Late Quaternary Mediterranean Outflow Water: implications from radiogenic Nd, Sr, Pb isotopes and clay minerals

Mediterranean Outflow Water (MOW) is characterised by higher temperatures and salinities than other ambient water masses. MOW spreads at water depths between 500 and 1500 m into the eastern North Atlantic and has been a source of salinity for the Atlantic Meridional Overturning Circulation. We used high-resolution Nd and Pb isotope records of past ambient seawater obtained from authigenic ferromanganese coatings of sediments in three gravity cores at 577, 1745 and 1974 m water depths in the Gulf of Cadiz and along the Portuguese margin complemented by a selection of surface sediments to reconstruct the extent and pathways of MOW over the past 23 000 years. In addition, radiogenic Nd, Pb and Sr isotope ratios obtained from total digestion of the residual clay fraction of the leached samples were used to evaluate any changes in the endmember compositions. The surface and downcore seawater Nd isotope data from all water depths exhibit only a very small variability close to the present day composition of MOW but do not reflect the present day Nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station, which is most likely the consequence of downslope sediment transport in the nepheloid boundary layer as well as the small variations in the Nd endmember compositions. In contrast, the seawater Pb isotope records show significant and systematic variations, which provide evidence for a significantly different pattern of the MOW pathways between 20 000 and 12 000 years ago compared with the subsequent period of time. A deeper situated MOW during the Last Glacial Maximum (LGM) raised during the early deglaciation with its shallowest position around Heinrich event H1, followed by a moderate deepening and the establishment of present-day MOW hydrography. The radiogenic isotope signatures of the residual clay fractions document a pulse of sediment input from the north during Heinrich event H1 around 14.8 ka, but other than that exhibit little varibility over time suggesting surprisingly constant sedimentary endmember compositions and mixing ratios since the LGM

The natural decline of potato cyst nematodes in the absence of a host crop and their movement by cultivation operations

This thesis has investigated the variation in PCN population density declines in the absence of a host crop and, the movement of PCN by cultivation operations in a potato rotation. The use of crop rotation as a management strategy for the control of potato cyst nematodes (PCN) is dependent on the natural decline rate of PCN. Any substantial variation among PCN populations will influence the adequacy and duration of crop rotation. Two experiments were undertaken to assess the extent of variation in PCN decline. Experiment 1 consisted of the annual sampling of semi-permanent field test stations to monitor the population decline in five infested fields, over four years. Large variations within the PCN population densities were found over the duration of the experiment, these included apparent increases in population density. These increases were not found for the controls in the field boundaries. The observed variations were probably due to the net movement of cysts in and around the stations as a result of soil movement by cultivation, as identified in further studies. Experiment 2 consisted of 45 plunge pits with soil from different PCN infested fields. The plunge pits were sampled at four monthly intervals, for twenty months. The range of decline was 11 to 69 % per annum. The variation in decline rates between the populations could not be accounted for by differences between G. pallida and G. rostochiensis populations or completely by soil type. This suggested that decline information was required on a site-specific basis and that sampling within a field is not reliable if cultivations are carried out between sampling dates. Further studies determined that PCN cysts are moved by cultivation operations. With the exception of the bed-former, all cultivations investigated were found to result in the movement of PCN. The range of movement by a cultivation operation was from within 1 m up to 5 m. The cultivation operation employed and its purpose determine the direction and extent of cyst movement

The Value of Evidence-Based Computer Simulation of Oral Health Outcomes for Management Analysis of the Alaska Dental Health Aide Program

Objectives: To create an evidence‐based research tool to inform and guide policy and program managers as they develop and deploy new service delivery models for oral disease prevention and intervention. Methods: A village‐level discrete event simulation was developed to project outcomes associated with different service delivery patterns. Evidence‐ based outcomes were associated with dental health aide activities, and projected indicators (DMFT, F+ST, T‐health, SiC, CPI, ECC) were proxy for oral health outcomes. Model runs representing the planned program implementation, a more intensive staffing scenario, and a more robust prevention scenario, generated 20‐year projections of clinical indicators; graphs and tallies were analyzed for trends and differences. Results: Outcomes associated with alternative patterns of service delivery indicate there is potential for substantial improvement in clinical outcomes with modest program changes. Not all segments of the population derive equal benefit when program variables are altered. Children benefit more from increased prevention, while adults benefit more from intensive staffing. Conclusions: Evidence‐ based simulation is a useful tool to analyze the impact of changing program variables on program outcome measures. This simulation informs dental managers of the clinical outcomes associated with policy and service delivery variables. Simulation tools can assist public health managers in analyzing and understanding the relationship between their policy decisions and long‐term clinical outcomes.The Ford Foundation

Plio-Pleistocene changes in water mass exchange and erosional inputs in the Fram Strait

We determined the isotopic composition of neodymium (Nd) and lead (Pb) of past seawater to reconstruct water mass exchange and erosional input between the Arctic Ocean and the Norwegian-Greenland Seas over the past 5 Ma. For this purpose, sediments of ODP site 911 (leg 151) located at 900 m water depth on the Yermak Plateau in the Fram Strait were used. The paleo-seawater variability of Nd and Pb isotopes was extracted from the sea water-derived metal oxide coatings on the sediment particles following the leaching method of Gutjahr et al. (2007). All radiogenic isotope data were acquired by Multi-Collector (MC) ICP-MS. The site 911 stratigraphy of Knies et al. (2009) was applied. Surface sediment Sr and Nd isotope data, as well as downcore Sr isotope data obtained on the same leaches are close to seawater and confirm the seawater origin of the Nd and Pb isotope signatures. The deep water Nd isotope time series extracted from site 911 was in general more radiogenic ("Nd = -7.5 to -10) than present day deep water ("Nd = -9.8 to -11.8) in the area of the Fram Strait (Andersson et al., 2008) and does not show a systematic trend with time. In contrast, the radiogenic isotope composition of Pb evolved from 206Pb/204Pb ratios around 18.7 to more radiogenic values around 19.2 between 2 Ma and today. The data indicate that mixing of water masses from the Arctic Ocean and the Norwegian-Greenland Seas has controlled the Nd isotope signatures of deep waters on the Yermak Plateau over the past 5 Ma. Prior to 1.7 Ma the Nd isotope signatures on the Yermak Plateau were less radiogenic than waters from the same depth in the central Arctic Ocean (Haley et al., 2008) pointing to a greater influence from the Norwegian-Greenland Seas. After 1.7 Ma the central Arctic and Yermak Plateau data have varied around similar values indicating water mass mixing overall similar to today. In contrast, the Pb isotope composition of deep waters in the Fram Strait appears to have been dominated by weathering inputs from glacially weathering old continental landmasses, such as Greenland or parts of Svalbard since 2 Ma. A similar control over the Pb isotope evolution of seawater since the onset of Northern Hemisphere Glaciation was recorded by ferromanganese crusts that grew from North Atlantic DeepWater in the western North Atlantic. References: Gutjahr, M., Frank, M., Stirling, C.H., Klemm, V., van de Flierdt, T. and Halliday, A.N. (2007): Reliable extraction of a deepwater trace metal isotope signal from Fe-Mn oxyhydroxide coatings of marine sediments.- Chemical Geology 242, 351-370 Haley B. A., M. Frank, R.F. Spielhagen and A. Eisenhauer (2008): Influence of brine formation on Arctic Ocean circulation over the past 15 million years. Nature Geoscience 1, 68–72 Andersson, P.S., Porcelli, D., Frank, M., Björk, G., Dahlqvist, R. and Gustafsson, Ö. (2008): Neodymium isotopes in seawater from the Barents Sea and Fram Strait Arctic- Atlantic gateways.- Geochim. Cosmochim. Acta 72, 2854-2867 Knies, J., J. Matthiessen, C. Vogt, J.S. Laberg, B.O. Hjelstuen, M.Smelror, E. Larsen, K. Andreassen, T. Eidvin and T.O. Vorren (2009): The Plio-Pleistocene glaciation of the Barents Sea–Svalbard region: a new model based on revised chronostratigraphy - Quaternary Science Reviews 28, 9-10, 812-82

ESTIMATING TEMPORAL ASSOCIATIONS IN ELECTROCORTICOGRAPHIC (ECoG) TIME SERIES WITH FIRST ORDER PRUNING

Granger causality (GC) is a statistical technique used to estimate temporal associations in multivariate time series. Many applications and extensions of GC have been proposed since its formulation by Granger in 1969. Here we control for potentially mediating or confounding associations between time series in the context of event-related electrocorticographic (ECoG) time series. A pruning approach to remove spurious connections and simultaneously reduce the required number of estimations to fit the effective connectivity graph is proposed. Additionally, we consider the potential of adjusted GC applied to independent components as a method to explore temporal relationships between underlying source signals. Both approaches overcome limitations encountered when estimating many parameters in multivariate time-series data, an increasingly common predicament in today\u27s brain mapping studies

Spatial and temporal trends of iron and iron isotope cycling in the Peruvian oxygen minimum zone

Iron (Fe) is a key element in the global ocean’s biogeochemical framework because of its essential role in numerous biological processes. A poorly studied link in the oceanic Fe cycle is the reductive release of Fe from sediments in oxygen depleted ocean regions - the oxygen minimum zones (OMZs). Changing rates of Fe release from OMZ sediments may have the potential to modulate ocean fertility which has far-reaching implications considering the high amplitude oxygen fluctuations throughout earth history as well as the ongoing ocean deoxygenation projected for the near future. In order to explore spatial and temporal trends of Fe cycling in OMZs, we present here Fe isotope and speciation data for surface sediments from a transect across the Peruvian upwelling area, one of the most pronounced OMZs of the modern ocean. Because of continuous dissimilatory Fe reduction and diffusive loss across the benthic boundary, sediments within the OMZ are strongly depleted in reactive Fe components, and the little reactive Fe left behind has a heavy isotope composition. In contrast, surface sediments below the OMZ are enriched in reactive Fe, with the majority being present as Fe oxides with comparably light isotope composition. This lateral pattern of Fe depletion and enrichment indicates that Fe released from sediments within the OMZ is reoxidized and precipitated at the oxycline. First-order calculations suggest that the amount of Fe mobilized within the OMZ and that accumulated at the boundaries are largely balanced. Therefore, benthic Fe fluxes in OMZs should be carefully evaluated prior to incorporation into global models, as much of the initially released Fe may be reprecipitated prior to vertical or offshore transport. First XRF core scanning results for partly laminated piston cores from the OMZ boundaries reveal downcore oscillations in the content of reactive Fe and redox-sensitive trace metals that are attributed to past changes in OMZ extension. Ongoing work on these cores will focus on their dating and the downcore investigation of Fe and trace metal records in order to better understand past Fe cycling within the Peruvian OMZ and potential interactions with climate variability

Plio-Pleistocene evolution of water mass exchange and erosional input at the Atlantic-Arctic gateway

Water mass exchange between the Arctic Ocean and the Norwegian-Greenland Seas has played an important role for the Atlantic thermohaline circulation and Northern Hemisphere climate. We reconstruct past water mass mixing and erosional inputs from the radiogenic isotope compositions of neodymium (Nd), lead (Pb), and strontium (Sr) at Ocean Drilling Program site 911 (leg 151) from 906 m water depth on Yermak Plateau in the Fram Strait over the past 5.2 Myr. The isotopic compositions of past bottom waters were extracted from authigenic oxyhydroxide coatings of the bulk sediments. Neodymium isotope signatures obtained from surface sediments agree well with present-day deepwater εNd signature of −11.0 ± 0.2. Prior to 2.7 Ma the Nd and Pb isotope compositions of the bottom waters only show small variations indicative of a consistent influence of Atlantic waters. Since the major intensification of the Northern Hemisphere Glaciation at 2.7 Ma the seawater Nd isotope composition has varied more pronouncedly due to changes in weathering inputs related to the waxing and waning of the ice sheets on Svalbard, the Barents Sea, and the Eurasian shelf, due to changes in water mass exchange and due to the increasing supply of ice-rafted debris (IRD) originating from the Arctic Ocean. The seawater Pb isotope record also exhibits a higher short-term variability after 2.7 Ma, but there is also a trend toward more radiogenic values, which reflects a combination of changes in input sources and enhanced incongruent weathering inputs of Pb released from freshly eroded old continental rocks

COVARIATE-ADJUSTED NONPARAMETRIC ANALYSIS OF MAGNETIC RESONANCE IMAGES USING MARKOV CHAIN MONTE CARLO

Permutation tests are useful for drawing inferences from imaging data because of their flexibility and ability to capture features of the brain that are difficult to capture parametrically. However, most implementations of permutation tests ignore important confounding covariates. To employ covariate control in a nonparametric setting we have developed a Markov chain Monte Carlo (MCMC) algorithm for conditional permutation testing using propensity scores. We present the first use of this methodology for imaging data. Our MCMC algorithm is an extension of algorithms developed to approximate exact conditional probabilities in contingency tables, logit, and log-linear models. An application of our non-parametric method to remove potential bias due to the observed covariates is presented

Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes

Global warming during the Paleocene-Eocene Thermal Maximum (PETM) ĝ1/4 ĝ€55 million years ago (Ma) coincided with a massive release of carbon to the ocean-atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean-atmosphere system associated with the PETM