Geochemistry and physics on sediment cores from the Peru Basin

We studied preservation/dissolution cycles and paleoproductivity in eight sediment cores from the Peru Basin south of the highly productive surface waters of the eastern equatorial Pacific. Stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy. Sediment cores which span the last 8 m.y., were retrieved during cruise 79 with RV SONNE close to the carbonate compensation depth (CCD). In general, sediments show Pacific-type carbonate cycles. We interpret a pronounced carbonate peak between 6 and 7 Ma as the result of a western and northern extension of the highly productive Peru Current. Decreased carbonate contents from the late Miocene to the late Pliocene might be associated with a slow contraction of the latitudinal extent of the high-productivity belt north of the study areas. During the Pliocene, carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets, which should have been associated with pulsations of the Antarctic ice cap. An abrupt collapse of the carbonate system occurred at 2.4 Ma. Higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation. During the Quaternary, carbonate fluxes are high during glacials and low during interglacials. Large amplitude variations with long broad minima and maxima, associated with small migrations of the lysocline and the CCD (< 200 m), are indicative of the preservation/dissolution history in the Peru Basin. During the early Pleistocene, climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record. During the last 800 kyr, variability in the carbonate record was dominated by the 100 kyr eccentricity cycle. Fluxes of biogenic material (calcium carbonate, organic carbon, opal, and barium) were greatest during glacials, which imply higher productivity and export production of the Peru Current during cold climatic periods. Dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate. After the Mid-Brunhes Event (400 ka), we observe a plateaulike shift to enhanced dissolution and to intensified productivity.

(Table 22-30) Revised composite depth scales of IODP Sites 320-U1331, U1332, U1333, U1334 and ODP Sites 199-1218, 199-1219, 199-1220

Integrated Ocean Drilling Program (IODP) Expedition 320 recovered high-quality paleomagnetic records with over 800 dated reversals and decimeter-scale cyclic sediments which provide an outstanding framework to inter-calibrate major fossil groups and refine magnetic polarity chrons for the early Miocene, the entire Oligocene and the late Eocene Epoch. In order to reconstruct the climate history of the Equatorial Pacific one of the major objectives of the Pacific Equatorial Age Transect (PEAT) is the compilation of a Cenozoic Megasplice which integrates all available bio-, chemo-, and magnetostratigraphic data including key records from Ocean Drilling Program (ODP) Leg 199. Here we present extended post-cruise refinements of the shipboard composite depth scales and composite records of IODP Expedition 320 Sites U1331, U1332, U1333, U1334 as well as ODP Leg 199 Sites 1218, 1219 and 1220. The revised composite records were used to perform a site-to-site correlation and integration of Leg 199 and Exp. 320 sites. Based on this decimeter scale correlation a high resolution integrated paleomagnetic and biostratigraphic framework for the Equatorial Pacific is established covering the time from 20 to 40 Ma. This unprecedented sedimentary compendium from the Equatorial Pacific will be the backbone for paleoceanographic reconstructions for the late Paleogene.

Geochemistry of ODP Site 125-786 volcanic rocks

Eocene-Oligocene volcanic rocks drilled at Site 786 in the Izu-Bonin forearc cover a wide range of compositions from primitive boninites to highly evolved rhyolites. K-Ar dating reveals at least two distinct episodes of magmatism; one at 41 Ma and a later one at 35 Ma. The early episode produced low-Ca boninites and bronzite andesites that form an oceanic basement of pillow lavas and composite intrusive sheets, overlain by flows and intrusive sheets of intermediate-Ca boninites and bronzite-andesites and a fractionated series of andesites, dacites, and rhyolites. The later episode produced high-Ca boninites and intermediate-Ca boninites, exclusively as intrusive sheets.

Biochar and compost effects on mobility of Cu and other soil parameters and plant growth

A pot experiment was conducted to determine the effects of three biochars and compost on plant growth and the immobilisation of Cu in a contaminated soil obtained from a former wood preservation site in the Gironde County Saint Médard d'Eyrans, France (N 44° 43.353, W 0° 30.938). To assess Cu mobility, amended soils were analysed using CaCl**2 leaching tests pre- and post-incubation, and post-growth. Amended and unamended soils were planted with sunflower, and the resulting plant material was assessed for yield (mass and height) and Cu concentration. All amendments significantly reduced leachable Cu compared to the unamended soil, however, the greatest reductions in leachable Cu were associated with the higher biochar application rate. The greatest improvements in plant yields were obtained with the higher application rate of biochar in combination with compost. pH, DOC, EH were measured in soils to help explain the leaching and plant growth trends. Soil pore water was collected during plant growth and analysed for metal concentration, pH and EH. Prior to treatment, background analyses were carried out on the soil and individual amendments (including PAH + metal concentrations measured by gas chromatography mass spectrometry and ICP-AES respectively).

Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Geochemistry of boninite and harzburgite of ODP Leg 125 basement samples

Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component. The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250? C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks elsewhere in the Western Pacific highlights large regional differences in petrogenesis in terms of mantle mineralogy, degree of partial melting, composition of subduction components, and the nature of pre-subduction lithosphere. It is likely that, on a regional scale, the initiation of subduction involved subducted crust and lithospheric mantle wedge of a range of ages and compositions, as might be expected in this type of tectonic setting.

Pollen and non-pollen palynomorph records of the Holocene part of the composite sediment core TMD from lake Tso Moriri (NW India) and of modern surface samples from the Tso Moriri region

The high-altitude lake Tso Moriri (32°55'46'' N, 78°19'24'' E; 4522 m a.s.l.) is situated at the margin of the ISM and westerly influences in the Trans-Himalayan region of Ladakh. Human settlements are rare and domestic and wild animals are concentrating at the alpine meadows. A set of modern surface samples and fossil pollen from deep-water TMD core was evaluated with a focus on indicator types revealing human impact, grazing activities and lake system development during the last ca. 12 cal ka BP. Furthermore, the non-pollen palynomorph (NPP) record, comprising remains of limnic algae and invertebrates as well as fungal spores and charred plant tissue fragments, were examined in order to attest palaeolimnic phases and human impact, respectively. Changes in the early and middle Holocene limnic environment are mainly influenced by regional climatic conditions and glacier-fed meltwater flow in the catchment area. The NPP record indicates low lake productivity with high influx of freshwater between ca. 11.5 and 4.5 cal ka BP which is in agreement with the regional monsoon dynamics and published climate reconstructions. Geomorphologic observations suggest that during this period of enhanced precipitation the lake had a regular outflow and contributed large amounts of water to the Sutlej River, the lower reaches of which were integral part of the Indus Civilization area. The inferred minimum fresh water input and maximum lake productivity between ca. 4.5-1.8 cal ka BP coincides with the reconstruction of greatest aridity and glaciation in the Korzong valley resulting in significantly reduced or even ceased outflow. We suggest that lowered lake levels and river discharge on a larger regional scale may have caused irrigation problems and harvest losses in the Indus valley and lowlands occupied by sedentary agricultural communities. This scenario, in turn, supports the theory that, Mature Harappan urbanism (ca. 4.5-3.9 cal ka BP) emerged in order to facilitate storage, protection, administration, and redistribution of crop yields and secondly, the eventual collapse of the Harappan Culture (ca. 3.5-3 cal ka BP) was promoted by prolonged aridity. There is no clear evidence for human impact around Tso Moriri prior to ca. 3.7 cal ka BP, with a more distinct record since ca. 2.7 cal ka BP. This suggests that the sedimentary record from Tso Moriri primarily archives the regional climate history.

(Table 1) Composite surface scraping samples and Coscinodiscus nodulifer abundance from DSDP Hole 64-480

Analysis of individual laminae in Recent sediments from the slopes of the Guaymas Basin indicates an increased abundance of the larger sizes (>60 µm) of Coscinodiscus nodulifer when upwelling conditions persist over the depositional site and an increase of the smaller sizes (<60 µm) when nonupwelling conditions exist. The size distributions of C. nodulifer in 10-cm composite samples from Hole 480 show a greater abundance of the large sizes (>60 µm) associated with well-laminated sections and more of the smaller sizes (<60 µm) in samples from the homogeneous sections. We have tentatively correlated the pronounced homogeneous zones with late Pleistocene glacial periods. These results indicate a persistence of nonupwelling conditions over Hole 480 during glacial periods (homogeneous zones) and a predominance of upwelling conditions during interglacial periods (laminated zones). Other evidence from diatom and silicoflagellate floral analysis seems to support these preliminary conclusions.

