ALBERT

Description: The process of fluid release from the subducting slab beneath the Izu arc volcanic front (Izu VF) was examined by measuring B concentrations and B isotope ratios in the Neogene fallout tephra (ODP Site 782A). Both were measured by secondary ion mass spectrometry, in a subset of matrix glasses and glassy plagioclase-hosted melt inclusions selected from material previously analyzed for major and trace elements (glasses) and radiogenic isotopes (Sr, Nd, Pb; bulk tephra). These tephra glasses have high B abundances (∼10–60 ppm) and heavy δ11B values (+4.5‰ to +12.0‰), extending the previously reported range for Izu VF rocks (δ11B, +7.0‰ to +7.3‰). The glasses show striking negative correlations of δ11B with large ion lithophile element (LILE)/Nb ratios. These correlations cannot be explained by mixing two separate slab fluids, originating from the subducting sediment and the subducting basaltic crust, respectively (model A). Two alternative models (models B and C) are proposed. Model B proposes that the inverse correlations are inherited from altered oceanic crust (AOC), which shows a systematic decrease of B and LILE with increasing depth (from basaltic layer 2A to layer 3), paralleled by an increase in δ11B (from ∼+1‰ to +10‰ to +24‰). In this model, the contribution of sedimentary B is insignificant (〈4% of B in the Izu VF rocks). Model C explains the correlation as a mixture of a low-δ11B (∼+1‰) ‘composite’ slab fluid (a mixture of metasediment- and metabasalt-derived fluids) with a metasomatized mantle wedge containing elevated B (∼1–2 ppm) and heavy δ11B (∼+14‰). The mantle wedge was likely metasomatized by 11B-rich fluids beneath the outer forearc, and subsequently down dragged to arc front depths by the descending slab. Pb–B isotope systematics indicate that, at arc front depths, ∼53% of the B in the Izu VF is derived from the wedge. This implies that the heavy δ11B values of Izu VF rocks are largely a result of fluid fractionation, and do not reflect variations in slab source provenance (i.e. subducting sediment vs. basaltic crust). Since the B content of the peridotite at the outer forearc (7–58 ppm B, mean 24±16 ppm) is much higher than beneath the arc front (∼1–2 ppm B), the hydrated mantle wedge must have released a B-rich fluid on its downward path. This ‘wedge flux’ can explain (1) the across-arc decrease in B and δ11B (e.g. Izu, Kuriles), without requiring a progressive decrease in fluid flux from the subducting slab, and (2) the thermal structure of volcanic arcs, as reflected in the B and δ11B variations of volcanic arc rocks.

Description: Siderophores are low molecular weight, iron-chelating ligands produced by nearly all microorganisms. Fungi synthesize a wide range of hydroxamate siderophores. This review considers the chemical and biological aspects of these siderophores, their distribution amongst fungal genera and their possible applications. Siderophores function primarily as iron transport compounds. Expression of siderophore biosynthesis and the uptake systems is regulated by internal iron concentrations. Transport of siderophores is an energy-dependent process and is stereoselective, depending on recognition of the metal ion coordination geometry. In addition to transporting iron, siderophores have other functions and effects, including enhancing pathogenicity, acting as intracellular iron storage compounds and suppressing growth of other microorganisms. Siderophores can complex other metals apart from iron, in particular the actinides. Because of their metal-binding ability there are potential applications for siderophores in medicine, reprocessing of nuclear fuel, remediation of metal-contaminated sites and the treatment of industrial waste.

Description: Fishery statistics for two abundant commercial squid, Illex argentinus (Ommastrephidae) and Loligo gahi (Loliginidae), in Falkland Islands waters (southwest Atlantic) between 1987 and 1999 were analysed. The areas of the highest densities of the two species are usually separated, with I. argentinus most abundant to the north-west of the Islands in February–May and L. gahi to the south-east in February–May and August–October. However, in some years, I. argentinus intrude in great numbers into nursery or feeding areas of L. gahi in April and May. It could, therefore, affect, either directly (via predation) or indirectly (by competition for food), the abundance and recruitment of the second cohort of L. gahi, exploited around the Islands between April and October. Catch per unit effort (CPUE) of I. argentinus in February–March did not correlate with that of L. gahi in February–May. In contrast, the CPUE of I. argentinus in April–May was negatively correlated with that of L. gahi in April–May and August–October of the same year. Possible reasons for these inverse abundance patterns of the two squid species, and their implications for fisheries management are discussed.

Description: In the Falkland waters, squid have maximum stomach fullness and lowest hunting activity in the evening. During the night, hunting activity increased until dawn while food was digesting, except for a short period around and after midnight when squid activity decreased.

Description: Cephalopods constitute a valuable resource of Portuguese fisheries, but there are no data on the adequacy of legal mesh size with regards to minimum landing size (MLS) (or weight). In the autumn of 1998 and the spring and summer of 1999 surveys were carried out off the northern coast of Portugal to study codend selectivity of finfish bottom trawls. Mesh sizes used were 65, 80 and 90 mm (full mesh size). During these surveys primarily targeting fish species, data were obtained for the octopus, Octopus vulgaris, the European squid, Loligo vulgaris and the broadtail shortfin squid, Illex coindetii. For the octopus, selectivity parameters were estimated for the 65 mm codend (L50 between 8.4 and 9.7 cm and selection factor (SF) 1.3 and 1.5) and for the 80 mm codend in the summer (L50 14.2 cm and SF 1.9). For the European squid, selectivity parameters were estimated in the autumn survey for the 80 and 90 mm mesh size codends (L50 9.7 and 11.4 cm, respectively, and SF 1.3 for both codends). For the broadtail shortfin squid, selectivity parameters were estimated in the summer for the 65 mm mesh size codend (L50 9.5 cm and SF 1.5). Considering that the finfish bottom trawl fishery uses a minimum mesh size of 65 mm, it is concluded that a high proportion of small octopus that has a minimum landing weight (MLW) of 0.75 kg (corresponding to a dorsal mantle length of 11.8 cm) is retained. For the European squid, whose MLS is 10 cm, a 65 mm mesh size would also retain an extremely high proportion of undersized individuals, but these occur in very small numbers in the fishery. The broadtail shortfin squid has no established MLS.

Description: Population structure and reproductive patterns of the long-finned squid Loligo plei off the coast of Santa Catarina, southern Brazil, were analysed from the biological samples of commercial catches landed in the Itajaı́ harbour from April 1995 to February 1998. The species were recruited to the trawl fishery at 130 mm mantle length (ML) and males were, on average, nearly 1.3 times larger than females. The exponents of males and females ML–weight relationships were 1.89 and 2.07, respectively, and differed significantly between maturity stages. Cohorts of both sexes did not persist into their second year, a feature that, coupled with the scarcity of spent animals, provided evidence for semelparity with nearly 1 year life span. An extended seasonal breeding and spawning pattern was characterised with a large reproduction event concentrated during the summer months extending through autumn and winter. It is suggested that the summer spawners hatch during the summer–early autumn, recruit to the fishery in the spring and reach maturity in the following summer, at the age of nearly 1 year. Squid spawned during the winter will hatch during winter–early spring, recruit to the fishery during the summer and autumn and spawn in their second winter. Between summer and winter spawning events, continuous spawning activity produce several microcohorts detected in trawlers catch. Summer spawners sustain the most important commercial concentrations. The relationship between L. plei population structure, seasonal abundance and the dynamics of environmental conditions off southern Brazil is discussed.

Description: The feeding habits of Beryx splendens and B. decadactylus were determined from stomach contents obtained on a monthly basis during commercial fishing off the Canary Islands in 1996–1997. Changes in diets were studied in relation to predator size and seasonal variation in the food composition. The diet of both species has much in common with regard to its main components of small fishes, crustaceans and cephalopods. More important differences were found in the fish prey of B. decadactylus. A variation in the diet of B. splendens was observed according to its length. Seasonal variations in feeding habits were associated with either variations in the abundance of prey or variations in the depth distribution of predator and prey.

Description: Experiments were conducted to investigate growth and proteolytic activity of the common octopus Octopus vulgaris, reared with different diets and ration levels during first feeding. Four ration levels were tested, 0.2, 2, 4 and 10 Artemia nauplii ml−1 day−1 and co-feeding techniques were tested using 10 Artemia nauplii ml−1 day−1 plus three different compound millicapsules. Total proteolytic activity, trypsin and chymotrypsin levels were recorded from eggs, hatchlings and during the first month of paralarval rearing. Five days after hatching, paralarval weight and proteolytic activity was dependent on food ration. The low-food treatment did not lead to an increase in hatchling weight, in contrast with the positive increase of the other treatments. After 20 days, best survival was observed in treatments fed 2 and 4 nauplii ml−1 day−1. High nauplii rations of 10 nauplii ml−1 day−1 plus millicapsule diet treatments produced higher growth and higher proteolytic, trypsin and chymotrypsin levels, but poor survival. Total proteolytic activity was correlated with paralarval weight, whereas trypsin and chymotrypsin were maintained at hatchling levels only for the high food and co-feeding treatments, and decreased in the others. The trypsin activity in the high-food treatment showed a sharp increase after 15 days and 880 μg of the mean dry weight (2.5 times hatchling weight). Millicapsules were ingested by the paralarvae after 5 days but did not lead to a significant increase in weight. Enriched Artemia nauplii seem to be useful only as an initial diet until a doubling in hatchling weight is achieved. This period can extend from 11 to 14 days at 20 °C, after which a larger prey and/or suitable microdiet is required.

Description: Several species of migratory, warm-water, oceanic fishes invaded Oregon waters during the summer of 1997. Also, the jumbo squid (Dosidicus gigas), common in the eastern tropical Pacific, was reported for the first time in 1997 and was caught in large numbers. The occurrence of these oceanic nekton was associated with inshore advection of anomalously warm water. During 1998, after arrival of the main El Niño signal, some warm-water coastal fishes appeared off Oregon. However, unlike observations off California, fewer species of warm-water coastal fishes were noted during the 1997–98 El Niño than during the 1982–83 El Niño.

Description: The common octopus, Octopus vulgaris Cuvier, 1797 is the most important cephalopod species in catches of the artisanal trap fishery in Canary Islands waters. Based on monthly samplings carried out off Gran Canaria (Canary Islands), 760 specimens of the common octopus, ranging from 4.8 to 165 mm ventral mantle length, were studied from June 1996 to July 1997, and from December 1997 to June 1999. The length–weight relationships found were W=0.0007×VML3.096 (n=760;r=0.95), W=0.0007×VML3.112 (n=481;r=0.86), W=0.0007×VML3.098 (n=247;r=0.77), for all the specimens caught, males and females, respectively. The proportion of males was significantly higher than females. Males predominated in all size intervals. Males and females become sexually mature at 105 and 113 mm of VML, respectively. Maturation and spawning occur all year around, with more intensity from January to July, with a peak in April. There is a second spawning period in October–November. The number of spermatophores produced increased with length and maturity stage. The production of spermatophores by individual body weight fluctuated from 0.29 to 0.03 spermatophores/g. The number of oocytes per gram of body weight fluctuated from 108 to 465. The real fecundity oscillated between 31 and 106 eggs spawned per gram of female body weight.

Description: Juvenile cuttlefish hatched in the laboratory were reared for 30 days with different enriched diets, in spring and in summer. The groups fed an enriched natural diet exhibited a high rate of survival even when seawater quality decreased during the summer. The natural diet enriched in polyunsaturated fatty acids (PUFA) induced faster growth in juvenile cuttlefish; the stimulating effect of PUFA on growth was evident during the very early juvenile stage, and the benefit resulted is conserved during further growth. The maximum daily ration was lower in groups fed with the enriched diet than in the control. These data indicate the importance of n−3 PUFA such as docosahexaenoic acid (DHA; 22:6n−3) and eicosapentaenoic acid (EPA; 20:5n−3) in cephalopod juvenile nutrition.

Description: The composition and distribution of squid captured between January and March during the 1996 baseline research on oceanography, krill and the environment survey off East Antarctica (80–150°E) was investigated. A total of 195 individuals were captured. The species collected were Galiteuthis glacialis, Mesonychoteuthis hamiltoni, Histioteuthis atlantica, H. eltaninae, Alluroteuthis antarcticus, Batoteuthis skolops and Pholidoteuthis boschmai. Concentrations of squid were low, ranging from 4.4 to 174.7 individuals 100,000−3. The majority of squid captured were G. glacialis (174 individuals, 89.2% of all squid captured), and most of these (n=171) were small paralarvae 〈25 mm in mantle length. G. glacialis were distributed predominantly west of 120°E in water that was colder, and where the distance from the coastline of the southern boundary of the Antarctic circumpolar current (SB-ACC) was maximal. This water mass had greater concentrations of phytoplankton, was more productive and had maximal sea-ice extent compared to the water mass east of 120°E. G. glacialis was therefore more abundant in water where the majority of krill and krill predators were present compared to warmer oceanic waters of the ACC to the east, where salps dominated.

Description: In order to provide a tool for the prevention of commercial frauds in fish products, a simple polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method has been developed. This method allows to clearly differentiate molluscs belonging to the family Loliginidae from those belonging to the family Ommastrephidae. Cephalopods' 16S r-DNA was amplified with PCR using a “universal” primer pair, and the amplification product was digested with AsnI restriction enzyme. The resulting electrophoretic patterns of families Loliginidae and Ommastrephidae showed characteristic 200 bp band and 600–700 bp band, respectively. With this methodology, the analysed species belonging to the genus Loligo have also been differentiated.

Description: The high concentrations of cadmium recorded in the digestive gland of cephalopods from various temperate and subpolar waters suggest that these molluscs have developed efficient cadmium detoxification mechanisms. The subcellular distribution of cadmium in the digestive gland cells was investigated in seven cephalopod species from the Bay of Biscay (France) and the Faroe Islands. In most species, cadmium was mainly found in the cytosolic fraction of the digestive gland cells, reaching up to 86% of the total cadmium for the squid Loligo vulgaris from the Bay of Biscay. But species with the highest total level of cadmium showed a higher percentage of cadmium associated to insoluble compounds. The quantification of metallothioneins (MTs) by the polarographic method was performed in order to evaluate the involvement of these proteins in the detoxification of the high amounts of bioaccumulated cadmium. Metallothionein levels in cephalopods ranged form 742±270 to 3478±1572 μg/g wet weight. No relationship could be established between total cadmium, cytosolic cadmium and MT levels suggesting the occurrence of other Cd-binding ligands. Although these proteins have not been characterised, as cadmium in the digestive gland of cephalopods is mainly associated with soluble ligands, a high potential transfer to predators can be predicted.

Description: Stages of merogony of a coccidian parasite were commonly observed during histological examination of the digestive tract of 7 crustacean species from Galician coastal waters. Study of the fine structure of these merogonial stages by transmission electron microscopy revealed the presence of a typical apicomplexan apical complex. Newly hatched Sepia officinalis obtained from egg masses, cultured in 3 separate tanks, were fed with three parasitised prawn species in infection experiments. Cuttlefish fed with Palaemon elegans and P. adpersus developed sexual stages and sporocysts diagnostic of Aggregata eberthi, identifying these prawns as new intermediate hosts of this parasite. No infection was found in Sepia fed with P. serratus, suggesting that this prawn could be an intermediate host of another species of Aggregata. By experimental infections of cultured cuttlefish, achieved here for the first time, the complete life cycle of A. eberthi in Spanish NE Atlantic waters was established.

Description: The formation of gas hydrates in gas and oil subsea pipelines often results in blockage and shutdown of these pipelines. Modern control methods depend on understanding the mechanisms through which gas hydrates form. This paper reviews our recent studies of clathrate hydrate formation and inhibition mechanisms using neutron diffraction, differential scanning calorimetry (DSC) and a multiple cell photo-sensing instrument. The structural transformations of water around methane during methane hydrate formation have been studied using neutron diffraction with isotope substitution over the temperature range 4–18 °C and at pressures of 3.4–14.5 MPa. The hydration sphere around methane in the liquid only changes significantly when methane hydrate is formed, with the water shell in the crystalline hydrate being about 1 Å larger than the shell in the liquid. The hydration shell is disordered during methane hydrate formation, with ordering of solvent separated methane molecules occurring only when hydrate has formed. The effects of the addition of three low dosage hydrate inhibitors, PVP, VC-713 and QAB on THF hydrate formation at the surface and in bulk solution have been examined. The QAB inhibitor exhibits the greatest hydrate crystal growth control, while VC-713 is most effective at inhibiting hydrate nucleation. Insight into the perturbations on host and guest molecules due to the presence of these inhibitor molecules has been obtained.

