Boulder Fields Research Articles

Characterization of failure modes and planned stabilization measures for the Ajanta caves in India

The Ajanta caves are classified as a UNESCO World-heritage monument, where ancient Buddhist rock-cut caves from the Second Century BC to 6th Century AD are found. The caves were carved manually in Basaltic rock mass in the Deccan trap basaltic flow of the Ajanta Formation of the Sahyadri Group in the Upper Cretaceous age. In the Ajanta caves, the hillside slopes are predominantly covered by surface boulders. Boulder dislocations caused by long-term rock mass deterioration, distressing, water percolation and weathering for a strike length of 600m, and a height of 75m; are a major concern when considering the safety of both visitors and site personnel, as well as with regard to the preservation of the historic UNESCO World Heritage site. This study was carried out to assess and characterize the formation of boulders with possible stabilization measures to be planned of a boulder field and slope surface is described and discussed herewith. The possible geological mode of development of the boulder field, rock mass characterization of slope, boulder stabilization philosophy is presented herewith along with planned various stabilization measures considering the esthetic value of the World Heritage site at Ajanta.

Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko

We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. We used images acquired by the OSIRIS Narrow Angle Camera, NAC, on 5 and 6 August 2014. The scale of these images (2.44−2.03 m/px) is such that boulders ≥7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowing of the surface (observation phase angle ranging from 48◦ to 53◦ ), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km 2 ), with a global number density of nearly 100/km 2 and a cumulative size-frequency distribution represented by a power-law with index of −3.6 +0.2/−0.3. The two lobes of 67P appear to have slightly different distributions, with an index of −3.5 +0.2/−0.3 for the main lobe (body) and −4.0 +0.3/−0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of −2.2 +0.2/−0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km 2 of localized areas on 67P. By comparing the cumulative size-frequency distributions of similar geomorphological settings, we derived similar power-law index values. This suggests that despite the selected locations on different and often opposite sides of the comet, similar sublimation or activity processes, pit formation or collapses, as well as thermal stresses or fracturing events occurred on multiple areas of the comet, shaping its surface into the appearance we see today.

Spatial heterogeneity of temperature across alpine boulder fields in New South Wales, Australia: multilevel modelling of drivers of microhabitat climate.

Understanding the spatial heterogeneity of temperatures across a region is significant for identification and protection of potential microhabitats for species conservation. However, this task is proving difficult because multiple factors drive the temperatures of microhabitats and their effect differs at different scales. In the Australian alpine region, boulder field habitats have been identified as important refugia for a range of small mammals. Vegetation cover and elevation have been found to drive thermal buffering at the level of single sampling sites within boulder fields, whereas the aspect and inclination of slopes have been found to affect thermal buffering at the level of clusters of boulder fields. But how the rock structure (number of rock layers, rock size and cavity of boulders) influences microclimate of boulder fields remains an open question. We used a multilevel modelling approach to detect the factors driving microhabitat temperatures in different seasons at different spatial scales in an Australian alpine region. We found that significant temperature differences existed within and between clusters of boulder fields in different seasons. Besides elevation and vegetation cover, the number of rock layers and rock cavity size also exerts important influences on extreme temperatures at the site (i.e. single boulder field) scale. Topographical variables such as slope gradient and elevation influenced minimum temperatures at the boulder field cluster scale. Variations in boulder field temperatures were significant at fine scales, with variations in minimum temperatures exceeding those of maximum temperatures. We suggest that variations in slope gradient and elevation, interacting with vegetation cover, the number of rock layers and rock cavity size can lead to fine-grained thermal variability, which potentially provides refugia for species at microsites, even when regional climatic conditions become less suitable for their survival.

