Grain-size distributions of pyroclastic deposits

A multivariate statistical technique (principal component analysis) has been used to investigate the granulometric features of 414 samples of pyroclastic rocks: 216 samples were collected from areas of recent and active volcanism in Central and Southern Italy; data for the remaining 198 samples were obtained from the literature and relate to products from Somma-Vesuvio, Mount St Helens and the Japanese volcanic arc. The analysis offers an improved means of discriminating pyroclastic deposits using their grain-size characteristics.     

Globalization, grapes and gender: Women's work in traditional and agro-export production in northern Chile

Recent changes in the global political economy have had dramatic effects on the lives of women as they are incorporated into globalization processes, such as the expansion of agribusiness, in often marginal and unstable ways. However, it is vital to consider how these globalization processes are mediated by women in ways that reflect local geo-historical contexts. This paper explores the expansion of the fruit export sector, land tenure, community organization and female employment in agriculture in northern Chile. Agro-export production has marginalized but not destroyed the small-scale farming sector and large-scale export farms co-exist with small-scale domestically-orientated farms. Female labour has been very important in the success of fresh fruit exports and many rural women negotiate both waged work in the fruit export economy and unwaged work on family farms. The paper explores the women's perceptions of agricultural work and how these relate to their identities as unpaid workers on the family farm and as waged workers in the agro-export sector. The paper thus attempts to explore the multiplicity of ways that women experience rapid changes in the agrarian sector and how these changes relate to the maintenance of more 'traditional'practices and identities.     

Process length variation in cysts of the dinoflagellate Protoceratium reticulatum,from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy

Mertens, K. N., Dale, B., Ellegaard, M., Jansson, I.‐M., Godhe, A., Kremp, A. & Louwye, S. 2010: Process length variation in cysts of the dinoflagellate Protoceratium reticulatum, from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy. Boreas, 10.1111/j.1502‐3885.2010.00193.x. ISSN 0300‐9483. Results are presented from a regional comparison of average process length variation in cysts of Protoceratium reticulatum and Lingulodinium polyedrum, extracted from surface sediments in the Skagerrak–Kattegat–Baltic estuarine system, with the environmental variables of seawater temperature and salinity. Although too few cysts of Lingulodinium polyedrum were recovered from the sediments to make reliable correlations, cysts of Protoceratium reticulatum were well represented, and average process length was correlated significantly with both salinity and temperature. Owing to dominant summer surface production, and regional covariation between salinity and density, we propose the use of the significant correlation with summer sea surface salinity (SSS_summer) by the equation SSS_summer=3.16 × average process length ?0.84 (R²=0.8). Application of this equation down‐core in Limfjord (northern Denmark) shows its usefulness as a regional palaeosalinity proxy.     

Changes in the energy content of common species from Hornsund, Southwest Spitsbergen

During the period August 1981 to July 1982, samples of six species of Amphipoda common to Hornsund were collected, and a study of their energy value changes was carried out. Only slight fluctuations of energy values were observed throughout the year, and no distinct seasonal changes as in the case of boreal organisms. Individuals of greater body size exhibit higher energy values. The lowest energy values 10.93 kJ g⁻¹ d.w. (SD = 3.01) and highest ash contents 29.8% (SD = 7.6) were found in small Amphipoda (e.g. Ischyrocerus anguipes) , while species attaining greater body size were characterized by higher energy values and lower ash contents, for example Gammarellus homari 16.96 kJ g⁻¹d.w. (SD = 0.50), and 22.9% (SD = 3.3%) ash.     

Early Holocene shore-displacement in southern central Sweden as recorded in elevated isolated basins

Sediment cores from seven basins in two regions, the SÖdertÖrn peninsula and central Närke in southern central Sweden, were subject to diatom analysis and radiocarbon dating of the isolation events. In the former area, the compiled shore-displacement curve covers the time period from the deglaciation to 5700 BP. The latter area is covered from 8200 to 6500 BP. The chronology is based on combined macrofossil and bulk ages with an acknowledged correction. The most elevated sedimentary basin on the SÖdertÖrn peninsula was isolated at the end of the brackish water phase of the Yoldia Sea. During the Ancylus Lake stage of the Baltic, one minor ingression is recorded in the same area. The end of the Ancylus Lake is dated to c. 8200 BP on the SÖdertÖrn peninsula and to c. 8100 BP in central Närke. There was an interval of c. 1000 ¹⁴C years when brackish water prevailed in central eastern Sweden. Mastogloia is a typical diatom genus for that period. The onset of the brackish-marine Litorina Sea is dated to c. 7000 BP in central Närke. The amplitude for the early Litorina Sea transgression (L 1) did not exceed 2 m. L 1 is recorded 2–3 m higher in central Närke compared to the SÖdertÖrn peninsula, i.e. the former area has experienced a more intense isostatic uplift since 6500 BP.     

Deconvolution of pyroclastic grain-size spectra for interpretation of transport mechanisms: an application to the AD 79 Vesuvio deposits

A computer code using sequential fragmentation/transport theory was used to deconvolute and characterize a large grain-size data set taken from the AD 79 Vesuvio deposits. The results allow us to interpret transport and deposition processes. Four principal morphological classes of grain-size spectra were recognized in the AD 79 deposits: 1 unimodal distributions with coarse modes and very good sorting; 2 polymodal distributions in which relative fractions of each subpopulation are considerably variable; 3 polymodal distributions, but with one mode greatly prevailing over the other ones; 4 flat spectra in which a large number of size classes show the same loading. Because different eruptive, transport and deposition conditions may have operated on pyroclasts which occur in the same bed, we have assigned grain-size subpopulations, with different modes to specific mechanisms of particle movement and sedimentation depending on the size range of the particles and the textures of the beds. The fragmentation/transport processes considered here occur either within dilute flows (as fall, traction, saltation and suspension loads) or in high-concentration flows (as a fluidized system or one with an extremely high sedimentation rate). Variation in strength and position of modes throughout the entire vertical section of AD 79 products illustrates changes in transport and deposition processes with time. Size spectra from Vesuvio quantitatively demonstrate contemporaneous deposition from fall and surge mechanisms as well as contributions from different levels of hydrovolcanic products. In contrast, vertical variations in size spectra within individual pyroclastic flow deposits suggest variation from high particle concentration near the base of the bed to more dilute depositional conditions towards the top. Lateral variations in size spectra for one marker horizon show how a local pyroclastic flow in a channel grades into a surge on the margins. This study supports the model of continuous modification in loadings of several discrete subpopulations during deposition from a single explosive cloud.     

Weichselian and Holocene palaeoenvironmental history of the Bol'shoy Lyakhovsky Island, New Siberian Archipelago, Arctic Siberia

Cryolithological, ground ice and fossil bioindicator (pollen, diatoms, plant macrofossils, rhizopods, insects, mammal bones) records from Bol'shoy Lyakhovsky Island permafrost sequences (73°20′N, 141°30′E) document the environmental history in the region for the past c. 115 kyr. Vegetation similar to modern subarctic tundra communities prevailed during the Eemian/Early Weichselian transition with a climate warmer than the present. Sparse tundra‐like vegetation and harsher climate conditions were predominant during the Early Weichselian. The Middle Weichselian deposits contain peat and peaty soil horizons with bioindicators documenting climate amelioration. Although dwarf willows grew in more protected places, tundra and steppe vegetation prevailed. Climate conditions became colder and drier c. 30 kyr BP. No sediments dated between c. 28.5 and 12.05 ¹⁴C kyr BP were found, which may reflect active erosion during that time. Herb and shrubby vegetation were predominant 11.6–11.3 ¹⁴C kyr BP. Summer temperatures were c. 4 °C higher than today. Typical arctic environments prevailed around 10.5 ¹⁴C kyr BP. Shrub alder and dwarf birch tundra were predominant between c. 9 and 7.6 kyr BP. Reconstructed summer temperatures were at least 4 °C higher than present. However, insect remains reflect that steppe‐like habitats existed until c. 8 kyr BP. After 7.6 kyr BP, shrubs gradually disappeared and the vegetation cover became similar to that of modern tundra. Pollen and beetles indicate a severe arctic environment c. 3.7 kyr BP. However, Betula nana, absent on the island today, was still present. Together with our previous study on Bol'shoy Lyakhovsky Island covering the period between about 200 and 115 kyr, a comprehensive terrestrial palaeoenvironmental data set from this area in western Beringia is now available for the past two glacial–interglacial cycles.