Oxygen stable isotope fractionation behavior of cerussite and hydrocerussite: New results and reconciliation of the recent literature

Recent empirical and theoretical calculations of the temperature-dependant oxygen stable isotope fractionation behavior of cerussite have highlighted potential problems with earlier work on this topic. The synthetic cerussite which was used earlier by the lead author to determine fractionation factors was re-examined using energy dispersive X-ray analysis, and found to be internally contaminated with inclusions of the phase hydrocerussite at levels of 5-10% by volume. The volume of hydrocerussite present within the samples is not sufficient to explain the entire discrepancy between this work and the empirical and theoretical calculations made earlier by the second author of this paper. Regardless of the exact causes of experimental failure or kinetic effects, the hydrocerussite contamination and the difficulty of demonstrating that these experiments reached isotopic equilibrium suggest that the use of cerussite oxygen isotope fractionation factors determined by slow precipitation experiments be discontinued in favor of the empirically calibrated fractionation factor 1000 ln α_{cerussite-water} = 2.29(10⁶/T²) − 3.56. In addition, we have determined that the oxygen isotope fractionation factor between hydrocerussite and water at 20 °C is 1.0232.     

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.     

Sediment accumulation rates in European lakes since AD 1850: trends,reference conditions and exceedence

Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions. Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from ²¹⁰Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates, 11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity (3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm⁻² yr⁻¹) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm⁻² yr⁻¹). SARs for other lake-types ranged between 0.012 and 0.024 g cm⁻² yr⁻¹. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future.     

The Norwegian plan for integrated ecosystem-based management of the marine environment in the Norwegian Sea

A White Paper on a new integrated management plan for the Norwegian Sea was launched by the Norwegian government in May 2009. Following international guidelines for ecosystem-based management, the plan provides an overall framework for managing all human activities (mainly oil and gas industry, fishing, and shipping) in the area to ensure the continued production and function of the ecosystem. The plan is based on an assessment of the present and projected future impact of human activities and of the interactions between them, taking into account deficits in current knowledge of ecosystem state and dynamics. Areas of particular value in terms of biodiversity or biological production were identified. In each of these valuable areas, any access for substantial human activity is to be carefully managed. To monitor the overall development of the Norwegian Sea, a set of indicators with associated environmental quality objectives have been selected. The approach used builds upon experience gained from the first integrated Norwegian management plan for a marine area, the Barents Sea–Lofoten region, developed in 2002–2006. Work towards a Norwegian management plan for the North Sea, including Skagerrak, was initiated in 2009.     

Bifurcation analysis of wind-driven flows with MOM4

In this paper, the methodology of bifurcation analysis is applied to the explicit time-stepping ocean model MOM4 using a Jacobian–Free Newton–Krylov (JFNK) approach. We in detail present the implementation of the JFNK method in MOM4 but restrict the preconditioning technique to the case for which the density distribution is prescribed. For a prescribed density field case, we present bifurcation diagrams, for the first time in MOM4, for the wind-driven ocean circulation. In addition, we show that the JFNK method can reduce the spin-up time to a steady equilibrium in MOM4 considerably if an accurate solution is required.     

Acoustic habitat and shellfish mapping and monitoring in shallow coastal water – Sidescan sonar experiences in The Netherlands

Sidescan sonar has been applied in a number of shallow water environments along the Dutch coast to map and monitor shellfish and seabed habitats. The littoral setting of these surveys may hamper data acquisition flying the towfish in zones of turbulence and waves, but also offers valuable opportunities for understanding, interpreting and validating sidescan sonar images because of the ability to ground-truth during low water periods, enabling easy identification and validation. Acoustical images of some of the mussel banks on the tidal flats of the Wadden Sea, recorded at high tide, show a marked resemblance with optical Google Earth images of the same banks. These sonar images may thus serve as ‘acoustic type signatures’ for the interpretation of sonar patterns recorded in deeper water where ground-truthing is more difficult and more expensive. Similarly, acoustic type signatures of (Japanese) oyster banks were obtained in the estuaries in the southwest of the Netherlands.     

Climate change projections for the surface ocean around New Zealand

The future status of the surface ocean around New Zealand was projected using two Earth System Models and four emission scenarios. By 2100 mean changes are largest under Representative Concentration Pathway 8.5 (RCP8.5), with a +2.5°C increase in sea surface temperature, and decreases in surface mixed layer depth (15%), macronutrients (7.5–20%), primary production (4.5%) and particle flux (12%). Largest macronutrient declines occur in the eastern Chatham Rise and subantarctic waters to the south, whereas dissolved iron increases in subtropical waters. Surface pH projections, validated against subantarctic time-series data, indicate a 0.335 decline to ～7.77 by 2100. However, projected pH is sensitive to future CO₂ emissions, remaining within the current range under RCP2.6, but decreasing below it by 2040 with all other scenarios. Sub-regions vulnerable to climate change include the Chatham Rise, polar waters south of 50°S, and subtropical waters north of New Zealand, whereas the central Tasman Sea is least affected.     

Use of the weighted Kappa coefficient in classification error assessment of thematic maps

Abstract

The weighted Kappa coefficient is applied to the comparison of thematic maps. Weighted Kappa is a useful measure of accuracy when the map classes are ordered, or when the relative seriousness of the different possible errors may vary. The calculation and interpretation of weighted Kappa are demonstrated by two examples from forest surveys. First, the accuracy of thematic site quality maps classified according to an ordinal scale is assessed. Error matrices are derived from map overlays, and two different sets of agreement weights are used for the calculation. Weighted Kappa ranges from 0.34 to 0.55, but it does not differ significantly between two separate areas. Secondly, weighted Kappa is calculated for a tree species cover classified according to a nominal scale. Weights reflecting the economic loss for the forest owner due to erroneous data are used for the computation. The value of weighted Kappa is 0.56.