Description: Two sediment cores from the northern North Atlantic, one from the Iceland Plateau and one from the Rockall Plateau, were investigated in order to examine the response of deep-sea benthic ostracodes to climate-related environmental changes since marine isotope stage (MIS) 7. Ostracode fauna was divided into three factor assemblages by using Q-mode factor analyses and diversity was calculated using the Shannon–Wiener index. The Iceland Plateau revealed an ‘interglacial assemblage’ dominated by Henryhowella, a transitional assemblage dominated by Eucythere, and a ‘background assemblage’ that consists of the common taxa Krithe and Cytheropteron. The presence of Henryhowella is linked to conditions that prevailed during the peak interglacial periods (MIS 5e and 1), characterized by increased food supply, well-oxygenated bottom water, and lateral advection. The presence of Eucythere, mainly during the interstadial periods, appears to be related to slightly increased food supply, whereas the ‘background assemblage’ is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times. On the Rockall Plateau the opportunistic ‘background assemblage’ (consisting mainly of Krithe, Argilloecia, and Cytheropteron) shows no obvious relation to climate changes. The ‘interglacial assemblage’ consists of several taxa dominated by Pelecocythere but, as on the Iceland Plateau, it also contains Henryhowella. The third assemblage is the ‘glacial assemblage’ that consists of a variety of taxa, several of which are known from the modern Arctic Ocean and the Greenland Sea shelf. Thus, this assemblage indicates glacial conditions on the Rockall Plateau that are comparable to those found in the present-day Arctic Ocean. Diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg-rafted debris (IRD) in the Rockall Plateau core. Both cores reveal lower surface-water productivity during the glacial compared to the interglacial periods and particularly low productivity during the IRD events, as inferred from carbonate contents. We assume, therefore, that ostracode diversity in the study areas is negatively correlated with food flux.

Description: Bolboform distribution in space and time is analysed from a circum-Antarctic belt of lower Eocene to uppermost Miocene sediments from the Southwest Pacific, Southeast Pacific (Bellinghausen Basin), Maud Rise and South Atlantic, and Indian Ocean (Kerguelen Plateau) regions. A correlation panel using established Cenozoic planktic foraminiferal and calcareous nannofossil zones is linked to the Bolboforma zonation scheme for the Southern Ocean. Evolution of surface watermasses and their boundaries, the major oceanic fronts, are tracked using the microfossil distributions and general sediment characteristics, and are in turn linked to the Bolboforma distribution. Specifically, the migration of both the Antarctic Polar Front and the Subtropical Front northwards from continental Antarctica, starting in the earliest Oligocene and culminating in the late Miocene establishment of ‘modern’ conditions, links the bolboforms in the Southern Ocean with subantarctic watermass conditions between the equivalent of today’s Subantarctic and Subtropical fronts. The occurrence of bolboforms in sediments including subtropical microfossil assemblages from north of the Subtropical Front, as in the Tasman Sea, is anomalous. We suggest that they were transported into this region by subsurface (intermediate depth) waters generated by subduction of subantarctic surface water at southern oceanic fronts. The distribution of bolboforms more widely outside the Southern Ocean may define the pathways of Southern Component Intermediate Water (Antarctic Intermediate Water) during the Tertiary, and may account for their bipolar distribution. Bolboforms exhibit a circum-Antarctic distribution prior to the development of a full circum-Antarctic circulation system following the opening of the Tasmanian and Drake gateways. It is inferred that a West Antarctic Seaway between the Ross Sea and Weddell Sea embayments may have afforded oceanic connection between the Southwest Pacific and the southern Atlantic during the Eocene–Oligocene, facilitating dispersal and such a distribution.

Description: Marine seismic wide-angle data acquisition and earthquake seismology observations are at the verge of a quantum leap in data quality and density. Advances in micro-electronic technology facilitates the construction of instrumcnts that enable large data volumes to be collected and that are small and cheap enough so that large numbers can be built and operated economically. The main improvements are a dramatic decrease of power consumption ( 〈 250 m W) and increase in clock stability ( 〈 0.05 ppm}. Several scenarios for future experiments arc discussed in this contrihution

Description: Volcanology has been in the past and in many respects remains a subject dominated by pure research grounded in the earth sciences. Over the past 30 years a paradigm shift has occurred in hazard assessment which has been aided by significant changes in the social theory of natural hazards and the first-hand experience gained in the 1990s by volcanologists working on projects conceived during the International Decade for Natural Disaster Reduction (IDNDR). Today much greater stress is placed on human vulnerability, the potential for marginalisation of disadvantaged individuals and social groups, and the requirement to make applied volcanology sensitive to the characteristics of local demography, economy, culture and politics. During the IDNDR a methodology, broadly similar to environmental impact analysis, has emerged as the preferred method for studying human vulnerability and risk assessment in volcanically active regions. The characteristics of this new methodology are discussed and the progress which has been made in innovating it on the European Union laboratory volcanoes located in western Europe is reviewed. Furnas (São Miguel, Azores) and Vesuvius in Italy are used as detailed case studies.

Description: Field experiments were conducted to investigate the effects of grazing and nutrient supply on sediment microflora in a freshwater habitat (Lake Erken, Sweden) and at the brackish Baltic Sea coast (Väddö, Sweden). The two sites were of similar productivity, but had contrasting herbivore composition. In a full-factorial experiment design, closed cages excluded macrozoobenthos (〉1 mm) from sediment patches, whereas open cages allowed grazer access. The cage design applied here proved to successfully prevent in- and epifauna to access the sediment in closed cages. In half of the treatments, nutrients were added to the water-column by a slow-release fertilizer. The experiments were seasonally replicated four times at Väddö and two times in Lake Erken. After 4–5 weeks, sediment cores were sampled and analyzed for chlorophyll, carbon, nitrogen and phosphorus. The benthic microalgae showed strong seasonal variation in biomass and internal nutrient content. At Väddö, neither grazing nor nutrients affected the algal biomass significantly, but significant grazer effects were detected on C:N:P ratios. In Lake Erken, grazer presence reduced algal biomass by ca. 50%, whereas nutrients were without effect on biomass or on nutrient content. Compared to results from hard substrata at the same sites, sediment microflora was less affected by nutrients and grazing. This may be due to the harsh physico-chemical environment on sediments, to low grazer density at the coastal site and to low availability of water column nutrients to sediment microalgae. In our experiments, sand-dwelling microphytobenthic communities represented a highly dynamic assemblage, which, however, is less structured by biotic interactions than epilithic periphyton

Description: The paper presents an overview of recent seafloor long-term single-frame multiparameter platform developed in the framework of the European Commission and Italian projects starting from the GEOSTAR prototype. The main features of the different systems are described as well as the sea missions that led to their validation. The ORION seafloor observatory network recently developed, based on the GEOSTAR-type platforms and engaged in a deep-sea mission at 3300 m w.d. in the Mediterranean Sea, is also described

Description: This article describes the use of flow-injection techniques combined with molecular spectroscopic detection (spectrophotometry, fluorescence and chemiluminescence) for the rapid determination of chemical parameters in environmental matrices. The emphasis is on field deployment in order to obtain high temporal and spatial resolution data without the need for discrete sample collection and storage. Specific examples considered are the determination of phosphorus in river water and dissolved iron in open ocean water. The environmental drivers for these determinations are presented and the analytical capabilities of flow-injection instrumentation for remote deployment are discussed. © 2002 Published by Elsevier Science B.V. All rights reserved.

Description: A method for the continuous underway determination of Fe(II) in polar waters is reported. Surface seawater is pumped into a shipboard clean room container using a towed fish with Teflon diaphragm pump. Fe(II) was determined by flow injection analysis using a modified FeLume. The seawater is filtered in-line and the sample containing Fe(II) is mixed with luminol (buffered to pH 10) inside a flow cell and the resulting luminescence signal measured by a Hamamatsu HC-135 photon counter linked to a laptop computer. No preconcentration of the samples was applied, to reduce possible interferences and increase the sampling frequency. The system was utilised during EISENEX, a meso-scale iron enrichment experiment sample in the Atlantic sector of the Southern Ocean. In EISENEX, when surveying the iron enriched patch, a sample was analysed every 110 s (60 s loading time and 50 s for analysis). The detection limit, as determined by analysis of seawater (maintained at 4 °C to minimise oxidation) spiked with known concentrations of Fe(II), ranged from 25 to 133 pM. The system was also applied to vertical profiles of Fe(II) during EISENEX.

Description: Numerous small-scale depositional cycles are present in the Miocene sediments of seismic sequence along the margin of Great Bahama Bank (ODP Leg 166). These cycles consist of decimetre- to metre-scale alternations between light-grey and dark-grey/black wackestones/packstones. The light-grey layers are well cemented and nearly uncompacted. They contain planktonic and benthic foraminifera, and bioclasts. Bioturbation in these layers is moderate. The dark-grey wackestones/packstones are uncemented, strongly compacted and normally strongly bioturbated. The main components are planktonic foraminifera and fine-grained bioclasts. The dark layers are rich in aragonite and organic carbon and contain around 80% carbonate. The light layers show low aragonite and organic carbon contents combined with carbonate values of up to 97.5%. Light δ13C and slightly negative δ18O values were observed in the dark uncemented layers while the cemented intervals show heavy δ13C values and slightly more positive δ18O values. The carbon isotope signal between the dark and the light layers shows variations of up to 1.45‰. Both δ13C and δ18O co-vary with carbonate content. The Formation MicroScanner images reflect the changes in carbonate mineralogy. The Natural Gamma-Ray Tool shows that variations in siliciclastic content of the examined succession displays a different frequency than the cyclic alternations in carbonate mineralogy. The internal stacking pattern of the cycles is closely tied to sea level. The dark layers are deposited during rising sea level, while the light layers reflect sediment production and export during highstand and falling sea level. These cycles thus represent a rather continuous sediment shedding pattern that is clearly related to the ramp morphology and differs from the highstand shedding pattern typical for rimmed flat-topped platforms. Most measured parameters suggest that primary sediment composition played an important role in the cementation process. The primary differences in composition were enhanced during shallow burial diagenesis. The initially high content of metastable carbonate phases in the periplatform sediments triggered rapid cementation of the primary aragonite-rich layers leading to the formation of the light beds. Dissolution of metastable high-Mg calcite and aragonite was followed by in situ precipitation of more stable dolomite and calcite. Diagenesis was enhanced by the coarse grain size of the primary aragonite-rich layers. In contrast the more pelagic, dark calcite-rich layers were only slightly affected by diagenesis and could preserve their aragonite content. The uncemented layers subsequently were subject to strong mechanical compaction, whereas the cemented beds stayed nearly uncompacted.

Description: Hydrocarbon gases have been sampled from both cold-seeping and heat-venting areas in the New Ireland fore arc basin in the vicinity of Lihir Island. Highest concentrations of up to 10 μl/l CH4 with a δ13CCH4 value of −54.9‰ PDB have been measured in the deep ocean water within a long and narrow deep sea basin located between Edison Seamount and an uplifted structure named “Mussel Cliff.” Surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as Calyptogena species and tube worms. Large authigenic calcite concretions occur in the sediments between 50- and 200-cm sediment depth. The carbon isotopes of the carbonates in the concretions range from −15‰ to −40‰ PDB indicating a mixture of two CO2 sources: normal marine-inorganic carbon fixed in biogenic shells and CO2 from anaerobe bacterial oxidation processes of methane. Accordingly, 14C-AMS dating suggests that authigenic calcite mineralisation incorporated relatively “young” carbon from methane oxidation. In contrast, the C1/C2 ratio of 234 and the δ13CCH4 value of −24.1‰ PDB in the hot hydrothermal vent of Lihir Harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with Lihir Volcano. The observed variable fluid characteristics within only 20-km distance between hot hydrothermal-venting and the methane-seeping deep sea area indicates highly variable heat flow situations and/or sediment distributions which control the gas geochemical characteristics in the New Ireland fore arc basin.

Description: A 500,000-yr-long deep-sea sediment-color record from the Northeast Atlantic was investigated to reconstruct the evolution of late Pleistocene climate variability on millennial time scales. Variations of the red–green color intensity are probably caused by climatically induced changes in the ice-rafted input of red-colored iron-bearing terrigenous material to the core site. The resolution of the age model impedes the detection of distinct spectral features at sub-Milankovitch periodicities. Hence, millennial-scale climate variability is quantified as time-dependent variance of the high-pass filtered color time series. The course of the estimated variance shows distinct patterns, which can be linked to continental ice mass. During the past 500,000 yr, large-amplitude millennial-scale climate variability occurs only if continental ice mass exceeds a threshold level, equivalent to sea level at approximately 40% of the lowering during the last glacial maximum.

Description: Paleoecological records from two Holocene peat bogs in northern Germany are linked by two microscopic volcanic ash layers, correlated by petrology and geochemistry to explosive volcanism on Iceland. The younger “Microlite tephra” cannot be correlated to any known eruption, while the older tephra layer is identified as a deposit of the Hekla 3 eruption. The tephra layers are dated by an age–depth regression of accelerator mass spectrometry 14C ages that have been calibrated and combined in probability distributions. This procedure gives an age of 730–664 cal yr B.C. for the “Microlite tephra” event and 1087–1006 cal yr B.C. for the Hekla 3 event. Accordingly, the tephra layers were deposited during the late Bronze Age. At this time, human settlement slowly increased pressure on the environment, as indicated by changes in woodland pollen composition at the two bogs. The tephra-marker horizons further show that the palynologically defined transition from the Subboreal to the Subatlantic Period is synchronous in the investigated area. However, the macroscopic visible marker in peat, the change from fibrous to sapric peat, the “Schwarztorf-Weißtorf-Kontakt,” is asynchronous. Bog vegetation did not immediately react in unison to a climatic change at this pollen zone boundary; instead, the timing of vegetation change depended on the location within the bog.

Description: We analyzed 238U, 234U, 232Th, 230Th, and 226Ra by thermal ionization mass spectrometry (TIMS) and Ba by inductively coupled plasma optical emission spectrometry (ICP-OES) on eight Mn/Fe crusts from the Mecklenburg Bay (SW Baltic) and on one from the Bothnian Bay (N Baltic) to test the 226Raex/Ba ratio as potential geochronometer. 226Raex/Ba ratios decrease as a function of depth within the concretions in all analyzed profiles. Calculated diffusion coefficients are relatively low (∼9 · 10−7 cm2/yr for Ra and 5 · 10−7 cm2/yr for Ba) and suggest that diffusion is negligible for the Ra and Ba record. In addition, 226Raex/Ba ages are consistent and independent from the growth rate and growth direction within a crust. Thus, the decline in 226Raex/Ba ratio is most likely due to radioactive decay of 226Raex, although the influence of varying oxic conditions has still to be evaluated. 226Raex/Ba growth rates range from 0.021 to 0.0017 mm/yr and tend to be lower than those calculated and based on stratigraphic methods (1 to 0.013 mm/yr). 226Raex/Ba ages of concretions from shallow water environment (20 m depth, Mecklenburg Bay/SW Baltic) cover a time interval from 990 ± 140 yr to 4310 ± 310 yr BP corresponding to the stabilization of the sea level close to the present position about 5500 to 4500 yr ago. One sample from greater depth (70 m, Bothnian Bay-/N Baltic) showed a higher 226Raex/Ba age of 6460 ± 520 yr BP

Description: The upper 500 or 1000 m of the water column in the Okhotsk Sea was sampled for living planktic foraminifera. The polar species Neogloboquadrina pachyderma (sinistral) strongly dominates the foraminiferal assemblage; the subpolar to temperate species Globigerina bulloides accounts for 10–25%. Other species account for up to 3% only. The shell δ18O and δ13C values of the species N. pachyderma (sin.) are compared to water δ18O values and δ13C values of dissolved inorganic carbon (DIC). The strong gradient in δ18O composition and temperature in the upper water column is reflected in the δ18O of N. pachyderma (sin.). Relative to the values expected for inorganic calcite precipitated under equilibrium conditions N. pachyderma (sin.) displays a vital effect of about 1‰ in δ18O. The δ13C composition of N. pachyderma (sin.) is about constant with water depth and the reflection of δ13CDIC in the foraminiferal shell seems to be masked by other effects. Most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column. The gradient of δ13CDIC extends well below this depth, therefore the lack of correlation can partly be attributed to this fact. The remaining discrepancy between δ13C of N. pachyderma (sin.) and δ13CDIC correlates with the carbonate ion concentration in the water column. This leads to the conclusion that the ‘carbonate ion effect’ (CIE), which has been derived from culturing experiments for other species [Spero et al. (1997) Nature 390, 497–500], is found here under natural conditions. When the magnitude of the CIE derived for G. bulloides is applied to N. pachyderma (sin.), CIE-corrected δ13C of N. pachyderma (sin.) is a direct reflection of δ13CDIC in the water column with a constant offset of 1.2‰.

Description: An area of massive barite precipitations was studied at a tectonic horst in 1500 m water depth in the Derugin Basin, Sea of Okhotsk. Seafloor observations and dredge samples showed irregular, block- to column-shaped barite build-ups up to 10 m high which were scattered over the seafloor along an observation track 3.5 km long. High methane concentrations in the water column show that methane expulsion and probably carbonate precipitation is a recently active process. Small fields of chemoautotrophic clams (Calyptogena sp., Acharax sp.) at the seafloor provide additional evidence for active fluid venting. The white to yellow barites show a very porous and often layered internal fabric, and are typically covered by dark-brown Mn-rich sediment; electron microprobe spectroscopy measurements of barite sub-samples show a Ba substitution of up to 10.5 mol% of Sr. Rare idiomorphic pyrite crystals (∼1%) in the barite fabric imply the presence of H2S. This was confirmed by clusters of living chemoautotrophic tube worms (1 mm in diameter) found in pores and channels within the barite. Microscopic examination showed that micritic aragonite and Mg-calcite aggregates or crusts are common authigenic precipitations within the barite fabric. Equivalent micritic carbonates and barite carbonate cemented worm tubes were recovered from sediment cores taken in the vicinity of the barite build-up area. Negative δ13C values of these carbonates (〉−43.5‰ PDB) indicate methane as major carbon source; δ18O values between 4.04 and 5.88‰ PDB correspond to formation temperatures, which are certainly below 5°C. One core also contained shells of Calyptogena sp. at different core depths with 14C-ages ranging from 20 680 to 〉49 080 yr. Pore water analyses revealed that fluids also contain high amounts of Ba; they also show decreasing SO42- concentrations and a parallel increase of H2S with depth. Additionally, S and O isotope data of barite sulfate (δ34S: 21.0–38.6‰ CDT; δ18O: 9.0–17.6‰ SMOW) strongly point to biological sulfate reduction processes. The isotope ranges of both S and O can be exclusively explained as the result of a mixture of residual sulfate after a biological sulfate reduction and isotopic fractionation with ‘normal’ seawater sulfate. While massive barite deposits are commonly assumed to be of hydrothermal origin, the assemblage of cheomautotrophic clams, methane-derived carbonates, and non-thermally equilibrated barite sulfate strongly implies that these barites have formed at ambient bottom water temperatures and form the features of a Giant Cold Seep setting that has been active for at least 49 000 yr.

Description: Suspended particles and particle aggregates, which formed from concentrated field samples on the roller table, were characterized biologically and chemically along a transect through the Baltic Sea in summer 1999. Phytoplankton composition in field samples was dominated by cyanobacteria, including the filamentous diazotrophic cyanobacteria Aphanizomenon ‘ baltica’, Nodularia spumigena and Anabaena spp. These species formed aggregates together with diatoms, mainly Skeletonema costatum and Chaetoceros spp. and with dinoflagellates, mainly withDinophysis norvegica . Compared to the Redfield ratio, concentration ratios of particulate organic carbon, nitrogen and phosphorus, [POC]:[PON]:[POP], indicated an enrichment of carbon, especially in aggregates. However, regression analysis indicated a higher production rate of PON relative to POP and POC and significant background concentrations of POC. In field samples the concentration of transparent exopolymer particles (TEP) varied around 200 μg Xanthan Equiv. l−1 and comprised a volume fraction of 2–7 ppm and an abundance of about 105 TEP ml−1. TEP were enriched in aggregates as inferred from volume ratios of TEP to conventional particles. It is suggested, that TEP contribute substantially to the background concentration of POC, while the high production rate of PON is attributed to nitrogen fixation of diazotrophic cyanobacteria.

Description: Hypotheses for the formation of many types of hydrothermal ore deposits often involve the direct contribution of magma-related fluids (e.g., Cu–Mo–Au porphyries) or their superimposition on barren hydrothermal cells (e.g., volcanic-hosted massive sulfide deposits). However, the chemical and phase compositions of such fluids remain largely unknown. We report preliminary results of a comprehensive study of fluid bubbles trapped inside glassy melt inclusions in primitive olivine phenocrysts and pillow-rim glasses from basaltic magmas from different tectonic environments, including mid-ocean ridges (Macquarie Island, SW Pacific and Mid-Atlantic Ridge 43°N Fracture Zone), ocean islands (Hawaii) and a variety of modern and ancient backarc–island arc settings (eastern Manus Basin, Okinawa and Vanuatu Troughs, Troodos, New Caledonia and Hunter Ridge–Hunter Fracture Zone). Fluid bubbles from all localities, studied using electron microscopy with EDS and laser Raman spectroscopy, are composed of CO2-(±H2O±sulfur)-bearing vapor and contain significant amounts of amorphous (Na–K–Ca–Fe alumino-silicates and dissorded carbon) and crystalline phases. The crystals are represented mainly by carbonates (magnesite, calcite, ankerite, dolomite, siderite, nahcolite and rhodochrosite), sulfates (anhydrite, gypsum, barite and anglesite), and sulfides (pyrite, arsenopyrite, chalcopyrite and marcasite), though other minerals (brukite, apatite, halite, clinoenstatite, kalsilite, nepheline, amphibole and mica) may occur as well. We argue that chemical components (e.g., C, H, S, Cl, Si, Al, Na, K, Fe, Mn, Cr, Ca, Mg, Ba, Pb and Cu) that later formed precipitates in fluid bubbles were originally dissolved in the magmatic fluid, and were not supplied by host glasses or phenocrysts after entrapment. Magma-related fluid rich in dissolved metals and other non-volatile elements may be a potential precursor to ore-forming solutions.

Description: To date, work on the Great Bahama Bank’s western, leeward margin has centred chiefly on seismic-scale expressions of carbonate sequences and systems tracts. However, periplatform, slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres. It is these small-scale, high-frequency cycles within the larger-scale facies successions of the Quaternary which form the main topic of this paper. Previous studies have shown that the small-scale cycles correlate to the orbitally forced, high-frequency sea-level changes. Therefore these cycles should indicate how sea level has affected the slope development and thus platform-margin evolution during this period. Through detailed, high-resolution sequence stratigraphy of the Great Bahama Bank’s leeward margin, obtained via δ18O isotope and mineralogical (XRD) analyses, confined by U/Th dating and nannofossil bioevents, a greater understanding of the bedding geometries within the Pleistocene–Holocene seismic sequences and clues as to the nature of the slope development has been achieved. The high-resolution seismic profiles indicate that since the Plio–Pleistocene change in geometry, in which the Great Bahama Bank developed into a rimmed platform, continued steepening and subsequent progradation of the leeward margin has typified slope development during the Quaternary, which is described as an accretionary slope. However, on the basis of our observations we conclude that only the early to lower middle Pleistocene section (isotope stages 45–20) and the Holocene (isotope stage 1) of the leeward margin is accretionary. This indicates that a degree of erosion and/or by-passing has occurred on the leeward margin since the lower middle Pleistocene (isotope stage 19). During the first part of this period (isotope stages 19–12) erosion and/or by-passing occurred in the middle to lower slope regions and toe-of-slope. By the end of the upper middle to late Pleistocene phase (isotope stages 11–2) erosion also occurred on the upper slope. This erosion by currents at the toe-of-slope and oversteepening of the upper and middle slopes have led to back-cutting upslope and resulted in the progressive retreat of the toe-of-slope towards the platform to the east. However, the rise in sea level since the Last Glacial Maximum to its present-day level has allowed high productivity on the platform top during the Holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks. This has led to the redevelopment of an accretionary slope and continued westward progradation of the Great Bahama Bank’s western, leeward margin.

Description: Stirred flow-through experiments were conducted for the first time with planktonic biogenic silica (BSi). We investigated the dissolution kinetics of uncleaned and chemically cleaned BSi collected in ocean surface water, sediment traps, and sediments from the Norwegian Sea, the Southern Ocean, and the Arabian Sea. The solubility at 2°C is rather constant (1000 to 1200 μM). The dissolution rates are, however, highly variable, declining with water depth, and phytoplankton reactivity is two to three orders of magnitude higher than pure siliceous oozes. The reactivity decrease correlates well with an increase in the integrated peak intensity ratios of Si-O-Si/Si-OH measured by Fourier transform infrared (FTIR) spectroscopy. The removal of organic or inorganic coatings enhance the reactivity by at least an order of magnitude. Atomic Al/Si ratios of 0.03 to 0.08 in sedimentary diatom frustules decrease significantly to 0.02 as a result of removal of inorganic coatings and detritals present. Near equilibrium, the dissolution rates exhibit a linear dependence on the degree of undersaturation. At higher degrees of undersaturation—that is, at low concentrations of dissolved silica—the dissolution rates of uncleaned samples define a nonlinear trend. The nonlinear kinetics imply that the dissolution of natural BSi is strongly accelerated in silica-depleted surface waters. The FTIR results suggest that internal condensation reactions reduce the amount of surface reaction sites and are partly responsible for the reactivity decrease with depth. The high content of Al in sedimentary BSi is likely caused by precipitation of dissolved silica with Al dissolved from minerals in sediment. Nonbiogenic silica as coatings or detritals are partly responsible for the solubility and reactivity decrease of BSi in sediments. One order of magnitude different rate constants measured in Norwegian Sea and Southern Ocean sediment trap material support the so-called opal paradox—that is, high BSi accumulation rates in sediments in spite of low BSi production rates in surface waters of the Southern Ocean.

Description: Experiments have been carried out to examine the aggregation of natural estuarine suspended sediment under controlled conditions in an annular flume programmed to simulate oscillating tidal currents in an estuary. The size distribution of the suspended particles was measured in-situ using a Lasentec P-100 laser-reflectance particle sizer with the sensing probe inserted directly through the wall of the flume. Parallel measurements of the solids concentration were made using a calibrated OBS sensor. The flume was filled with river water collected from above the influence of salt water. Various quantities of natural estuary sediment were added to the flume to provide solids concentrations of nominally 100, 800 and 4000 mg 1−1. A series of experiments was performed in which the flume was run through consecutive, four hour cycles where the mean current velocity in the flume changed sinusoidally from 5 to 45 cm sec−1. For each sediment concentration the experiment was repeated with some of the fresh water replaced by particle-free seawater to give salinities of 0, 0.2, 2.0 and 10. Over a typical velocity cycle, suspended sediment concentrations decreased with decreasing current velocity, initially slowly, and then more rapidly. The concentration and size of material in suspension minimised over the low velocity period as particles settled. After a certain lag, sediment erosion occurred with increasing velocity and suspended solids concentration increased to a point where all the sediment was in suspension. The particle size data showed that during declining velocity conditions the median size of the particles initially increased as velocity decreased and then decreased as settling of the larger particles from suspension outweighed the aggregation process. During the erosion phase the median diameters increased initially but then decreased and levelled off as current velocity increased further. This was interpreted as mobilisation of aggregated particles followed by breakage as velocity increased. In general the degree of aggregation, and thus deposition, increased with salinity and with solids concentration. Solids concentration had by far the greatest effect on aggregation and deposition rate.

Description: The high precision measurement of the Sr/Ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can affect the Sr/Ca ratio of corals, and produce inaccuracies of the order of 2–4 °C. In the present study, a number of cores of the massive hermatypic scleractinian coral Porites, from the central Great Barrier Reef, have been analyzed for Sr/Ca at weekly to monthly resolution. Results from a 24 year record from Myrmidon Reef show an overall variation from 22.7 °C to 30.4 °C. The record shows a warming/cooling trend with maximum warming centred on the 1986–1987 summer. While some bleaching was reported to have occurred at Myrmidon Reef in 1982, the Sr/Ca record indicates that subsequent summer temperatures were much higher. The 4.5 year record from Stanley Reef shows a maximum SST of 30 °C during the 1997–1998 El Niño event. The calibrations from Myrmidon and Stanley Reefs are in excellent agreement with previously published calibrations from nearby reefs. While corals do not calcify in equilibrium with seawater due to physiological control on the uptake of Sr and Ca into the lattice of coralline aragonite, it can be argued that, provided only a single genus such as Porites sp. is used, and that the coral is sampled along a major vertical growth axis, then the Sr/Ca ratio should vary uniformly with temperature. Similarly, objections based on the spatial and temporal variability of the Sr/Ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the Sr/Ca activity ratio, and there does not appear to be a change in this ratio over the growth period of the coral. Evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the Sr/Ca–SST relationship. Thermal stress, resulting from either extremely warm or cool temperatures, can produce anomalously low Sr/Ca derived SSTs as a result of the breakdown of the biological control on Sr/Ca fractionation. It is considered that other stresses, such as increased nutrients and changes in light intensity, can also lead to a breakdown in the Sr/Ca–SST relationship. Two of the main issues affecting the reliability of the Sr/Ca method are the calibration of the Sr/Ca ratio with measured SST and the estimation of tropical last glacial maximum (LGM) palaeotemperatures. Instead of producing a constant calibration, just about every one published so far is different from the others. What is obvious is that for most calibrations while the slope of the calibration equation is similar, the intercepts are not. While the cause for this variation is still unknown, it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals’ physiology. Sr/Ca derived SST estimates for the LGM and deglaciation of 5 °C–6 °C cooler than present are at odds with estimates of 2 °C–3 °C cooling by other climate proxies. The apparent lack of reef growth during the LGM suggests that SSTs were too cold in many parts of the tropics for reefs to develop. This would lend support to the idea that tropical SSTs were much cooler than what the CLIMAP data suggests.

Description: Längsee is a small meromictic lake in Carinthia, SE Alps, with partially varved Lateglacial sediments. The Längsee tephra correlates to the Neapolitan Yellow Tuff (NYT), an eruption from the Campanian Volcanic Province, Italy. This tephra provides a Lateglacial chronostratigraphic time marker from central Italy across the Adriatic Sea to the southeastern Alps. The Längsee tephra is discussed in the context of pollen, geochemical, and microstratigraphical data from a profundal sediment core from Längsee. The age of 14,120 cal yr BP for the NYT has been accepted from the Monticchio chronology. The timescale for the Lateglacial in the Längsee record is based on laminae counts and has been linked to calendar year ages using the NYT tephrachronological marker. Consequently, the mass expansion of Betula has been dated at 14,270 cal yr BP. The expansion of P. sylvestris started concurrent with the NYT, and about 180 yr later, at 13,940 cal yr BP, P. sylvestris forests were established. The Younger Dryas biozone at Längsee is characterized only by a slight increase in non-arboreal pollen and dominated by pine with visible variations only in pine pollen types. Differentiation of pine pollen types allowed the recognition of three minor fluctuations during the Lateglacial interstadial. Two of these oscillations tentatively have been correlated with the Aegelsee and Gerzensee oscillations in Switzerland as well as with vegetation changes in NW Germany.

Description: Two modes of decrease in load bearing capacity of granular materials are discussed in view of experimental results. Both relate to the fact that frictional materials exhibit nonassociated plastic flow and they undergo considerable volume changes, either contraction or dilation. One mode consists of the instability that may occur in certain regions of stress space and potentially result in liquefaction of the granular material. It is the fact that loading of contracting soil (resulting in large plastic strains) can occur under decreasing stresses that may lead to unstable behavior under undrained conditions. As long as the soil remains drained, it will remain stable in the region of potential instability. The other mode is initiated by localization of plastic strains and subsequent development of shear bands, which in granular materials is followed by a decrease in load bearing capacity. These two modes are mutually exclusive and they occur for different loading and material conditions as discussed here on the basis of experimental observations.

Description: Results are presented for the first in-depth investigation of Tl isotope variations in marine materials. The Tl isotopic measurements were conducted by multiple collector-inductively coupled plasma mass spectrometry for a comprehensive suite of hydrogenetic ferromanganese crusts, diagenetic Fe–Mn nodules, hydrothermal manganese deposits and seawater samples. The natural variability of Tl isotope compositions in these samples exceeds the analytical reproducibility (±0.05‰) by more than a factor of 40. Hydrogenetic Fe–Mn crusts have ϵ205Tl of +10 to +14, whereas seawater is characterized by values as low as −8 (ϵ205Tl represents the deviation of the 205Tl/203Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 104). This ∼2‰ difference in isotope composition is thought to result from the isotope fractionation that accompanies the adsorption of Tl onto ferromanganese particles. An equilibrium fractionation factor of α∼1.0021 is calculated for this process. Ferromanganese nodules and hydrothermal manganese deposits have variable Tl isotope compositions that range between the values obtained for seawater and hydrogenetic Fe–Mn crusts. The variability in ϵ205Tl in diagenetic nodules appears to be caused by the adsorption of Tl from pore fluids, which act as a closed-system reservoir with a Tl isotope composition that is inferred to be similar to seawater. Nodules with ϵ205Tl values similar to seawater are found if the scavenging of Tl is nearly quantitative. Hydrothermal manganese deposits display a positive correlation between ϵ205Tl and Mn/Fe. This trend is thought to be due to the derivation of Tl from distinct hydrothermal sources. Deposits with low Mn/Fe ratios and low ϵ205Tl are produced by the adsorption of Tl from fluids that are sampled close to hydrothermal sources. Such fluids have low Mn/Fe ratios and relatively high temperatures, such that only minor isotope fractionation occurs during adsorption. Hydrothermal manganese deposits with high Mn/Fe and high ϵ205Tl are generated by scavenging of Tl from colder, more distal hydrothermal fluids. Under such conditions, adsorption is associated with significant isotope fractionation, and this produces deposits with higher ϵ205Tl values coupled with high Mn/Fe.

Description: A geographically related database called MAGIC has been developed, using GIS (Geographic Information System) technology, for MArine Gas seeps and seep IndiCators. A complementary bibliographic database (GASREF) stores details of related publications. The databases include data relating to natural seabed gas seeps and features such as pockmarks, cold seep communities, and methane-derived carbonates which are known to be found in association with seeps. The databases are compiled from published reports (so far restricted to those written in English), and users are able to interrogate the system for specified features from user-defined areas.

Description: The speed at which air-breathing marine predators that forage by diving should swim is likely to depend on a variety of factors that differ substantially from those relevant in animals for which access to oxygen is unlimited. We used loggers attached to free-living penguins to examine the speed at which three species swam during periods searching for prey and compared this to their speeds during actual prey pursuit. All penguin species appeared to travel at similar speeds around 2 m/s during normal commuting between the surface and feeding depths, which accords closely with minimum costs of transport. However, Adélie penguins, Pygoscelis adeliae, slowed down to feed, Magellanic penguins, Spheniscus magellanicus, speeded up and king penguins, Aptenodytes patagonicus, travelled at a variety of speeds, although mean speed did not change from normal commuting. Since energy expenditure, and therefore oxygen usage, in swimming animals increases with the cube of the speed, we hypothesized that prey escape speed (a function of prey size) and prey density would prove critical in determining optimum pursuit speeds in predators. Simple models of this type help explain why it is that some penguin species apparently benefit by increasing speed to capture prey while others benefit by decreasing speed.

Description: Fluid and melt inclusions in minerals of two native iron-bearing dyke rocks from Disko, Greenland, were investigated using heating and cooling microscopic techniques. The melt inclusions in olivine are homogenized at temperatures of 1170–1200 °C. The melts are characterized by high SiO2, K2O and TiO2 and low MgO contents. The co-existence of combined melt–fluid (gas) inclusions in olivine implies that the olivine phenocrysts crystallized from a heterogeneous magma at low pressure. Gas bubbles were investigated in the glass of the rock. Water and four crystalline phases were observed at room and low temperatures on the walls of the bubbles: serpentine, naphthalene, clathrate, and an unknown phase. The complex composition of trapped volatiles is reflected in considerable ranges of clathrate melting and solidus temperatures (20 to 7.5 °C and −82.6 to −73 °C, respectively). Melt equilibrium with metallic iron at T=1450 K suggests that logfO2=−13.95. The calculated composition of C–O–H fluid in equilibrium with Fe, Fe3C and FeS is characterized by high CH4 and H2 contents. During cooling at the postmagmatic stage, polymerization proceeds, and heavy hydrocarbons are formed inside vesicles. The presence of organic compounds in inclusions trapped at a magmatic stage is a natural consequence of unusual reducing condition during crystallization.

Description: The widespread Pliocene (ca. 2 Ma) orthopyroxene-bearing tholeiites represent by far the most voluminous but short-lived magmatic phase of the Cenozoic Iblean volcanic province. We have studied major, volatile (H2O, S, and Cl), and light lithophile (Li, Be, and B) elements and 7Li/6Li and 11B/10B isotopic ratios of olivine- and orthopyroxene-hosted glass inclusions and their host pillow-rim glasses using EPMA and SIMS. Most variations of major elements, H2O (0.2–0.5 wt.%), Cl (100–350 ppm), and especially of Li (4.6–5.8 ppm), Be (0.5–0.8 ppm) and B (0.6–1.1 ppm) are believed to reflect heterogeneity of the Iblean magma source. Crystallization of these magmas occurred at shallow crustal depths in the range of 1250–1140 °C and oxygen redox conditions corresponding to FMQ–NNO buffers. Olivine [75.8–83.8 mol% Fo], orthopyroxene [Mg#=80.3–85.6], plagioclase [54.2–69.9 mol% An] and spinel [Mg#=40.9–49.6 and Cr#=59.6–63.8] are common liquidus phases. Variable sulfur concentrations in glass inclusions (280–1330 ppm S) and host matrix glasses (160–670 ppm S) reflect degassing of rising and erupting magma. The abundances of SO42− dissolved in the melt (9–38% of total S) fit well to the redox conditions deduced from Fe2+/Fe3+ratios of the coexisting spinel. Glass inclusions scatter significantly in 7Li/6Li and 11B/10B isotopic ratios even within single specimens (δ7Li=−3.4‰ to +1.2‰ and δ11B=−17.1‰ to −3.1‰). The lowest δ7Li (−3.4‰ to +1.2‰) and δ11B (−13.9‰ to −16.1‰) probably reflect isotopically light mantle domains beneath the Iblean Plateau. The shift of δ11B toward more positive values (up to −3.1‰) at nearly the same low δ7Li (−3.4‰ to 0.9‰) is explained by assimilation of 〈2 wt.% altered basaltic rocks.

Description: Scattering and absorption characteristics of water cloud droplets containing black carbon (BC) inclusions are calculated at a visible wavelength of by a combination of ray-tracing and Monte Carlo techniques. In addition, Lorenz–Mie calculations are performed assuming that the same amount of BC particles are mixed with water droplets externally. The results show that it is unlikely under normal conditions that BC aerosols can modify scattering and absorption properties of cloud droplets in any significant way except for geographical locations very close to major sources of BC. The differences in the single-scattering co-albedo and asymmetry parameter between BC-fraction-equivalent internal and external mixtures are negligibly small for normal black carbon loadings, which makes possible the use of the much simpler external mixing model in radiative transfer modeling irrespective of the actual form of mixing. For a fixed amount of BC internally mixed with cloud droplets, the absorption is maximal when the effective radius of the BC inclusions is about 0.05–.

Description: We report ion microprobe analyses of S and O isotopes in glass inclusions and their host clinopyroxenes (Cpx) from Miocene basaltic hyaloclastites drilled during Ocean Drilling Program (ODP) Leg 157. This is the first study where high-precision in situ δ34S and δ18O measurements were applied in order to constrain the isotopic variability of intraplate magmas and to have insights into establishment of isotopic equilibrium between the melt and crystallizing phenocrysts. Glass inclusions range from tholeiitic to alkali basaltic composition and contain varying to very high proportions of sulfur dissolved as sulfate (S6+/Stotal = 0.40 to 0.87) at S contents of 800 to 2100 ppm. The δ34S values varying from -1.0 to +8.5 ± 1.5‰, exceed significantly the range reported for fresh submarine midocean ridge basalt (MORB) and oceanic island basalt (OIB) glasses, and positively correlate with Cl concentrations and S6+/Stotal ratios. The δ18O values in glass inclusions and their host Cpx crystals analyzed within 50 μm distance away from inclusions are also strongly variable (inclusions: +5.0 to +8.2 ± 0.7‰; Cpx: +5.7 to +8 ± 0.7‰) and are in agreement with O-isotope equilibrium between Cpx and basaltic melt. A broad δ18O range (+5.6 to +7.3‰) decoupled from that of the melt inclusions was also found in the Cpx crystals measured 〉500 μm away from inclusions. The variations of δ34S and δ18O in glass inclusions are interpreted as resulting from a combination of degassing and assimilation processes. Hydrothermally altered basaltic crust (δ34S = +4.0 to +9.6‰, δ18O = +9.0‰) mixed with oceanic sediments (δ18O ≈ 25‰) and containing up to 5 wt.% of seawater sulfate (δ34S = +21‰, δ18O = +9.5‰) represents the most probable contaminating end-member. The oxygen isotope heterogeneity found in most Cpx crystals and their glass inclusions implies that magma contamination and inclusion-trapping occurred during a few years only, i.e., too short for O isotopic homogeneity to be reestablished in the entire crystals.

Description: Hydrothermal gases from shallow seafloor vents in the Bay of Plenty, New Zealand contain CO2, CH4, and the higher gaseous hydrocarbons up to i-, n-C4H10. The gases are similar to those discharged at fumaroles on the nearby White Island. Carbon isotope compositions for CO2 fall between −3.4‰ and −5.5‰ PDB and reflect a shallow magmatic carbon source. The δ13C values of CH4 range from −24.6‰ to −28.9‰ PDB and the δD values vary between −122‰ and −135‰ SMOW. The CH4 isotope values and the presence of the higher hydrocarbon compounds such as C2H6 and C3H8 with δ13C values near −20‰ PDB suggest hydrocarbon production by high-temperature maturation of sedimentary organic matter and mixing (∼1:1) of the thermogenic CH4 with abiogenic CH4. Long-chained hydrocarbons occur in dredged samples close to the active vents. Their n-alkane distribution has a high to moderate odd–even predominance and an extensive hopane series, indicative of higher land-plant waxes and prokaryotic membranes in the source. Substantial amounts of unsubstituted polynuclear aromatic hydrocarbons (PAH) mark the transition from aliphatic- to aromatic-dominated bitumens, consistent with extensive source maturation resulting from thermal stress. The bitumens are interpreted as pyrolysates derived from buried near-coastal vegetation and terrestrial detritus under various thermal regimes, mixed with immature seafloor organic matter.

Description: Seismic velocities obtained from ocean-bottom hydrophone, expanding spread profile and multi-channel seismic data were used to compile a velocity model for the Mediterranean Ridge along a 220-km-long transect extending from the Sirte Abyssal Plain to the Cleft region near the Hellenic Trough. A 200–300-m-thin layer of Plio–Quaternary sediments with velocities of 1800–2200 m s−1 covers the whole Ridge. The Messinian evaporites (4000–4500 m s−1) occur in the southwest as a tectonically thickened layer and in a basin just northeast of the crest of the Ridge. In the intervening region however, the evaporites appear absent and the seismic velocities are generally lower. Arched reflectors, imaged in the depth-migrated section, suggest that the sediments beneath the Ridge crest belong to a Pre-Messinian accretionary wedge. Beneath the Messinian evaporites a northeastward-thinning layer of probable Tertiary sediments shows laterally increasing velocities from 3300 m s−1 to 4600 m s−1. Assuming that the layer thinning is caused by compaction due to increased overburden alone, we have calculated a porosity reduction from 15% to 4% and an associated fluid expulsion of 10 km3 km−1 along the trench axis. This corresponds to c. 60% of the initial fluid volume of an undeformed sediment column from the abyssal plain. The almost impermeable evaporitic cap over these sediments leads to high fluid pressures at the base of the evaporites, likely to make this horizon the basal décollement of the modern accretionary system. A 2.5-km-thick unit of probable Mesozoic carbonates with velocities of 4500–4600 m s−1 is inferred at c. 8 km depth. The top of the oceanic crust occurs at a depth of about 10 km. The results from this study have widespread implications for the understanding of the regional geological history.

Description: The Mediterranean Ridge is a unique accretionary complex, consisting of five key elements: the frontal slope, the upper slope, the crest of the Ridge, the Cleft area, and the Inner Plateau. The IMERSE data show that these correspond roughly to the locus of frontal accretion, of underplating, of a pre-Messinian wedge, of complex faulting and possible strike-slip tectonics, and of a backstop of Hellenic nappes covered by a Messinian forearc basin. The frontal portion of the complex is a post-Messinian accretionary wedge (composed of Messinian evaporites and overlying tightly folded Plio–Quaternary sediments), underlain by pre-Messinian sequences attached to the African Plate. The basal detachment at the front of the wedge occurs at the base of the evaporites. Moving further to the northeast (the upper slope), the basal detachment cuts to deeper levels leading to the development of duplex structures where pre-Messinian units are subcreted beneath the Messinian evaporites. Just behind the subcreted units, the evaporites thin and may be absent on the crest of the Ridge. This region we interpret as the site of a pre-Messinian accretionary wedge: we suggest that following the deposition of thick evaporites in the Messinian, the pre-Messinian accretionary tectonics continued as subsurface accretion (subcretion) beneath the evaporites. Although the crest of the Ridge is largely devoid of evaporites, local deep evaporite basins observed here formed as local closed basins on top of the pre-Messinian wedge. We infer that the Messinian sealevel was at about the level of the Ridge crest, that is 3000 m below present. Allowing for isostatic adjustment to the removal of the water load, this would imply a sealevel drop of at least 2000 m. The Cleft basins mark the northeast limit of the accretionary complex. Thick evaporite deposits to the northeast (beneath the Inner Plateau) may have been deposited in a Messinian forearc basin. The evaporites of the Inner Plateau are underlain by a thin pre-Messinian sequence and by crystalline basement of the Hellenic nappes. This basement forms the backstop to the accretionary complex.

Description: Ten ODP sites drilled in a depth transect (2164–4775 m water depth) during Leg 172 recovered high-deposition rate (〉20 cm/kyr) sedimentary sections from sediment drifts in the western North Atlantic. For each site an age model covering the past 0.8–0.9 Ma has been developed. The time scales have a resolution of 10–20 kyr and are derived by tuning variations of estimated carbonate content to the orbital parameters precession and obliquity. Based on the similarity in the signature of proxy records and the spectral character of the time series, the sites are divided into two groups: precession cycles are better developed in carbonate records from a group of shallow sites (2164–2975 m water depth, Sites 1055–1058) while the deeper sites (2995–4775 m water depth, Sites 1060–1063) are characterized by higher spectral density in the obliquity band. The resulting time scales show excellent coherence with other dated carbonate and isotope records from low latitudes. Besides the typical Milankovitch cyclicity significant variance of the resulting carbonate time series is concentrated at millennial-scale changes with periods of about 12, 6, 4, 2.5, and 1.5 kyr. Comparisons of carbonate records from the Blake Bahama Outer Ridge and the Bermuda Rise reveal a remarkable similarity in the time and frequency domain indicating a basin-wide uniform sedimentation pattern during the last 0.9 Ma.

Description: Long-range, low-resolution and deep-towed, high-resolution side-scan sonar records, high-resolution seismic profiles and core samples were used to study the relatively small canyon fed turbidite systems west of Corsica and Sardinia. The margin west of Corsica is dissected by deep (up to 1500 m), straight canyons that have steep axial gradients (10° slopes are common) and that extend from land to sea without a break in gradient. The submarine canyon axes are readily mapped by their stronger acoustic backscatter. The axes have scour holes and trains of gravel or pebble waves. Canyoned slopes have widespread, shallow sediment failures. Five separate depositional lobes are recognised, extending beyond the canyon mouths. Deep-towed, high-resolution seismic profiles across part of one lobe show stacked sedimentary sheets, a few tens of kilometres wide. Cores from these sheets contain coarse to medium sand beds that are up to 3 m thick, with some mud clasts in the middle of the beds and up to 3% clay in the sand matrix. A drape of nannofossil ooze on top of cores indicates that the main activity through the canyons is at times of low sea level. The lobes tend to appear as weak backscatter, with fringes of a braid-like pattern of stronger backscatter. The reasons for this acoustic pattern are not fully understood, though in general the sand bodies are found where backscatter is relatively weak. The size of the canyon-mouth lobes is proportional to the size of the subaerial drainage basins. The limited sediment supply accounts for the absence of a well-developed submarine ramp despite the sand-dominated input from multiple sources.

Description: Seven lithological units, alternating between horizons enriched in biogenic opal (diatoms) and carbonate (foraminifera) and units composed largely of terrigenous sediment with very low biogenic admixture, were distinguished in a series of Late Quaternary sediment cores from the Sea of Okhotsk. Sediments were characterised using on-board visual description, smear-slides analyses, grain-size composition and magnetic susceptibility (MS) records. Five tephra marker layers, identified as Ko, TR, K2, K3 and K4, were distinguished using petrological, mineralogical and geochemical analyses. Age models were developed by comparing lithological units, tephra stratigraphy and MS records with oxygen isotope curves and with records of biogenic CaCO3, opal content, and sediment grain-size composition in three AMS radiocarbon dated Okhotsk cores. This chronological framework allowed us to investigate climate control over the sedimentation regime and productivity, and to clarify the formation times of the lithological and tephra units. The data show that sediment MS variations in the south-eastern area of the glacial Okhotsk Sea arose primarily from volcanic material input. The sedimentation in all other parts of the sea was mainly controlled by the supply of terrigenous material. The cores show a tight correlation between MS, sediment grain size and climate change in the Okhotsk Sea: coarse sediments with a high MS were accumulated during the cold period-oxygen isotope stages (MIS) 2, 4, 6; fine sediments with a low ice-rafted debris (IRD) content and MS were formed in the warm isotope stages. According to the oxygen isotope stratigraphy and radiocarbon data, the Ko, TR, K2, K3 and K4 tephra were deposited at 7.7, 8.0, 26.0 kyr BP, in MIS 4 about 60–70 kyr ago, and near MIS 5.4, respectively. Comparison of tephra mineralogy, petrology, spatial distributions and ages with the history of Kurile–Kamchatka volcanism allows us to identify likely candidates for the tephra source eruptions. The combined use of MS records, tephrochronology and lithological unit sequences provides a detailed basis for Okhotsk Sea sediment stratigraphy.

Description: In the context of the IMERSE project, several crossings of the deformation front of the western Mediterranean Ridge were made in the region of the Sirte Abyssal Plain, the Messina Abyssal Plain and the intervening region. In this paper, we present seismic images and interpretations across the deformation front, with particular emphasis on the role the Messinian evaporites have played in controlling the accretionary tectonics of the thin frontal portion of the wedge. The seismic images show that the basal detachment generally is located at the base of the evaporites. From a consideration of the mechanics of the wedge, for both Coulomb and plastic rheologies, we show that the low wedge taper (c. 2°) requires that the detachment is characterised by extreme fluid overpressuring (within 2% of lithostatic in places) and that the basal yield stress (less than 1 MPa) is lower than that of a wet salt décollement zone. This supports the seismic interpretation that the detachment occurs in overpressured sediments beneath the impermeable evaporites. Lateral variations in the accretionary style can be related to lateral variations in evaporite thickness, the effectiveness of the evaporite as an impermeable seal and to local relief on the subducting plate; these factors control the escape of fluids from beneath the evaporites and hence fluid pressure and basal yield stresses.

Description: A combination of weight and reflectance measurements as well as scanning electron microscope (SEM) analyses on planktic foraminiferal tests from two sites in the Nordic Seas were used to investigate the pelagic carbonate preservation during the last five glacial–interglacial cycles. In general, a pattern showing good preservation during glacial times and enhanced corrosion during interglacial times can be observed. Marine Isotope Stage 11 (MIS 11) reveals the strongest corrosional features with an estimated 45% total loss of the foraminiferal carbonate before shell fragmentation. One reason for the enhanced interglacial corrosion may be a high regional surface productivity during these intervals, which led to increased dissolution rates in the deep sea driven by metabolic carbon dioxide. However, the carbonate preservation changes may also be linked to global changes in the marine carbonate system. Although the reason for the observed dissolution pattern in the Nordic Seas remains speculative, it seems to be in phase with the rhythm of glacial–interglacial carbonate preservation in the Pacific Ocean but out of phase with the rest of the Atlantic. The data further support the hypothesis that much of the glacial decrease in the atmospheric CO2 may be attributed to the changes in the alkalinity of the oceans.

Description: Pre-Permian sedimentary basins in the southeastern North Sea have been previously interpreted from potential field data but only poorly imaged on seismic sections due to the presence of salt layers and a thick Mesozoic and Cenozoic cover. Furthermore, potentially low prospectivity for hydrocarbon resources has resulted in sparse penetration of Pre-Permian sediments in the southeastern North Sea. We present images of large Palaeozoic basins obtained through reprocessing and pre-stack depth migration of seismic data from the MONA LISA project. The depth images show in detail the structure of pre-Permian basins beneath the Danish basin and the Ringkøbing-Fyn High, providing new insights into Upper Palaeozoic basin formation in the North Sea.

Description: Seismic P-wave travel times collected during METEOR cruise M24 are inverted to derive a three-dimensional model of the P-wave velocity structure of the northern part of Gran Canaria, Canary Islands. The data consist of 6689 P-wave travel times from 1487 offshore air-gun shots which were recorded by both land-based seismometers and ocean bottom hydrophones. The crustal structure is well imaged by the data set as demonstrated by analysis of the resolution and tests with synthetic data. The volcanic island is characterized by generally high P-wave velocities (〉5.5 km/s) and a heterogeneous structure with large lateral velocity variations. High P-wave velocities are found around the centers of the Miocene shield volcanoes in the vicinity of Agüimes, San Nicolas, and Agaete as well as the center of the Pliocene Roque Nublo volcano. The velocity structure suggests a high percentage of dense intrusive rocks. Some of the intrusive rocks were emplaced during the eruption of 〉1000 km3 of Miocene felsic magmas following the basaltic shield phase. The velocity structure beneath La Isleta peninsula and its submarine continuation is interpreted as a volcanic rift zone with abundant dikes. The velocities decrease to 〈5 km/s north of the coastline. A high velocity zone thinning away from the central edifice is interpreted as the massive island flank extending up to 50 km off the coast which is underlain by prevolcanic Neogene–Jurassic sediments. The igneous part of the oceanic crust exhibits an anomalous structure with a relatively small thickness (∼3 km) layer 3 and a 2–4-km-thick layer 2, probably reflecting a modification of the crust due to long-lasting magmatic intrusive activity during the evolution of the Canary Islands. The Moho north of Gran Canaria is found at a depth of ∼15 km. The structure of Gran Canaria and the adjacent ocean basin is thought to be the result of a diffuse mantle upwelling under a slowly moving plate.

Description: We compiled a global data set of volcanic degassing during both explosive and quiescent volcanic events. The data set comprises estimates of gas emissions of volcanoes from Europe (e.g. Etna), Asia (e.g. Merapi), the Americas (e.g. Fuego), Africa (e.g. Erta Ale) and ocean islands (e.g. Kilauea) over the past 100 yr. The set includes 50 monitored volcanoes and ∼310 extrapolated explosively erupting volcanoes. Among the ∼360 volcanoes, 75% are located in the Northern and 25% in the Southern Hemisphere. We have estimated the total annual global volcanic sulfur emission into the atmosphere to be on the order of 7.5–10.5×1012 g/yr S (here as SO2), amounting to 10–15% of the annual anthropogenic sulfur output (∼70×1012 g/yr S during the decade 1981–1990) and 7.5–10.5% of the total global sulfur emission (e.g. biomass burning, anthropogenic, dimethylsulfide) with ∼100×1012 g/yr S. The estimates of other volcanic gases emitted (e.g. H2S, HCl) are based on the assumption that the different gas components emitted by a volcano are in equilibrium with each other. Accordingly, the molar ratios of the gas species in high-temperature fumaroles are similar to molar ratios equilibrated at depth where the gas separates from the magma. Thus, we can use the directly measured SO2 fluxes and known molar ratios (e.g. H2S/SO2) for a semi-quantitative estimate of other gas components emitted (e.g. H2S). The total annual emission of HCl is 1.2–170×1012 g/yr, that of H2S 1.5–37.1×1012 g/yr, of HF 0.7–8.6×1012 g/yr, of HBr 2.6–43.2×109 g/yr, and of OCS 9.4×107–3.2×1011 g/yr. We estimate an emission of 1.3×107–4.4×1010 g/yr for CS2.

Description: In order to explain biological zonation, shore height above the ordnance level is frequently used as an indicator of the abiotic gradient in intertidal ecosystems. This is based on the implicit assumption that shore height is directly correlated with inundation frequency and/or duration. Despite the importance of inundation for tidal ecosystems, measurements have rarely been taken directly by measuring inundation at the site of investigation. We measured mean high tide (MHT) and flooding frequency at three sites on the Dutch Barrier Island of Schiermonnikoog. To assess the scale dependence, we compared local measurements with the estimated inundation frequencies based on the official tide gauge (OTG) farther away. Locally measured MHT water levels differed among sites and were consistently higher than estimated MHT water levels. With this data, we subsequently estimated the inundation frequency of vegetation plots from our measurements and correlated it with species distribution. In a logistic regression inundation frequency accounted for twice the variance in explaining the dominance of three salt marsh species than shore height. The discrepancy in annual inundation frequency of the vegetation between sites was ≦300% for a given shore height. Within each site replicated estimates of inundation frequency proved to be consistent (scale 10–50 m). Estimated and measured inundation frequencies thus reliably correlated at a small-scale (tens of metres), but not at a larger scale (hundreds of metres to kilometres). If inundation frequency is used as an explanatory variable, it will therefore be advisable to consider the spatial heterogeneity of the measurements, in particular if different sites are to be compared. We give mean inundation frequencies of three dominant salt marsh species (Elymus athericus, Festuca rubra, Artemisia maritima) measured over 1 year.

Description: Variations in oxygen conditions below the permanent halocline influence the ecosystem of the Baltic Sea through a number of mechanisms. In this study, we examine the effects of physical forcing on variations in the volume of deep oxygenated water suitable for reproductive success of central Baltic cod. Recent research has identified the importance of inflows of saline and oxygenated North Sea water into the Baltic Sea for the recruitment of Baltic cod. However, other processes have been suggested to modify this reproduction volume including variations in timing and volume of terrestrial runoff, variability of the solubility of oxygen due to variations in sea surface temperature as well as the influence of variations in wind stress. In order to examine the latter three mechanisms, we have performed simulations utilizing the Kiel Baltic Sea model for a period of a weak to moderate inflow of North Sea water into the Baltic, modifying wind stress, freshwater runoff and thermal inputs. The model is started from three-dimensional fields of temperature, salinity and oxygen obtained from a previous model run and forced by realistic atmospheric conditions. Results of this realistic reference run were compared to runs with modified meteorological forcing conditions and river runoff. From these simulations, it is apparent that processes other than major Baltic inflows have the potential to alter the reproduction volume of Baltic cod. Low near-surface air temperatures in the North Sea, the Skagerrak/Kattegat area and in the western Baltic influence the water mass properties (high oxygen solubility). Eastward oriented transports of these well-oxygenated highly saline water masses may have a significant positive impact on the Baltic cod reproduction volume in the Bornholm Basin. Finally, we analysed how large scale and local atmospheric forcing conditions are related to the identified major processes affecting the reproduction volume.

Description: Algal community species composition, as estimated by high performance liquid chromatography (HPLC) pigments and microscopy analysis, and trace metal speciation (Cu and Co) and distributions (Fe, Zn, Co and Cu) were measured along a summer transect across the Skagerrak. In waters of Baltic origin, with elevated trace metals levels, but very low macronutrients, a mix of dinoflagellates and haptophytes dominated the low biomass. In the Jutland current, which had high dissolved iron concentrations, a mixed bloom (4–6 μg/l chl a) of diatoms (major species—Leptocylindricus danica) and dinoflagellates (Ceratium sp.) was present. In the waters of the central Skagerrak derived from the North Sea, below the low salinity Baltic water, a large diatom (major species—L. danica) bloom (7.7 μg/l) was present at 35 m. This bloom formed below the pycnocline, and was located at the nutricline for silicate. The lowest concentrations of trace metals were found in the water of North Sea origin. Synechococcus-like cyanobacteria were observed in the upper waters across the survey area, as were strong binding ligands for Cu, but no clear numerical relationship existed between them, as had been observed by Moffett [Deep-Sea Res. 42 (1995) 1273]in the Sargasso Sea. The [Co]/[Zn] hypothesis of Sunda and Huntsman [Limnol. Oceanogr. 40 (1995) 1404] for coccolithophorids and diatoms was examined using the field data collected.

Description: We compared the effect of CO2 concentration ([CO2], ranging from ∼5 to ∼34 μmol l−1) at four different photon flux densities (PFD=15, 30, 80 and 150 μmol m−2 s−1) and two light/dark (L/D) cycles (16/8 and 24/0 h) on the coccolithophore Emiliania huxleyi. With increasing [CO2], a decrease in the particulate inorganic carbon to particulate organic carbon (PIC/POC) ratio was observed at all light intensities and L/D cycles tested. The individual response in cellular PIC and POC to [CO2] depended strongly on the PFD. POC production increased with rising [CO2], irrespective of the light intensity, and PIC production decreased with increasing [CO2] at a PFD of 150 μmol m−2 s−1, whereas below this light level it was unaffected by [CO2]. Cell growth rate decreased with decreasing PFD, but was largely independent of ambient [CO2]. The diurnal variation in PIC and POC content, monitored over a 38-h period (16/8 h L/D, PFD=150 μmol m−2 s−1), exceeded the difference in carbon content between cells grown at high (∼29 μmol l−1) and low (∼4 μmol l−1) [CO2]. However, consistent with the results described above, cellular POC content was higher and PIC content lower at high [CO2], compared to the values at low [CO2], and the offset was observed throughout the day. It is suggested that the observed sensitivity of POC production for ambient [CO2] may be of importance in regulating species-specific primary production and species composition

Description: Sandbox experiments of accretionary wedges were performed incorporating a thin weak layer of micro glass beads. The impact of heterogeneous sedimentary input on wedge mechanics, evolution and mass transfer was investigated. We report the first experimentally documented growth of basal duplexes. These occurred for high basal friction conditions, with restricted output of the lower section. The upper and lower sections were completely decoupled due to the intervening layer of glass beads, with frontal accretion occurring in the upper section simultaneously with basal duplex formation and underplating of subsequent generations of duplexes. IMERSE multichannel seismic reflection data from the Western Mediterranean Ridge (WMR) image Tertiary clastics beneath a thick section of Messinian evaporites. The base of the evaporites is identified as the primary décollement for deformation in the frontal part of the accretionary complex. Constriction of the channel of subducting Tertiary sediments, as well as internal deformation observed as arcward-dipping reflectors argue for basal underplating and/or two different active décollements. We propose an evolution of the WMR in accordance with the sandbox experimental results. A weak mid-level detachment (base of evaporites) combined with a strong basal detachment produce mechanical decoupling and basal accretion of toeward-verging duplexes.

Description: Seismic reflection observations from the IMERSE cruise have confirmed the presence of at least two localised thick evaporite basins on the crest and Inner Plateau of the Mediterranean Ridge accretionary complex. The discovery is supported by interval velocity results from both near-normal incidence reflection data and wide-angle seismic data. These evaporite basins are located north of a deep trough known as the Cleft and at a currently active thrust zone south of the Cleft, on the crest of the Mediterranean Ridge. The polarity of the seismic reflections associated with the base of the evaporite shows a phase reversal relative to the seafloor. This high amplitude phase reversed reflection indicates a decrease in velocity between the evaporite and the underlying sediment. The existence of these thick evaporite deposits suggests that the distribution of Messinian salt is much thicker (∼1.8–2 km) on parts of the Ridge crest than initially perceived by previous investigations. We propose that these thick evaporite deposits were deposited in localised basins on the Ridge, formed in response to pre- and syn-Messinian tectonics. The evaporites on the Inner Plateau basin most likely represent the infill of a Messinian forearc basin. The existence of local deep evaporite basins on the crest of the Ridge at depths of 2.7–3.3 km below sea level at the present day supports the hypothesis that the Mediterranean Sea level must have dropped by around 3 km below its present sea level during the Messinian salinity crisis.

Description: A pockmark field was discovered during EM-300 multi-beam bathymetric surveys on the lower continental slope off the Big Sur coast of California. The field contains ∼1500 pockmarks which are between 130 and 260 m in diameter, and typically are 8–12 m deep located within a 560 km2 area. To investigate the origin of these features, piston cores were collected from both the interior and the flanks of the pockmarks, and remotely operated vehicle observation (ROV) video and sampling transects were conducted which passed through 19 of the pockmarks. The water column within and above the pockmarks was sampled for methane concentration. Piston cores and ROV collected push cores show that the pockmark field is composed of monotonous fine silts and clays and the cores within the pockmarks are indistinguishable from those outside the pockmarks. No evidence for either sediment winnowing or diagenetic alteration suggestive of fluid venting was obtained. 14C measurements of the organic carbon in the sediments indicate continuous sedimentation throughout the time resolution of the radiocarbon technique (∼45 000 yr BP), with a sedimentation rate of ∼10 cm per 1000 yr both within and between the pockmarks. Concentrations of methane, dissolved inorganic carbon, sulfate, chloride, and ammonium in pore water extracted from within the cores are generally similar in composition to seawater and show little change with depth, suggesting low biogeochemical activity. These pore water chemical gradients indicate that neither significant accumulations of gas are likely to exist in the shallow subsurface (∼100 m) nor is active fluid advection occurring within the sampled sediments. Taken together the data indicate that these pockmarks are more than 45 000 yr old, are presently inactive, and contain no indications of earlier fluid or gas venting events.

Description: The Mediterranean Ridge is an accretionary wedge consisting of a large pile of tectonically deformed sediments. In the past the Mediterranean Ridge has been interpreted as a prism related to Hellenic subduction. However, geophysical evidence (Pasiphae cruise, 1988) has indicated the presence of a high-velocity body southward of the Hellenic trench, which was subsequently interpreted as an extended continental backstop. During the recent IMERSE project, coincident wide-angle and normal-incidence seismic data were collected over the ridge along the NE–SW MEDRIFF corridor (Explora cruise, 1994). The objectives of the IMERSE project were to acquire the seismic observations necessary for a high-resolution structural model of the western Mediterranean Ridge, including the structure of the newly interpreted continental backstop. Here we present the results of recent re-modelling of two-ship, expanding spread, seismic refraction data (ESP-8 and -9) recorded during the Pasiphae cruise. The modelling of these data has allowed an approximate constraint on the position of the juncture between the Mediterranean accretionary complex and its buttress. Also presented are processing and modelling results of the recently acquired IMERSE wide-angle data. Travel-time modelling of these data has allowed the construction of six, multi-azimuth, velocity–depth models. These models show the existence of high-velocity material at depth (P-wave velocity〉5 km/s), inferred to be extended backstop, and constrain its southward extent. All models show the presence of a Messinian evaporite layer near the surface. The evaporite layer is observed to vary in thickness (from 0 to 2.0 km), with the existence of local thickening and thinning, due to depositional factors, tectonism and salt dissolution. In addition, combined analysis of the wide-angle velocity models with coincident seismic reflection and swath bathymetry data indicates that the geometry of the continental backstop varies laterally as a consequence of transform faulting, possibly related to the southward rotation of the Peloponnesus thrust sheet and backstop emplacement.

Description: Two cores recovered from the Discovery Basin and one reference core from a location outside the Basin were investigated in detail in order to decipher the influence of hypersaline brines on sediment geochemistry. The cores contain a tephra layer (presumable Y-5) and carbonate microfossils which permit a tentative chrono- and lithostratigraphic correlation. A layer containing up to 60 wt% biogenic opal and 6.6 wt% organic carbon was identified in one basin core, which probably represents the best preserved example of eastern Mediterranean sapropel S-1. The basin is filled with a concentrated solution of MgCl2 which is enriched in dissolved sulfate and has the highest salinity ever encountered in the marine environment. Pore water profiles demonstrate that this brine dissolves sedimentary calcite to form secondary carbonate- and sulfate-bearing minerals. Of these, dolomite, magnesite and gypsum were identified by X-ray diffractometry; thermodynamic calculations show that these phases form in equilibrium with the anomalous brine composition.

Description: Sr and Nd isotopic compositions of Arctic marine sediments characterize changes of sediment source regions and trace shelf–ocean particle pathways during glacial–interglacial transitions in the eastern Arctic Ocean. In the 140-ka sedimentary record of a marine core from Yermak Plateau, north of Svalbard, 87Sr/86Sr ratios and εNd values vary between 0.717 and 0.740 and −9.3 and −14.9, respectively. Sr and Nd isotopic composition both change characteristically during glacial–interglacial cycles and are correlated with the extension of the Svalbard/Barents Sea ice sheet (SBIS). The downcore variation in Sr and Nd isotopic composition indicates climatically induced changes in sediment provenance from two isotopically distinct end-members: (1) Eurasian shelf sediments as a distal source; and (2) Svalbard bedrock as a proximal source that coincide with a change in transport mechanism from sea ice to glacial ice. During glacier advance from Svalbard and intensified glacial bedrock erosion, εNd values decrease gradually to a minimum value of −14.9 due to increased input of crystalline Svalbard bedrock material. During glacial maxima, the SBIS covered the entire Barents Sea shelf and supplied increasing amounts of Eurasian shelf material to the Arctic Ocean as ice rafted detritus (IRD). εNd values in glacial sediments reach maximum values that are comparable to the average value of modern Eurasian shelf and sea ice sediments (εNd=−10.3). This confirms ice rafting as a major sediment transport mechanism for Eurasian shelf sediments into the Arctic Ocean and trace a sediment origin from the Kara Sea/Laptev Sea shelf area. After the decay of the shelf-based SBIS, the glacial shelf sediment spikes during glacial terminations I (εNd=−10.6) and II (εNd=−10.1) εNd values rapidly decrease to values of −12.5 typical for interglacial averages. The downcore Sr isotopic composition is anticorrelated to the Nd isotopic composition, but may be also influenced by grain-size effects. In contrast, the Nd isotopic composition in clay- to silt-size fractions of one bulk sediment sample is similar to within 0.3–0.8 εNd units and seems to be a grain-size independent provenance tracer.

Description: ODP sites 1055–1062 recover a bathymetric transect from 1800 to 4800 water depth in the subtropical NW-Atlantic (Carolina Slope, Blake–Bahama Outer Ridge). This sediment drift region is known for high deposition rates (〉40 cm/kyr) and offers the excellent opportunity to investigate the history of water mass circulation and chemistry as well as depositional changes during the Quaternary. A late Pleistocene time interval from 250 to 350 kyr (marine isotope stages 8–10) was investigated with centennial- to millennial-scale time resolution. Stable isotope records of benthic foraminifera provide new detailed insights on variations in climate and deep water ventilation. The δ13C records indicate well ventilated North Atlantic water masses between 2200 and 3000 m water depth during the time interval from stage 9 to interstadial 8.5. During the glacial stages 8.4 and 10.2, however, the decrease in δ13C reflects an extension of nutrient-rich Antarctic Bottom Water (AABW) up to 2200 m water depth. This is paralleled by a shoaling of the lysocline as indicated by the carbonate records. A comparison between carbonate dissolution proxies points out that the carbonate dissolution at the hemipelagic sites was not only influenced by the different carbonate ion concentration of the water masses (AABW contra North Atlantic Deep Water) but also by the organic carbon flux to the sea floor especially at the shallower sites, whereby the decay of organic matter enhanced carbonate dissolution in the sediments. Additionally the varying depth position and strength of the Deep Western Boundary Current (DWBC) plays an important role on the depositional system along the Blake–Bahama Outer Ridge. Comparisons between current intensities as inferred from grain size analyses, sand, and carbonate contents suggest that high intensities of the DWBC during cold stages caused an erosion of the fine carbonate and an enrichment of the sand fraction at shallower depth. During warm stages the main core of DWBC moved to greater depth and allowed the settling of finer material at shallower depth. Synchronously this led to an increased supply of carbonate and extremely high carbonate concentrations below 3500 m water depth.

Description: The benthic environment in the Gulf of Cadiz, north-eastern Atlantic, is strongly affected by the Mediterranean outflow water undercurrent (MOW) which flows northwards along the western Iberian Margin at 500–1500 m water depth. Foraminiferal census counts of living and dead assemblages from 27 surface samples ranging from 103 to 1917 m water depth, and the examination of hard substrates reveal a close correlation of the fauna with the local hydrography and sediment facies. Four different faunal groups are separated by factor analysis of the living fauna. Assemblage 1 contains typical lower slope species and dominates samples from the lower MOW core layer and in the North Atlantic deep water below. Shelf edge foraminifera are common in assemblage 2a which shows the highest proportions in samples from 103 to 272 m. Assemblage 2b is dominated by upper slope species and suspension-feeders that are frequent in the upper MOW core layer and in distal settings between 396 and 901 m. Species from assemblage 3 prefer epibenthic habitats and are recorded with high proportions exclusively in the immediate flow paths of the upper MOW between 496 and 881 m. Colonisation structures and species composition of epibenthic assemblages from the proximal facies largely differ from those in distal settings. In general, epibenthic foraminifers only use elevated substrates under the influence of near-bottom flow. Under high current velocities, epibenthic foraminifers prefer large and heavy objects. They colonise high attachment levels where a maximum yield of advected food particles can be achieved. In distal settings at lower flow velocities, the elevation height does not exceed 20 mm above the surrounding sediment surface. This level is related to a hydrologic transition layer with high concentrations of suspended particles. The comparison of microhabitat preferences and faunal structure under high and low current velocities reveal that substrate stability may be a confining environmental variable for endobenthic and shallow epibenthic foraminifers. The observations also indicate that the preferential settling height of epibenthic foraminifera is related to the highest lateral flux rates of food particles within reach from the sea floor. A dynamic selection of elevated microhabitats is only used by 7.8% of all species recognised in the Gulf of Cadiz area.

Description: We propose a new“multicollector technique” for the thermal ionization mass spectrometer (TIMS) measurement of calcium (Ca) isotope ratios improving average internal statistical uncertainty of the 44Ca/40Ca measurements by a factor of 2–4 and average sample throughput relative to the commonly used “peak jumping method” by a factor of 3. Isobaric interferences with potassium (40K+) and titanium (48Ti+) or positively charged molecules like 24Mg19F+, 25Mg19F+, 24Mg16O+ and 27Al16O+ can either be corrected or are negligible. Similar, peak shape defects introduced by the large dispersion of the whole Ca isotope mass range from 40–48 atomic mass units (amu) do not influence Ca-isotope ratios. We use a 43Ca/48Ca double spike with an iterative double spike correction algorithm for precise isotope measurements

Description: The Catalina Schist (California) contains an amphibolite-grade (0.8–1.1 GPa; 640–750 jC) melange unit consisting of mafic and ultramafic blocks in high-Mg, schistose melange matrix with varying modal proportions of talc, chlorite, anthophyllite, calcic-amphibole, enstatite, and minor phases including zircon, rutile, apatite, spinel, and Fe–Ni sulfides. This melange unit is interpreted as a kilometer-scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone, the study of which may yield insight into chemical mixing processes at greater depths in subduction zones. Relationships among the major and trace element compositions of the mafic and ultramafic blocks in the melange, the rinds developed at the margins of these blocks, and the surrounding melange matrix are compatible with the evolution of the melange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing. Simple, linear mixing models are compatible with the development of the melange matrix primarily through simple mixture of the ultramafic and mafic rocks, with Cr/Al ratios serving as indicators of the approximate proportions of the two lithologies. This conclusion regarding mafic–ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the melange matrix with rinds developed at the margins of mafic and ultramafic blocks. The overall process involved development of metasomatic assemblages through complex fluid-mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials, which are rich in layer silicates and amphibole. This deformation was sufficiently intense to transpose fabrics, progressively disaggregate more rigid, block-derived materials in weaker chorite- and talc-rich melange, and in some particularly weak lithologies (e.g., chlorite-, talc-, and amphibole-rich materials), intimately juxtapose adjacent lithologies at the (sub-)cm scale (approaching grain scale) sampled by the whole-rock geochemical analyses. Chemical systematics of various elements in the melange matrix can be delineated based on the Cr/Al-based mixing model. Simple mixing relationships exhibited by Al, Cr, Mg, Ni, Fe, and Zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the melange matrix. The compositional patterns of many other elements are explained by either redistribution (local stripping or enrichment) at varying scales within the melange (Ca, Na, K, Ba, and Sr) or massive addition from external sources (Si and H2O), the latter probably in infiltrating H2O-rich fluids that produced the dramatic O and H isotopic shifts in the melange. Melange formation, resulting in the production of high-variance ultramafic assemblages withhigh volatile contents, may aid retention of volatiles (in this case, H2O) to greater depths in subduction zones than in original subducted mafic and sedimentary materials. The presence of such assemblages (i.e., containing minerals such as talc, chlorite, and Mg-rich amphiboles) would impact the rheology of the slab–mantle interface and perhaps contribute to the low-velocity seismic structure observed at/near the slab–mantle interface in some subduction zones. If operative along the slab–mantle interface, complex mixing processes such as these, involving the interplay between fluid-mediated metasomatism and deformation, also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas, producing ‘‘fluids’’ with geochemical signatures inherited from interactions with hybridized rock compositions.

Description: During previous field experiments in the North Sea it was often assumed that the water column in such shallow coastal tidal waters is vertically well mixed and stratification was neglected when discussing the Normalized Radar Cross Section modulation caused by the sea floor. In this paper the influence of quasi resonant internal waves with the sea bed on the radar imaging mechanism of submarine sand waves itself is investigated. In situ data of the tidal current velocity and several water quality parameters such as sea surface temperature, fluorescence, and beam transmittance were measured in the Southern Bight of the North Sea in April 1991. Simulations of the total NRCS modulation caused by sand waves and internal waves as a function of the current gradient or strain rate induced by the internal wave current field at the sea surface have been carried out using the quasi-steady approximation and linear internal wave theory. As a first approximation the strain rate depending on stratification was calculated using the two-layer model. These simulations demonstrate that at least a density difference between the two layers of the order of Δρ ≈ 1 kg m–3 is necessary for a sinusoidal thermocline to effect the total NRCS modulation considerably. The NRCS modulation as a function of wind friction velocity has been calculated independently and is discussed with regard to the strain rate of the surface current field caused by the superimposed imaging mechanisms of sand waves and internal waves. It turned out that the existence of a surface roughness-wind stress feedback mechanism cannot be excluded.

Description: The feeding habits of Beryx splendens and B. decadactylus were determined from stomach contents obtained on a monthly basis during commercial fishing off the Canary Islands in 1996–1997. Changes in diets were studied in relation to predator size and seasonal variation in the food composition. The diet of both species has much in common with regard to its main components of small fishes, crustaceans and cephalopods. More important differences were found in the fish prey of B. decadactylus. A variation in the diet of B. splendens was observed according to its length. Seasonal variations in feeding habits were associated with either variations in the abundance of prey or variations in the depth distribution of predator and prey.

Description: Satellite-based optical observations of surface waters have been used to assess the main environmental interactions in the north-western Black Sea, as a contribution to the EROS 21 project. Such observations allow evaluations of the presence and abundance of water constituents (primarily phytoplankton pigments), providing essential information on the processes which are taking place in the area and on their spatial and temporal scales. An analysis of ocean colour imagery was performed, using historical data collected by the CZCS (1978–1986), and by the MOS before, during and after the EROS 21 oceanographic cruise which took place in April/May 1997. The time series of CZCS-derived parameters (i.e. chlorophyll-like pigment concentration) originates from the archive generated by the OCEAN project. The MOS data were processed to apply sensor calibration, to correct for atmospheric contamination so as to assess water-leaving radiances for each visible channel, and to estimate geophysical parameters such as pigment concentration and in-water optical depth, which is correlated to suspended matter concentration. The atmospheric correction was performed with a novel algorithm developed especially for MOS application. The bio-optical algorithms used to derive in-water parameters were obtained by comparison with the concurrent in situ measurements of optically active parameters collected in the north-western Black Sea in the framework of the EROS 21 project. The multi-satellite data set highlights the differences between western and eastern sub-basins, inshore and offshore domains, northern and southern near-coastal areas. In the Danube delta area, the water constituents trace complex interactions of near-coastal and basin-wide features of the Black Sea.

Description: The Hf isotope composition of seawater does not match that expected from dissolution of bulk continental crust. This mismatch is generally considered to be due to retention of unradiogenic Hf in resistant zircons during incomplete weathering of continental crust. During periods of intense glacial weathering, zircons should break down more efficiently, resulting in the release of highly unradiogenic Hf to the oceans. We test this hypothesis by comparing Nd and Hf isotope time series obtained from NW Atlantic ferromanganese crusts. Both isotope systems show a decrease associated with the onset of northern hemisphere glaciation. The observed changes display distinct trajectories in ϵNd–ϵHf space, which differ from previously reported arrays of bulk terrestrial material and seawater. Such patterns are consistent with the release of highly unradiogenic Hf from very old zircons, facilitated by enhanced mechanical weathering

Description: We present comprehensive radiogenic isotope (Os, Pb, Hf, Nd, Sr) and trace element data on basaltic lavas from Pitcairn Island and the Pitcairn seamounts and examine the origin of the enriched mantle isotopic signature (EM-1) found in these lavas. The 187Os/188Os ratios of the lavas range from 0.131 to 0.254, while those of the high-Os concentration samples (〉50 pg/g) lie between 0.131 and 0.148. All 187Os/188Os ratios are higher than the bulk silicate Earth reference value of 0.127. Since ancient subcontinental lithospheric mantle (SCLM) is expected to have a 187Os/188Os ratio less than 0.127, it appears that recycled SCLM plays no role in the Pitcairn source. Variations in 187Os/188Os ratios appear to be unconnected with those of 206Pb/204Pb ratios in Pitcairn lavas, suggesting that Pb and Os isotopic variations are controlled by different factors. Modeling shows that variations in Pb isotopic compositions may mainly reflect the proportion of recycled sediment in the source, while those of 187Os/188Os ratios may reflect the proportion of peridotite mantle versus recycled oceanic crust. The occurrence of negative Nb anomalies in some of the lavas, a correlation between Nb anomaly and 87Sr/86Sr ratios (0.7036–0.7051), and extremely unradiogenic and strongly correlated Nd and Hf isotopic compositions (ϵNd of −5.9 to +1.1 and ϵHf of −5.3 to +2.2) together suggest that the Pitcairn mantle source contains a recycled continental crustal component. The slope of the ϵHf vs. ϵNd correlation is shallower for Pitcairn Island than for the Pitcairn seamounts or the global OIB array, and may be due to a variable ratio of recycled mud to sand in the Pitcairn source. A trace element mixing model also indicates the presence of small amounts of recycled pelagic and terrigenous sediment and permits variable amounts of depleted components such as recycled MORB, gabbro and depleted mantle. The 206Pb/204Pb ratios of the Pitcairn lavas vary between 17.47 and 18.10 and are very unradiogenic compared to those of other ocean island basalts. By contrast, 208Pb/204Pb ratios are high and relatively homogeneous at values of ∼39.0. This observation along with the measured Th/U ratios of the lavas, which range up to 14.1, indicate a long-term history of U loss in the Pitcairn source. In 207Pb/204Pb–206Pb/204Pb space, the data form a linear array that can be interpreted in terms of mixing between a minor recycled sediment end member and more depleted material. Lead isotopic compositions suitable for the recycled end member were investigated using a three-stage evolution model by Monte Carlo methods and suggest ages between 0.7 and 1.9 Ga for the recycled sediment. The relationships between measured Th/U and radiogenic 208Pb*/206Pb* ratios suggest that the isotopic arrays displayed by the lavas were produced by mixing, probably occurring during magma genesis.

Description: The occurrence of bottom simulating reflections (BSRs) along the Sunda margin off Indonesia is investigated for the first time using seismic reflection data from three surveys conducted across the subduction zone and the forearc domain off southern Sumatra to central Java. BSRs commonly concur with the base of the thermodynamically stable hydrate zone and are thus an important indicator for gas hydrates. Along the Sunda Arc, BSR occurrence is restricted to the forearc domain in regions likely to represent a focussing of fluid flow, such as the forearc basin slopes or anticline structures. Dissociation of gas hydrates due to uplift along anticline structures may be an important secondary cause of BSR formation. The absence of BSRs in the forearc basin center despite continuous sedimentation to ensure carbon supply may be related to the very high sedimentation rate (〉0.4 km/Ma) which causes unused carbon to pass through the stability zone even for a high rate constant of methanogenesis. In addition, the interbedding of low- and high-permeability layers renders fluid flow across layering ineffective. No BSR phases could be detected along the accretionary prism or the outer high, although the P–T regime would allow a potential BSR to lie within the accretionary sedimentary column.

Description: The structure of the Mid-Atlantic Ridge at 5°S was investigated during a recent cruise with the FS Meteor. A major dextral transform fault (hereafter the 5°S FZ) offsets the ridge left-laterally by 80 km. Just south of the transform and to the west of the median valley, the inside corner (IC – the region bounded by the ridge and the active transform) is marked by a major massif, characterized by a corrugated upper surface. Fossil IC massifs can also be identified further to the west. Unusually, a massif almost as high as the IC massif also characterizes the outside corner (OC) south of the inactive fracture zone and to the east of the median valley. This OC massif has axis-parallel dimensions identical to the IC massif and both are bounded on their sides closest to the spreading axis by abrupt, steep slopes. An axial volcanic ridge is well developed in the median valley both south of the IC/OC massifs and in an abandoned rift valley to the east of the OC massif, but is absent along the new ridge-axis segment between the IC and OC massifs. Wide-angle seismic data show that between the massifs, the crust of the median valley thins markedly towards the FZ. These observations are consistent with the formation of the OC massif by the rifting of an IC core complex and the development of a new spreading centre between the IC and OC massifs. The split IC massif presents an opportunity to study the internal structure of the footwall of a detachment fault, from the corrugated fault surface to deeper beneath the fault, without recourse to drilling. Preliminary dredging recovered gabbros from the scarp slope of the rifted IC massif, and serpentinites and gabbros from the intersection of this scarp with the corrugated surface. This is compatible with a concentration of serpentinites along the detachment surface, even where the massif internally is largely plutonic in nature.

Description: We present the first transect of dissolved 10Be depth profiles across the Antarctic Circumpolar Current (ACC) in the Atlantic sector. North of the Polar Front the 10Be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms/g at depth. Deep water 10Be concentrations of particular water masses are consistent with earlier results obtained further north. South of the Polar Front and in the Weddell Sea the distribution of 10Be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher (up to 2000 atoms/g) than further north, probably as a result of mixing and advection of water masses of Pacific origin. Overall the deep water 10Be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that 10Be can be viewed as a quasi-conservative tracer. This provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the Southern Ocean such as 230Th: in deep waters north of the ACC/Weddell Gyre boundary (AWB) 10Be/230Th has a relatively constant value (1.7±0.3×109 atoms/dpm) over a wide density range whereas south of the AWB the ratio is significantly lower (1.1±0.2×109 atoms/dpm). This normalisation to 10Be corroborates that 230Th is enriched by 50% due to accumulation south of the AWB as a consequence of minimal particulate fluxes. The quasi-conservative behaviour deduced from our results also implies that 10Be can only be used as a tracer for Southern Ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly.

Description: A detailed bathymetric and magnetic survey of the eastern flank of the East Pacific Rise at 14°14′S covering seafloor ages of 0–10 Ma has been carried out and used, along with a flowline profile on the conjugate western ridge flank, to reveal the spreading history and the temporal ridge crest segmentation. Additional information from basaltic lavas is included to study the relationship between physical and magmatic segment boundaries. The sequence of magnetic reversals indicates a total spreading rate of 150 mm/yr since 10 Ma. Symmetric spreading, however, occurred only since 2.8 Ma. Between 7 and 2.8 Ma spreading was asymmetric, with a higher spreading rate toward the east. Migration events of at least five overlapping spreading centres (OSC) left discordant zones on the Nazca plate consisting of hummocky basins and motley texture of curved lineations striking a few degrees oblique to the strike of the ridge crest. Four of the OSCs were right-stepping and migrated northward and one was left-stepping and migrated southward. By transferring Pacific lithosphere to the Nazca plate, these migration events may account for most of the asymmetric accretion observed. The basaltic samples from the eastern flank have been analysed and back tracked to the position of eruption on the ridge crest. In terms of their geochemical signature (Mg# 0.41–0.68) the samples reveal that the magmatic segment boundary between the Garrett transform and 14°30′S has remained stationary over the last 10 Myr and therefore provide no evidence for a link between magmatic and physical segmentation. We therefore propose that migrating non-transform ridge axis discontinuities are governed by propagating giant cracks; as a crack front advances a melt reservoir is tapped and magma rises passively into the crack and erupts subsequently on the seafloor. Some of the OSCs seem to have originated close to transform faults and therefore argue that far-field stresses, perhaps caused by the evolution of the Bauer microplate, rather than mantle upwelling create non-transform ridge axis discontinuities.

Description: Amodel is presented that simulates the formation of marine aggregates from particles of different origin inside amodel of pelagic biological processes. Experiments are carried out with parameterizations appropriate for different types of aggregates, using different kinds of physical forcing, and compared to observations of dissolved inorganic nitrogen (DIN), particulate organic nitrogen (PON), marinesnow concentration, and sedimentation. The occurrence of large, macroscopically visible aggregates (marinesnow) can best be simulated with parameterizations that have been derived from in situ observations of marinesnow, but not with aparameterization sufficient for dense particles. The parameterization strongly determines the amount and timing of deep export, as well as the post-bloom development of the food web in the upper layers. Detritus in aggregates plays a role mainly during times when zooplankton are abundant, as e.g. in the western Arabian Sea during Southwest Monsoon. Then the large aggregates as fast sinking vehicles may remove detritus quickly from shallow and mid-water depth, preventing the accumulation of nutrients that are produced via detritus decomposition. In this region, detritus contributes strongly to deep sedimentation. The nitrogenbudget at this location with regard to the observations cannot be closed: depending on model type, either the model simulates too high sedimentation, or too high DIN. Possible causes for this mismatch include undercollection by sediment traps, inaccurate representation of physical processes in the model and the neglect of biological processes, such as production of dissolved organic matter or denitrification.

Description: Observations during a spring phytoplankton bloom in the northeast Atlantic between March and May 1992 in the Biotrans region at 47°N, 20°W, are presented. During most of the observation period there was a positive heat flux into the ocean, winds were weak, and the mixed layer depth was shallow (〈40 m). Phytoplankton growth conditions were favourable during this time. Phytoplankton biomass roughly doubled within the euphotic zone over the course of about 7 days during mid-April, and rapidly increased towards the end of the study until silicate was depleted. However, the stratification of the water column was transient, and the spring bloom development was repeatedly interrupted by gales. During two storms, in late March and late April, the mixed-layer depth increased to 250 and 175 m, respectively. After the storm events significant amounts of chlorophyll-a, particulate organic carbon and biogenic silica were found well below the euphotic zone. It is estimated that between 56% and 65% of the seasonal new production between winter and early May was exported from the euphotic zone by convective mixing, in particular, during the two storm events. Data from the NABE 47°N study during spring 1989 are re-evaluated. It is found that convective particle export was of importance during the early part of that bloom too, but negligible during the height of the bloom in May 1989. The overall impact of convective particle export during spring 1989 was equivalent to about 36% of new production. In view of these and previously published findings it is concluded that convective transport during spring is a significant process for the export of particulate matter from the euphotic zone in the temperate North Atlantic

Description: Warming of the deep water in the Weddell Sea has important implications for Antarctic bottom water formation, melting of pack ice, and the regional ocean–atmosphere heat transfer. In order to evaluate warming trends in the Weddell Sea, a historical data set encompassing CTD and bottle data from 1912 to 2000 was analyzed for temporal trends in the deep water masses: warm deep water (WDW) and Weddell Sea deep water (WSDW). The coldest WDW temperatures were primarily associated with the Weddell Polynya of the mid-1970s. Subsequent warming occurred at a rate of ∼0.012±0.007°C yr−1 from the 1970s to 1990s. This warming was comparable to the global, average surface water warming observed by Levitus et al. (Science 287 (2000) 2225), to the warming of the WSBW in the central Weddell Sea observed by Fahrbach et al. (Filchner–Ronne Ice Shelf Program, Report No. 12, Alfred-Wegener-Institut, Bremerhaven, Germany, 1998a, p. 24), and to the surface ice temperature warming from 1970 to 1998 in the Weddell Sea observed by Comiso (J. Climate 13 (2000) 1674). The warming was not compensated by an increase in salinity, and thus the WDW became less dense. The location of the warmest temperature was displaced towards the surface by ∼200 m from the 1970s to the 1990s. Although the average WSDW potential temperatures between 1500 and 3500 m were warmer in the 1990s than in the 1970s, high variability in the data prevented identification of a well-defined temporal trend

Description: Subduction rates of the water into southern Indian Ocean permanent thermocline from 23.5 to Full-size image (〈1 K) are calculated from a kinematic and a water-age approach and are compared with surface buoyancy flux calculations. The different estimates compare well within error margins, indicating that the effect of transient eddies on the subduction process is of second order. Considering only northward transport components, the overall transfer of water into the Indian Ocean thermocline is about Full-size image (〈1 K) (Full-size image (〈1 K)), with equal contributions from lateral and vertical (essentially Ekman pumping) components. Ekman pumping dominates the upper density range (Full-size image (〈1 K)), while for denser water the largest contribution stems from lateral input of Mode Waters. High silicate concentrations in the Mode Waters indicate that Southern Ocean waters participate in the formation process. The source water properties in salinity, oxygen, and nutrients along the surface of the deepest winter mixed layer are given.

Description: The Indian Ocean differs from the other two large oceans in not possessing an annual-mean equatorial upwelling regime. While the subtropical cells (STCs) of the Atlantic and Pacific Oceans connect subtropical subduction regimes with tropical upwelling via equatorward thermocline flows and coastal undercurrents, much of the upwelling in the Indian Ocean occurs in the coastal regimes of the northern hemisphere. Consequently, the counterpart of the STCs of the other oceans has to be a cross-equatorial cell connecting the southern subtropical subduction zone via the Somali Current with the upwelling areas off Somalia and Oman. The southward return flow is by interior Ekman transports. This annual-mean picture is accomplished by a dominance of the summer monsoon, during which only northern upwelling occurs, over the winter monsoon. Pathways of the thermocline flows related to the shallow overturning circulations are investigated here and estimates of subduction and upwelling are presented. From the observed mean northward flow of thermocline waters within the Somali Current and the interior southward cross-equatorial return flow the magnitude of the cross-equatorial cell is estimated at 6 Sv, with part of the thermocline waters being supplied by the Indonesian Throughflow. From observations we estimate that the northern upwelling occurs dominantly through the offshore outflows of the Somali Current by the Southern Gyre and Great Whirl and to a lesser degree off Oman. However, we also present model results suggesting a much lower role of Somali upwelling and a significant contribution from open-ocean upwelling in cyclonic domes around India and Sri Lanka. An interesting aspect of the Indian Ocean cross-equatorial cell is the mechanism by which the Ekman transport crosses the equator. Typically, Ekman transports during the summer (winter) monsoon are southward (northward) on both sides of the equator, while mean meridional winds on the equator are in the respective opposite direction. Earlier model evidence had suggested that this type of forcing should lead to an equatorial roll with northward surface flow and southward subsurface flow during the summer monsoon and reverse orientation during the winter monsoon. Observational evidence is presented here, based on shipboard ADCP sections, moored stations and surface drifters, confirming the existence of the equatorial roll. It is strongly developed in the western Indian Ocean during the SW monsoon where the wind conditions for the roll are best met. While in the central Indian Ocean and during the winter monsoon the roll appears to be a more transient phenomenon, superimposed by equatorial-wave currents. The evidence further suggests that the roll is mostly confined to the surface-mixed layer and is, therefore, of little consequence for the meridional heat transport.

Description: Recent benthic foraminiferal assemblages were analyzed in the Gulf of Cadiz, northeastern Atlantic, to study the impact of the Mediterranean Outflow Water (MOW) undercurrent on the benthic environment. Foraminiferal counts and the analysis of specimens attached to hard substrates from 26 surface samples reveal a relationship of epibenthic assemblages with sedimentary and hydrodynamic environment. Epibenthic species make up as much as 60% of the living assemblage at proximal sites with high current velocities and 3–18% in distal areas or near the margins of the MOW flow paths at low velocities. These foraminifers inhabit elevated substrates only within the MOW, which evidently provides an ecological niche for opportunistic suspension feeders. They adapt their settling elevation dynamically and occur at greater heights above the ambient sediment surface under stronger currents. Mobility, fixation strength, suspension feeding, and reproduction efficiency emerge as individual capabilities promoting the occupation of elevated substrates by certain epibenthic species. The active microhabitat selection is pursued as basic strategy of these foraminifers to optimize their food acquisition. A better access to food sources stimulates reproduction and leads to a greater contribution of foraminiferal tests to the surface sediments. Elevated epibenthos percentages from the dead assemblage and current velocities prevailing at the sampling sites are closely correlated. A compilation including other data from southern Portugal, Florida Straits, and the English Channel infers an exponential relationship between epibenthic abundances and flow strength implying that endobenthic species prevail even under high current velocities. A linear model provides a significantly better fit for the Gulf of Cadiz data however. This relation is used for a case study in order to estimate near-bottom current strengths for the late Holocene Peak III contourite in core M39008-3. Trends and absolute values of current velocities, inferred from the benthic foraminiferal proxy, are the same scale as estimates obtained from sediment grain-size distribution and hydrodynamic models. Epibenthic foraminifera thus bear a high potential as proxy for palaeocurrent studies that even may overcome objections by predetermined grain-size distributions in deep-sea cores.

Description: Paired benthic Cd/Ca and δ13C records have been generated along core M35003 in the western tropical Atlantic. Decreased glacial water column dissolved cadmium (Cdw) and increased benthic δ13C indicate enhanced ventilation with nutrient-deplete intermediate waters, in line with similar inferences from other North Atlantic mid-depth records. An abrupt early deglacial δ13C collapse that is associated with a marked positive Cdw anomaly indicates a transient collapse of mid-depth ventilation from North Atlantic sources, conceivably in conjunction with the H1 meltwater anomaly. The Cdw record displays fine-scale fluctuations that mimic the Greenland Dansgaard/Oeschger (D/O) cycles and show decreased Cdw during stadials. This pattern is opposite to Cdw variations in a deep water record from Bermuda Rise that display increased Cdw concentrations during stadials. The divergent pattern between mid-depth and deep water Cdw records indicates millennial-scale switches between deep and shallow convection in the glacial North Atlantic, at the pace of the D/O climatic cycles. Several high-amplitude anomalies occur in the Cdw record that reach levels similar to those observed today in the North Pacific. While a substantial nutrient increase in the mid-depth North Atlantic cannot be ruled out during these events, changes of pore water chemistry and Cd/P fractionation during biological uptake offer alternative scenarios to explain the peak Cdw maxima.

