Chemical and Sr isotopic compositions of 3 step leachates and residues of bulk samples, zeolites, and smectites from Lower Miocene sediments at ODP Site 166-1007

Massive clinoptilolite authigenesis was observed at about 1105 meters below sea floor (mbsf) in lower Miocene wellcompacted carbonate periplatform sediments from the Great Bahama Bank [Ocean Drilling Program, ODP Leg 166, Site 1007]. The diagenetic assemblage comprises abundant zeolite crystallized within foraminifer tests and sedimentary matrix, as well as Mg smectites. In carbonate-rich deposits, the formation of the zeolite requires a supply of silica. Thus, the objective of the study is to determine the origin of the silica supply, its diagenetic evolution, and consequently the related implications on interpretation of the sedimentary record, in terms of local or global paleoceanographic change. For lack of evidence for any volcaniclastic input or traces of Si-enriched deep fluids circulation, an in situ biogenic source of silica is validated by isotopic data and chemical modeling for the formation of such secondary minerals in shallow-water carbonate sequences. Geochemical and strontium isotopic data clearly establish the marine signature of the diagenetic zeolite, as well as its contemporaneous formation with the carbonate deposition (Sr model ages of 19.6-23.2 Ma). The test of saturation for the pore fluids specifies the equilibrium state of the present mineralogical assemblage. Seawater-rock modeling specifies that clinoptilolite precipitates from the dissolution of biogenic silica, which reacts with clay minerals. The amount of silica (opal-A) involved in the reaction has to be significant enough, at least 10 wt.%, to account for the observed content of clinoptilolite occurring at the most zeolite-rich level. Modeling also shows that the observed amount of clinoptilolite (~19%) reflects an in situ and short-term reaction due to the high reactivity of primary biogenic silica (opal-A) until its complete depletion. The episodic occurrence of these well-lithified zeolite-rich levels is consistent with the occurrence of seismic reflectors, particularly the P2 seismic sequence boundary located at 1115 mbsf depth and dated as 23.2 Ma. The age range of most zeolitic sedimentary levels (biostratigraphic ages of 21.5-22 Ma) correlates well with that of the early Miocene glaciation Mi-1 and Mi-1a global events. Thus, the clinoptilolite occurrence in the shallow carbonate platform environment far from volcanogenic supply, or in other sensitive marine areas, is potentially a significant new proxy for paleoproductivity and oceanic global events, such as the Miocene events, which are usually recognized in deep-sea pelagic sediments and high latitude deposits.

Sulfur contents and S, C and O isotopic compositions in serpentinized peridotites at ODP Site 153-920

The opaque mineralogy and the contents and isotope compositions of sulfur in serpentinized peridotites from the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) area were examined to understand the conditions of serpentinization and evaluate this process as a sink for seawater sulfur. The serpentinites contain a sulfur-rich secondary mineral assemblage and have high sulfur contents (up to 1 wt.%) and elevated d34S_sulfide (3.7 to 12.7?). Geochemical reaction modeling indicates that seawater-peridotite interaction at 300 to 400°C alone cannot account for both the high sulfur contents and high d34S_sulfide. These require a multistage reaction with leaching of sulfide from subjacent gabbro during higher temperature (~400°C) reactions with seawater and subsequent deposition of sulfide during serpentinization of peridotite at ~300°C. Serpentinization produces highly reducing conditions and significant amounts of H2 and results in the partial reduction of seawater carbonate to methane. The latter is documented by formation of carbonate veins enriched in 13C (up to 4.5?) at temperatures above 250°C. Although different processes produce variable sulfur isotope effects in other oceanic serpentinites, sulfur is consistently added to abyssal peridotites during serpentinization. Data for serpentinites drilled and dredged from oceanic crust and from ophiolites indicate that oceanic peridotites are a sink for up to 0.4 to 6.0 mln ton seawater S per year. This is comparable to sulfur exchange that occurs in hydrothermal systems in mafic oceanic crust at midocean ridges and on ridge flanks and amounts to 2 to 30% of the riverine sulfate source and sedimentary sulfide sink in the oceans. The high concentrations and modified isotope compositions of sulfur in serpentinites could be important for mantle metasomatism during subduction of crust generated at slow spreading rates.

Cenozoic oxygen isotopic values for benthic foraminifera from DSDP and ODP low and high latitude marine sediment cores

The climate during the Cenozoic era changed in several steps from ice-free poles and warm conditions to ice-covered poles and cold conditions. Since the 1950s, a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores. The statistical methodology of time series analysis has also evolved, allowing more information to be extracted from these records. Here we provide a comprehensive view of Cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 Myr ago. We quantitatively describe several prominent features of the oxygen isotope record, taking into account the various sources of uncertainty (including measurement, proxy noise, and dating errors). The estimated transition times and amplitudes allow us to assess causal climatological-tectonic influences on the following known features of the Cenozoic oxygen isotopic record: Paleocene-Eocene Thermal Maximum, Eocene-Oligocene Transition, Oligocene-Miocene Boundary, and the Middle Miocene Climate Optimum. We further describe and causally interpret the following features: Paleocene-Eocene warming trend, the two-step, long-term Eocene cooling, and the changes within the most recent interval (Miocene-Pliocene). We review the scope and methods of constructing Cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks, which capture besides global ice volume also bottom water temperatures at low (less than 30°) and high latitudes. This review concludes with an identification of future directions for data collection, statistical method development, and climate modeling.

(Table 1) 40Ar/39Ar plateau and isochron ages for basalts from the Réunion hotspot track

Concordant plateau and isochron ages were calculated from 40Ar/39Ar incremental heating experiments on volcanic rocks recovered by drilling at four Leg 115 sites and two industry wells along the volcanic lineament connecting Reunion Island to the Deccan flood basalts, western Indian Ocean. The new ages provide unequivocal evidence that volcanic activity migrated southward along this sequence of linear ridges. The geometry and age distribution of volcanism are most compatible with origin above a stationary hotspot centered beneath Reunion. The hotspot became active with rapid eruption of the Deccan flood basalts, western India, and subsequent volcanic products record the northward motion of the Indian and African plates over the hotspot through Tertiary time. The radiometric ages are in general accord with basal biostratigraphic age estimates, although some adjustments in current magnetobiostratigraphic time scales may be required.

Time-series of seagrass and land cover maps from 1972 to 2010, in South East Queensland, Australia, with links to GeoTIFFs

Long term global archives of high-moderate spatial resolution, multi-spectral satellite imagery are now readily accessible, but are not being fully utilised by management agencies due to the lack of appropriate methods to consistently produce accurate and timely management ready information. This work developed an object-based remote sensing approach to map land cover and seagrass distribution in an Australian coastal environment for a 38 year Landsat image time-series archive (1972-2010). Landsat Multi-Spectral Scanner (MSS), Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) imagery were used without in situ field data input (but still using field knowledge) to produce land and seagrass cover maps every year data were available, resulting in over 60 map products over the 38 year archive. Land cover was mapped annually using vegetation, bare ground, urban and agricultural classes. Seagrass distribution was also mapped annually, and in some years monthly, via horizontal projected foliage cover classes, sand and deep water. Land cover products were validated using aerial photography and seagrass maps were validated with field survey data, producing several measures of accuracy. An average overall accuracy of 65% and 80% was reported for seagrass and land cover products respectively, which is consistent with other studies in the area. This study is the first to show moderate spatial resolution, long term annual changes in land cover and seagrass in an Australian environment, created without the use of in situ data; and only one of a few similar studies globally. The land cover products identify several long term trends; such as significant increases in South East Queensland's urban density and extent, vegetation clearing in rural and rural-residential areas, and inter-annual variation in dry vegetation types in western South East Queensland. The seagrass cover products show that there has been a minimal overall change in seagrass extent, but that seagrass cover level distribution is extremely dynamic; evidenced by large scale migrations of higher seagrass cover levels and several sudden and significant changes in cover level. These mapping products will allow management agencies to build a baseline assessment of their resources, understand past changes and help inform implementation and planning of management policy to address potential future changes.

