δ¹⁸Odw conditions present today. Densest WMDW were formed during most of Marine Isotopic Stage (MIS) 2 and during the D–O Stadials not associated with HEs, while lightest WMDW dominated during D–O Interstadials. The δ¹⁸Odw record shows a D–O variability pattern likely controlled by changes in the composition and intensity of the local run-off and also to changes in the δ¹⁸Ow signal of the Atlantic inflow. Changes in the residence time of the Mediterranean waters, governed by the global sea level, are also considered to exert an important role governing Mediterranean δ¹⁸Ow and salinity, particularly during MIS 2. Overall, our results are consistent with the formation of dense WMDW during D–O stadials and even denser during most of MIS 2.     

Deposition of semi-volatile organochlorine compounds in the free troposphere of the eastern North Atlantic Ocean

Deposition samples were taken at a height of 2367 m above sea level (m.a.s.l.) on the Island of Tenerife from May 1999 until July 2000 and analysed for 19 polychlorinated biphenyl (PCB) congeners, hexachlorobenzene (HCB), hexachlorocyclohexanes (HCH) and DDTs. This site is located above the inversion layer, so samples represent background concentrations of the free troposphere. The average deposition fluxes of HCB, total HCH, DDTs and PCBs were 86, 400, 110 and 780 ng m(-2) yr(-1), respectively, being lower than those reported at sea level in continental or marine areas. All compounds are generally found in higher abundance in the wet precipitation samples. However, these samples only represent a fraction, e.g. 33%, of the total deposition load. Annual mass balance calculations show that wet precipitation is essentially responsible for the deposition of the low molecular weight OC whereas dry deposition accounts for more than 50% of the higher molecular weight PCBs.     

Phase relationship between sea level and abrupt climate change

Direct traces of past sea levels are based on the elevation of old coral reefs at times of sea level highstands. However, these measurements are discontinuous and cannot be easily correlated with climate records from ice cores. In this study we show a new approach to recognizing the imprint of sea level changes in continuous sediment records taken from the continental slope at locations that were continuously submerged, even during periods of sea level lowstand. By using a sediment core precisely synchronized with Greenland ice cores, we were able to recognize major floods of the Mediterranean continental shelf over the past 270 kyr. During the last glacial period five flooding events were observed at the onset of the warmest Greenland interstadials. Consistent correspondence between warm climate episodes and eustatic sea level rises shows that these global flooding events were generated by pronounced melting of the Northern Hemisphere ice sheets, due to rapid intensification of Atlantic Meridional Overturning Circulation.The method described in this study opens a new perspective for inter-hemispheric synchronization of marine climate records if applied in other continental margins from the Southern Hemisphere or the equatorial regions.     

Review on Tidal Energy Technologies and Research Subjects

Tidal current power is one of the promising and reliable renewable energies with the advantage of continuous and predictable resource. It can make stable electricity regardless of weather conditions or seasons all year around. The required technologies for tidal current power in the ocean have been developed for years and now recognized that it could be commercialized after intensive field tests and successful demonstrations. There are several tidal farm development projects in the world, such as the MeyGen project in UK with its commercialization at hand. However, various research subjects in the tidal current energy field are seeking improvements and industrialization of tidal current power in terms of economy and technical reliability. This paper introduces the resource assessment procedure of tidal energy that has been applied in Korea coastal regions. The key research subjects for tidal current power together with the interaction effect of multi-arrangement is described. Also, this paper is to introduce the research output of each subject such as turbine design, experimental validation, turbine interaction and wake, multi-array module, FSI (fluid-structure interaction), and duct application.     

Amino acid composition of sediments from a deltaic environment

Nineteen amino acids in sediments from the Ebro Delta (Spain) have been determined by HPLC. According to quantitative and qualitative data it is suggested that the distributions reflect organic autochthonous contributions and are constrained by environmental conditions of deposition.In the more reducing areas (8.7–11.6 mg total amino acids/g of dry sediment) hydroxyproline, threonine, glycine and glutamic acid are the major amino acids, while in the off-shore stations (1.0–2.7 mg total amino acids/g of dry sediment) ornithine, lysine, phenylalanine, serine and valine are dominant. In these samples absolute concentrations decrease with water depth.The analysis of two cores has shown that sulfur-containing and neutral branched-chain amino acids are the least resistant to geochemical degradation. Within the basic fraction, which appeared to be the most stable, ornithine is produced geochemically and preferentially in the more oxic sediments.     