Integrating multibeam sonar and underwater video data to map benthic habitats in an East Antarctic nearshore environment

An integrated analysis of biological and geoscientific data collected from the nearshore marine environment of the Vestfold Hills was used to identify benthic habitats and associated communities and examine relationships between benthic community composition and environmental characteristics. A 48 km2 area was surveyed using a multibeam echosounder system (MBES) to produce high-resolution bathymetry and backscatter intensity maps of the seabed. Epibenthic community data and in situ observations of substrate composition and seafloor bedforms and features were obtained from towed underwater video.A comparison of top-down and bottom-up approaches to defining benthic habitats was used to improve understanding of the applicability of mapping methodologies. On a broad scale, both approaches produced habitat classes distinguished largely by geomorphic features, with substrate and depth identified as the main controls of benthic community composition, however, the relationship between benthic community composition and environmental characteristics is complex with many variables contributing to differences in community composition.The top-down approach was based on geomorphic units defined using abiotic characteristics and the assemblages identified within the geomorphic were very broad with only weak distinction between assemblages. Conversely, the bottom-up approach generated additional habitat classes, identified clear defining taxa for each class, greater distinction between the benthic communities, and allowed identification of additional environmental factors (i.e. sea ice cover) that influence benthic community distribution that are not discernible from geomorphic information alone. The habitat types identified and mapped using the bottom-up approach include shallow boulder fields and exposed bedrock which are dominated by dense macroalgae communities, and steep slopes, muddy basins and sandy plains which are dominated by invertebrate communities.The results indicate that a bottom-up approach is preferable for benthic habitat mapping, however, where detailed information is not available, geomorphic information provides a reasonable indication of the distribution of benthic habitats and communities. This study highlights the utility of multibeam sonar for interpretation of seafloor morphology and substrate and the multibeam data provide a physical framework for understanding benthic habitats and the distribution of benthic communities. This research provides the scientific context and spatial framework for managing the Vestfold Hills nearshore marine environment and provides a baseline for assessing environmental change.

Diagnostic characteristics and paleodynamics of supraglacial rock avalanches, Innerdalen, Western Norway

Misinterpretation of rock-avalanche deposits in mountain environments is not uncommon because of the complex interactions between rock avalanches and glaciers. This paper for the first time presents a detailed description of suspicious rock-boulder deposits, which are remnants of a rock avalanche onto a Late Pleistocene glacier. The boulder deposits cover around 1.1km2 and are distributed over an area of around 7.5km2 and a variety of landforms: three closely nested distinct terminal moraines (0.45km2) and dislocated terminal moraines (0.34km2) entirely built up of large boulders, lateral moraines that decrease in elevation over a short distance and connect to the terminal moraines, small patches (0.02km2) of boulders that occur in islands on a peat-dominated valley floor, and large patches of boulder fields (0.25km2 in size) hanging 350m above the valley floor. The latter are disconnected from any potential source area. 10Be cosmogenic nuclide ages of the three terminal moraines give an indistinguishable Late Pleistocene age of 13.6±1.4ka, whereas the largest boulder field that is located on the opposite side of the valley from the failed mountain yields a 10Be age of 14.1±0.4ka, which is slightly older but indistinguishable from the moraine deposits within uncertainty margins. All boulder deposits add up to a volume of 31×106m3. The interpretation of a single rock-avalanche source for those landforms is further confirmed by numerical runout modeling using DAN3D. A failure of the entire volume from Skarfjellet Mountain would result in a runout pattern that is identical to that of the distributed boulder fields when considering that the valley was filled with a glacier around 350m thick. The rock avalanche would not reach the position of the terminal moraines; however, a glacial re-advance could have transported the boulders to that position. The Late Pleistocene rock avalanche was followed by a Holocene rock avalanche with a volume of 23×106m3 and a typical lobate deposit damming the Innerdalen Valley and creating a lake. 10Be ages indicate that this event occurred 7.97±0.94ka ago. Structural measurements performed on high-resolution LiDAR scans show a strongly jointed source rock with three joint sets with dip/dip direction 81/034, 86/331, and 77/354 and a foliation with 22/003. The kinematic of the failures can thus be a combination of small-scale wedge failures and planar sliding on shallow dipping foliation. Our detailed description can enable a better identification and interpretation of similar deposits in other mountain areas.