(Appendix) Recent surface areas and historical lengths of glaciers from Patagonia and Tierra del Fuego, South America

Fluctuations in the length of 72 glaciers in the Northern and Southern Patagonia Icefield (NPI and SPI, respectively) and the Cordillera Darwin Icefield (CDI) were estimated between 1945 and 2005. The information obtained from historical maps based on 1945 aerial photographs was compared to ASTER and Landsat satellite images and to information found in the literature. The majority of glaciers have retreated considerably, with maximum values of 12.2 km for Marinelli Glacier in the CDI, 11.6 km for O'Higgins Glacier in the SPI and 5.7 km for San Rafael Glacier in the NPI. Among the 20 glaciers that have retreated the most relative to their size, small (less than 50 km**2) and medium (between 50 and 200 km**2) glaciers are the most affected. However, no direct relation between glacier retreat and size was found for the 72 glaciers studied. The highest percentage retreat in the CDI was by the CDI-03 Glacier (37.9%) and Marinelli Glacier (37.6%). In the SPI, relative retreats were heterogeneous and fluctuated between 27.2% (Amelia Glacier) and 0.4% (Viedma Glacier). In the NPI, relative retreat was very high for Strindberg and Cachet glaciers (35.9% and 27.6%, respectively) but for the remaining glaciers in this icefield it ranged between 11.8% (Piscis Glacier) and 3.6% (San Quintin Glacier). In addition to surface area, the surface slope (calculated on the basis of the DEM SRTM) was also related to the relative retreat and no straightforward relation was found. From a global point of view, we suggest that glacier retreat in the region is controlled firstly by atmospheric warming, as it has been reported in this area. Besides the general increase in temperature observed, no signal of a geographical pattern for the fluctuations in glacier length was found. Consequently, glaciers appear to initially react to local conditions most probably induced by their exposition, geometry and hypsometry. The heterogeneity of rates of retreat suggests that differences in basin geometry, glacier dynamics and response time are key features to explain fluctuations of each glacier.

(Figures S2a-c) Phase diagrams of the upper crust, the lower crust and the upper mantle based on averaged compositions of the oceanic crust and mantle

The age of the subducting Nazca Plate off Chile increases northwards from 0 Ma at the Chile Triple Junction (46°S) to 37 Ma at the latitude of Valparaíso (32°S). Age-related variations in the thermal state of the subducting plate impact on (a) the water influx to the subduction zone, as well as on (b) the volumes of water that are released under the continental forearc or, alternatively, carried beyond the arc. Southern Central Chile is an ideal setting to study this effect, because other factors for the subduction zone water budget appear constant. We determine the water influx by calculating the crustal water uptake and by modeling the upper mantle serpentinization at the outer rise of the Chile Trench. The water release under forearc and arc is determined by coupling FEM thermal models of the subducting plate with stability fields of water-releasing mineral reactions for upper and lower crust and hydrated mantle. Results show that both the influx of water stored in, and the outflux of water released from upper crust, lower crust and mantle vary drastically over segment boundaries. In particular, the oldest and coldest segments carry roughly twice as much water into the subduction zone as the youngest and hottest segments, but their release flux to the forearc is only about one fourth of the latter. This high variability over a subduction zone of < 1500 km length shows that it is insufficient to consider subduction zones as uniform entities in global estimates of subduction zone fluxes. This article is protected by copyright. All rights reserved.

Distribution of biological, anthropogenic, and volcanic constituents in the San Francisco Bay Coastal System

Although conventional sediment parameters (mean grain size, sorting, and skewness) and provenance have typically been used to infer sediment transport pathways, most freshwater, brackish, and marine environments are also characterized by abundant sediment constituents of biological, and possibly anthropogenic and volcanic, origin that can provide additional insight into local sedimentary processes. The biota will be spatially distributed according to its response to environmental parameters such as water temperature, salinity, dissolved oxygen, organic carbon content, grain size, and intensity of currents and tidal flow, whereas the presence of anthropogenic and volcanic constituents will reflect proximity to source areas and whether they are fluvially- or aerially-transported. Because each of these constituents have a unique environmental signature, they are a more precise proxy for that source area than the conventional sedimentary process indicators. This San Francisco Bay Coastal System study demonstrates that by applying a multi-proxy approach, the primary sites of sediment transport can be identified. Many of these sites are far from where the constituents originated, showing that sediment transport is widespread in the region. Although not often used, identifying and interpreting the distribution of naturally-occurring and allochthonous biologic, anthropogenic, and volcanic sediment constituents is a powerful tool to aid in the investigation of sediment transport pathways in other coastal systems.

Major components and major and trace elements from ODP Site 175-1085

We have analyzed 33 Pliocene bulk sediment samples from Ocean Drilling Program Site 1085 in the Cape Basin, located offshore of western Africa in the Angola-Benguela Current system, for 17 major and trace elements, and interpreted their associations and temporal variations in the context of an allied data set of CaCO3, opal, and Corg. We base our interpretations on elemental ratios, accumulation rates, inter-element correlations, and several multi-element statistical techniques. On the basis of qualitative assessment of downhole changes in the distributions of P and Ba, utilized as proxies of export production, we conclude that highs in bulk and biogenic accumulation that occur at 3.2 Ma, 3.0 Ma, 2.4 Ma, and 2.25 Ma were caused by increases in export production as well as terrigenous flux, and record a greater sequestering of organic matter during these time periods. Studies of refractory elements and other indicator proxies (SiO2, Al2O3, TiO2, Fe2O3, MgO, V, Cr, Sr, and Zr) strongly suggest that the terrigenous component of the bulk sediment is composed of two compositional end-members, one being 'basaltic' in composition and the other similar to an 'average shale'. The basaltic end-member comprises approximately 10-15% of the total bulk sediment and its presence is consistent with the local geology of source material in the drainage basin of the nearby Orange River. The increase in bulk accumulation at 2.4 Ma appears to reflect a greater relative increase in basaltic input than the relative increase in shale-type input. Although studies such as this cannot precisely identify the transport mechanisms of the different terrigenous components, these results are most consistent with variations in sea level (and associated changes in shelf geometry and fluvial input) being responsible for the changing depositional conditions along the Angolan Margin during this time period.

Grain-size distribution, sedimentation rate and x-ray fluorescence data of four sediment cores off the Senegal River estuary

Fine-grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively. A north-south elongated mud depocenter extends along the Senegalese coast in mid-shelf position. Shallow-acoustic profiling was carried out to determine extent, geometry and internal structures of this sedimentary body. In addition, four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter. A general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive. Intervals characterized by high terrigenous input, high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland. From 2750 to 1900 and from 1000 to 700 cal a BP, wetter conditions are recorded off Senegal, an observation which is in accordance with other records from NW-Africa. Nevertheless, the three employed proxies (sedimentation rate, grain size and elemental distribution) do not always display consistent inter-core patterns. Major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system. The Senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface. Early Holocene deceleration in the rate of the sea-level rise could have enabled initial mud deposition on the shelf. These favorable conditions for mud deposition occur coevally with a humid period over NW-Africa, thus, high river discharge. Sedimentation started preferentially in the northern areas of the mud belt. During mid-Holocene, a marine incursion led to the formation of an embayment. Afterwards, sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates. These sub-recent shifts in depocenters location are caused by migrations of the Senegal River mouth. During late Holocene times, the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards.

Benthic cover map of Heron Reef derived from a high-spatial-resolution multi-spectral satellite image using object based image analysis

Providing accurate maps of coral reefs where the spatial scale and labels of the mapped features correspond to map units appropriate for examining biological and geomorphic structures and processes is a major challenge for remote sensing. The objective of this work is to assess the accuracy and relevance of the process used to derive geomorphic zone and benthic community zone maps for three western Pacific coral reefs produced from multi-scale, object-based image analysis (OBIA) of high-spatial-resolution multi-spectral images, guided by field survey data. Three Quickbird-2 multi-spectral data sets from reefs in Australia, Palau and Fiji and georeferenced field photographs were used in a multi-scale segmentation and object-based image classification to map geomorphic zones and benthic community zones. A per-pixel approach was also tested for mapping benthic community zones. Validation of the maps and comparison to past approaches indicated the multi-scale OBIA process enabled field data, operator field experience and a conceptual hierarchical model of the coral reef environment to be linked to provide output maps at geomorphic zone and benthic community scales on coral reefs. The OBIA mapping accuracies were comparable with previously published work using other methods; however, the classes mapped were matched to a predetermined set of features on the reef.