ALBERT

Description: A geochemical survey of 197 fluid discharges (cold and thermal waters and bubbling pools) and 15 gas emissions from the western sector of the Sabatini Volcanic District and the Tolfa Mountains (Latium, Central Italy) was carried out in 2007–2008. The chemical and isotopic compositions of the fluid discharges indicate the occurrence of two main sources: 1) relatively shallow aquifers with Ca(Na,K)–HCO3 and Ca(Mg)–HCO3 compositions when trapped in volcanic and sedimentary formations, respectively; and 2) a deep reservoir, which is hosted in the Mesozoic carbonate sequence, rich in CO2 and having a Ca–SO4(HCO3) composition. Dissolution of a CO2-rich gas phase into the shallow aquifers produces high-TDS and high-pCO2 cold waters, while oxidation of deep-derived H2S to SO4 2− generates low-pH (b4) sulfate waters. The δ13C–CO2 values for gas emissions (from−2.8 to+2.7‰vs. VPDB) suggest that the origin of CO2 associated with the deep fluids ismainly related to thermo-metamorphic reactions within the carbonate reservoir, although significant mantle contribution may also occur. However, R/Ra values (0.37–0.62) indicate that He is mainly produced by a crustal source, with a minor component from a crust-contaminated mantle. On the basis of the δ13C–CH4 and δD–CH4 values (from −25.7 to −19.5‰ vs. VPDB and from −152 to −93.4‰ vs. VSMOW, respectively) CH4 production is associated with thermogenic processes, possibly related to abiogenic CO2 reduction within the carbonate reservoir. The δ34S–H2S values (from+9.3 to +10.4‰ vs. VCDT) are consistent with the hypothesis of a sedimentary source of sulfur from thermogenic reduction of Triassic sulfates. Geothermometric evaluations based on chemical equilibria CO2–CH4 and, separately, H2S suggest that the reservoir equilibriumtemperature is up to ~300 °C. The δDand δ18O data indicate thatwater recharging both the shallow and deep aquifers has a meteoric origin. Fluid geochemistry, coupled with gravimetric data and tectonic lineaments, supports the idea that significant contributions from a deep-seated geothermal brine are present in the Stigliano thermal fluid discharges. Exploration surveys investigated this area during 70's–90's for geothermal purposes. Nevertheless, presently the area is still under-exploited. The presence of thermal waters and anomalous heat flow together with the demographic growth of the last years,makes this site a suitable location for direct applications of the geothermal resource.

Description: Published

Description: 160-181

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: reserved

Description: For the past 50 years it has been assumed that the principal pathway for the deep limb of the Atlantic Meridional Overturning Circulation (AMOC) is the Deep Western Boundary Current (DWBC). However, recent observations of Lagrangian floats have shown that the DWBC is not necessarily a unique, dominant, or continuous pathway for these deep waters. A significant portion of the deep water export from the subpolar to the subtropical gyres follows a pathway through the interior of the Newfoundland and subtropical basins, which is constrained by the western boundary and the western flank of the Mid-Atlantic Ridge. The hypothesis that deep eddy-driven recirculation gyres are a mechanism for partitioning the deep limb of the AMOC into the DWBC and this interior pathway is investigated here. Eulerian and Lagrangian analyses of the output of ocean general circulation models at eddy-resolving, eddy-permitting, and non-eddy permitting resolutions are used to test this hypothesis. Eddy-driven recirculation gyres, simulated in the eddy-resolving and eddy-permitting models and similar to recirculations inferred from hydrographic data, are shown to shape the export pathways of deep water from the subpolar to the subtropical gyres.