Assessing the application of laser scanning and 3D inspection in the study of prehistoric cairn sites: The case study of Tahkokangas, Northern Finland

Laser scanning has the potential of becoming an indispensable documentation method in archaeology. To test its application in interpretatively challenging archaeological settings, a part of the prehistoric cemetery of Tahkokangas in Northern Finland was scanned. The site consists of stone settings of varying form whose elevation and morphology indicate a date of 600–200 BC. A boulder field where six of the ten settings on the site are located was scanned. The structures were difficult to interpret on-site due to their inconspicuous nature. In this paper, in order to circumvent the problem, the gathered 3D data is processed into meshes and false colored by height. The meshes and the height colorization allow detailed structural interpretation of the settings.The 3D material allows new directions for the study of the site. Previously undetected extensions of the largest stone setting were discovered. Also the structural analysis of the setting suggests that additional support structures may have been used. Along with the findings, limitations and advantages of laser scanning and 3D inspection are discussed. The results and conclusions show laser scanning to be a useful documentation method even when studying indistinct sites for which the scanner was not originally designed for. Still, the method does not produce new information, but merely aids in its perception and interpretation.

Laboratory analysis of the habitat occupancy of the crab Rhithropanopeus harrisii (Gould) in an invaded ecosystem: The north-eastern Baltic Sea

The Harris mud crab (Rhithropanopeus harrisii) arrived to the Baltic Sea in 1936. It was not until the late 2000es when the species considerably expanded its distribution area towards the northern Baltic Sea and formed a viable and expanding population. This introduction represents an appearance of a completely new function, as such larger epibenthic predators were previously missing from north-eastern Baltic Sea. In order to assess potential impacts of the crab to the invaded ecosystem, knowledge of the crab habitat preferences is required. This study experimentally evaluated the habitat occupancy of the Harris mud crab. The crab stayed more in vegetated boulders compared to unvegetated boulders or sandy habitats. There was an interactive effect between the presence of prey and crab population density with prey availability increasing the crab's affinity towards less favored habitats when population densities were low. Increased aggression between crab individuals increased their affinity towards otherwise less occupied habitats. Less favored habitats were typically inhabited by smaller individuals and presence of prey increased occupancy of some habitats for larger crabs. The experiment demonstrated that the crab may inhabit a large variety of habitats with stronger affinity towards boulder fields covered with the brown macroalga Fucus vesiculosus. This implies stronger impact of crab in such habitats in the invaded ecosystem.

Microhabitat use by mountain pygmy‐possum (Burramys parvus): Implications for the conservation of small mammals in alpine environments

AbstractThe Australian alpine region harbours a wide range of species, many of which are endemic and of high conservation value. Among these species, the endangered mountain pygmy‐possum, Burramys parvus, is of particular interest because this specialized marsupial is highly sensitive to extreme temperatures. The selection of microhabitats by B. parvus is a critical but poorly understood element of its biological characteristics. To understand the microhabitat preferences of B. parvus, we performed detailed investigations of the thermal properties of alpine boulder fields. The selection of a preferred microclimate was demonstrated by comparing temperatures and environmental conditions in preferred and non‐preferred boulder fields. The variability of the daily temperature depended on the depth at which measurements were made within the boulder fields. Temperatures were more stable as depth increased. The results suggest that B. parvus prefers to occupy deep boulder fields at high elevations with good rock structure (small rock and cavity size with multiple layers) and long snow duration because these boulder fields can provide a favourable microclimate. At 1 m depth, the maximum temperatures in the hottest part of the year were 1.27°C cooler in preferred compared to non‐preferred boulder fields. In the coldest part of the year, immediately following the melting of persistent snow cover, the minimum temperatures at a depth of 1 m were 1.67°C warmer in preferred compared to non‐preferred boulder fields. On average, the snow duration was 27 days greater in the boulder fields preferred by B. parvus than in non‐preferred boulder fields. Our results emphasize the value of boulder field microhabitats as thermal refuges for small mammals in rocky habitats within alpine environments in the light of continuing habitat loss and climate change.