Palaeoclimatic signals recognized by chemometric treatment of molecular stratigraphic data

The high-resolution stratigraphy of various marker compounds has been studied, using GC, HPLC and GC-MS, in a 13 m gravity core recovered from the Kane Gap region, eastern equatorial Atlantic, which provides a record of the glacial/interglacial episodes over the last million years. Downhole variations in many presumed source-specific components are observed (e.g. in n-alkanes from terrigenous land plants and dinosterol from dinoflagellates), which may be due to perturbations or cyclicities resulting from climatic change. Fluctuations in the unsaturation of alkenones attributable to variations in water temperatures show correlations with the glacial/interglacial cycles recorded in the δ¹⁸O values for planktonic foraminifera, thereby providing a potential organic geochemical measure of past climates. These molecular abundance data can be linked to the palaeotemperature record, following computer treatments using principal component and spectral analyses. Molecular stratigraphy shows promise as a new chemostratigraphical tool where other means of stratigraphy fail, for example, through calcium carbonate dissolution.     

Cyclic terpenoids of contemporary resinous plant detritus and of fossil woods, ambers and coals

Cyclic terpenoids present in the solvent extractable material of fossil woods, ambers and brown coals have been analyzed. The sample series chosen consisted of wood remains preserved in Holocene to Jurassic sediments and a set of of ambers from the Philippines (copalite), Israel, Canada and Dominican Republic. The brown coals selected were from the Fortuna Garsdorf Mine and Miocene formations on Fiji.The fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons, and aromatized species were present at high concentrations, with a major amount of two-ring aromatic compounds. Tricyclic diterpenoids were the predominant compounds in the ambers. Aromatized derivatives were the major components, consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons. The saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon (C₁, C₂, etc.) substituents. Kaurane and phyllocladane isomers were present in only minor amounts. Bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples, but only traces of sesterterpenoids and triterpenoid derivatives were found.The brown coal extracts were composed of major amounts of one- and two-ring aromatized terpenoids, with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers. This was especially noticeable for the German coal, where the triterpenoids were predominant. Open C-ring aromatized structures were also present in this coal. Steroid compounds were not detectable, but some hopanes were found as minor components in the German brown coal.An overview of the skeletal structure classes identified in each sample, as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper. It can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis, constituting a general pathway for all terpenoids.     

Application of the Mussel Watch concept in studies of the distribution of hydrocarbons in the coastal zone of the Ebro Delta

The Mussel Watch concept was applied in a study of man-induced chemical changes in the Ebro Delta on the Catalonian coast to obtain a preliminary assessment of the distribution of synthetic organic compounds, petroleum and biogenic hydrocarbons in the local coastal zone. Mussels, oysters and clams were selected as the indicator organisms. Levels of petroleum accumulated by mussels were generally high, in the order of 100–800 μg^?1 dry weight, equivalent to those in mussels in the most polluted harbours and bays of California. The relative distributions of the steranes and pentacyclic triterpanes in the mussels were significantly different from those found in petroleum from a local field, indicating that local petroleum was not contributing to the present contamination. The composition of biogenic compounds was variable, probably reflecting differences in the composition of local plankton communities, PCB levels were high in relation to current levels in mussels from US sites, reflecting continuing PCB use in Spain. The Delta appears to be a point source of a number of organochlorine compounds, including HCB, the DDT compounds, endrin and γ-chlordane. Levels of the DDT compound o,p′-DDD, a pharmacologically active substance, were unexpectedly high; identification was confirmed by GS/MS. Many unidentified peaks were present on EC chromatograms, indicating a more complex pattern of contamination than might be suggested by printed summaries of data.     

An allostratigraphic approach to a non-marine basin: the north-western part of Cretaceous Kyongsang Basin, SE Korea

The north-western part of the Cretaceous Kyongsang Basin, south-east Korea, comprises alluvial deposits of conglomerate, gravelly sandstone, sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities. The discontinuities trend NW–SE and are marked by distinct facies transitions, abrupt emplacement of conglomerate and thin but persistent mudstone beds. Sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south-east with alluvial fans on the northern margin. Each allomember can be characterized by distinctive architecture of channel-fills, clast composition of conglomerate and sandstone/mudstone ratio. Successive units show an eastward shift in the locus of deposition, suggesting basinward relocations of alluvial systems. Such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution, probably caused by fault movements. This study shows that detailed mapping, combined with architectural analysis, and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin.