Flow of Canadian basin deep water in the Western Eurasian Basin of the Arctic Ocean

The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data show that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross-slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.     

Utilizing soil geochemistry,ground magnetic,and radiometric surveys to outline a blue ridge,ultramafic body in North Carolina

A soil geochemical survey for Ni plus magnetic and radiometric surveys were used to outline a small dunite body on Rich Mountain, North Carolina. The dunite body is poorly exposed and is enclosed by garnet-bearing amphibolite of the Ashe Formation. Of the geophysical techniques used, the magnetic survey gives a better definition of the known extent of the body than the radiometric survey. However, the 400-ppm Ni contour from the soil program appears to best define the dunite and suggests that it extends farther to the north and east than was indicated from geologic mapping. Though HF digestion yields higher Ni values than HNO₃ + HCl digestion, the patterns are the same. The Mn content of the soil at the Rich Mountain locality probably could also be used to outline the dunite body.     

Distributed velocity method of solving the convective-dispersion equation: 2. Error analysis and comparison with other methods

This is the second part of a two-part paper presenting a new method for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers, the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives and the ability to treat leach- or solubitity-limited sources. To the extent it has been tested to date, the distributed velocity method (DVM) appears to satisfy these demands. This part presents an error analysis employing statistical sampling and regression analysis techniques, and comparisons of DVM with other methods for convective-dispersive transport.     

Surface soil moisture parameterization of the VIC-2L model: Evaluation and modification

HAPEX-MOBILHY data, consisting of one year of hourly atmospheric forcing data at Caumont (SAMER No. 3, 43.68°N, 0.1°W) were used repeatedly to run the two-layer Variable Infiltration Capacity (VIC-2L) land-surface scheme until the model reached equilibrium in its water and energy balance. The equilibrium results are compared with one year of weekly soil moisture measurements at different depths, the estimated latent heat fluxes for 35 days of the intensive observation period (IOP), and the accumulated evaporation, runoff and drainage for the entire soya crop season. The latent heat flux comparisons show that VIC-2L tends to underestimate the evaporation due to the low soil moisture in its upper layer. The soil moisture comparison shows that the total soil water content is well simulated in general, but the soil water content in the top 0.5 m is underestimated, especially in May and June. These comparisons suggest that the lack of a mechanism for moving moisture from the lower to the upper soil layer in VIC-2L is the main cause for model error in the HAPEX-MOBILHY application. A modified version of VIC-2L, which has a new feature that allows diffusion of moisture between soil layers, and a 0.1 m thin layer on top of the previous upper layer, is described. In addition, the leaf area index (LAI) and the fraction vegetation cover are allowed to vary at each time step in a manner consistent with the rest PILPS-RICE Workshop, rather than being seasonally fixed. With these modifications, the VIC-2L simulations are re-evaluated. These changes are shown to resolve most of the structural deficiencies in the original version of the model. The sensitivity analysis of the new version of the model to the choices of soil depths and root distribution show that the evapotranspiration and soil moisture at the model equilibrium state are more sensitive to the root distribution than to the soil depth.     

Temporal dynamics of dissolved combined neutral sugars and the quality of dissolved organic matter in the Northwestern Sargasso Sea

The dynamics of dissolved combined neutral sugars (DCNS) were assessed in the upper 250 m at the Bermuda Atlantic Time-series Study (BATS) site between 2001 and 2004. Our results reveal a regular annual pattern of DCNS accumulation with concentrations increasing at a rate of 0.009–0.012 μmol C L^?1 d^?1 in the surface 40 m from March to July and reaching maximum mean concentrations of 2.2–3.3 μmol C L^?1. Winter convective mixing (between January and March) annually exported surface-accumulated DCNS to the upper mesopelagic zone (100–250 m), as concentrations increased there by 0.3–0.6 μmol C L^?1. The exported DCNS was subsequently removed over a period of weeks following restratification of the water column. Vertical and temporal trends in DCNS yield (% of DOC) supported its use as a diagenetic indicator of DOM quality. Higher DCNS yields in surface waters suggested a portion of the DOM accumulated relatively recently compared to the more recalcitrant material of the upper mesopelagic that had comparably lower yields. DCNS yields and mol% neutral sugar content, together, indicated differences in the diagenetic state of the surface-accumulated and deep pools of DOM. Seasonally accumulated, recently produced DOM with higher DCNS yields was characterized by elevated mol% of galactose and mannose+xylose levels. Conversely, more recalcitrant DOM from depths >100 m had lower DCNS yields but higher mol% of glucose. Lower DCNS yields and elevated mol% glucose were also observed in the surface waters during winter convective mixing, indicating an entrainment of a diagenetically altered DOM pool into the upper 100 m. A multivariate statistical analysis confirms the use of DCNS as an index of shifts in DOM quality at this site.     

The importance of population,climate change and CO2 plant physiological forcing in determining future global water stress

Future levels of water stress depend on changes in several key factors including population, climate-change driven water availability, and a carbon dioxide physiological-forcing effect on evaporation and run-off. In this study we use an ensemble of the HadCM3 climate model forced with a range of future emissions scenarios combined with a simple water scarcity index to assess the contribution of each of these factors to the projected population living in water stress over the 21st century.Population change only scenarios increase the number of people living in water stress such that at peak global population 65% of people experience some level of water stress. Globally, the climate model ensemble projects an increase in water availability which partially offsets some of the impacts of population growth. The result is 1 billion fewer people living in water stress by the 2080s under the high end emissions scenarios than if population increased in the absence of climate change.This study highlights the important role plant-physiological forcing has on future water resources. The effect of rising CO₂ is to increase available water and to reduce the number of people living in high water stress by around 200 million compared to climate only projections. This effect is of a similar order of magnitude to climate change.     

Assessing multifaceted vulnerability and resilience in order to design risk-mitigation strategies

Vulnerability studies have evolved significantly in recent decades. Although not overly theoretical compared with some other fields of science, some important conceptual progress has been made. At the practical level, vulnerability indicators have been used either at a generic level or for particular hazard contexts. However, these indicators are often predictably too narrow in their coverage of aspects of vulnerability. An important need remains to produce more conceptually informed vulnerability indicators or parameters and more satisfactory operational tools to assess weaknesses and resilience in coping with natural risks. In this paper, we present the methodology developed in the context of a recently concluded EU funded project, ENSURE (Enhancing resilience of communities and territories facing natural and na-tech hazards). The resulting vulnerability and resilience assessment framework tool adopts a systemic approach embedding and integrating as much as possible the multifaceted and articulated nature of concepts such as vulnerability and resilience. The tool guides evaluators towards a comprehensive and context-related understanding of strengths and fragilities of a given territory and community with respect to natural extremes. In this paper, both the framework tool and its application to Sondrio in Italy, which is exposed to flash floods, are presented and discussed. The merits and demerits of the new tool are discussed, and the results of the application to Sondrio indicate where data are currently missing, suggesting the kind of data, which will need to be gathered in future to achieve more complete assessments. The results also suggest vulnerability reduction policies and actions and further ways of revising the existing framework tool in the future.     

Field methods for amending marine sediment with activated carbon and assessing treatment effectiveness

Previous laboratory studies have shown reductions in PCB bioavailability for sediments amended with activated carbon (AC). Here we report results on a preliminary pilot-scale study to assess challenges in scaling-up for field deployment and monitoring. The goals of the preliminary pilot-scale study at Hunters Point Shipyard (San Francisco, USA) were to (1) test the capabilities of a large-scale mixing device for incorporating AC into sediment, (2) develop and evaluate our field assessment techniques, and (3) compare reductions in PCB bioavailability found in the laboratory with well-mixed systems to those observed in the field with one-time-mixed systems. In this study we successfully used a large-scale device to mix 500kg of AC into a 34.4m(2) plot to a depth of 1ft, a depth that includes the majority of the biologically active zone. Our results indicate that after 7 months of AC-sediment contact in the field, the 28-day PCB bioaccumulation for the bent-nosed clam, Macoma nasuta, field-deployed to this AC-amended sediment was approximately half of the bioaccumulation resulting from exposure to untreated sediment. Similar PCB bioaccumulation reductions were found in laboratory bioassays conducted on both the bivalve, M. nasuta and the estuarine amphipod, Leptocheirus plumulosus, using sediment collected from the treated and untreated field plots one year after the AC amendment occurred. To further understand the long-term effectiveness of AC as an in situ treatment strategy for PCB-contaminated sediments under field conditions, a 3-year comprehensive study is currently underway at Hunters Point that will compare the effectiveness of two large-scale mixing devices and include both unmixed and mixed-only control plots.     

Comparison of recharge estimates at a small watershed in east-central Pennsylvania,USA

The common recommendation that recharge should be estimated from multiple methods is sound, but the inherent differences of the methods make it difficult to assess the accuracy of differing results. In this study, four methods for estimating groundwater recharge and two methods for estimating base flow (as a proxy for recharge) are compared at two hydrologic research sites in east-central Pennsylvania, USA. Results from the multiple methods all provided reasonable estimates of groundwater recharge that differed considerably. The estimates of mean annual recharge for the period 1994-2001 ranged from 22.9 to 35.7 cm—about 45% of the mean of all estimates. For individual years, recharge estimates from the multiple methods ranged from 30 to 42% of the mean value during the dry years and 64 to 76% of the mean value during wet years. Comparison of multiple methods was found to be useful for determining the range of plausible recharge rates and highlighting the uncertainty of the estimates.