A study of burrow morphology in representative axiidean and gebiidean mud shrimps, from the Persian Gulf and Gulf of Oman, Iran

Mud shrimps (formerly Thalassinidea) are common burrow dwelling decapod crustaceans in the littoral zone of the Persian Gulf and Gulf of Oman. Their burrow morphology was investigated using foam casting methods. The present study shows that the burrow morphology in Upogebia carinicauda is not consistent and the recorded variations are based on habitat type and some physical characteristics of sediments. Adult burrow morphology in sandy-muddy substrate with shells, and boulder field habitats were Y-shaped and complex burrows of horizontal channels with turning chambers and vertical connections to internal passages or crevices of boulders, respectively. In burrows of U. carinicauda, some narrow passages, connected to the upper part of adult burrows in sandy-muddy habitats, belong to juveniles. Another species, Neocallichirus jousseaumei was found under boulders in sandy-muddy habitats of the Gulf of Oman and Qeshm Island, Persian Gulf. Since this type of habitat is special in some features, no conspicuous ex-current openings (usually obvious as conical mounds of extruded sediment) have been observed on the sediment surface; as these were hidden among the boulders surrounded by mixed sand and shells. The only method for observing this type of burrow was to remove the boulders by hand or lever.

Seismic origin of the Atacama Desert boulder fields

Extensive fields of large boulders are common around the base of hills in the Atacama Desert. How these boulders are transported from nearby hillslopes is unclear given the lack of rainfall of the region. Here we document the central role of seismicity, not runoff, in transporting and smoothing >1 ton boulders all across the hyperarid core of the Atacama Desert. The generally granitoid boulders emerge as corestones on hillslopes at an erosion rate of 0.1–1mMa−1. Thereafter, physical and cosmogenic isotopic evidence suggests that boulders slide and bounce rather than roll down hills and onto adjacent flats. In the transport process, the largest boulders are split and the smaller ones are weathered to grus, narrowing average boulder mass to ~2tons (<1m3). At the base of hills, the boulders bunch together and rub during the frequent earthquakes in the region, producing distinctive smoothing around boulder mid-sections, and silt moats around the boulder bases. Our measurements show a strong correlation between boulder field density and rubbing, and only when the density exceeds 60–70% does rubbing become common. Except for slow removal by rubbing, the boulders seem to undergo no further erosion while in the flats. Exposure times for some boulders are >12Ma, making them among the oldest continuously exposed features on the Earth. Boulder rubbing is just one geologic feature among many in the Atacama that underscore the role that seismicity probably plays in shaping landscapes of the waterless worlds of the solar system.

Thermal buffering effect of alpine boulder field microhabitats in Australia: Implications for habitat management and conservation

Identifying and protecting microhabitats with conservation value is becoming a high priority for conservationists under projected climate change. Information on the buffering effects of microhabitats and its major drivers is a prerequisite to implementing effective conservation. We collected hourly temperature data from 70 alpine–subalpine sites nested within 9 boulder field clusters in an area measuring approximately 60km×30km in New South Wales, Australia, over a period of more than 2years. We studied the thermal buffering effect of the boulder fields and investigated the factors driving the effect using multilevel (i.e., sampling points nested within boulder field clusters) regression modeling. We found remarkable seasonal and spatial variations in the thermal buffering effect of boulder fields. Boulder fields buffered the surface temperature maxima by 2.91°C at a depth of 50cm and 4.39°C at a depth of 100cm, while they buffered the surface temperature minima by 0.54°C at the depth of 50cm and 1.36°C at the depth of 100cm, with temperature range reduced by 3.45°C and 6.48°C in warmer period and by 1.23°C and 2.05°C in colder period at two depths. We defined thermal buffering in temperature ranges as the thermal buffering capacity (TBC) as an exemplar for multilevel modeling. We found that vegetation cover and elevation affected the TBC at the point level, whereas the aspect and inclination of slopes affected the TBC at the cluster level. These findings are instructive for the protection of habitats, as high priority should be given to those habitats that offer effective TBC. Furthermore, the environmental factors identified to be driving TBC provide important input to the management of species habitats.

Chronology of rock falls and slides in a desert mountain range: Case study from the Sonoran Desert in south-central Arizona

In order to respond to the general paucity of information on the chronology of ubiquitous small rock falls and slides that litter the slopes of desert mountain ranges, a case study in the Sonoran Desert reveals new insight into the desert geomorphology of mountain slopes. Rock falls and rock slides in the McDowell Mountains that abut metropolitan Phoenix, USA, fall in three chronometric groupings dated by conventional radiocarbon and rock varnish microlamination methods. First, the oldest events are >74ka and take the form of stable colluvial boulder fields — positive relief features that are tens of meters long and a few meters wide. Second, randomly sampled slides and falls of various sizes and positions wasted during wetter periods of the terminal Pleistocene and Holocene. Third, an anomalous clustering of slides and falls occurred during the late Medieval Warm Period (Medieval Climatic Anomaly) when an extreme storm was a possible but unlikely trigger. One speculative hypothesis for the cluster of Medieval Warm Period events is that a small to moderate sized earthquake shook heavily shattered bedrock — close to failure — just enough to cause a spate of rock falls and slides. A second speculative hypothesis is that this dry period enhanced physical weathering processes such as dirt cracking. However, the reasons for the recent clustering of rock falls remain enigmatic. While the temporal distribution of slides and falls suggests a minimal hazard potential for homes and roads on the margins of the McDowell Mountains, this finding may not necessary match other desert ranges in metropolitan Phoenix or mountains with different rock types and structures that abut other arid urban centers.

The natural exclusion of red deer from large boulder grazing refugia and the consequences for saxicolous bryophyte and lichen ecology

Large boulder grazing refugia permitted comparison of saxicolous bryophyte and lichen assemblages with those boulder tops accessible to red deer (Cervus elaphus) on a sporting estate in northwest Scotland. Plant succession was predicted to occur unchecked by grazing on the tops of these large boulders with cascading effects on bryophytes and lichens—assuming boulders had been in place over the same time period. Fifty pairs of boulders (one ≥2 m and the other accessible to red deer) were selected at random from various locations below north-facing crags. Percentage cover of each bryophyte and lichen species was estimated from three randomly placed quadrats on each boulder top. Due consideration was given to the influence of island biogeography theory in subsequent model simplification. Mean shrub cover and height, leaf-litter, bryophyte cover and bryophyte species richness were significantly higher within quadrats on large boulder tops that naturally excluded red deer. Lichen cover and lichen species richness were significantly higher on boulder tops accessible to red deer. Lichen cover was in a significant negative relationship with bryophyte cover, shrub cover and litter cover. Bryophyte cover showed a significant positive relationship with shrub height but there was an optimum shrub cover. Natural exclusion of red deer from the tops of large boulders has facilitated plant succession. The results suggest that grazing arrests the lithosere on boulder tops accessible to red deer at an early plagioclimax favouring saxicolous lichens. The results are relevant to situations where red deer might be excluded from boulder fields that hold lichen assemblages of conservation value.

Development, Control, and Empirical Evaluation of the Six-Legged Robot SpaceClimber Designed for Extraterrestrial Crater Exploration

In the recent past, mobile robots played an important role in the field of extraterrestrial surface exploration. Unfortunately, the currently available space exploration rovers do not provide the necessary mobility to reach scientifically interesting places in rough and steep terrain like boulder fields and craters. Multi-legged robots have proven to be a good solution to provide high mobility in unstructured environments. However, space missions place high demands on the system design, control, and performance which are hard to fulfill with such kinematically complex systems. My dissertation focuses on the development, control, and evaluation of a six-legged robot for the purpose of lunar crater exploration considering the requirements arising from the envisaged mission scenario. The performance of the developed system is evaluated and optimized based on empirical data acquired in significant and reproducible experiments performed in a laboratory environment in order to show the capability of the system to perform such a task and to provide a basis for the comparability with other mobile robotic solutions.

The advertisement call of the Cape Melville Treefrog Litoria andiirrmalin (Anura: Hylidae)

The Cape Melville Treefrog, Litoria andiirrmalin McDonald 1997, is a hylid frog restricted to granite boulder fields and associated rainforest of the Melville Range on Cape Melville, north-eastern Australia. The species has remained poorly known because the Melville Range is rugged and remote, with limited accessibility during the summer wet season when frog activity is generally greatest. Litoria andiirrmalin is a large frog that inhabits boulder-pile habitat in the vicinity of streams. The original description had little information on breeding biology. The tadpole was not known at that time but has been described recently (Meyer et al. 2013). The call was not recorded but was described as “a rapid, gentle toc toc toc toc toc” (McDonald 1997).

Safety-related improvisation in led outdoor activities: An exploratory investigation into its occurrence and influencing factors

IntroductionLed outdoor activities (LOA), defined here as instructed activities taking place in an outdoor setting that have an educational goal associated with them, can involve a degree of uncertainty and risk. Participating in LOA activities that involve an acceptable level of risk can be beneficial as they provide an opportunity for participants to engage with risk, to test their capabilities, and to learn from mistakes (Cline, 2007; Dickson, 2012). Despite LOA organisations' best efforts to keep levels of risk acceptable, the dynamic environment in which many LOAs take place means that LOA leaders and their participants can sometimes find themselves in situations that their organisation has not anticipated, and hence are outside their organisation's procedures or their own experiences or knowledge. These situations may have the potential to negatively impact the safety of the activity leaders and participants. Research from other domains has shown that one means of devising solutions to such unplanned for safety critical situations is through improvisation (e.g. Weick, 1993; Mendonca, 2007; Grotan, Storseth, Ro, & Skjerve, 2008). This study considers safety-related improvisation in LOAs.Improvisation is an ambiguous concept in relation to safety. Inappropriately devised or poorly executed improvisation has contributed to adverse outcomes for activity leaders and participants. Examples include the Mangatepopo Gorge incident in 2008, in which six students and their teacher were swept over a spill weir and drowned after following their LOA leader's improvised plan to exit the flooded Mangatepopo gorge in New Zealand (Brookes, Smith, & Corkill, 2009), and the Ptarmigan Peak incident in Alaska, in which two students died after the failure of the improvised roping and anchoring system devised by the activity leaders led to all four roped climbing groups becoming detached from the slope and falling into a boulder field (Williamson, Ratz & Miller, 1997). To the contrary, evidence from other safety critical domains such as firefighting and emergency response services (e.g. Klein, 1999, pp.19-20; Bigley & Roberts, 2001; Roux-Dufort and Vidiallet, 2003), and aviation (e.g. National Transportation Safety Board, 2010) indicates that appropriate, effective improvisation can save lives. This suggests that improvisation by LOA leaders and their organisations, if appropriate and effective, may also have the potential to impact positively on the safety of participants and leaders in the event that they find themselves in an unanticipated, safety critical situation. An improved understanding of improvisation in relation to LOAs may, therefore, provide new insights into safety for LOA organisations. As a first step in this line of inquiry, research is required to understand the nature of improvisation during LOAs.This article presents the findings from an exploratory study that was undertaken as part of a wider research program examining improvisation by LOA leaders. Specifically, a survey study was undertaken to provide broader evidence that improvisation takes place in safety critical situations within the LOA domain. The aims of this study were to identify the circumstances in which safety-related improvisation occurs, the forms in which it manifests, and to establish what factors influence safety-related improvisation by LOA leaders.What is improvisation?Improvisation, as it is referred to in this study, is an adaptive strategy used when faced with situations for which no procedures exist, or where circumstances prevent known procedures from being deployed. It is not considered as a replacement for well designed emergency procedures. Various definitions of improvisation exist in the literature. For example, it is defined as "creative and spontaneous behaviour of managing an unexpected event" (Magni, Proserpio, Hoegl, & Provera, 2009, p. 1045), and an unplanned response that takes place in a turbulent, rapidly changing environment (Chelariu, Johnston, & Young, 2002). …

