ALBERT

Description: An idealized numerical model of the tropical Atlantic Ocean is used to study the structure, energetics and heat flux of the Atlantic tropical instability waves (TIWs). The model results compare well with the observations, and they both show that, unlike commonly assumed, the TIWs in the Atlantic exist on both sides of the equator and are generated not only in the summer but from May to January. Furthermore it is demonstrated that the Atlantic TIWs are generated by barotropic instability of the shear between the equatorial undercurrent and the northern south equatorial current and make a surprisingly small contribution to the heat budget of the equatorial mixed layer. The model results reveal that the often published strong meridional heat flux divergence of the TIWs is largely compensated for by their vertical heat flux divergence.

Description: Estimates of significant wave height and period, together with tidal current speed over a semi-lunar cycle, were used to predict the area on the Australian continental shelf over which unconsolidated sediment was mobilised (threshold exceedance). These sediment-entraining processes were examined independently to quantify their relative importance on the continental shelf. Using observed grain size data, mobilisation from swell waves occurred on ∼31% and tidal currents on ∼41% of the continental shelf. Swell wave energy is sufficient to mobilise fine sand (0.1 mm diameter) to a water depth of 142 m on the Otway Shelf near the western entrance to Bass Strait. Tidal currents in King Sound (northwest shelf) are capable of mobilising large areas of medium sand (0.35 mm diameter) 100% of the time. Superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave-induced or tidal currents dominate, some areas where waves and tides are of relatively equal importance and still other areas where neither is significant. We define six shelf regions of relative wave and tidal energy: zero (no-mobility); waves-only, wave-dominated, mixed, tide-dominated and tides-only. Our results provide a predictive, process-based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor.

Description: The majority of squid families (Teuthoidea: Cephalopoda) exchange sodium for ammonium, creating a low-density fluid that imparts lift for neutral buoyancy. However, previous methods for measuring ammonium did not distinguish between NH4+ and various other amine compounds. The present study, using single column ion chromatography, reassessed the cation concentrations in several midwater cephalopod species. High NH4+ levels were confirmed for histioteuthid, cranchiid, and chiroteuthid and related squids. A strong relationship is reported between ammonium content and body mass in Histioteuthis heteropsis, suggesting a gradual accumulation of ammonium coincident with an ontogenetic migration to greater depths. The bathypelagic squids Bathyteuthis abyssicola and Bathyteuthis berryi, on the other hand, contained very little ammonium but rather contained large quantities of an as yet unidentified cation. The ecological significance of this compound is not yet known. Morphology in Bathyteuthid squids suggests that the unknown cation is contained intracellularly and so, unlike sequestered ammonia, does not diminish the space available for muscle tissue. Accordingly, protein measurements in B. berryi mantle muscle are on par with shallower-living muscular squids, and in situ submersible observations reveal strong locomotory abilities relative to other deep-water squids.

Description: Mud extrusion is frequently observed as a dewatering phenomenon in compressional tectonic settings such as subduction zones. Along the Middle American Trench, several of these features have been recently discovered. This paper presents a heat flow study of actively venting Mound Culebra, offshore Nicoya Peninsula, and is complemented by data from geophysical surveys and coring. The mud diapir is characterised by methane emission and authigenic carbonate formation at its crest, and is composed of overconsolidated scaly clays and clast-bearing muds. Compared with the conductive background heat flow, the flux through the mud dome is elevated by 10–20 mW/m2, possibly related to advection of heat by fluids rising from greater depth. Decreased chlorinity in the pore waters from gravity cores may support a deep-seated fluid origin. Geothermal measurements across the mound and temperature measurements made with outriggers on gravity corers were corrected for the effects of thermal refraction, forced by the topography of the mound. Corrected values roughly correlate with the topography, suggesting advection of heat by fluids rising through the mound, thereby generating the prominent methane anomaly over the dome and nurturing vent biota. However, elevated values occur also to the southeast of the mound. We believe that the overconsolidated clays and carbonates on the crest form an almost impermeable lid. Fluids rising from depth underneath the dome are therefore partially channelled towards the flanks of the mound.

Description: Recent trawling in the Southern Ocean has yielded an unusual and relatively large collection of deep-sea octopods, comprising four species in two genera. Several deep-sea genera, which are inadequately characterised, have been reported previously from the Southern Ocean. Within this paper, all the relevant historical type material has been examined and a full revision has been undertaken. Species previously considered to be representative of the genus Bentheledone have either been moved to Thaumeledone or are considered nomen dubium. A revised diagnosis of Thaumeledone is provided together with redescriptions of its Southern Ocean species as well as a description of a new species. A new genus has been erected to accommodate the remainder of the new specimens.

Description: The sediment composition of deep-sea cores from the central Arctic Ocean, the Fram Strait, and the Yermak Plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200,000 years. Layers with high amounts of coarse, terrigenous ice-rafted debris (IRD) and often high contents of smectite were deposited during extensive glaciations in northern Eurasia, when ice sheets reached the northern continental margins of the Barents and Kara seas and discharged icebergs into the Arctic Ocean. Intercalated layers with relatively low IRD and smectite contents, but abundant planktic foraminifers in the coarse fraction were deposited during periods of Atlantic Water inflow to the Arctic Ocean and seasonally open waters (leads) in a sea ice cover with only few icebergs in the Arctic Ocean. High IRD contents in the sediments reflect the presence of ice sheets on the Kara and Barents seas shelves and the hinterland during the entire oxygen isotope stage 6 (ca 190–130 ka), in substage 5b (ca 90–80 ka), at the stage boundary 5/4 (around 75 ka), and in late stage 4/early stage 3 (ca 65–50 ka). These results are in excellent correlation with those from recent field work in northern Scandinavia, European Russia, Siberia, and on the shelves. Relatively low amounts of IRD in central Arctic Ocean sediments from the Late Weichselian glacial maximum (ca 24–18 ka) correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time. Oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the Arctic Ocean. The synchroneity of freshwater events and IRD input suggests a common source. Strongest events were associated with deglaciations of the Barents and Kara seas after the ice sheets had blocked the outflow of large rivers for several millennia. The outflow of freshwater from large ice-dammed lakes occurred at ca 130, 80–75, and 52 ka. Freshwater events in the central Arctic Ocean during the last deglaciation (ca 18 ka) were relatively small compared to the previous events. This indicates that during most of the Late Weichselian glacial maximum a river outflow from northern Siberia to the Arctic Ocean was possible. Atlantic Water inflow to the Arctic Ocean and seasonally open waters in the ice (leads) occurred during the interglacials ofoxygen isotope stage 1 and substage 5e, during several interstadials (stage 3, substages 5a and 5c), and to a lesser degree within stadials and glacials (stages 2, 4, and 6). With the exception ofthe interglacials, these periods were times ofstrong ice growth on the continents as revealed by terrestrial data. The coincidence suggests that open waters in the Arctic Ocean and the Nordic Seas were an important moisture source (in addition to more southerly sources) which fostered the growth of ice sheets on northern Eurasia.

Description: Repeated hydrographic observations between 1996 and 2001 of the deep water mass distribution on four sections in the western Labrador Sea and northwestern North Atlantic at about 56°N, 53°N, 48°N and 43°N show significant changes in the water mass characteristics. These changes are spreading southward mainly with the Deep Western Boundary Current (DWBC). Shallower convection forms a convective water mass known as upper Labrador Sea Water (ULSW). During periods of deep convection in the Labrador Sea, ULSW was described to be formed in the western boundary current region. In the post deep convection period 1996 to 2001 ULSW was formed in the western and central Labrador Sea and spreads mainly westward towards and along the western boundary. At 53°N ULSW moves southward as a part of the deep Labrador Current, also constituting the upper part of the DWBC. In the early 1990s the deep convection produced a large volume of deep Labrador Sea Water (LSW) which filled intermediate layers of the central region of the Labrador Sea. After these years the convection became weaker, with no apparent LSW renewal in 1996, partial mixing down to 1500 m in 1997 and no notable LSW formation between 1998 and 2001. At the southwestern exit of the Labrador Sea at 53°N the deep LSW in 2001 was least in thickness and highest in salinity and temperature compared to the years since 1996. This reflects restratification which resulted in an increase in the density stratification between 1000 and 2000 m in the central Labrador Sea as well as year-to-year transformation of the LSW core. LSW passes 43°N off the Grand Banks about 1 to 2 years after it was first seen at 56°N. At the 48°N and 43°N sections the northward flowing North Atlantic Current (NAC), farther offshore than the DWBC, complicates the property distributions. Saltier and warmer LSW recirculates northward with the NAC at 43°N. Between 1996 and 2001 the Gibbs Fracture Zone Water (GFZW) turned colder and fresher. The Denmark Strait Overflow Water (DSOW) showed two periods of cooling and freshening, separated by an abrupt (rapid) increase in temperature and salinity within a year. The arrival time of this increase at the different locations implies a DSOW spreading time that is no more than two years from 56°N to 43°N near the western boundary, or four years from the sill of the Denmark Strait to the Grand Banks.

Description: Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe–Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe–Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ϵ205Tl greater than +2.5, whereas anoxic sediments have ϵ205Tl of less than −1.5 (ϵ205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ϵ205Tl values of oxic sediments probably reflect authigenic Fe–Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe–Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe–Mn crusts distributed globally (ϵ205Tl=+12.8±1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe–Mn crusts that are older than 25 Ma show a systematic increase of ϵ205Tl with decreasing age, from about +6 at 60–50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ϵ205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time.

Description: Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (〈5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°×1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.

Description: Ostracods secrete their valve calcite within a few hours or days, therefore, its isotopic composition records ambient environmental conditions of only a short time span. Hydrographic changes between the calcification of individuals lead to a corresponding range (max.–min.) in the isotope values when measuring several (≥5) single valves from a specific sediment sample. Analyses of living (stained) ostracods from the Kara Sea sediment surface revealed high ranges of 〉2‰ of δ18O and δ13C at low absolute levels (δ18O: 〈3‰, δ13C: 〈−3‰) near the river estuaries of Ob and Yenisei and low ranges of ∼1‰ at higher absolute levels (δ18O: 2–5.4‰, δ13C: −3‰ to −1.5‰) on the shelf and in submarine paleo-river channels. Comparison with a hydrographic data base and isotope measurements of bottom water samples shows that the average and the span of the ostracod-based isotope ranges closely mirror the long-term means and variabilities (standard deviation) of bottom water temperature and salinity. The bottom hydrography in the southern part of the Kara Sea shows strong response to the river discharge and its extreme seasonal and interannual variability. Less variable hydrographic conditions are indicative for deeper shelf areas to the north, but also for areas near the river estuaries along submarine paleo-river channels, which act as corridors for southward flowing cold and saline bottom water. Isotope analyses on up to five single ostracod valves per sample in the lower section (8–7 cal. ka BP) of a sediment core north of Yenisei estuary revealed δ18O and δ13C values which on average are lower by 0.6‰ in both, δ18O and δ13C, than in the upper core section (〈5 cal. ka BP). The isotope shifts illustrate the decreasing influence of isotopically light river water at the bottom as a result of the southward retreat of the Yenisei river mouth from the coring site due to global sea level rise. However, the ranges (max.–min.) in the single-valve δ18O and δ13C data of the individual core samples are similar in the upper and in the lower core section, although a higher hydrographic variability is expected prior to 7 cal. ka BP due to river proximity. This lack of variability indicates the southward flow of cold, saline water along a submarine paleo-river channel, formerly existing at the core location. Despite shallowing of the site due to sediment filling of the channel and isostatic uplift of the area, the hydrographic variability at the core location remained low during the Late Holocene, because the shallowing proceeded synchronously with the retreat of the river mouth due to the global sea level rise.

Description: The iron (Fe) isotope compositions of 37 hydrogenetic ferromanganese deposits from various oceans have been analysed by MC-ICPMS; they permit the construction of a global map of Fe isotopic values. The isotopic compositions range between −1.2 and −0.1‰ in δ57FeIRMM14. Averages for the Atlantic and the Pacific are −0.41 and −0.88‰, but their standard deviations are identical (0.27, 1σ) and the data very largely overlap. No correlation is found with Pb or Nd isotope compositions and there is no evidence that the observed oceanic Fe isotopic heterogeneity is directly controlled by variations in continental sources. The small quantities of Fe that can be introduced from hydrothermal sources render as unlikely the possibility that the isotopic variations reflect variable proportions of continental and hydrothermal Fe, as recently proposed. The more likely explanation is that the variations are induced locally within the ocean. The exact sources of fractionation remain unclear. Likely possibilities are the dissolution and reprecipitation processes that liberate Fe from sediments during anoxic events, dissolution in surface waters or processes occurring during growth of the crusts

Description: Iron(III) photoreduction and the responses of phytoplankton under ultraviolet (UV) and photosynthetically available radiation (PAR) were investigated with the presence of hydroxycarboxylic acid (glucaric acid (GA), a model compound for organic acids excreted by phytoplankton). The incubation experiments were carried out on board using seawater samples collected in the location of the winter ice edge (WIE) and the spring ice edge (SIE) of the Southern Ocean. In this paper, we focus on the results of experiment in WIE. Throughout the experiments, dissolved Fe(II), major nutrients and in vivo fluorescence were monitored regularly. In addition, Chl-a, POC/PON, cell densities of phytoplankton and bacteria, bacterial production, organic peroxide, hydrogen peroxide and total CO2 were measured. The results from the WIE show that iron enrichment had a substantial effect on phytoplankton growth rate. Fe(III) addition in the presence of GA (FeGA) gave higher Fe(II) concentration and higher growth rate of phytoplankton than those in controls. Our results suggest that hydroxycarboxylic acid had a significant chemical and biological impact. The presence of GA influenced iron photochemistry and iron availability to phytoplankton. Phytoplankton growth responses to iron enrichments in incubations under UV and PAR were completely dissimilar. It seems that FeGA addition prominently changes the harmful effect of UV on the phytoplankton population. This study provides preliminary information on how the photoreduction of iron(III) and the phytoplankton growth are affected by iron enrichment in the presence of hydroxycarboxylic acid.

Description: Signals from 11 shots and 8 earthquakes, and numerous teleseismic events were recorded along the 400-km seismic line INDEPTH III in central Tibet and interpreted together with previous seismic and tectonic data. The abnormal behavior of various mantle phases reveals a complex Moho-transition zone, especially in the northern part of the line, in the Changtang Block, where the lower crust and the mantle show unusually low velocities, a shingled appearance of Pn and no low-velocity layer in the upper crust. The strong east-west anisotropy in the Changtang Block is related to an easterly escape movement of the whole lithosphere, facilitated by the warm and weak layers in the lower crust and the upper mantle, bounded apparently by two prominent west-east running fault zones.

Description: During ODP Leg 193, 4 sites were drilled in the active PACMANUS hydrothermal field on the crest of the felsic Pual Ridge to examine the vertical and lateral variations in mineralization and alteration patterns. We present new data on clay mineral assemblages, clay and whole rock chemistry and clay mineral strontium and oxygen isotopic compositions of altered rocks from a site of diffuse low-temperature venting (Snowcap, Site 1188) and a site of high-temperature venting (Roman Ruins, Site 1189) in order to investigate the water-rock reactions and associated elemental exchanges. The volcanic succession at Snowcap has been hydrothermally altered, producing five alteration zones: (1) chlorite +/- illite-cristobalite-plagioclase alteration apparently overprinted locally by pyrophyllite bleaching at temperatures of 260-310degreesC; (2) chlorite +/- mixed-layer clay alteration at temperatures of 230degreesC; (3) chlorite and illite alteration; (4) illite and chlorite +/- illite mixed-layer alteration at temperatures of 250-260degreesC; and (5) illite +/- chlorite alteration at 290-300degreesC. Felsic rocks recovered from two holes (1189A and 1189B) at Roman Ruins, although very close together, show differing alteration features. Hole 1189A is characterized by a uniform chlorite-illite alteration formed at similar to250degreesC, overprinted by quartz veining at 350degreesC. In contrast, four alteration zones occur in Hole 1189B: (1) illite chlorite alteration formed at similar to300degreesC; (2) chlorite +/- illite alteration at 235degreesC; (3) chlorite illite and. mixed layer clay alteration; and (4) chlorite illite alteration at 220degreesC. Mass balance calculations indicate that the chloritization, illitization and bleaching (silica-pyrophyllite assemblages) alteration stages are accompanied by different chemical changes relative to a calculated pristine precursor lava. The element Cr appears to have a general enrichment in the altered samples from PACMANUS. The clay concentrate data show that Cr and Cu are predominantly present in the pyrophyllites. Illite shows a significant enrichment for Cs and Cu relative to the bulk altered samples. Considerations of mineral stability allow us to place some constraints on fluid chemistry. Hydrothermal fluid pH for the chloritization and illitization was neutral to slightly acidic and relatively acidic for the pyrophyllite alteration. In general the fluids, especially from Roman Ruins and at intermediate depths below Snowcap, show only a small proportion of seawater mixing (〈10%). Fluids in shallow and deep parts of the Snowcap holes, in contrast, show stronger seawater influence. Copyright (C) 2004 Elsevier Ltd.

