Seed dispersal characteristics to polar regions by means of visitors

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year's first season (2007-2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica's climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios Scenario A1B [Nakicenovic N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (~33,054) are higher than those of scientists (~7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continent's climate changes.

Grain sizes, carbon content and clay minerals of sediments obtained from north Germany and the Baltic Sea

Clay mineralogy and geotechnical properties of Tarras clay, basin clays and tills from some parts of Schleswig-Holstein: Tarras clay of lower Eocene age, Quaternary till containing various admixtures of Tarras clay as well as basin clay and varve-clay from Schleswig-Holstein were investigated. Grain size distribution and soil mechanic characteristics were determined, which indicated different geotechnical properties for each sediment type.

(Table 1) Mean grain sizes and standard deviations of gas hydrate samples

Methane hydrates are present in marine seep systems and occur within the gas hydrate stability zone. Very little is known about their crystallite sizes and size distributions because they are notoriously difficult to measure. Crystal size distributions are usually considered as one of the key petrophysical parameters because they influence mechanical properties and possible compositional changes, which may occur with changing environmental conditions. Variations in grain size are relevant for gas substitution in natural hydrates by replacing CH4 with CO2 for the purpose of carbon dioxide sequestration. Here we show that crystallite sizes of gas hydrates from some locations in the Indian Ocean, Gulf of Mexico and Black Sea are in the range of 200-400 µm; larger values were obtained for deeper-buried samples from ODP Leg 204. The crystallite sizes show generally a log-normal distribution and appear to vary sometimes rapidly with location.

(Table 1) Crystal sizes of measured samples

Due to experimental difficulties grain size distributions of gas hydrate crystallites are largely unknown in natural samples. For the first time, we were able to determine grain size distributions of six natural gas hydrates for samples retrieved from the Gulf of Mexico and from Hydrate Ridge offshore Oregon from varying depths. High-energy synchrotron radiation provides high photon fluxes as well as high penetration depth and thus allows for investigation of bulk sediment samples. The gas hydrate crystallites appear to be (log-) normally distributed in the natural samples and to be of roughly globular shape. The mean grain sizes are in the range from 300-600 µm with a tendency for bigger grains to occur in greater depth, possibly indicating a difference in the formation age. Laboratory produced methane hydrate, starting from ice and aged for 3 weeks, shows half a log-normal curve with a mean value of ~40 µm. This one order-of-magnitude smaller grain sizes suggests that care must be taken when transposing grain-size sensitive (petro-)physical data from laboratory-made gas hydrates to natural settings.

(Table 1) Crystal sizes of measured samples from the Bush Hill region in the Gulf of Mexico and from ODP Leg 204 at the Hydrate Ridge offshore Oregon

The grain sizes of gas hydrate crystallites are largely unknown in natural samples. Single grains are hardly detectable with electron or optical microscopy. For the first time, we have used high-energy synchrotron diffraction to determine grain sizes of six natural gas hydrates retrieved from the Bush Hill region in the Gulf of Mexico and from ODP Leg 204 at the Hydrate Ridge offshore Oregon from varying depth between 1 and 101 metres below seafloor. High-energy synchrotron radiation provides high photon fluxes as well as high penetration depth and thus allows for investigation of bulk sediment samples. Gas hydrate grain sizes were measured at the Beam Line BW 5 at the HASYLAB/Hamburg. A 'moving area detector method', originally developed for material science applications, was used to obtain both spatial and orientation information about gas hydrate grains within the sample. The gas hydrate crystal sizes appeared to be (log-)normally distributed in the natural samples. All mean grain sizes lay in the range from 300 to 600 µm with a tendency for bigger grains to occur in greater depth. Laboratory-produced methane hydrate, aged for 3 weeks, showed half a log-normal curve with a mean grain size value of c. 40 µm. The grains appeared to be globular shaped.

Geochemistry, grain sizes and radiocarbon age of sediment core Lz1005 from Amery Oasis, East Antarctica

The clay mineralogical composition of a 552 cm long sediment core from Lake Terrasovoje in Amery Oasis, East Antarctica, was analysed and compared with that in surface sediments from other locations in the vicinity. The lower part of the sediment core is formed by sub- and proglacial sediments with a dominance of smectite and illite, and lower amounts of kaolinite and chlorite. The upper part of the core is deposited after 12 500 cal yr bp and mainly composed of illite and kaolinite, with low amounts of smectite and chlorite, such as found in samples from rock outcrops and covering sediments throughout Amery Oasis. The clay composition in the lower section of core Lz1005 suggest that the basin of Lake Terrasovoje was filled by a 150-200 m thickened Nemesis Glacier prior to 12 500 cal yr bp rather than by local ice caps.

Bubble sizes in waters of the Atlantic Ocean

Typical size of bubbles obtained from cavitation inception pressure measured in the surface layer of the Atlantic Ocean in situ aboard R/V Professor Vize in 1971 and Nerey in 1973 are reported. These results do not contradict ones of bubble size measurements using optical or acoustical techniques. Variability of bubble size is discovered and described. This variability is related to passing from one geographical region to another (from 68°55'S to 61°52'N), to changes in depth (from 5 to 100 m) and in day time, as well as to spatial fluctuations within an aquatic area. It is suggested that, in addition to wave breaking, there is another source of bubbles at depth 10-20 m that associates with hydrobiological processes.