Ultrasonic velocities of North Sea chalk samples: influence of porosity, fluid content and texture

We have studied 56 unfractured chalk samples of the Upper Cretaceous Tor Formation of the Dan, South Arne and Gorm Fields, Danish North Sea. The samples have porosities of between 14% and 45% and calcite content of over 95%. The ultrasonic compressional‐ and shear‐wave velocities (V_P and V_S) for dry and water‐saturated samples were measured at up to 75 bar confining hydrostatic pressure corresponding to effective stress in the reservoir. The porosity is the main control of the ultrasonic velocities and therefore of the elastic moduli. The elastic moduli are slightly higher for samples from the South Arne Field than from the Dan Field for identical porosities. This difference may be due to textural differences between the chalk at the two locations because we observe that large grains (i.e. filled microfossils and fossil fragments) that occur more frequently in samples from the Dan Field have a porosity‐reducing effect and that samples rich in large grains have a relatively low porosity for a given P‐wave modulus. The clay content in the samples is low and is mainly represented by either kaolinite or smectite; samples with smectite have a lower P‐wave modulus than samples with kaolinite at equal porosity. We find that ultrasonic V_P and V_S of dry chalk samples can be satisfactorily estimated with Gassmann's relationships from data for water‐saturated samples. A pronounced difference between the V_P/V_S ratios for dry and water‐saturated chalk samples indicates promising results for seismic amplitude‐versus‐offset analyses.     

Enrichment of alkanes within a phytoplankton bloom during an in situ iron enrichment experiment in the western subarctic Pacific

During the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study ΙΙ (SEEDS-II), we monitored variations in the concentrations of non-methane hydrocarbons (NMHCs), CH₃Cl, N₂O, and CH₄ within a phytoplankton bloom. Stable isotopic compositions were also determined to evaluate the sources of the variations. Although there was little variation in either the concentrations or the stable isotopic compositions of alkenes, CH₃Cl, N₂O, and CH₄ during the 23-day observation period, alkane concentrations increased substantially as the phytoplankton bloomed. The column-integrated quantities of alkanes increased to 3 times pre-bloom levels for C₂H₆, 5 times for C₃H₈, and 20 times for n-C₄H₁₀. The δ¹³C values of both C₂H₆ and C₃H₈ remained almost constant while concentrations increased, whereas that of n-C₄H₁₀ increased by about 12‰. To evaluate the sources of the alkanes produced during the bloom, we compared their δ¹³C values with those of alkanes produced in axenic phytoplankton cultures in our laboratory. We concluded that during the SEEDS-ΙΙ experiment the major portions of C₂H₆ and C₃H₈ were produced during the autolysis of diatoms cells, whereas n-C₄H₁₀ was produced during autolysis of other phytoplankton cells such as cryptophytes and dinoflagellates.     

Importance of vegetation type for mercury sequestration in the northern Swedish mire, Rödmossamyran

Even if mires have proven to be relatively reliable archives over the temporal trends in atmospheric mercury deposition, there are large discrepancies between sites regarding the magnitude of the anthropogenic contribution to the global mercury cycle. A number of studies have also revealed significant differences in mercury accumulation within the same mire area. This raises the question of which factors, other than mercury deposition, affect the sequestration of this element in peat. One such factor could be vegetation type, which has the potential to affect both interception and retention of mercury. In order to assess how small-scale differences in vegetation type can affect mercury sequestration we sampled peat and living plants along three transects on a northern Swedish mire. The mire has two distinctly different vegetation types, the central part consists of an open area dominated by Sphagnum whereas the surrounding fen, in addition to Sphagnum mosses, has an understory of ericaceous shrubs and a sparse pine cover. A few main patterns can be observed in our data; (1) Both peat and Sphagnum-mosses have higher mercury content (both concentration and inventory) in the pine-covered fen compared to the open Sphagnum area (100% and 71% higher for peat and plants, respectively). These differences clearly exceed the 33% difference observed for lead-210, which is considered as a good analogue for atmospheric mercury deposition. (2) The differences in mercury concentration between peat profiles within a single vegetation type can largely be attributed to differences in peat decomposition. (3) When growing side by side in the open Sphagnum area, the moss species Sphagnum subsecundum has significantly higher mercury concentrations compared to S. centrale (24 ± 3 and 18 ± 2 ng Hg g⁻¹, respectively). Based on these observations we suggest that species composition, vegetation type and decomposition can affect the mercury sequestration in a peat record, and that any changes in these properties over time, or space, have the potential to modify the mercury deposition signal recorded in the peat.     