Description: The isotopic composition of Phanerozoic marine sediments provides important information about changes in seawater chemistry. In particular, the radiogenic strontium isotope (87Sr/86Sr) system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric CO2 concentrations. However, the 87Sr/86Sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium (Sr) output flux, which is primarily controlled by the burial of calcium carbonate (CaCO3) at the ocean floor. The Sr budget of the Phanerozoic ocean, including the associated changes in the amount of CaCO3 burial, is therefore only poorly constrained. Here, we present the first stable isotope record of Sr for Phanerozoic skeletal carbonates, and by inference for Phanerozoic seawater (δ88/86Srsw), which we find to be sensitive to imbalances in the Sr input and output fluxes. This δ88/86Srsw record varies from ∼0.25‰ to ∼0.60‰ (vs. SRM987) with a mean of ∼0.37‰. The fractionation factor between modern seawater and skeletal calcite Δ88/86Srcc-sw, based on the analysis of 13 modern brachiopods (mean δ88/86Sr of 0.176±0.016‰, 2 standard deviations (s.d.)), is -0.21‰ and was found to be independent of species, water temperature, and habitat location. Overall, the Phanerozoic δ88/86Srsw record is positively correlated with the Ca isotope record (δ44/40Casw), but not with the radiogenic Sr isotope record ((87Sr/86Sr)sw). A new numerical modeling approach, which considers both δ88/86Srsw and (87Sr/86Sr)sw, yields improved estimates for Phanerozoic fluxes and concentrations for seawater Sr. The oceanic net carbonate flux of Sr (F(Sr)carb) varied between an output of -4.7x1010mol/Myr and an input of +2.3x1010mol/Myr with a mean of -1.6x1010mol/Myr. On time scales in excess of 100Myrs the F(Sr)carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the “aragonite” and “calcite” sea episodes. On time scales less than 20Myrs the F(Sr)carb seems to be controlled by variable combinations of carbonate burial rate, shelf carbonate weathering and recrystallization, ocean acidification, and ocean anoxia. In particular, the Permian/Triassic transition is marked by a prominent positive δ88/86Srsw-peak that reflects a significantly enhanced burial flux of Sr and carbonate, likely driven by bacterial sulfate reduction (BSR) and the related alkalinity production in deeper anoxic waters. We also argue that the residence time of Sr in the Phanerozoic ocean ranged from ∼1Myrs to ∼20Myrs.

Description: IODP Expedition 307 made it for the first time possible to investigate the entire body of a cold-water coral carbonate mound. Here we provide new insights into the long-term history of Challenger Mound on the European continental margin off Ireland. This study is based on age determinations (230Th/U, 87Sr/86Sr) and geochemical signals (Mg/Li and Ba/Ca) measured in the scleractinian cold-water coral Lophelia pertusa from IODP Site 1317 in the Porcupine Seabight. The paleoceanographic reconstructions reveal that coral growth in the Porcupine Seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and Bottom-Water Temperatures (BWT) between ∼8–10 °C, related to the water mass stratification of the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Water (ENAW). The geochemical signals from the coral skeletons can be explained by the close interaction between cold-water coral growth, sea-surface productivity and the surrounding water masses - the boundary layer between MOW and ENAW. Enhanced sea-surface productivity and the build-up of a stable water mass stratification between ENAW and MOW caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between∼3.0 - 2.1 Ma. With the decrease in sea-surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between∼1.7 - 1 Ma. During the late Pleistocene (over the last∼0.5 Myr) mound growth was restricted to interglacial periods. During glacials the water mass boundary between ENAW/MOW probably was below the mound summit and hence food supply was not sufficient for corals to grow.

Description: The aragonitic skeletons of scleractinian cold-water corals can serve as valuable archives in paleoceanographic studies. The potential of δ88/86Sr, Sr/Ca, Mg/Ca, Li/Ca and Mg/Li ratios of the cold-water coral Lophelia pertusa to record intermediate water mass properties has been investigated. Here we used samples from several locations along the European continental margin spanning a large temperature range from 6 to 14 °C. Stable strontium isotope measurements were carried out with the recently developed double spike TIMS technique and our results differ from those obtained with less precise methods. In contrast to the strong positive relationship with temperature of previous studies, our results suggest that δ88/86Sr measured in scleractinian cold-water corals is not controlled by seawater temperature, but reflects the Sr isotopic composition of seawater with an offset of Δ88/86Sr = − 0.196‰. As found in previous studies, the elemental ratios Sr/Ca, Li/Ca and Mg/Li measured in corals are significantly related to water temperature and do not correlate with salinity. Moreover, Sr/Ca ratios in L. pertusa display the expected inverse correlation with temperature. However, the variance in the Sr/Ca data severely limits the accuracy of paleotemperature estimates. The Li/Ca and Mg/Ca ratios reveal other influences besides temperature such as pH and/or growth or calcification rate. However, corresponding Mg/Li ratios in L. pertusa are more tightly related to temperature as they remove these secondary effects. In particular, the Mg/Li ratio in L. pertusa may serve as a new promising paleotemperature proxy for intermediate water masses. Our dataset represents the most extensive geochemical examination of L. pertusa to date, revealing a temperature sensitivity of 0.015 mol/mmol/°C for Mg/Li. However, using this temperature dependence and the precision of 5.3% (2SD) only temperature variations larger than ~ 1.5 °C can be resolved with 95% confidence.

Description: The understanding of the paleoenvironment during initiation and early development of deep cold-water coral carbonate mounds in the NE Atlantic is currently a focus of international research. The Integrated Ocean Drilling Program (IODP) Expedition 307 drilled the 155 m high Challenger Mound in the Porcupine Seabight (SW off Ireland) in order to investigate for the first time sediments from the base of a giant carbonate mound. In this study we focus in high resolution on 12 m of sediments from Site 1317 encompassing the mound base. The mound initiation and start-up phase coincide with the intensification of the Northern Hemisphere Glaciation (INHG) at around 2.7 Ma. Further carbonate mound development seems to be strongly dependent on rapid changes in paleoceanographic and climatic conditions at the Pliocene–Pleistocene boundary, especially characterized and caused by the interaction of intermediate water masses, the Mediterranean Outflow Water (MOW), the Eastern North Atlantic Water (ENAW) and the influence of Southern Component Water (SCW). This study is based on well-established proxies such as δ18O and δ13C of planktonic (Globigerina bulloides) and benthic foraminifera (Fontbotia wuellerstorfi, Discanomalina coronata, Lobatula lobatula, Lobatula antarctica, and Planulina ariminensis) as well as grain size parameters to identify the paleoenvironmental and paleoecological setting favourable for the initial coral colonization on the mound. Stable oxygen and carbon isotope records of benthic foraminiferal species indicate that L. lobatula provides a reliable isotopic signature for paleoenvironmental reconstructions. In particular, δ18O values of L. lobatula indicate that initial mound growth started in a glacial mode with moderate excursions in δ18O values. Carbon isotope values of D. coronata are significantly offset compared to other epibenthic species. This offset may be related to vital effects. Bottom water temperatures, calculated using standard equations based on δ18O of foraminiferal tests, range between 7 and 11 °C, consistent with the known temperature range conducive for cold-water coral growth and development. Bottom currents transporting intermediate water masses of southern origin (Mediterranean and Bay of Biscay) enhanced at 2.6 Ma supporting first coral settlements with the INHG. The benthic δ13C and the sortable silt records indicate that the early Pleistocene hydrodynamic regime was characterized by weaker current intensities associated with vertical movements of MOW or its replacement by SCW at intermediate depth. After these sluggish phases enhanced MOW flow dominated again and led to stronger current intensities and most probably sediment erosion on Challenger Mound. Erosion in combination with early diagenetic (oxidation) processes overprinted the sediment layers as indicated by dissolved coral skeletons, the increase in Ca-content and sediment density, minimum δ13Cplanktonic values, as well as the occurrence of gypsum and pyrite, implying a careful evaluation of original and overprinted geochemical signals. We conclude that the Challenger Mound development was already influenced by short-term variability of water masses from southern origin and possible erosional events comparable to the late Pleistocene setting.

Description: Tidal processes play an important role in the dynamics of shelf circulation in the Laptev Sea. The Unstructured Grid Finite Volume Coastal Ocean Model (FVCOM) is used to simulate the tidal dynamics in the Lena Delta region of the Laptev Sea in ice-free barotropic case. The grid element size ranges from 400 m to 5 km. The major semidiurnal tidal waves M2M2 and S2S2 are investigated with the M2M2 being the most important in generating large sea level amplitudes and currents over shallow areas. A correction to the tidal elevation at the open boundary is proposed, which minimizes the discrepancy between the model prediction and observations. The observations include both recent mooring data and the standard set of tide gauge measurements used in previous studies. The comparison of results to known tidal solutions is carried out. The paper also discusses the residual circulation and energy fluxes and assesses the impact of additional bathymetric information. Highlights • Our simulations reproduce the semidiurnal tidal waves M2M2 and S2S2 in the Laptev Sea region. • We develop special procedure for the construction of optimal open boundary conditions for tidal elevation for M2M2 and S2S2 constituents. • The simulated tidal maps show an improved agreement with observations. • We analyze barotropic currents, residual circulation and evolution of energy fluxes in the region. • We consider the energy balance for the M2M2 and S2S2 waves and the sensitivity to the bathymetry.