Description: A set of published paleoclimate proxy records from the northern hemisphere, capturing different climate processes, is used to study glacial–interglacial differences in climate variability at centennial-to-millennial timescales during the past fifty thousand years. These proxy records reveal the existence of distinct oscillatory modes of the climate system. Glacial climate variability is dominated by a single mode, the Dansgaard–Oeschger cycles, composed of stadial and interstadial states. This glacial mode results in well-expressed covariations of the proxies, which are paced by a fundamental 1470-year signal. In contrast, there is no compelling evidence for a dominant and persistent centennial-to-millennial climate cycle during the Holocene. Interglacial climate variations seem to covary less pronounced than those of the last glacial period, suggesting the simultaneous activity of independent climate modes, each characterized by its own natural periods, between approximately 400–3000 years. A conceptual model is introduced to interpret this contrast in covariation at glacial–interglacial timescales. It is assumed that different climate modes can be represented by relaxation oscillators with different natural periods in the centennial-to-millennial band. Interactions among such oscillators may lead to a phase-synchronization and the development of a new climate mode with a joint frequency. We suggest that the coupled state with its synchronized dynamics resembles a glacial whereas the decoupled state represents an interglacial with its reduced covariations of climate fluctuations. The synchronization greatly enhances the frequency stability of the coupled system, and has the potential to reconcile the stability of the glacial 1470-year pacing cycle with an origin within the Earth's climate system.

Description: The Ifaty coral record from off SW Madagascar provide a 336-year coral oxygen isotope record that is used to investigate the natural variability of the western Indian Ocean subtropical SST dipole and ENSO. The coral oxygen isotope record primarily reflects past sea-surface temperature (SST) variability on seasonal to multidecadal scales. To validate the SST reconstructions derived from oxygen isotopes, Sr/Ca ratios were obtained for selected time windows (1973–1995, 1863–1910, 1784–1809, 1688–1710). The period 1675–1760 was found to be the coolest period of the entire record with anomalies of 0.3–0.5 °C that includes the Late Maunder Minimum (1675–1710). The warmest periods, as indicated by our data, occur between 1880 and 1900 and the upper part of the Ifaty record (1973–1995). We generated a time series of coral δ18O for different seasons of the year to investigate austral winter and summer SST variability that influences rainfall intensity over southern Africa. Winter coral δ18O is coherent with winter SST on decadal and multidecadal time scales between 1854 and 1995. We suggest that the Ifaty winter time series provides a record of winter SST variability over the Mozambique Channel/Agulhas Current region over 336 years. Strong Indian Ocean subtropical dipole events, occurring during austral summer, are displayed in the Ifaty record. The austral summer coral δ18O is coherent and in phase with ENSO indices on interannual time scales (2–4 years) between 1880–1920, 1930–1940 and after 1970. Our data indicate that the impact of ENSO on SW Indian Ocean SST and atmospheric circulation was also strong between 1680–1720 and 1760–1790, in agreement with other studies. We show evidence that these variations are caused by changes in the regional hydrologic balance. The results demonstrate that the impact of ENSO cycles in the region of the SW Indian Ocean has changed significantly since 1970 and relate to a warming of southwestern Indian Ocean surface waters altering the spatial signature of ENSO.

Description: The response of coccolithophore assemblages to short-term millennial and centennial climatic changes over the last 50 kyr is studied in core M39029-7 from the Gulf of Cadiz (Atlantic Ocean) and core MD95-2043 from the Alboran Sea (Western Mediterranean Sea). The nannoplankton data are compared with oxygen isotopes, U37k′-SST and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short-term climatic changes. Coccolithophores indicate that Heinrich events (HE) were characterised by the presence of cold, low salinity and turbid water masses on both sides of the Strait of Gibraltar. High abundances of the Lower Photic Zone (LPZ) species Florisphaera profunda in the Gulf of Cadiz synchronous with HE are interpreted as being an evidence of upper water-column stratification on the Atlantic side. These episodes coincided with input of terrigenous material, especially during H2. Surface waters during Dansgaard-Oeschger (DO) Stadials were also cold and turbid, while most of DO Interstadials were characterised by warm-water flora. The increase in small placoliths (small Gephyrocapsa and Emiliania huxleyi (〈4 μm)) reveals a higher coccolithophore production during DO Interstadials and the Holocene. Conversely, HE and most of DO Stadials show peaks of E. huxleyi (〉4 μm), which is considered here as a cold-water indicator. The sharp decrease in large specimens of E. huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks—at least approximately—the deglaciation and the beginning of the Holocene. Peaks of F. profunda are observed during Termination 1 (T1) in the Alboran Sea. They are isochronous with the “Organic-Rich Layer 1” recognised in the Western Mediterranean. In this interval, the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation. Quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the Alboran Sea than in the Gulf of Cadiz during the Holocene.

Description: Secular variations in the Pb isotopic composition of a mixed hydrogenous-hydrothermal ferromanganese crust from the Bauer Basin in the eastern Equatorial Pacific provide clear evidence for changes in hydrothermal contributions during the past 7 Myr. The nearby Galapagos Rise spreading center provided a strong hydrothermal flux prior to 6.5 Ma. After 6.5 Ma, the Pb became stepwise more radiogenic and more similar to Equatorial Pacific seawater, reflecting the westward shift of spreading to the presently active East Pacific Rise (EPR). A second, previously unrecognized enhanced hydrothermal period occurred between 4.4 and 2.9 Ma, which reflects either off-axis hydrothermal activity in the Bauer Basin or a late-stage pulse of hydrothermal Pb from the then active, but waning Galapagos Rise spreading center. Hafnium isotope time-series of the same mixed hydrogenous-hydrothermal crust show invariant values over the past 7 Myr. Hafnium isotope ratios, as well as Nd isotope ratios obtained for this crust, are identical to that of hydrogenous Equatorial Pacific deep water crusts and clearly indicate that hydrothermal Hf, similar to Nd, does not travel far from submarine vents. Therefore, we suggest that hydrothermal Hf fluxes do not contribute significantly to the global marine Hf budget.

Description: Depth and flipper movements were simultaneously measured during 23 dives for a free-swimming green turtle (Chelonia mydas) at Ascension Island. A few characteristic dive profiles that have been widely reported in hard-shelled turtles were recorded. Flipper movements revealed that, on dives to midwater, there was generally active swimming, compared to long periods of inactivity on dives to the seafloor. During all dives, there were clear changes in the flipper beat frequency during the descent. On leaving the surface, flippers beats occurred quickly (typically 30–40 beats min−1) and then as the descent continued the frequency declined (typically to about 10–14 beats min−1). These observations match the general pattern reported for other air-breathing divers for increased effort at the start of the descent to overcome initial positive buoyancy.

Description: Oxygen isotope profiles along the growth axis of fossil bivalve shells of Macoma calcarea were established to reconstruct hydrographical changes in the eastern Laptev Sea since 8400 cal yr B.P.. The variability of the oxygen isotopes (δ18O) in the individual records is mainly attributed to variations in the salinity of bottom waters in the Laptev Sea with a modern ratio of 0.50‰/salinity. The high-resolution δ18O profiles exhibit distinct and annual cycles from which the seasonal and annual salinity variations at the investigated site can be reconstructed. Based on the modern analogue approach oxygen isotope profiles of radiocarbon-dated bivalve shells from a sediment core located northeast of the Lena Delta provide seasonal and subdecadal insights into past hydrological conditions and their relation to the Holocene transgressional history of the Laptev Sea shelf. Under the assumption that the modern relationship between δ18Ow and salinity has been constant throughout the time, the δ18O of an 8400-cal-yr-old bivalves would suggest that bottom-water salinity was reduced and the temperature was slightly warmer, both suggesting a stronger mixture of riverine water to the bottom water. Reconstruction of the inundation history of the Laptev Sea shelf indicates local sea level ∼27 m below present at this time and a closer proximity of the site to the coastline and the Lena River mouth. Due to continuing sea level rise and a southward retreat of the river mouth, bottom-water salinity increased at 7200 cal yr B.P. along with an increase in seasonal variability. Conditions comparable to the modern hydrography were achieved by 3800 cal yr B.P.

Description: In November 2000, a second iron enrichment experiment (EisenEx) was carried out in the Southern Ocean. Iron was added on the 8th of November in the centre of an eddy at 21°E, 48°S. During the cruise, the carbonate parameters dissolved inorganic carbon (DIC), fugacity of CO2 (fCO2) and pH on the hydrogen ion scale (pHT) were determined from water samples from both inside and outside the iron fertilized patch. Before the start of the experiment, the surface properties of the eddy were quite uniform with respect to the carbonate system and representative of the High Nutrient Low Chlorophyll (HNLC) regions in the Southern Ocean. The response of the carbon dioxide system to the initial ≈4 nM iron (Fe) infusion and to two subsequent reinfusions at 15 m depth was measured every day during the study. The changes in the carbon dioxide system and major nutrients were strongly influenced by the meteorological conditions with a rapid succession of calm, often sunny spells and storm force winds during the 21 days of experiment. Twenty days after the first Fe-infusion, the maximum changes of the carbonate parameters in surface waters of the patch relative to outside patch were −15 μmol kg−1 in DIC, −23 μatm in fCO2, +0.033 units in pHT, −1.61 μM in nitrate and −0.16 μM in phosphate in a mixed layer of 80 m depth. In addition to the daily measurements, several transects were made across the patch that showed a response of the carbonate system to the influence of iron, concomitant with a response in nutrients and chlorophyll. The relative changes in dissolved inorganic carbon to nutrient concentrations inside the patch during the experiment give N/P=12, C/P=82, C/N=5.9, C/Si=2.9 and N/Si=0.5. The effect of the influx of atmospheric CO2 on the DIC inventory was small with values between 0.05 and 0.10 μmol kg−1 day−1, and did not significantly affect these ratios. Although the observed change in DIC in the Fe-enriched surface waters was lower than in the previous Fe-enrichment experiments, the equivalent biological C-uptake of 1.08×109 mol C across the patch after 20 days was significant due to the large horizontal dispersion of the patch. The ratio of biological carbon uptake to Fe added (Cbiological uptake/Feadded) was 2.5×104 mol mol−1.

Description: In the shallow subtidal of Kiel Fjord (western Baltic Sea), the blue mussel Mytilus edulis is the dominant competitor for space. Vertically suspended settlement substrata in the upper 6 in of the water column almost invariably become dominated by M. edulis within a few summer months. However, not all naturally available hard substrata bear mussel monocultures. In three in situ experiments we investigated the dominance of mussels and the influence of local consumers on establishment and dynamics of a benthic community: (a) the natural course of succession in the absence of benthic consumers was followed on vertically suspended settlement substrata, (b) settling plates were exposed to natural recruitment being either accessible or inaccessible to all benthic consumers, and (c) the three major local consumer species, viz. the shore crab Carcinus maenas, the starfish Asterias rubens and the periwinkle Littorina littorea, were enclosed separately in cages containing a settling panel to assess species-specific consumer effects on recruitment. The results illustrate that in this region of the Baltic Sea mussels do have the potential to dominate ungrazed substrata within a few weeks and that top-down effects (predation and grazing) may control community structure. While some species - mussels in particular - were suppressed by consumption, others seemed to benefit from the presence of consumers. Thus, barnacles and algae thrived when consumers were present. Blue mussels being the locally dominant competitor, the beneficial effects of consumers on barnacles and algae were presumably indirect ones through consumer-caused release from asymmetrical competition. The isolated effects of C maenas, A. rubens and L. littorea, on recruitment differed in quality (positive vs. negative), quantity (strength of effect) and specificity. Barnacle recruitment was significantly reduced in the presence of both starfish and shore crabs. Diatom recruitment was significantly reduced by snails and shore crabs. Scyphozoan recruitment was significantly reduced by crabs only, but was significantly increased by snails. The influence of the shore crabs was most remarkable: recruitment by any potential coloniser species was impeded to a point where in the presence of single individuals of C. maenas the plates stayed perfectly clean macroscopically

Description: Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, with 100% as target; (ii) percent of specimens with optimum length in catch, with 100% as target; and (iii) percentage of ‘mega-spawners‘ in catch, with 0% as target, and 30–40% as representative of reasonable stock structure if no upper size limit exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Epinephelus aeneus demonstrate their usefulness. It is argued that such simple indicators have the potential to allow more stakeholders such as fishers, fish dealers, supermarket managers, consumers and politicians to participate in fisheries management and eventually hold and reverse the global pattern of convenience overfishing, which is defined here as deliberate overfishing sanctioned by official bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts.

Description: This study explores a chemo-thermo-dynamic subduction zone model that solves for slab dehydration during subduction. We investigate how changes in the incoming plate's hydration and thermal structure may effect the efficiency of sub-arc water release from sediments, crust, and serpentinized mantle. We find that serpentinized lithospheric mantle may not only be an important fluid source to trigger arc melting but is also an efficient ‘transport-lithology’ to recycle chemically bound water into the deeper mantle. In fact, an old slab may remain sufficiently cold during subduction to retain up to 40% of its initial ‘mantle’ water at 8 GPa (∼240-km depth) after serpentine transforms to higher pressure hydrous phase A. Furthermore, deep water recycling at subduction zones is parameterized in terms of slab age and speed. Coupling this parameterization to a parameterized mantle convection evolution model allows us to calculate the mantle-surface geologic water cycle throughout the Earth's history. We find that the present-day Earth mantle may be highly outgassed containing only a small fraction of the Earth's water, which would mostly be recycled water from the exosphere.

Description: From the aerial parts of Sideritis ozturkii, three new flavonoids, chrysoeriol 7-O-[2‴-O-caffeoyl-6‴-O-acetyl-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside], chrysoeriol 7-O-[2‴-O-caffeoyl-β-d-glucopyranosyl-(1→ 2)-β-d-glucopyranoside] and chrysoeriol 7-O-[2‴-O-p-coumaroyl-6‴-β-O-acetyl-d-glucopyranosyl-(1→2)-β-d-glucopyranoside] named as ozturkosides A, B and C, respectively, were isolated, along with three known phenylethanoid glycosides, verbascoside, leucoseptoside A, martynoside and five known diterpenoids, 7-epicandicandiol, linearol, sidol, sideroxol, epoxyisolinearol. The structures were elucidated mainly by spectroscopic methods.

Description: The model of ecological speciation implies that habitat differences may split a species by strong selection and rapid adaptation even under sympatric conditions. Recent studies on the polychaete Scoloplos armiger in the Wadden Sea, North Sea, indicate sibling species existing in sympatry: the intertidal 'Type I' with holobenthic development out of egg cocoons and the subtidal 'Type S' shedding pelagic larvae into the open water. In the current study, Type I and S are compared in habitat-related traits of reproductive timing and physiological response to hypoxia and sulphide. Spawnings of Type I and Type S recorded over six years overlap in spring and both appear to be triggered by rise in sea temperature above 5°C. Type S exhibits an additional autumn spawning (at water temperatures around 10 °C) which was unknown till now and is absent in Type I. High overall abundances of pelagic larvae in the Wadden Sea are shown. Since the pelagic dispersal mode has been neglected so far, reassessment of S. armiger population dynamics models is suggested. Tolerance against sulphide and hypoxia were both lower in Type S than in Type I. This correlates with a measured 5 to 10-fold lower sulphide concentration in the subtidal compared to the intertidal habitat. Physiological tolerance and divergence in developmental mode appear as traits which may have ultimately led to reproductive isolation between Type I and Type S. Their role in allopatric and sympatric speciation scenarios in S. armiger is discussed.

Description: During TTR11 Cruise (2001), three areas of active fluid venting and mud volcanism were investigated in the Black Sea below the oxic zone at depths varying between 800 and 2200 m. Authigenic carbonates often associated with microbial mats were recovered from the sea floor and the shallow subsurface. Structural and petrographic observations allowed the distinction of five different types of authigenic carbonates; three of these consist of carbonate-cemented layered hemipelagic sedimentary units, while the other two consist of carbonate-cemented mud breccia sediment and authigenic micrite slabs. The carbonate cements consist predominantly of micritic Mg calcite. Their δ13CCaCO3 varies between −8.5‰ and −46.9‰ at the different sampling locations, indicating that authigenic carbonates incorporate variable proportions of carbon derived from the anaerobic oxidation of methane (AOM), the oxidation of organic matter and from sea water. Methane is the dominant component among other hydrocarbon gases in these sediments. Its relative amount varies from 99.9% to 95.1% of total hydrocarbon gases and its δ13C values range from ≅−40‰ to ≅−74‰. Methane in sediments associated with the carbonate crusts shows carbon isotopic values 25–30‰ lighter than the authigenic carbonates at all the studied sites, indicating that methane present in the seeping fluids confers a distinct isotopic signature to the carbonate deposits at each location. Models proposed for the formation of carbonate slabs in the subsurface imply methane seepage impeded by homogenous clayey laminae or by pre-existing slabs, coupled with microbial activity oxidising methane and organic matter present in the sediment. Mud breccia crust pavements on the sea floor form by carbonate cementation of methane-charged sediment. Gas saturation of the sediment is confirmed by the presence of gas hydrates, whose shape indicates an association with authigenic carbonates, supporting the idea that sedimentary structures can control gas distribution

Description: The release of ballast water from transoceanic vessels is a major vector for the introduction of nonindigenous species into the Laurentian Great Lakes. This study assessed the effectiveness of treating unballasted transoceanic vessels using three different biocides: glutaraldehyde plus a surfactant adjuvant (Disinfekt 1000®), sodium hypochlorite (NaOCl), and SeaKleen™ (menadione and menadione metabisulfite 2:8). Efficacy against several classes of aquatic organisms was evaluated using 24 h acute toxicity experiments and 11 day ballast tank simulation experiments. The results indicate substantial, compound-specific variations in organism sensitivity. For water-only exposures, NaOCl and SeaKleen™ were most effective: NaOCl had the lowest LC90 (90% lethal concentration value) for the oligochaete Lumbriculus variegatus (1.0 mg L−1), while SeaKleen™ had the lowest LC90 for the amphipod Hyalella azteca (2.5 mg L−1). Sediments profoundly affected efficacy, particularly for NaOCl: At a 1:4 sediment-water ratio, the estimated LC90 for L. variegatus was 〉 2,000 mg L−1. Sediment quality also impacted efficacy: Sediments with higher organic carbon content typically required greater biocide concentrations to achieve comparable toxicity. Efficacy was further evaluated with 11 day bioassays using sediments from unballasted vessels. Results indicated that NaOCl and Disinfekt 1000® were more effective than predicted based on small scale sediment-water exposures. Overall, the data suggest that although NaOCl may be effective under water-only conditions, the higher concentrations required in the presence of sediments may cause corrosion problems for ballast tanks. Because of this, less reactive, non-oxidizing biocides such as SeaKleen™ and Disinfekt 1000® may be better candidates for treating sedimented tanks.

Description: Three tephra layers have been identified in the upper 15 m of a 190-m section of peat beneath the Philippi fen. They provide significant lithological and chronological markers throughout the fen and the Aegean region. The upper tephra (PhT1) consists of shards of a transparent calcalkaline felsic glass and fragments of plagioclase, augite, hypersthene, and rare hornblende, magnetite, apatite and quartz. Peat directly beneath PhT1 gave a radiocarbon approximate age of 13,000 yr. The middle tephra layer (PhT2), which resembles PhT1 in chemistry and petrography but contains more crystals and lithic fragments, rests on peat dated ca 18,000 14C yr BP. The lower tephra (PhT3) has colorless to brown glass shards with a trachytic chemistry and a mineral assemblage of sanidine, sodic plagioclase, biotite, aegirine-augite, hornblende, titanite and apatite. Bracketing radiocarbon ages imply that PhT3 accumulated about ∼30,000 14C yr BP. The likely ages of PhT1 and PhT2, together with their mineralogical and chemical characteristics, suggest that these tephras came from the volcanic field of Thera in the Hellenic arc. PhT2 particularly was derived from a major, known explosive eruption ca 18,000 yr BP, the Cape Riva eruption, correlative to the Y-2 tephra layer. Evidence for PhT3 suggests derivation from the Campanian Province of Italy, and correlation with the Campanian Ignimbrite and the Y-5 ash beneath the Mediterranean Sea.

Description: Eclogites from the Earth's mantle found in kimberlites provide important information on craton formation and ancient geodynamic processes because such eclogites are mostly Archean in age. They have equilibrated over a range of temperatures and pressures throughout the subcratonic mantle and some are diamond-bearing. Most mantle eclogites are bimineralic (omphacite and garnet) rarely with accessory rutiles. Contrary to their overall mineralogical simplicity, their broadly basaltic-picritic bulk compositions cover a large range and overlap with (but are not identical to) much younger lower grade eclogites from orogenic massifs. The majority of mantle eclogites have trace element geochemical features that require an origin from plagioclase-bearing protoliths and oxygen isotopic characteristics consistent with seawater alteration of oceanic crust. Therefore, most suites of eclogite xenoliths from kimberlites can be satisfactorily explained as samples of subducted oceanic crust. In contrast, eclogite xenoliths from Kuruman, South Africa and Koidu, Sierra Leone stem from protoliths that were picritic cumulates from intermediate pressures (1–2 Ga) and were subsequently transposed to higher pressures within the subcratonic mantle, consistent with craton growth via island arc collisions. None of the eclogite suites can be satisfactorily explained by an origin as high pressure cumulates from primary melts from garnet peridotite.

Description: A search for antibacterial activity in different organs/tissues of the horse mussel, Modiolus modiolus, was conducted. Dried samples were extracted with 60% (v/v) acetonitrile, containing 0.1% (v/v) trifluoroacetic acid. Due to high salt content, two liquid phases were obtained; an acetonitrile-rich phase (ACN extract) and an aqueous phase. The aqueous phase was further subjected to solid phase extraction (SPE). Eluates from SPE and ACN extracts were tested for antibacterial, lysozyme, and toxic activity. Antibacterial activity was demonstrated in extracts from several tissues, including plasma, haemocytes, labial palps, byssus, mantle, and gills. Some of the extracts were sensitive to proteinase K treatment, indicating antibacterial peptides and/or proteins. Lysozyme-like activity and toxic activity against Artemia salina nauplii was detected in fractions from the gills, mantle, muscle, and haemocytes. Results from this study indicate that M. modiolus is a promising source for identifying novel drug lead compounds.

Description: We provide an overview of the basic concepts of scaling and dimensional analysis, followed by a review of some of the recent work on applying these concepts to modeling instrumented indentation measurements. Specifically, we examine conical and pyramidal indentation in elastic–plastic solids with power-law work-hardening, in power-law creep solids, and in linear viscoelastic materials. We show that the scaling approach to indentation modeling provides new insights into several basic questions in instrumented indentation, including, what information is contained in the indentation load–displacement curves? How does hardness depend on the mechanical properties and indenter geometry? What are the factors determining piling-up and sinking-in of surface profiles around indents? Can stress–strain relationships be obtained from indentation load–displacement curves? How to measure time dependent mechanical properties from indentation? How to detect or confirm indentation size effects? The scaling approach also helps organize knowledge and provides a framework for bridging micro- and macro-scales. We hope that this review will accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to materials scientists and engineers, and (2) providing a better understanding of instrumented indentation measurements.

Description: Using contemporary CO2 data from the subsurface Weddell Sea, the source/sink function of this region against the changing atmospheric CO2 level has been investigated. As in the central Weddell Sea, surface water is supplied by upwelling of subsurface water, the CO2 content is also forced by it. TCO2 data of four cruises were used to determine a robust value for the subsurface Warm Deep Water (WDW). After accounting for biological activity in the surface layer and salinity differences between the subsurface and surface waters, the forcing CO2 partial pressure (pCO2) was calculated from the TCO2 of the WDW and the conservative alkalinity as taken from the literature. As the WDW contains negligible anthropogenic CO2, the pCO2 forcing by the WDW has been prevalent both in the pre-industrial and modern Weddell Sea. The calculated pCO2 forcing amounts to 300–310 μatm at a minimum in late winter/early spring and possibly 30 μatm more during spring and summer. This figure does not represent the actual pCO2, but rather the value before air–sea exchange gets effective. Hence, in pre-industrial times when the atmospheric pCO2 was about 280 μatm, the Weddell Sea must have been a relatively strong source of atmospheric CO2. Because of the steadily rising atmospheric CO2 levels to more than the pCO2 forcing by the WDW, the Weddell Sea turned into a CO2 sink in recent times. The storage of anthropogenic CO2 in the Weddell Sea surface layer is estimated to be 4.1 mol C m−2. Applying the WDW forcing method to O2, a steady state O2 uptake from the atmosphere of 3.6 mol O2 m−2 year−1 is computed.

Description: The electric generating capacity of Turkey must be tripled by 2010 to meet Turkey’s electric power consumption, if the annual 8% growth in electric power consumption continues. Turkey has to make use of its renewable energy resources, such as wind and solar, not only to meet the increasing energy demand, but also for environmental reasons. Studies show that Iskenderun (36°35′N; 36°10′E) located on the Mediterranean coast of Turkey is amongst the possible wind energy generation regions. In the present study, the wind energy potential of the region is statistically analyzed based on 1-year measured hourly time-series wind speed data. The probability density distributions are derived from time-series data and distributional parameters are identified. Two probability density functions are fitted to the measured probability distributions on a monthly basis. The wind energy potential of the location is studied based on the Weibull and the Rayleigh models.

Description: The Sarulla graben is a composite Plio-Pleistocene basin developed along the northwest striking, dextral-slip Sumatra fault in a region where the fault coincides with the Sumatra volcanic arc. Offset of the 0.27±0.03 Ma Tor Sibohi rhyodacite dome by an active strand of the Sumatra fault, the Tor Sibohi fault (TSF), indicates a slip rate of about 9 mm/y. This value is lower than previous regional estimates of ∼25–30 mm/y for Holocene slip on the Sumatra fault determined from stream offsets in the Taratung region. This discrepancy may be due to (1) a difference between Holocene and late Quaternary rates of slip and (2) additional slip on other faults in the Sarulla area. Since the magnitude of undated stream offsets along the TSF in the Sarulla area is similar to those in the Taratung area, the discrepancy is likely to be due largely to a change in slip rate over time. Within the Sarulla area, major volcanic centers include the Sibualbuali stratavolcano (∼0.7–0.3 Ma), the Hopong caldera (∼1.5 Ma), and the Namora-I-Langit dacitic dome field (0.8–0.1 Ma). These centers generated the majority of the ash-flow tuffs and tuffaceous sediments filling the Sarulla graben, and appear to have been localized by structural features related to the Sumatra fault zone. Four geothermal systems within the Sarulla area are closely linked to major faults and volcanic centers. In three of the systems, reservoir permeability is clearly dominated by specific structures within the Sumatra fault system. In the fourth geothermal system, Namora-I-Langit geothermal field, permeability may be locally influenced by faults, but highly permeable fractures are widely distributed.