Alkalinization and acidification of stream water with changes in atmospheric deposition in a tropical dry evergreen forest of northeastern Thailand

Field surveys on atmospheric deposition and stream water chemistry were conducted in an evergreen forest in northeastern Thailand characterized by a tropical savanna climate with distinct dry and wet seasons. Atmospheric deposition of ion constituents by throughfall and stemflow was shown to increase in the beginning and end of the wet season, reflecting the precipitation pattern. The pH and electrical conductivity of stream water increased with alkalinity and base cation concentrations due to mineralization of organic matter by the first rain and retention of anions in soil during the start of the wet season. After initial alkalinization, the pH and alkalinity declined rapidly with the highest SO₄^2? concentration displayed in the middle towards the end of the wet season. The magnitude of peaks in SO₄^2? concentration (13.5–60.6 μmol_c/L) reflects deposition during the first 2 months of the wet season (March and April) in respective years (60.8–170 mol_c/ha). Release of SO₄^2? with H⁺, which is retained in soil during the early wet season, may cause acidification later in the season. The deposition and concentration of SO₄^2? declined over 6 years. However, the pH of stream water declined with increasing concentrations of SO₄^2? and other major ions. The release of materials accumulated in the ecosystem was facilitated by the decrease in SO₄^2? concentration/deposition and increased precipitation in the middle–late wet season. The retention‐release cycle of SO₄^2? largely contributed to both seasonal and interannual variations in stream water chemistry in the tropical savanna climate studied.     

Future makers or future takers? A scenario analysis of climate change and the Great Barrier Reef

The extent to which nations and regions can actively shape the future or must passively respond to global forces is a topic of relevance to current discourses on climate change. In Australia, climate change has been identified as the greatest threat to the ecological resilience of the Great Barrier Reef, but is exacerbated by regional and local pressures. We undertook a scenario analysis to explore how two key uncertainties may influence these threats and their impact on the Great Barrier Reef and adjacent catchments in 2100: whether (1) global development and (2) Australian development is defined and pursued primarily in terms of economic growth or broader concepts of human well-being and environmental sustainability, and in turn, how climate change is managed and mitigated. We compared the implications of four scenarios for marine and terrestrial ecosystem services and human well-being. The results suggest that while regional actions can partially offset global inaction on climate change until about mid-century, there are probable threshold levels for marine ecosystems, beyond which the Great Barrier Reef will become a fundamentally different system by 2100 if climate change is not curtailed. Management that can respond to pressures at both global and regional scales will be needed to maintain the full range of ecosystem services. Modest improvements in human well-being appear possible even while ecosystem services decline, but only where regional management is strong. The future of the region depends largely on whether national and regional decision-makers choose to be active future ‘makers’ or passive future ‘takers’ in responding to global drivers of change. We conclude by discussing potential avenues for using these scenarios further with the Great Barrier Reef region's stakeholders.     

Assessing the designs and effectiveness of Japan's emissions trading scheme

After years of discussions and trials, Japan's domestic emissions trading scheme remains purely voluntary. The newly elected Democratic Party of Japan (DPJ) has taken a firmer stance on climate change, initially intending to establish a nationwide mandatory cap-and-trade as early as 2011. This has promoted several questions regarding the possible designs and feasibility of such a scheme. This article describes the key features of the two trial schemes implemented, thus far, assesses the effectiveness of their implementation and discusses what will be the likely areas of contention should the Japanese government introduce a mandatory cap-and-trade in the future. The analyses indicate that the initial years of ‘Japan's Voluntary Emissions Trading Scheme’ (JVETS) implementation have shown positive performance, although its scale has remained limited. The ‘Trial Implementation of an Integrated Domestic Market for Emissions Trading’ emerged as a hybrid scheme, one that incorporated varying interests. Significant institutional developments have taken place in recent years, however the effectiveness of the present trial scheme also seems restricted.     

Configuration,history and impact of the Norwegian Channel Ice Stream

The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jæren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW‐oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jæren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega‐scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial‐fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Vøring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation.