Annual growth zones in stems of Hypericum irazuense (Guttiferae) in the Costa Rican páramos

The high peaks of the Cordillera de Talamanca in Costa Rica support shrub- and grass-dominated páramo ecosystems that experience stand-replacing wildfires. The dry season that facilitates these fires results in dormancy in plant growth and provides an opportunity to use dendrochronological analyses to determine ages of plants in burn sites to support studies of fire history and postfire vegetation recovery. This study investigates the formation of annual growth zones in stems of the common shrub Hypericum irazuense. Unlike other páramo shrubs, H. irazuense rarely resprouts following fire, instead recovering through seedling recruitment following seed dispersal from the unburned periphery. Laboratory analysis of 19 prepared cross sections from 15 stems shows that samples of H. irazuense from burned areas can provide an estimate of the minimum number of years since the previous fire, supporting earlier work based on field examination of stems. Including a time lag for seedling recruitment or resprouting refines that estimate. Counts of growth zones in most sections coincided with dates of the last known fires. The presence of annual growth zones in H. irazuense places the species within a relatively small group of woody Neotropical species for which annual rings or growth zones have been demonstrated.     

Spatial variations of sea-level rise and impacts: An application of DIVA

Due to complexities of creating sea-level rise scenarios, impacts of climate-induced sea-level rise are often produced from a limited number of models assuming a global uniform rise in sea level. A greater number of models, including those with a pattern reflecting regional variations would help to assure reliability and a range of projections, indicating where models agree and disagree. This paper determines how nine new patterned-scaled sea-level rise scenarios (plus the uniform and patterned ensemble mean rises) influence global and regional coastal impacts (wetland loss, dry land loss due to erosion and the expected number of people flooded per year by extreme sea levels). The DIVA coastal impacts model was used under an A1B scenario, and assumed defences were not upgraded as conditions evolved. For seven out of nine climate models, impacts occurred at a proportional rate to global sea-level rise. For the remaining two models, higher than average rise in sea level was projected in northern latitudes or around populated coasts thus skewing global impact projections compared with the ensemble global mean. Regional variability in impacts were compared using the ensemble mean uniform and patterned scenarios: The largest relative difference in impacts occurred around the Mediterranean coast, and the largest absolute differences around low-lying populated coasts, such as south, south-east and east Asia. Uniform projections of sea-level rise impacts remain a useful method to determine global impacts, but improved regional scale models of sea-level rise, particularly around semi-enclosed seas and densely populated low-lying coasts will provide improved regional impact projections and a characterisation of their uncertainties.     

Deep western boundary current dynamics and associated sedimentation on the Eirik Drift, Southern Greenland Margin

Growing interest in the dynamics and temporal variability of the deep western boundary current (DWBC) in the northern North Atlantic has led to numerous studies of the modern hydrography and palaeoceanography of this current system. The DWBC is fed by the two dense water-masses that spill over the Greenland–Iceland–Scotland Ridge; Denmark Strait Overflow Water (DSOW) and Iceland Scotland Overflow Water (ISOW). These overflows entrain ambient water masses, primarily Labrador Sea Water (LSW), as they cross the Iceland and Irminger Basins before merging in the vicinity of south-east Greenland. A number of studies have been performed around the Eirik Drift, located off the southern Greenland margin, downstream of this main merging point. However, the relationship between the DWBC and the associated sedimentation at this location has yet to be fully elucidated. New hydrographic data show that the current's main sediment load is carried by only one of its components, the DSOW. Seismic surveys and sediment cores confirm that Holocene sedimentation is limited to areas underlying the most offshore part of the current, where the hydrographic data show the highest concentration of DSOW. Active sedimentation through the Holocene therefore appears to have been controlled by proximity to the sediment-laden DSOW.Our interpretation of new and historic geostrophic transport and tracer data from transects around the southern Greenland margin also suggests that the DWBC undergoes significant growth through entrainment as it flows around the Eirik Drift. We attribute this to multiple strands of ISOW following different depth-dependent pathways between exiting the Charlie Gibbs Fracture Zone and joining the DWBC. Comparison of our new data with other modern hydrographic datasets reveals significant temporal variability in the DWBC, associated with variations in the position, structure and age since ventilation of the current in the vicinity of Eirik Drift. The complexity of the current dynamics in this area has implications for the interpretation of hydrographic and palaeoceanographic data.     

Reports from the Smithsonian’s Global Volcanism Network,April 2008

Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 33, no. 4, April 2008 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations.     

Reports from the Smithsonian’s Global Volcanism Network,February 2008

Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 33, no. 2, February 2008 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations.     

Smithsonian Institution’s Global Volcanism Network

Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 32, no. 4, April 2007 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations.     

Persistent weak thermal stratification inhibits mixing in the epilimnion of north-temperate Lake Opeongo,Canada

Persistent weak temperature stratification characterizes the epilimnion of Lake Opeongo, Ontario, Canada, and reduces the magnitude of turbulent mixing. Throughout July and August 2009, the epilimnion was isothermal for only 34 % of the record, while for 28 % of the record there was at least a 2 °C temperature difference across the 5 m deep epilimnion. During these stratified periods, there were increases in gradient Richardson numbers (Ri _g ), and decreases in rates of dissipation of turbulent kinetic energy ( $\varepsilon$ ), the turbulence activity parameter (I = ε/νN ²), an indicator of active mixing, and vertical eddy diffusivity (K _z ) inferred from temperature microstructure profiles. During periods of shear induced mixing, values of ε approached 10^?6 m² s^?3 and decreased during periods of increasing Ri _g . For 0 < Ri _g  < 1, average values of I were ~1,000 and values of K _z were slightly higher than 10^?4 m² s^?1. For Ri _g >1, average values of I were ~300 and K _z was reduced by one to three orders of magnitude. Mixing during cold fronts occurred over time scales of minutes to hours, which worked to erode diurnal thermoclines. However, during periods of persistent secondary thermoclines, mixing was suppressed throughout the epilimnion.     

Predicting rock mechanical properties of carbonates from wireline logs (A case study: Arab-D reservoir,Ghawar field,Saudi Arabia)

Four hundred plug samples from the Arab-D carbonate reservoir, Ghawar field, were tested for acoustic and mechanical properties at increasing triaxial stress. The results show that the rock mechanical parameters are primarily functions of porosity and, to a lesser degree, of mineralogy, texture and pore fabric (in order of degree of impact from higher to lower). The rock mechanical parameters of the intact matrix rock show no significant changes with stress under reservoir condition.     

Trends in Australian rainfall: contribution of tropical cyclones and closed lows

Over the past 40 years there have been significant changes in Australian rainfall with increases in the north-west and decreases in the east. Tropical cyclones (TCs) and other closed low pressure systems are important synoptic systems that provide a large proportion of Australia’s annual rainfall. This study examines the proportion of rainfall that can be attributed to TCs over the 1970–2009 period, and to TCs combined with other closed lows over the 1989–2009 period. The contribution of these systems to Australian rainfall trends is also analysed. Tropical cyclones are found to have little influence on rainfall trends over the full time period. However, when the more recent 21-year period is considered, TCs and other closed low pressure systems can partially explain the positive rainfall trend in the north-west. Similarly, other closed low pressure systems, such as cut-off lows and east coast lows, can explain some of the negative rainfall trend in the south-east. The contribution of TCs and other closed low pressure systems to rainfall trends in the north and south-east is found to be predominantly due to respective increases and decreases in the rainfall producing efficiency of the systems. An understanding of the influence of these synoptic systems on Australian rainfall in the current climate is vital for evaluating how Australia's water budget may change in future climates.