Cosmogenic 3He production rate in the high tropical Andes (3800 m, 20°S): Implications for the local last glacial maximum

To improve both precision and accuracy of cosmic-ray exposure dating methods, there is a crucial need of calibration sites constraining the production rate of cosmogenic isotopes. This is particularly true in the high tropical area, where existing scaling models present significant discrepancies. This study presents a new calibration site for cosmogenic 3He, located at ∼3800 m in the tropical Altiplano (19.9°S, 67.6°W), on the southern flank of the Tunupa volcano, in the vicinity of the Salar de Uyuni. It consists in a fluvio-glacial outwash that is stratigraphically bracketed by two successive lacustrine shorelines. These shorelines are well-dated by 14C and U-series dating (n=57), allowing determination of the age of the boulder field at the surface of the delta, at 15.3±0.5 ka (1σ). Eleven andesitic boulders were sampled on this fluvio-glacial surface and the cosmogenic 3He contents of their pyroxene phenocrysts and amphiboles was analyzed. The nucleogenic contribution from 6Li capture is well-constrained by determining the (U–Th–Sm)/4He age of these rocks. This correction is minimal (<2%) and does not represent a significant source of uncertainty. Cosmogenic 3He (3Hec) concentrations are characterized by a very high reproducibility: 10 samples overlap within 1σ analytical error. This suggests that pre- or post-deposition processes have minimal impact on the 3Hec data. Furthermore, there is no correlation between the Li and the 3Hec content of the mineral, indicating that 3Hec production from cosmogenic thermal neutron is here negligible.Combined with the absolute dating of the delta, these 3Hec data yield a local production rate of 999±38 (1σ) at g−1 yr−1, at 3800 m and 19.89°S. After scaling with the time dependent scaling scheme of (Stone, 2000), this result yields a rate of 121±5 (1σ) at g−1 yr−1 at high latitude and sea level. This new calibration is the highest among the existing global dataset. It will thus permit the establishment of new robust glacial chronologies in the high Tropics, with an uncertainty lower than 5% at 1σ. Such precision may have important implications in paleoclimatology, notably because it will allow comparison with other well-dated paleoclimatic archives. Including this new data, the updated global 3Hec production rate is 122±15 atg−1yr−1, using the time-dependent scaling of Stone (2000).The new site-specific 3Hec production rate is used here to refine glacier fluctuations on Cerro Tunupa, confirming that the local last glacial maximum was synchronous with the Lake Tauca highstand (15.5 ka). Data also suggest that a dramatic glacial retreat occurred at about 15 ka, few hundred years before the Lake Tauca regression, synchronously with the onset of the Bolling-Allerod.

Physical and biological effects of introduced oysters on biodiversity in an intertidal boulder field

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 482:119-132 (2013) - DOI: https://doi.org/10.3354/meps10241 Physical and biological effects of introduced oysters on biodiversity in an intertidal boulder field Dannielle S. Green*, Tasman P. Crowe Marine Biodiversity, Ecology and Evolution group, School of Biology and Environmental Sciences, University College Dublin, Dublin 4, Ireland *Email: danniellesgreen@gmail.com ABSTRACT: Invasive species have been identified as a serious threat to biodiversity, particularly in protected habitats. The Pacific oyster Crassostrea gigas, which is invasive in many parts of the world, can form very dense populations affecting the abundance and distribution of native organisms. We experimentally separated the effects of the cover and state (physical structure or biological activities) of C. gigas on the development of invertebrate and macroalgal assemblages. Living (biologically active) and dead (physical structure only) oysters were glued in increasing cover to the tops of cleaned boulders and deployed within an intertidal boulder field. After 14 mo, diversity, evenness and assemblage structure of invertebrates and algae were affected by C. gigas, and results varied depending on the cover and state of oysters. Interestingly, boulders with the lowest cover of living C. gigas supported the most diverse assemblages. Differences in assemblage structure were driven by changes in the establishment of several key species including Fucus vesiculosus and Littorina littorea, which were facilitated by oysters and the honeycomb worm Sabellaria alveolata, which was inhibited by oysters. S. alveolata, an ecosystem engineer that can generate reefs protected by the European Union Habitats directive, mainly established on the underside of boulders but was nonetheless greatly reduced by increasing cover of dead or living oysters on the topside. This work highlights the importance of understanding the direct and indirect mechanisms by which invasive species alter biodiversity and how effects vary as invaders increase in abundance. KEY WORDS: Invasive species · Biodiversity · Protected habitats · Ecosystem engineer · Density dependent · Crassostrea gigas · Sabellaria alveolata Full text in pdf format PreviousNextCite this article as: Green DS, Crowe TP (2013) Physical and biological effects of introduced oysters on biodiversity in an intertidal boulder field. Mar Ecol Prog Ser 482:119-132. https://doi.org/10.3354/meps10241 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 482. Online publication date: May 22, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Thermally mediated body temperature, water content and aggregation behaviour in the intertidal gastropodNerita atramentosa

AbstractIntertidal organisms are vulnerable to global warming as they already live at, or near to, the upper limit of their thermal tolerance window. The behaviour of ectotherms could, however, dampen their limited physiological abilities to respond to climate change (e.g. drier and warmer environmental conditions) which could substantially increase their survival rates. The behaviour of ectotherms is still mostly overlooked in climate change studies. Here, we investigate the potential of aggregation behaviour to compensate for climate change in an intertidal gastropod species (Nerita atramentosa) in South Australia. We used thermal imaging to investigate (1) the heterogeneity in individual snail water content and body temperature and surrounding substratum temperature on two topographically different habitats (i.e. rock platform and boulders) separated by 250 m at both day‐ and night‐times, (2) the potential relationship between environment temperature (air and substratum) and snail water content and body temperature, and (3) the potential buffering effect of aggregation behaviour on snail water content and body temperature. Both substratum and snail temperature were more heterogeneous at small spatial scales (a few centimetres to a few metres) than between habitats. This reinforces the evidence that mobile intertidal ectotherms could survive locally under warmer conditions if they can locate and move behaviourally in local thermal refuges.N. atramentosabehaviour, water content and body temperature during emersion seem to be related to the thermal stability and local conditions of the habitat occupied. Aggregation behaviour reduces both desiccation and heat stresses but only on the boulder field. Further investigations are required to identify the different behavioural strategies used by ectothermic species to adapt to heat and dehydrating conditions at the habitat level. Ultimately, this information constitutes a fundamental prerequisite to implement conservation management plans for ectothermic species identified as vulnerable in the warming climate.

A preliminary investigation of diversity, abundance, and distributional patterns of chitons in intertidal boulder fields of differing rock type in South Australia

The rock type of hard substrata marine habitats can affect numerous benthic invertebrates, but little is known of the effects on molluscan assemblages, for example, the chitons often found under intertidal boulders. We compared chiton assemblage composition, abundance, species richness, and patterns of frequency distribution in 10 boulder fields containing either hard metamorphic/igneous boulders or soft limestone boulders in two geographical areas in South Australia. Similar species richness occurred in both types of boulder fields, but hard rock boulder fields had greater overall abundances, because of particularly large abundances of some common species. Differences in abundances of common species also resulted in significantly different assemblages occurring between the boulder field types. Some species appeared aggregated among boulders, but this pattern was variable between boulders in differing areas and of differing rock type. In one area, a common species had variable aggregation that caused frequency distributions to differ significantly between boulders of different rock types. These results indicate that rock type needs to be considered when investigating ecological patterns and processes involving specialist molluscs such as under-boulder chitons and to ensure comprehensive marine reserve planning for protecting rare invertebrates in rocky intertidal reefs.