180 resultados para Accumulation of peat per year
Resumo:
Pollen analytical studies were carried out on two sediment cores from Outer Flensburg Fjord taken by N. Exon (1972). 1) Based on the occurrence of Fagopyrum, the lower peat horizon (ca. 40 cm below mean sea level) of the inner lagoon near Beveroe developed after 1400 AD. The dominance of Pinus indicates that its formation may have taken place as late as the end of the 17th. Century. 2) Core No. 10872 from a water depth of 26.5 m contains the pollen zones VIII through the beginning of XI (Overbeck, 1950). Although salinity maxima fall in zone IX, they are not reflected in the pollen curves which show the normal picture found in South Jütland.
Resumo:
The anthropogenic release of carbon dioxide (CO2) into the atmosphere leads to an increase in the CO2 partial pressure (pCO2) in the ocean, which may reach 950 ?atm by the end of the 21st century. The resulting hypercapnia (high pCO2) and decreasing pH ("ocean acidification") are expected to have appreciable effects on water-breathing organisms, especially on their early-life stages. For organisms like squid that lay their eggs in coastal areas where the embryo and then paralarva are also exposed to metal contamination, there is a need for information on how ocean acidification may influence trace element bioaccumulation during their development. In this study, we investigated the effects of enhanced levels of pCO2 (380, 850 and 1500 ?atm corresponding to pHT of 8.1, 7.85 and 7.60) on the accumulation of dissolved 110mAg, 109Cd, 57Co, 203Hg, 54Mn and 65Zn radiotracers in the whole egg strand and in the different compartments of the egg of Loligo vulgaris during the embryonic development and also in hatchlings during their first days of paralarval life. Retention properties of the eggshell for 110mAg, 203Hg and 65Zn were affected by the pCO2 treatments. In the embryo, increasing seawater pCO2 enhanced the uptake of both 110mAg and 65Zn while 203Hg showed a minimum concentration factor (CF) at the intermediate pCO2. 65Zn incorporation in statoliths also increased with increasing pCO2. Conversely, uptake of 109Cd and 54Mn in the embryo decreased as a function of increasing pCO2. Only the accumulation of 57Co in embryos was not affected by increasing pCO2. In paralarvae, the CF of 110mAg increased with increasing pCO2, whereas the 57Co CF was reduced at the highest pCO2 and 203Hg showed a maximal uptake rate at the intermediate pCO2. 54Mn and 65Zn accumulation in paralarvae were not significantly modified by hypercapnic conditions. Our results suggest a combined effect of pH on the adsorption and protective properties of the eggshell and of hypercapnia on the metabolism of embryo and paralarvae, both causing changes to the accumulation of metals in the tissues of L. vulgaris.
Resumo:
The assemblages inhabiting the continental shelf around Antarctica are known to be very patchy, in large part due to deep iceberg impacts. The present study shows that richness and abundance of much deeper benthos, at slope and abyssal depths, also vary greatly in the Southern and South Atlantic oceans. On the ANDEEP III expedition, we deployed 16 Agassiz trawls to sample the zoobenthos at depths from 1055 to 4930 m across the northern Weddell Sea and two South Atlantic basins. A total of 5933 specimens, belonging to 44 higher taxonomic groups, were collected. Overall the most frequent taxa were Ophiuroidea, Bivalvia, Polychaeta and Asteroidea, and the most abundant taxa were Malacostraca, Polychaeta and Bivalvia. Species richness per station varied from 6 to 148. The taxonomic composition of assemblages, based on relative taxon richness, varied considerably between sites but showed no relation to depth. The former three most abundant taxa accounted for 10-30% each of all taxa present. Standardised abundances based on trawl catches varied between 1 and 252 individuals per 1000 m2. Abundance significantly decreased with increasing depth, and assemblages showed high patchiness in their distribution. Cluster analysis based on relative abundance showed changes of community structure that were not linked to depth, area, sediment grain size or temperature. Generally abundances of zoobenthos in the abyssal Weddell Sea are lower than shelf abundances by several orders of magnitude.
Resumo:
Permafrost landscapes experience different disturbances and store large amounts of organic matter, which may become a source of greenhouse gases upon permafrost degradation. We analysed the influence of terrain and geomorphic disturbances (e.g. soil creep, active-layer detachment, gullying, thaw slumping, accumulation of fluvial deposits) on soil organic carbon (SOC) and total nitrogen (TN) storage using 11 permafrost cores from Herschel Island, western Canadian Arctic. Our results indicate a strong correlation between SOC storage and the topographic wetness index. Undisturbed sites stored the majority of SOC and TN in the upper 70 cm of soil. Sites characterised by mass wasting showed significant SOC depletion and soil compaction, whereas sites characterised by the accumulation of peat and fluvial deposits store SOC and TN along the whole core. We upscaled SOC and TN to estimate total stocks using the ecological units determined from vegetation composition, slope angle and the geomorphic disturbance regime. The ecological units were delineated with a supervised classification based on RapidEye multispectral satellite imagery and slope angle. Mean SOC and TN storage for the uppermost 1?m of soil on Herschel Island are 34.8 kg C/m**2 and 3.4 kg N/m**2, respectively.
Resumo:
Though much attention has been focused in recent years on the melting of ice from Greenland and Antarctica, nearly half of the ice volume currently being lost to the ocean is actually coming from other mountain glaciers and ice caps. Ice loss from a group of islands in northern Canada accounts for much of that volume. In a study published in April 2011 in the journal Nature, a team of researchers led by Alex Gardner of the University of Michigan found that land ice in both the northern and southern Canadian Arctic Archipelago has declined sharply. The maps above show ice loss from surface melting for the northern portion of the archipelago from 2004-2006 (left) and 2007-2009 (right). Blue indicates ice gain, and red indicates ice loss. In the six years studied, the Canadian Arctic Archipelago lost an average of approximately 61 gigatons of ice per year. (A gigaton is a billion tons of ice.) The research team also found the rate of ice loss was accelerating. From 2004 to 2006, the average mass loss was roughly 31 gigatons per year; from 2007 to 2009, the loss increased to 92 gigatons per year. Gardner and colleagues used three independent methods to assess ice mass, all of which showed the same trends. The team used a model to estimate the surface mass balance of ice and the amount of ice discharged. They also compiled and analyzed measurements from NASA's Ice, Cloud and Land Elevation Satellite (ICESat) to assess changes in the surface height of ice. Finally, they gathered observations from NASA's Gravity Recovery and Climate Experiment (GRACE) to determine changes in the gravity field in the region, an indicator of the amount of ice gained or lost. The Canadian Arctic Archipelago generally receives little precipitation, and the amount of snowfall changes little from year to year. But the rate of snow and ice melting varies considerably, so changes in ice mass come largely from changes in summertime melt. During the 2004 to 2009 study period, the Canadian Arctic Archipelago experienced four of its five warmest years since 1960, likely fueling the melting. Gardner notes that from 2001 to 2004, the sum of melting from all mountain glaciers and ice caps around the world (but not the Greenland and Antarctic ice sheets) contributed an estimated 1 millimeter per year to global sea level rise. Recent estimates suggest the Greenland and Antarctic ice sheets add another 1.3 millimeters per year to sea level. "This means 1 percent of the land ice volume-mountain glaciers and ice caps-account for about half of all ice loss to the world's oceans," Gardner said. "Most of the ice loss is coming from the Canadian Arctic Archipelago, Alaska, Patagonia, the Himalayas, and the smaller ice masses surrounding the main Greenland and Antarctic ice sheets."