Description: Carbonate preservation records from a number of drill sites in the North Atlantic and adjacent Norwegian–Greenland Sea (NGS) are used to reconstruct variations in North Atlantic Deep Water (NADW) production over the past 3 Myr. Before the initiation of major Northern Hemisphere glaciation, good carbonate preservation was recorded in the North Atlantic and the NGS supporting the superconveyor model of accelerated NADW formation in the late Pliocene. After the inception of main Northern Hemisphere glaciation, NADW formation in the NGS was blocked-off during the period 2.8–1.9 Ma. Carbonate was only badly preserved due to (1) low production of carbonate shells in surface waters, (2) sluggish renewal of deep waters induced by a rather stable sea-ice cover, and/or (3) production of carbonate-corrosive dense brines during sea-ice formation (e.g. sea ice dissolution mode). In contrast, contemporaneous good preservation in the adjacent North Atlantic indicates efficient NADW production. During the middle Matuyama (1.9–1.4 Ma), the first intrusions of the Proto-Norwegian Current into a narrow corridor in the southeastern NGS are evidenced by much better carbonate preservation. A decrease both in carbonate content and preservation towards the north and west of this corridor indicates the proximity of the polar front and gives evidence that NADW production was efficiently triggered by the Atlantic water entrainment mode. During the past 1.2 Myr carbonate preservation patterns in the NGS clearly reflect major global events like the Mid-Pleistocene Transition and the mid-Brunhes dissolution event. The onset of the Mid-Pleistocene Transition at 1.2 Ma is characterized by a complete shift to higher carbonate contents in the southeastern NGS and Labrador Sea. Overall, good preservation during both interglacials and glacials is only interrupted by high-frequency, short-term dissolution spikes, which were induced by ice sheet collapse and development of extensive meltwater lids. As a consequence, NADW was produced nearly continuously during glacials in the Nordic Seas. However, due to its lower density it was entrained into intermediate water levels in the North Atlantic and, thus, enforced the intermediate water circulation loop, whereas a decrease in lower-NADW production is observed contemporaneously.

Description: A combined volcanological, geochemical, paleo-oceanological, geochronological and geophysical study was undertaken on the Kurile Basin, in order to constrain the origin and evolution of this basin. Very high rates of subsidence were determined for the northeastern floor and margin of the Kurile Basin. Dredged volcanic samples from the Geophysicist Seamount, which were formed under subaerial or shallow water conditions but are presently located at depths in excess of 2300 m, were dated at 0.84±0.06 and 1.07±0.04 Ma with the laser 40Ar/39Ar single crystal method, yielding a minimum average subsidence rate of 1.6 mm/year for the northeast basin floor in the Quaternary. Trace element and Sr–Nd–Pb isotope data from the volcanic rocks show evidence for contamination within lower continental crust and/or the subcontinental lithospheric mantle, indicating that the basement presently at ∼6-km depth is likely to represent thinned continental crust. Average subsidence rates of 0.5–2.0 mm/year were estimated for the northeastern slope of the Kurile Basin during the Pliocene and Quaternary through the determination of the age and paleo-environment (depth) of formation of sediments from a canyon wall. Taken together, the data from the northeastern part of the Kurile Basin indicate that subsidence began in or prior to the Early Pliocene and that subsidence rates have increased in the Quaternary. Similar rates of subsidence have been obtained from published studies on the Sakhalin Shelf and Slope and from volcanoes in the rear of the Kurile Arc. The recent stress field of the Kurile Basin is inferred from the analysis of seismic activity, focal mechanism solutions and from the structure of the sedimentary cover and of the Alaid back-arc volcano. Integration of these results suggests that compression is responsible for the rapid subsidence of the Kurile Basin and that subsidence may be an important step in the transition from basin formation to its destruction. The compression of the Kurile Basin results from squeezing of the Okhotsk Plate between four major plates: the Pacific, North American, Eurasian and Amur. We predict that continued compression could lead to subduction of the Kurile Basin floor beneath Hokkaido and the Kurile Arc in the future and thus to basin closure.

Description: Measurement strategies for understanding the oceanic CO2 (carbon dioxide) system are moving towards in situ and ship of opportunity sampling techniques. Automated instrumentation with high accuracy and sampling frequencies will enable a greater understanding of the fluxes of marine carbon and lead to a more reliable constrain on the calculated uptake of anthropogenic CO2 by the oceans. This paper describes the automated marine pH sensor (AMpS); new instrumentation and methodology for the determination of seawater pH using dual spectrophotometric measurements of sulfonephthalein indicator in a semi-continuous seawater stream. The pH values measured during a recent study in the Weddell Sea are used to illustrate the excellent properties of the AMpS. The method has an on-line precision of better than 0.001 pH units and an estimated accuracy of better than 0.004 pH units. The instrument is compact, portable and has a measurement frequency of 20 samples per hour. The instrument is ideally suitable for operation on ships of opportunity.

Description: Extensive deposits of methane hydrate characterize Hydrate Ridge in the Cascadia margin accretionary complex. The ridge has a northern peak at a depth of about 600 m, which is covered by extensive carbonate deposits, and an 800 m deep southern peak that is predominantly sediment covered. Samples collected with benthic instrumentation and from Alvin push cores reveal a complex hydrogeologic system where fluid and methane fluxes from the seafloor vary by several orders of magnitude at sites separated by distances of only a few meters. We identified three distinct active fluid regimes at Hydrate Ridge. The first province is represented by discrete sites of methane gas ebullition, where the bulk of the flow occurs through channels in which gas velocities reach 1 m s−1. At the northern summit of the ridge the gas discharge appears to be driven by pressure changes on a deep gas reservoir, and it is released episodically at a rate of ∼6×104 mol day−1 following tidal periodicity. Qualitative observations at the southern peak suggest that the gas discharge there is driven by more localized phenomena, possibly associated with destabilization of massive gas hydrate deposits at the seafloor. The second province is characterized by the presence of extensive bacterial mats that overlay sediments capped with methane hydrate crusts, both at the northern and southern summits. Here fluid typically flows out of the sediments at rates ranging from 30 to 100 cm yr−1. The third province is represented by sites colonized by vesicomyid clams, where bottom seawater flows into the sediments for at least some fraction of the time. Away from the active gas release sites, fluid flows calculated from pore water models are in agreement with estimates using published flowmeter data and numerical model calculations. Methane fluxes out of mat-covered sites range from 30 to 90 mmol m−2 day−1, whereas at clam sites the methane flux is less than 1 mmol m−2 day−1.

Description: Southern Kermadec arc stratovolcanoes (of predominantly basaltic and andesitic composition) provide a depth transect of the transition between effusive and explosive submarine volcanism. Observations along 4.6 km of towed-camera track from the crests and upper flanks of the Clark and Rumble III volcanoes reveal a consistent pattern of substrate types that are interpreted to record effusive and explosive eruption processes. Below 700 m water depth, substrates are dominated by massive/blocky flows, pillow lavas, pillow and angular block talus, localized sheet flows, and minor granule-sand volcaniclastic detritus. The latter typically forms a substrate mode of 5–20%. Above 450 m, sand lapilli (that is in part winnowed and rippled), have a substrate mode of 50–100%, with minor components of massive flows, pillow lavas, and coarse talus. This difference in abundance of sand lapilli between 450 and 700 m is interpreted to record the transition between effusive and explosive (both phreatic and phreatomagmatic) eruptions. Between 600 and 700 m, a varied distribution of sand-lapilli abundance is interpreted as recording a mix of effusive and explosive eruptions, consistent with possible differences in the physical interaction of magma–water and known compositional magma heterogeneity.

Description: We have developed a model of fluid flow and pressure development in sedimentary basins that incorporates pore volume loss due to mechanical compaction and to chemical diagenesis (quartz cementation, grain contact quartz dissolution and illitization). Mechanical compaction is modeled to be a function of effective stress. In this model, pore volume loss due to mechanical compaction will be retarded when overpressure develops. The diagenetic processes are modeled as being kinetically controlled and the reaction progress depends only on the temperature history. Hence pore volume loss due to chemical compaction is not retarded by overpressure. By including diagenetic effects on overpressure development, the pressure model should be more generally applicable than models that consider mechanical compaction to be the sole process that reduces porosity. To demonstrate the potential importance of chemical compaction in the formation of fluid overpressures in different settings, we calibrated our model with data obtained from the Halten Terrace offshore mid-Norway and from the Gulf of Mexico. In both cases, the diagenetic processes have the potential to control on the timing and magnitude of overpressuring. From 25% and up to 80% of the present-day overpressure may be caused by pore volume loss resulting from diagenetic reactions. Pressure build-up from diagenetic processes also potentially controls the timing of hydraulic fracturing. If diagenetic processes are actively contributing to overpressure generation, then unrealistically low shale permeabilities are not needed to retain overpressures for geologic time periods (〉10 My).

Description: We present a numerical model that improves our capability to simulate multiphase, non-isothermal flow in variably saturated porous and fractured media at magmatic temperatures and shallow crustal pressures. Simulations of heat and fluid flow in variably saturated host rock near a magmatic intrusion provide insight into contact metamorphic processes, including dryout, condensation, and resaturation effects and implications for host-rock alteration. The numerical code, an enhanced version of FEHM, uses a finite-element/finite-volume technique incorporating implicit Newton–Raphson iteration to solve non-linear conservation equations for mass and energy, using thermodynamic properties of water and air in the ranges 10°C≤T≤1500°C, 0.00123≤P≤1000 MPa and 10°C≤T≤1500°C, 0.00123≤P≤22 MPa, respectively. The study area is located at Paiute Ridge, eastern Nevada Test Site, Nevada, USA, where hypabyssal mafic intrusions were emplaced at about 8.5–8.6 Ma (Ar/Ar age estimate) and cooled contemporaneously with part of a geomagnetic field reversal, inferred from paleomagnetic data from over 100 sites in intrusions and remagnetized host ash-flow tuffs. We used a radial model of heat flow and multiphase pore fluid flow adjacent to a 1200°C intrusion to characterize the thermal evolution of the contact metamorphic system. For likely initial pore saturations of 0.4–0.6, an expanding dryout zone near the intrusion and a condensation zone of enhanced saturation (S≤0.8) extends 150–400 m from the intrusion. Host-rock temperatures reach 800°C near the contact and cool below 100°C within 2000 yr after emplacement, two to four times faster than predicted by a simple conduction model. The thermal history of the system is very sensitive to initial saturation. The multiphase thermal model allows bounds to be placed on the rate of change of the transitional part of the geomagnetic field during the field reversal recorded at Paiute Ridge. We assume that magnetization acquisition took place during the life of the thermal system that developed in the intrusions and contact rocks and that the paleomagnetic data provide a quasi-continuous record of the transitional part of the reversal. Sites in intrusions and thermally annealed ash-flow tuffs reveal subtle yet systematic variations in paleomagnetic directions. We combine the directional data with robust thermal (temperature/time) models to estimate the rate of change of the geomagnetic field. Modeled times of 140–290 yr and 215–440 yr for the duration of magnetization acquisition at two different sites correspond to estimated rates of change of 0.06–0.13°/yr for the field during the transitional part of the reversal.

Description: Near the eastern end of the Tonale fault zone, a segment of the Periadriatic fault system in the Italian Alps, the Adamello intrusion produced a syn-kinematic contact aureole. A temperature gradient from ∼250 to ∼700 °C was determined across the Tonale fault zone using critical syn-kinematic mineral assemblages from the metasedimentary host rocks surrounding deformed quartz veins. Deformed quartz veins sampled along this temperature gradient display a transition from cataclasites to mylonites (frictional–viscous transition) at 280±30 °C. Within the mylonites, zones characterized by different dynamic recrystallization mechanisms were defined: Bulging recrystallization (BLG) was dominant between ∼280 and ∼400 °C, subgrain rotation recrystallization (SGR) in the ∼400–500 °C interval, and the transition to dominant grain boundary migration recrystallization (GBM) occurred at ∼500 °C. The microstructures associated with the three recrystallization mechanisms and the transitions between them can be correlated with experimentally derived dislocation creep regimes. Bulk texture X-ray goniometry and computer-automated analysis of preferred [c]-axis orientations of porphyroclasts and recrystallized grains are used to quantify textural differences that correspond to the observed microstructural changes. Within the BLG- and SGR zones, porphyroclasts show predominantly single [c]-axis maxima. At the transition from the SGR- to the GBM zone, the texture of recrystallized grains indicates a change from [c]-axis girdles, diagnostic of multiple slip systems, to a single maximum in Y. Within the GBM zone, above 630±30 °C, the textures also include submaxima, which are indicative of combined basal 〈a〉- and prism [c] slip.

Description: Ice Complexes, extremely ice-rich permafrost deposits with large ice wedges, are widely distributed in the Arctic region of northeast Siberia. They present excellent archives for the reconstruction of Late Quaternary paleoenvironmental conditions in non-glaciated areas. In 1998, 1999, and 2000 Russian and German scientists worked together on the Bykovsky Peninsula southeast of the Lena Delta in order to investigate the Ice Complex and its associated sediments. Intensive cryolithological and sedimentological studies, Radiocarbon age determinations, paleobotanical studies, micropaleontological investigations, studies of mammal and insect fossils, and stable isotope analyses of ground ice were performed. Radiocarbon data have been obtained from the entire exposed sequence covering approximately the last 60,000 years. The results indicate that compared with modern time the investigated Ice Complex sequence was formed during two cooler and more arid stages of the Late Pleistocene with relatively uniform environmental conditions, separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration. The Late Pleistocene environmental changes were not as strong as those occurring during the Pleistocene/Holocene transition where a sharp break is evident.

Description: The relative incompatibility of Ar and K are fundamental parameters in understanding the degassing history of the mantle. Clinopyroxene is the main host for K in most of the upper mantle, playing an important role in controlling the K/Ar ratio of residual mantle and the subsequent time-integrated evolution of 40Ar/36Ar ratios. Clinopyroxene also contributes to the bulk Ar partition coefficient that controls the Ar degassing rate during mantle melting. The partitioning of Ar and K between clinopyroxene and quenched silicate melt has been experimentally determined from 1 to 8 GPa for the bulk compositions Ab80Di20 (80 mol% albite-20 mol% diopside) and Ab20Di80 with an ultraviolet laser ablation microprobe (UVLAMP) technique for Ar analysis and the ion microprobe for K. Data for Kr (UVLAMP) and Rb (ion probe) have also been determined to evaluate the role of crystal lattice sites in controlling partitioning. By excluding crystal analyses that show evidence of glass contamination, we find relatively constant Ar partition coefficients (DAr) of 2.6 × 10−4 to 3.9 × 10−4 for the Ab80Di20 system at pressures from 2 to 8 GPa. In the Ab20Di80 system, DAr shows similar low values of 7.0 × 10−5 and 3.0 × 10−4 at 1 to 3 GPa. All these values are several orders of magnitude lower than previous measurements on separated crystal-glass pairs. DK is 10 to 50 times greater than DRb for all experiments, and both elements follow parallel trends with increasing pressure, although these trends are significantly different in each system studied. The DK values for clinopyroxene are at least an order of magnitude greater than DAr under all conditions investigated here, but DAr appears to show more consistent behavior between the two systems than K or Rb. The partitioning behavior of K and Rb can be explained in terms of combined pressure, temperature, and crystal chemistry effects that result in changes for the size of the clinopyroxene M2 site. In the Ab20Di80 system, where clinopyroxene is diopside rich at all pressures, DK and DRb increase with pressure (and temperature) in an analogous fashion to the well-documented behavior of Na. For the Ab80Di20 system, the jadeite content of the clinopyroxene increases from 22 to 75 mol% with pressure resulting in a contraction of the M2 site. This has the effect of discriminating against the large K+ and Rb+ ions, thereby countering the effect of increasing pressure. As a consequence DK and DRb do not increase with pressure in this system. In contrast to the alkalis (Na, K, and Rb), DKr values are similar to DAr despite a large difference in atomic radius. This lack of discrimination (and the constant DAr over a range of crystal compositions) is also consistent with incorporation of these heavier noble gases at crystal lattice sites and a predicted consequence of their neutrality or “zero charge.” Combined with published DAr values for olivine, our results confirm that magma generation is an efficient mechanism for the removal of Ar from the uppermost 200 km of the mantle, and that K/Ar ratios in the residuum are controlled by the amount of clinopyroxene. Generally, Ar is more compatible than K during mantle melting because DAr for olivine is similar to DK for clinopyroxene. As a result, residual mantle that has experienced variable amounts of melt extraction may show considerable variability in time-integrated 36Ar/40Ar.