Description: Mineral assemblage, trace element content and Nd and Pb isotope signatures were analysed on the fine fraction (〈20 μm) of sedimentary records from the Northern Mendeleev Ridge in the Central Arctic Ocean. Our aim was to identify the detrital particle provenance and to interpret the changes over the past ∼250 ka in the relative contribution of the different source-areas in relation to paleoenvironmental conditions. The clay mineral assemblage and the Nd and Pb isotope signatures depict systematic changes over the Late Quaternary. The bulk mineralogy exhibits increases in the relative contribution of carbonate minerals vs. silicates in interglacial/deglacial intervals. In glacial intervals, the mineral assemblage of the 〈20 μm fraction is characterised by an enrichment in kaolinite, counterbalanced by a decrease in illite. The Nd and Pb isotope signatures of 〈20 μm fraction are interpreted using a three end-member mixing model, involving crustal supplies from North America and Canada, from the Siberian margin and some from volcanic material. A compilation of geochemical signatures of geological terraines surrounding the Arctic Ocean allowed each end-member to be assigned a representative signature, averaging the signal of the eroded terraines. The Suspended Particulate Matter (SPM) of the MacKenzie River represents an average signature of the sedimentary supplies delivered from the North American platform and Canadian margin. The SPM of the Lena River reflects the mean sedimentary signature of the Siberian platform. The Okhotsh-Chukotka province from the Eastern border of Siberia is identified as the most probable volcanic source. Late Quaternary evolution of the estimated relative contribution of the three end-members confirms that the sediment provenances in the Central Arctic Ocean remain close to the current conditions during past interglacials/deglacials MIS1–3, MIS5/TII and MIS7/TIII. In contrast, glacial conditions (MIS4 and MIS6) record minimum supplies from the American margin, associated with increased volcanic contribution, to the Mendeleev Ridge core location suggesting a different sea-ice circulation associated with a low sea-level and reduced shelf area. Highlights • Nd and Pb isotope signatures of fine detrital sediment fraction are tracer of sources. • Glacial and interglacials are characterised by systematic changes in sediment sources. • The volcanic Okhotsh-Chukotka province has major contribution during glacials.

Description: Deep-sea benthic communities and their structural and functional characteristics are regulated by surface water processes. Our study focused on the impact of changes in water depth and food supplies on small-sized metazoan bottom-fauna (meiobenthos) along a bathymetric transect (1200–5500 m) in the western Fram Strait. The samples were collected every summer season from 2005 to 2009 within the scope of the HAUSGARTEN monitoring program. In comparison to other polar regions, the large inflow of organic matter to the sea floor translates into relatively high meiofaunal densities in this region. Densities along the bathymetric gradient range from approximately 2400 ind. 10 cm-2 at 1200 m to approximately 300 ind. 10 cm-2 at 4000 m. Differences in meiofaunal distribution among sediment layers (i.e., vertical profile) were stronger than among stations (i.e., bathymetric gradient). At all the stations meiofaunal densities and number of taxa were the highest in the surface sediment layer (0–1 cm), and these decreased with increasing sediment depth (down to 4–5 cm). However, the shape of the decreasing pattern differed significantly among stations. Meiofaunal densities and taxonomic richness decreased gradually with increasing sediment depth at the shallower stations with higher food availability. At deeper stations, where the availability of organic matter is generally lower, meiofaunal densities decreased sharply to minor proportions at sediment depths already at 2–3 cm. Nematodes were the most abundant organisms (60–98%) in all the sediment layers. The environmental factors best correlated to the vertical patterns of the meiofaunal community were sediment-bound chloroplastic pigments that indicate phytodetrital matter. Highlights • Small-scale heterogeneity is the main source of variation in meiofauna community. • Trophic conditions influence vertical patterns of meiofauna distribution. • Meiofauna abundance and biomass decrease with increasing water depth.

Description: TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a sea surface temperature (SST) proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs). In this study, we appraise the applicability of TEX86 and View the MathML sourceTEX86L in subpolar and polar regions using surface sediments. We present TEX86 and View the MathML sourceTEX86L data from 160 surface sediment samples collected in the Arctic, the Southern Ocean and the North Pacific. Most of the SST estimates derived from both TEX86 and View the MathML sourceTEX86L are anomalously high in the Arctic, especially in the vicinity of Siberian river mouths and the sea ice margin, plausibly due to additional archaeal contributions linked to terrigenous input. We found unusual GDGT distributions at five sites in the North Pacific. High GDGT-0/crenarchaeol and GDGT-2/crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and/or methanotrophic archaea to the sedimentary GDGT pool here. Apart from these anomalous findings, TEX86 and View the MathML sourceTEX86L values in the surface sediments from the Southern Ocean and the North Pacific do usually vary with overlaying SSTs. In these regions, the sedimentary TEX86-SST relationship is similar to the global calibration, and the derived temperature estimates agree well with overlaying annual mean SSTs at the sites. However, there is a systematic offset between the regional View the MathML sourceTEX86L-SST relationships and the global calibration. At these sites, temperature estimates based on the global View the MathML sourceTEX86L calibration are closer to summer SSTs than annual mean SSTs. This finding suggests that in these subpolar settings a regional View the MathML sourceTEX86L calibration may be a more suitable equation for temperature reconstruction than the global calibration.