Geochemistry on water profiles from the Kara Sea

As a part of the Russian-German project "Siberian River-Runoff (SIRRO)" the major element composition of the dissolved load and the major and trace element composition of particulate load and bottom sediment of the Yenisei River and Estuary were analyzed and examined in context of the basin lithology and climate. In addition, the processes controlling the transformation of the river load in the estuarine mixing zone were investigated. The chemical composition of the dissolved and particulate load of the Yenisei fluvial endmember is generally comparable to that of other major world rivers. The dissolved load is chiefly controlled by carbonate weathering and the chemical composition of the river suspended particulate matter (SPM) is similar to that of the North American Shale Composite (NASC), which represents the weathering product of the upper continental crust. The Chemical Index of Alteration (CIA) of the Yenisei SPM amounts to 71, which indicates moderate chemical weathering. With regard to the SPM geochemistry, the Yenisei occupies an intermediate position between the adjacent rivers Khatanga and the Lena. Drastic changes in the composition of the river load are seen in the mixing zone between fresh and salt water. While dissolved Na, Ca, Mg, K, CI, S04, F, Br, Sr and HC03 behave conservatively, dissolved Fe is completely removed from solution at very low salinities. Particulate Mn exhibits a pronounced mid-salinity minimum concomitant with a maximum of dissolved Mn, which is probably related to suboxic conditions in the area of the so-called "marginal filter", where highest turbidities are found. The Mn-minimum in SPM is paralleled by depletions of the elements Ba, Zn, Cd, Ni, Cu and V, which can be associated with manganese particles. The estuarine bottom sediments are composed of mud and sand and the sedimentological parameters of the bottom sediments have to be considered for the interpretation of the bulk geochemical data. The chemical composition of the mud is comparable to the SPM, whereas the sand is relatively enriched in Si/Al, Ba/Al, Zr/Al and Sr/Al ratios and depleted in transition metals.

Geochemistry of tephra from the Taupo Volcanic Zone

The Taupo Volcanic Zone (TVZ), central North Island, New Zealand, is the most frequently active Quaternary rhyolitic system in the world. Silicic tephras recovered from Ocean Drilling Programme Site 1123 (41°47.16'S, 171°29.94'W; 3290 m water depth) in the southwest Pacific Ocean provide a well-dated record of explosive TVZ volcanism since ~1.65 Ma. We present major, minor and trace element data for 70 Quaternary tephra layers from Site 1123 determined by electron probe microanalysis (1314 analyses) and laser ablation inductively coupled plasma mass spectrometry (654 analyses). Trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie-lines between three sediment cores (1123A, 1123B and 1123C) recovered from Site 1123. These tephra tie-lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the Site 1123 composite record. Trace element fingerprinting of tephras identifies ~4.5 m and ~7.9 m thick sections of repeated sediments in 1123A (49.0-53.5 mbsf [metres below seafloor]) and 1123C (48.1-56.0 mbsf), respectively. These previously unrecognised repeated sections have resulted in significant errors in the Site 1123 composite stratigraphy and age model for the interval 1.15-1.38 Ma and can explain the poor correspondence between d18O profiles for Site 1123 and Site 849 (equatorial Pacific) during this interval. The revised composite stratigraphy for Site 1123 shows that the 70 tephra layers, when correlated between cores, correspond to ~37-38 individual eruptive events (tephras), 7 of which can be correlated to onshore TVZ deposits. The frequency of large-volume TVZ-derived silicic eruptions, as recorded by the deposition of tephras at Site 1123, has not been uniform through time. Rather it has been typified by short periods (25-50 ka) of intense activity bracketed by longer periods (100-130 ka) of quiescence. The most active period (at least 1 event per 7 ka) occurred between ~1.53 and 1.66 Ma, corresponding to the first ~130 ka of TVZ rhyolitic magmatism. Since 1.2 Ma, ~80% of tephras preserved at Site 1123 and the more proximal Site 1124 were erupted and deposited during glacial periods. This feature may reflect either enhanced atmospheric transport of volcanic ash to these sites (up to 1000 km from source) during glacial conditions or, more speculatively, that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea-level changes. Only 8 of the ~37-38 Site 1123 tephra units (~20%) can be found in all three cores, and 22 tephra units (~60%) are only present in one of the three cores. Whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume. Instead it is postulated that tephra preservation at Site 1123 is 'patchy' and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents. At this site, at least 5 cores would need to have been drilled within a proximity of 10's to 100's of metres of each other to yield a >99% chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1.65 Ma.