Far-travelled ash in past and future eruptions: combining tephrochronology with volcanic studies

Studies of recent eruptions have improved our understanding of volcanic ash transport and deposition, but have also raised important questions about the behaviour of far-travelled (distal) volcanic ash. In particular, it is difficult to reconcile estimates of distal ash mass and transport distance determined from eyewitness accounts, mapped deposits, satellite-based observations and cryptotephra records. Here we address this problem using data from well-characterized eruptions that, collectively, include all four data types. Data from recent eruptions allow us to relate eyewitness accounts to mapped deposits on the ground and satellite-based observations of ash in the air; observations from an historical eruption link eyewitness accounts to cryptotephra deposits. Together these examples show that (i) 10–20% of the erupted mass is typically deposited outside the mapped limits; (ii) estimates of the ash mass transported in volcanic clouds cannot account for all of this unmapped ash; and (iii) ash fall observed at distances beyond mapped deposits can have measurable impacts, and can form cryptotephra deposits with high (>~1000 cm⁻³) shard counts. We conclude that cryptotephra data can be incorporated into volcanological studies of ash transport and deposition and provide important insight into both the behaviour and impacts of far-travelled volcanic ash particles.     

New constraints on fluid sources in orogenic gold deposits,Victoria, Australia

Fluid inclusion microthermometry, Raman spectroscopy and noble gas plus halogen geochemistry, complemented by published stable isotope data, have been used to assess the origin of gold-rich fluids in the Lachlan Fold Belt of central Victoria, south-eastern Australia. Victorian gold deposits vary from large turbidite-hosted ‘orogenic’ lode and disseminated-stockwork gold-only deposits, formed close to the metamorphic peak, to smaller polymetallic gold deposits, temporally associated with later post-orogenic granite intrusions. Despite the differences in relative timing, metal association and the size of these deposits, fluid inclusion microthermometry indicates that all deposits are genetically associated with similar low-salinity aqueous, CO₂-bearing fluids. The majority of these fluid inclusions also have similar ⁴⁰Ar/³⁶Ar values of less than 1500 and ³⁶Ar concentrations of 2.6–58 ppb (by mass) that are equal to or much greater than air-saturation levels (1.3–2.7 ppb). Limited amounts of nitrogen-rich fluids are present at a local scale and have the highest measured ⁴⁰Ar/³⁶Ar values of up to 5,700, suggesting an external or distinct source compared to the aqueous fluids. The predominance of low-salinity aqueous–carbonic fluids with low ⁴⁰Ar/³⁶Ar values, in both ‘orogenic’ and ‘intrusion-related’ gold deposits, is attributed to fluid production from common basement volcano-sedimentary sequences and fluid interaction with sedimentary cover rocks (turbidites). Aqueous fluid inclusions in the Stawell–Magdala deposit of western Victoria (including those associated with N₂) preserve mantle-like Br/Cl and I/Cl values. In contrast, fluid inclusions in deposits in the eastern structural zones, which contain more abundant shales, have elevated molar I/Cl ratios with maximum values of 5,170 × 10⁻⁶ in the Melbourne Zone. Br/I ratios in this zone range from 0.5 to 3.0 that are characteristic of fluid interaction with organic-rich sediments. The maximum I/Cl and characteristic Br/I ratios provide evidence for organic Br and I released during metamorphism of the shales. Therefore, the regional data provide strong evidence for the involvement of sedimentary components in gold mineralisation, but are consistent with deeper metamorphic fluid sources from basement volcano-sedimentary rocks. The overlying sediments are probably involved in gold mineralisation via fluid–rock interaction.     

Seasonal Variations of Water Masses and Sea Level in the Southwestern Part of the Okhotsk Sea

A new grid data set for the southwestern part of the Okhotsk Sea was compiled by using all the available hydrographic data from the Japan Oceanographic Data Center, World Ocean Atlas 1994 and the other additional data sources with the resolution of about 10 km. We examine the seasonal variations of areas and volumes of Soya Warm Current Water (SWCW) and East Sakhalin Current Water (ESCW) and show that the exchanges of these water masses drastically occur in April and November. The peculiar variation of sea level in this region is also related with the water mass exchange. Sea level at the Hokkaido coast of the Okhotsk Sea reaches its minimum in April about two months later than in the case of ordinary mid-latitude ocean, and its maximum in December besides the summer peak. The winter peak of sea level in December is caused by the advent of fresh and cold ESCW which is accumulated at the subsurface layers (20–150 m) through the Ekman convergence by the prevailing northerly wind. Sea level minimum in April is caused by the release of the convergence and the recovery of dense SWCW that is saline and much colder than that in summer.     

Seasonal factors affecting surfactant biodegradation in Antarctic coastal waters: comparison of a polluted and pristine site

This report is the first seasonal study of anthropogenic pollutant biodegradation rates in Antarctic coastal waters. The capacity of surface waters from Rothera Research Station, Adelaide Island, Antarctica, to biodegrade the anionic surfactant sodium dodecyl sulphate (SDS) was quantified in biodegradation tests from April 1988 to January 1999. Large temporal differences in the persistence of SDS were observed. In mid-winter (July), the SDS-biodegradation half life was twice that measured in mid-summer (January), despite small temperature differences (up to 2.45 degrees C). Comparisons between water from a pristine site and a site receiving grey-waste water from the station showed that some acclimation to SDS was occurring in the contaminated water. This resulted in SDS half lives up to to approximately 80 h shorter in the polluted water compared with the pristine site in the summer months when a large population of SDS-degrading bacteria had developed. Biodegradation half lives in Antarctic coastal waters (160-460 h) were generally far higher than those observed in temperate waters.     

The Role of Community Identity in Cattlemen Response to Florida Panther Recovery Efforts

The concept of community identity has often been employed to explain ways in which communities respond to agents that impact community well-being. Using a case study of the Florida cattlemen community, we examine how cattlemen understand and perceive regulatory efforts to recover the Florida panther on private ranch lands. The data comes from participants in the Florida cattlemen community, and was collected through in-depth interviews (n = 13), group interviews (n = 32), and written comments associated with a survey about panther conservation (n = 78). Our findings indicate that some cattlemen in Florida have a strong sense of community identity. Perceptions of government actions and variation in economic risks are critical factors in understanding how this community responds to federal interventions. Our findings suggest that the concept of community identity can be used to explain the responses of agricultural landowners to governmental policies that are perceived as a threat to collective identity.