Using tephrochronology to date temperate ice: correlation between ice tephras on Livingston Island and eruptive units on Deception Island volcano (South Shetland Islands, Antarctica)

Tephra layers are interstratified in the ice caps of the South Shetland Islands. Although previously poorly investigated, they are potential targets for the application of tephrochronology and, hence, may provide temporal constraints on glaciological models for the region. Several tephra layers crop out in the coastal ice-cliffs and ablation ramps of Livingston Island. Using stratigraphical position, granulometry and bulk sample geochemistry, the tephra layers can be divided into three groups (TPH1, TPH2 and TPH3, from top to base). The source for all of the tephras is unequivocally identified as Deception Island, a large active volcano in Bransfield Strait, situated about 35 km south of Livingston Island. TPH1 (a single layer) is strongly correlated compositionally with tephra erupted in 1970 from centres close to Telefon Bay. This is the first time it has been possible to correlate a distal tephra with a pyroclastic unit in the source volcano in the Antarctic Peninsula region. TPH2 (usually two layers, sometimes only one) was probably erupted from a tuff cone centre within the Crater Lake cluster of vents. From historical accounts, it is deduced that the numerous co-eruptive Crater Lake vents were active prior to 1829 and, from their relatively fresh appearance, an eighteen-century age for the eruptions is possible. TPH3 comprises at least four discrete tephra layers with a much wider compositional range than either TPH1 or TPH2. It may have been erupted during successive months or years. Compositional comparisons of TPH3 with possible source vents on Deception Island are ambiguous, but there is a reasonably good similarity with tephras erupted at Wensleydale Beacon and/or Vapour Col. However, it is also conceivable that the source(s) for TPH3 are no longer preserved on Deception Island. The age of the TPH3 eruptions is unknown but it must be prior to 1829 and is unlikely to be more than a few centuries

Efeitos da adição de propilenoglicol ou monensina à silagem de milho sobre a cinética de degradação dos carboidratos e produção cumulativa de gases in vitro Effects of adding propylene glycol or monensin to corn silage on the degradation kinetics of carbohydrates and in vitro cumulative gas production

Avaliaram-se os efeitos dos aditivos propilenoglicol e/ou monensina sobre a degradabilidade média e efetiva dos carboidratos totais, pH e produção cumulativa de gases da silagem de milho por meio da técnica in vitro semi-automática de produção de gases. Os tratamentos constituíram-se de silagem de milho (SM); SM associada ao propilenoglicol (SM+PG); SM associada à monensina (SM+MO); SM associada ao propilenoglicol e à monensina (SM+PG+MO) avaliados com duas, quatro, seis, 12, 24, 48 e 96 horas. A adição de monensina ou monensina associada ao propilenoglicol aumentou (P<0,05) a degradabilidade dos carboidratos totais às duas horas. SM+MO apresentou maior degradabilidade efetiva dos carboidratos totais em todas as taxas de passagem. A utilização de monensina reduziu a produção cumulativa de gases das 12 às 96 horas. Entre os tratamentos, SM+MO apresentou o menor potencial de produção de gases (221ml/g carboidratos totais) e o menor tempo de colonização (1,08 horas) em relação aos tratamentos SM e SM+PG (1,58 e 1,49 horas, respectivamente). A produção cumulativa de gases e degradabilidade dos carboidratos totais apresentaram elevada correlação, variando de 94 a 97% (P<0,01). O pH do meio foi inversamente correlacionado à degradabilidade dos carboidratos totais (r= -79%, P<0,01). O uso de monensina pode ser uma boa alternativa para se melhorarem os parâmetros da cinética de degradação da silagem de milho.<br>The effects of the additives propylene glycol and/or monensin on the degradation of total carbohydrates, pH, and cumulative gas production of corn silage by the semi-automated in vitro gas production technique were evaluated. The treatments were corn silage (CS); CS plus propylene glycol (CS+PG); CS plus monensin (CS+MO), and CS plus propylene glycol and monensin (CS+PG+MO), which were evaluated at two, four, six, 12, 24, 48, and 96 hours. The addition of monensin or monensin plus propylene glycol increased (P<0.05) the degradation of total carbohydrates at 2h. The effective degradations of total carbohydrates for CS+MO treatment (55.2; 42.7; and 36.5%) were the highest in all passage rates. The use of monensin reduced cumulative gas production from 12 to 96h. CS+MO treatment had the lowest potential of gas production (221ml/g total carbohydrates), and the lowest Lag phase (1.08h), as compared to CS and CS+PG treatment (1.58 and 1.49h, respectively). Cumulative gas production and degradation of total carbohydrates were highly correlated (94 to 97%; P<0.01). The pH was inversely correlated to degradability of total carbohydrates (r= -0.79; P<0.01). Thus, monensin may be used for improving the ruminal degradability of corn silage