Compilation of 220 sediment core d13C data from the glacial Atlantic Ocean

We compare a compilation of 220 sediment core d13C data from the glacial Atlantic Ocean with three-dimensional ocean circulation simulations including a marine carbon cycle model. The carbon cycle model employs circulation fields which were derived from previous climate simulations. All sediment data have been thoroughly quality controlled, focusing on epibenthic foraminiferal species (such as Cibicidoides wuellerstorfi or Planulina ariminensis) to improve the comparability of model and sediment core carbon isotopes. The model captures the general d13C pattern indicated by present-day water column data and Late Holocene sediment cores but underestimates intermediate and deep water values in the South Atlantic. The best agreement with glacial reconstructions is obtained for a model scenario with an altered freshwater balance in the Southern Ocean that mimics enhanced northward sea ice export and melting away from the zone of sea ice production. This results in a shoaled and weakened North Atlantic Deep Water flow and intensified Antarctic Bottom Water export, hence confirming previous reconstructions from paleoproxy records. Moreover, the modeled abyssal ocean is very cold and very saline, which is in line with other proxy data evidence.

Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean

Investigations of piston cores from the Vema Channel and lower flanks of the Rio Grande Rise suggest the presence of episodic flow of deep and bottom water during the Late Pleistocene. Cores from below the present-day foraminiferal lysocline (at ~4000 m) contain an incomplete depositional record consisting of Mn nodules and encrustations, hemipelagic clay, displaced high-latitude diatoms, and poorly preserved heterogeneous microfossil assemblages. Cores from the depth range between 2900 m and 4000 m contain an essentially complete Late Pleistocene record, and consist of well-defined carbonate dissolution cycles with periodicities of ~100,000 years. Low carbonate content and increased dissolution correspond to glacial episodes, as interpreted by oxygen isotopic analysis of bulk foraminiferal assemblages. The absence of diagnostic high-latitude indicators (Antarctic diatoms) within the dissolution cyclss, however, suggests that AABW may not have extended to significantly shallower elevations on the lower flanks of the Rio Grande Rise during the Late Pleistocene. Therefore episodic AABW flow may not necessarily be the mechanism responsible for producing these cyclic events. This interpretation is also supported by the presence of an apparently complete Brunhes depositional record in the same cores, suggesting current velocities insufficient for significant erosion. Fluctuations in the properties and flow characteristics of another water mass, such as NADW, may be involved. The geologic evidence in core-top samples near the present-day AABW/NADW transition zone is consistent with either of two possible interpretations of the upper limit of AABW on the east flank of the channel. The foraminiferal lysocline, at ~4000 m, is near the top of the benthic thermocline and nepheloid layer, and may therefore correspond to the upper limit of relatively corrosive AABW. On the other hand, the carbonate compensation depth (CDD) at ~4250 m, which corresponds to the maximum gradient in the benthic thermocline, is characterized by rapid deposition of relatively fine-grained sediment. Such a zone of convergence and preferential sediment accumulation would be expected near the level of no motion in the AABW/NADW transition zone as a consequence of Ekman-layer veering of the mean velocity vector in the bottom boundary layer. It is possible that both of these interpretations are in part correct. The "level of no motion'' may in fact correspond to the CCD, while at the same time relatively corrosive water of Antarctic origin may mix with overlying NADW and therefore elevate the foraminifera] lysocline to depths above the level of no motion. Closely spaced observations of the hydrography and flow characteristics within the benthic thermocline will be required in order to use sediment parameters as more precise indicators of paleo-circulation.

Current meter measurements from five moorings in the subpolar North Atlantic east of the Grand Banks of Newfoundland

The southwestern part of the subpolar North Atlantic east of the Grand Banks of Newfoundland and Flemish Cap is a crucial area for the Atlantic Meridional Overturning Circulation. Here the exchange between subpolar and subtropical gyre takes place, southward flowing cold and fresh water is replaced by northward flowing warm and salty water within the North Atlantic Current (NAC). As part of a long-term experiment, the circulation east of Flemish Cap has been studied by seven repeat hydrographic sections along inline image (2003-2011), a 2 year time series of current velocities at the continental slope (2009-2011), 19 years of sea surface height, and 47 years of output from an eddy resolving ocean circulation model. The structure of the flow field in the measurements and the model shows a deep reaching NAC with adjacent recirculation and two distinct cores of southward flow in the Deep Western Boundary Current (DWBC): one core above the continental slope with maximum velocities at mid-depth and the second farther east with bottom-intensified velocities. The western core of the DWBC is rather stable, while the offshore core shows high temporal variability that in the model is correlated with the NAC strength. About 30 Sv of deep water flow southward below a density of sigma-theta = 27.68 kg/m**3 in the DWBC. The NAC transports about 110 Sv northward, approximately 15 Sv originating from the DWBC, and 75 Sv recirculating locally east of the NAC, leaving 20 Sv to be supplied by the NAC from the south.

Dr. Price testing groundwater salinity at SRS-6

http://digitalcommons.fiu.edu/fce_lter_photos/1337/thumbnail.jpg

Nd and Sm isotopic record from fossil fish teeth recovered from ODP Site 177-1090

Neodymium (Nd) isotopes were measured on 181 samples of fossil fish teeth recovered from Oligocene to Miocene sections at Ocean Drilling Program Site 1090 (3700 m water depth) on Agulhas Ridge in the Atlantic sector of the Southern Ocean. A long-term decreasing trend toward less radiogenic Nd isotope compositions dominates the record. This trend is interrupted by shifts toward more radiogenic compositions near the early/late Oligocene boundary and the Oligocene/Miocene boundary. Overall, epsilon-Nd values at Agulhas Ridge are more radiogenic than at other Atlantic locations, and are similar to those at Indian Ocean locations. The pattern of variability is remarkably similar to Nd isotope results from Walvis Ridge (South Atlantic) and Ninetyeast Ridge (Indian Ocean). In contrast, Agulhas Ridge and Maud Rise Nd isotope records do not show similar patterns over this interval. Results from this study indicate that deep water in the Atlantic flowed predominantly from north to south during the Oligocene and Miocene, and that export of Northern Component Water (NCW) to the Southern Ocean increased in the late Oligocene. There is also evidence for efficient exchange of deep waters between the Atlantic sector of the Southern Ocean and the Indian Ocean, although the direction of deep water flow is not entirely clear from these data. The shifts to more radiogenic Nd isotopic compositions most likely represent increases in the flux of Pacific waters through Drake Passage, and the timing of these events reflect development of a mature Antarctic Circumpolar Current (ACC). The relative timing of increased NCW export and ACC maturation support hypotheses that link deep water formation in the North Atlantic to the opening of Drake Passage.

Geochemistry of surface sediment cores (Table 4)

The mineralogy and geochemistry of a suite of nine manganese nodules from the South Atlantic have been determined. The Ce/La ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the Antarctic Bottom Water as has previously been successfully carried out in the Pacific Ocean. The Ce/La ratios of the nodules decrease in the sequence Lazarev Sea, Weddell Sea (10.4 and 9.7)>East Georgia Basin (6.5 and 7.1)>Argentine Basin (5.0), but then increase in the Brazil Basin (6.2) and Angola Basin (9.8 and 15.1). A further decrease was observed in the Cape Basin (7.6). An extremely high Ce/La ratio of 24.4 had already been determined for nodules sampled north of the Nares Abyssal Plain in the western North Atlantic. These data reflect the more complicated pattern of bottom water flow in the South Atlantic than in the South Pacific. The penetration of more oxygenated North Atlantic Deep Water into the South Atlantic accounts for the higher Ce/La ratios in the nodules from the Angola and Brazil basins. Based on this study, the flow path of the Antarctic Bottom Water could only be traced as far north as the Argentine Basin. The unique geochemistry of nodules from the central Angola Basin (high Mn/Fe and Ce/La ratios, high contents of Ni, Cu, Zn and Mo) appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules.

Benthic (C. wuellerstorfi) d18O, d13C and Cd/Ca in sediment core NEAP 4K across the last deglaciation

We present evidence that the characteristic chemical signature (based on coupled benthic foraminiferal Cd/Ca and d13C) of Antarctic Intermediate waters (AAIW) penetrated throughout the intermediate depths of the Atlantic basin to the high-latitude North Atlantic during the abrupt cooling events of the last deglaciation: Heinrich 1 and the Younger Dryas. AAIW may play the dynamic counterpart to the "bipolar seesaw" when near-freezing salty bottom waters from the Antarctic (AABW) sluggishly ventilate the deep ocean. Our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters (NADW) and fresh southern sourced waters (AABW and AAIW). Further, the glacial ocean may be susceptible to the more finely balanced relative densities of NADW and AAIW, due to either freshwater input or a reversal of the salinity gradient, such that the ocean is poised for NADW collapse via a negative salinity feedback. The unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters.

Dissolution of a spatially variable DNAPL (dense non aqueous phase liquid) source

Dissolution of non-aqueous phase liquids (NAPLs) or gases into groundwater is a key process, both for contamination problems originating from organic liquid sources, and for dissolution trapping in geological storage of CO2. Dissolution in natural systems typically will involve both high and low NAPL saturations and a wide range of pore water flow velocities within the same source zone for dissolution to groundwater. To correctly predict dissolution in such complex systems and as the NAPL saturations change over time, models must be capable of predicting dissolution under a range of saturations and flow conditions. To provide data to test and validate such models, an experiment was conducted in a two-dimensional sand tank, where the dissolution of a spatially variable, 5x5 cm**2 DNAPL tetrachloroethene source was carefully measured using x-ray attenuation techniques at a resolution of 0.2x0.2 cm**2. By continuously measuring the NAPL saturations, the temporal evolution of DNAPL mass loss by dissolution to groundwater could be measured at each pixel. Next, a general dissolution and solute transport code was written and several published rate-limited (RL) dissolution models and a local equilibrium (LE) approach were tested against the experimental data. It was found that none of the models could adequately predict the observed dissolution pattern, particularly in the zones of higher NAPL saturation. Combining these models with a model for NAPL pool dissolution produced qualitatively better agreement with experimental data, but the total matching error was not significantly improved. A sensitivity study of commonly used fitting parameters further showed that several combinations of these parameters could produce equally good fits to the experimental observations. The results indicate that common empirical model formulations for RL dissolution may be inadequate in complex, variable saturation NAPL source zones, and that further model developments and testing is desirable.

Clay mineralogy of South Atlantic surface sediments

Surface samples, mostly from abyssal sediments of the South Atlantic, from parts of the equatorial Atlantic, and of the Antarctic Ocean, were investigated for clay content and clay mineral composition. Maps of relative clay mineral content were compiled, which improve previous maps by showing more details, especially at high latitudes. Large-scale relations regarding the origin and transport paths of detrital clay are revealed. High smectite concentrations are observed in abyssal regions, primarily derived from southernmost South America and from minor sources in Southwest Africa. Near submarine volcanoes of the Antarctic Ocean (South Sandwich, Bouvet Island) smectite contents exhibit distinct maxima, which is ascribed to the weathering of altered basalts and volcanic glasses. The illite distribution can be subdivided into five major zones including two maxima revealing both South African and Antarctic sources. A particularly high amount of Mg- and Fe-rich illites are observed close to East Antarctica. They are derived from biotite-bearing crystalline rocks and transported to the west by the East Antarctic Coastal Current. Chiorite and well-crystallized dioctaedral illite are typical minerals enriched within the Subantarctic and Polarfrontal-Zone but of minor importance off East Antarctica. Kaolinite dominates the clay mineral assemblage at low latitudes, where the continental source rocks (West Africa, Brazil) are mainly affected by intensive chemical weathering. Surprisingly, a slight increase of kaolinite is observed in the Enderby Basin and near the Filchner-Ronne Ice shelf. The investigated area can be subdivided into ten, large-scale clay facies zones with characteristic possible source regions and transport paths. Clay mineral assemblages of the largest part of the South Atlantic, especially of the western basins are dominated by chlorite and illite derived from the Antarctic Peninsula and southernmost South America and supported by advection within the Circumantarctic Deep Water flow. In contrast, the East Antarctic provinces are relatively small. Assemblages of the eastern basins north of 30°S are strongly influenced by African sources, controlled by weathering regimes on land and by a complex interaction of wind, river and deep ocean transport. The strong gradient in clay mineral composition at the Brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins.

Core scans and lithologic analysis of Subglacial Lake Whillans sediment cores

The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in understanding this subglacial network and its affect on ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no evidence of erosion or deposition by flowing water. By inference, these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt. Consequently, water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting subglacial topography and surface slope. Sediment on the lake floor consists of till deposited during intermittent grounding of the ice stream following flood events. The fabrics within the till are weaker than those thought to develop in thick deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and unlikely to have a large stabilizing effect on the ice stream's grounding zone.

Particle positions of numerical experiments 1 to 4

In mixed sediment beds, erosion resistance can change relative to that of beds composed of a uniform sediment because of varying textural and/or other grain-size parameters, with effects on pore water flow that are difficult to quantify by means of analogue techniques. To overcome this difficulty, a three-dimensional numerical model was developed using a finite difference method (FDM) flow model coupled with a distinct element method (DEM) particle model. The main aim was to investigate, at a high spatial resolution, the physical processes occurring during the initiation of motion of single grains at the sediment-water interface and in the shallow subsurface of simplified sediment beds under different flow velocities. Increasing proportions of very fine sand (D50=0.08 mm) were mixed into a coarse sand matrix (D50=0.6 mm) to simulate mixed sediment beds, starting with a pure coarse sand bed in experiment 1 (0 wt% fines), and proceeding through experiment 2 (6.5 wt% fines), experiment 3 (10.5 wt% fines), and experiment 4 (28.7 wt% fines). All mixed beds were tested for their erosion behavior at predefined flow velocities varying in the range of U 1-5=10-30 cm/s. The experiments show that, with increasing fine content, the smaller particles increasingly fill the spaces between the larger particles. As a consequence, pore water inflow into the sediment is increasingly blocked, i.e., there is a decrease in pore water flow velocity and, hence, in the flow momentum available to entrain particles. These findings are portrayed in a new conceptual model of enhanced sediment bed stabilization.

On the feasibility of time-lapse superconducting gravimetry for reservoir monitoring

The feasibility of monitoring fluid flow subsurface processes that result in density changes, using the iGrav superconducting gravimeter, is investigated. Practical targets include steam-assisted gravity drainage (SAGD) bitumen depletion and water pumping from aquifers, for which there is currently a void in low-impact, inexpensive monitoring techniques. This study demonstrates that the iGrav has the potential to be applied to multi-scale and diverse reservoirs. Gravity and gravity gradient signals are forward modeled for a real SAGD reservoir at two time steps, and for surface-fed and groundwater-fed aquifer pumping models, to estimate signal strength and directional dependency of water flow. Time-lapse gravimetry on small-scale reservoirs exhibits two obstacles, namely, a µgal sensitivity requirement and high noise levels in the vicinity of the reservoir. In this study, both limitations are overcome by proposing (i) a portable superconducting gravimeter, and (ii) a pair of instruments under various baseline geometries. This results in improved spatial resolution for locating depletion zones, as well as the cancellation of noise common in both instruments. Results indicate that a pair of iGrav superconducting gravimeters meet the sensitivity requirements and the spatial focusing desired to monitor SAGD bitumen migration at the reservoir scales. For SAGD reservoirs, the well pair separation, reservoir depth, and survey sampling determine the resolvability of individual well pair depletion patterns during the steam chamber rising phase, and general reservoir depletion patterns during the steam chamber spreading phase. Results show that monitoring water table elevation changes due to pumping and tracking whether groundwater or surface water is being extracted are feasible.

Study of Tsunami-Induced Fluid and Debris Load on Bridges using the Material Point Method

Thesis (Ph.D.)--University of Washington, 2016-08

Environmental impacts of freshwater use and suspended solids in life cycle assessment

Perturbation of natural ecosystems, namely by increasing freshwater use and its degradative use, as well as topsoil erosion by water of land-use production systems, have been emerging as topics of high environmental concern. Freshwater use has become a focus of attention in the last few years for all stakeholders involved in the production of goods, mainly agro-industrial and forest-based products, which are freshwater-intensive consumers, requiring large inputs of green and blue water. This thesis presents a global review on the available Water Footprint Assessment and Life Cycle Assessment (LCA)-based methods for measuring and assessing the environmental relevance of freshwater resources use, based on a life cycle perspective. Using some of the available midpoint LCA-based methods, the freshwater use-related impacts of a Portuguese wine (white ‘vinho verde’) were assessed. However, the relevance of environmental green water has been neglected because of the absence of a comprehensive impact assessment method associated with green water flows. To overcome this constraint, this thesis helps to improve and enhance the LCA-based methods by providing a midpoint and spatially explicit Life Cycle Impact Assessment (LCIA) method for assessing impacts on terrestrial green water flow and addressing reductions in surface blue water production caused by reductions in surface runoff due to land-use production systems. The applicability of the proposed method is illustrated by a case study on Eucalyptus globulus conducted in Portugal, as the growth of short rotation forestry is largely dependent on local precipitation. Topsoil erosion by water has been characterised as one of the most upsetting problems for rivers. Because of this, this thesis also focuses on the ecosystem impacts caused by suspended solids (SS) from topsoil erosion that reach freshwater systems. A framework to conduct a spatially distributed SS delivery to freshwater streams and a fate and effect LCIA method to derive site-specific characterisation factors (CFs) for endpoint damage on aquatic ecosystem diversity, namely on algae, macrophyte, and macroinvertebrates organisms, were developed. The applicability of this framework, combined with the derived site-specific CFs, is shown by conducting a case study on E. globulus stands located in Portugal as an example of a land use based system. A spatially explicit LCA assessment was shown to be necessary, since the impacts associated with both green water flows and SS vary greatly as a function of spatial location.

Fine tuning for the tropics: application of eDNA technology for invasive fish detection in tropical freshwater ecosystems

Invasive species pose a major threat to aquatic ecosystems. Their impact can be particularly severe in tropical regions, like those in northern Australia, where >20 invasive fish species are recorded. In temperate regions, environmental DNA (eDNA) technology is gaining momentum as a tool to detect aquatic pests, but the technology's effectiveness has not been fully explored in tropical systems with their unique climatic challenges (i.e. high turbidity, temperatures and ultraviolet light). In this study, we modified conventional eDNA protocols for use in tropical environments using the invasive fish, Mozambique tilapia (Oreochromis mossambicus) as a detection model. We evaluated the effects of high water temperatures and fish density on the detection of tilapia eDNA, using filters with larger pores to facilitate filtration. Large-pore filters (20 μm) were effective in filtering turbid waters and retaining sufficient eDNA, whilst achieving filtration times of 2-3 min per 2-L sample. High water temperatures, often experienced in the tropics (23, 29, 35 °C), did not affect eDNA degradation rates, although high temperatures (35 °C) did significantly increase fish eDNA shedding rates. We established a minimum detection limit for tilapia (1 fish/0.4 megalitres/after 4 days) and found that low water flow (3.17 L/s) into ponds with high fish density (>16 fish/0.4 megalitres) did not affect eDNA detection. These results demonstrate that eDNA technology can be effectively used in tropical ecosystems to detect invasive fish species. © 2016 John Wiley & Sons Ltd.