Late Pleistocene history of turbidite sedimentation in a submarine canyon off the northern Great Barrier Reef, Australia

Cores from slopes east of the Great Barrier Reef (GBR) challenge traditional models for sedimentation on tropical mixed siliciclastic-carbonate margins. However, satisfactory explanations of sediment accumulation on this archetypal margin that include both hemipelagic and turbidite sedimentation remain elusive, as submarine canyons and their role in delivering coarse-grained turbidite deposits, are poorly understood. Towards addressing this problem we investigated the shelf and canyon system bordering the northern Ribbon Reefs and reconstructed the history of turbidite deposition since the Late Pleistocene. High-resolution bathymetric and seismic data show a large paleo-channel system that crosses the shelf before connecting with the canyons via the inter-reef passages between the Ribbon Reefs. High-resolution bathymetry of the canyon axis reveals a complex and active system of channels, sand waves, and local submarine landslides. Multi-proxy examination of three cores from down the axis of the canyon system reveals 18 turbidites and debrites, interlayered with hemipelagic muds, that are derived from a mix of shallow and deep sources. Twenty radiocarbon ages indicate that siliciclastic-dominated and mixed turbidites only occur prior to 31 ka during Marine Isotope Stage (MIS) 3, while carbonate-dominated turbidites are well established by 11 ka in MIS1 until as recently as 1.2 ka. The apparent lack of siliciclastic-dominated turbidites and presence of only a few carbonate-dominated turbidites during the MIS2 lowstand are not consistent with generic models of margin sedimentation but might also reflect a gap in the turbidite record. These data suggest that turbidite sedimentation in the Ribbon Reef canyons, probably reflects the complex relationship between the prolonged period (> 25 ka) of MIS3 millennial sea level changes and local factors such as the shelf, inter-reef passage depth, canyon morphology and different sediment sources. On this basis we predict that the spatial and temporal patterns of turbidite sedimentation could vary considerably along the length of the GBR margin.

Design criteria for a barrier-based gas-liquid flow distributor for parallel microchannels

This paper presents criteria for the design of a flow distributor for even distribution of gas and liquid flows over parallel microchannels. The design criteria are illustrated for the case of a nitrogen-water Taylor flow (1

Holocene climate change, vegetation history and human impact in the Central Mediterranean: evidence from the Maltese Islands

Holocene climates and human impact in the Mediterranean basin have received much attention, but the Maltese Islands in the Central Mediterranean, although a pivotal area, have been little researched. Here, sedimentary and palynological data are presented for three cores from the Holocene coastal and shallowmarine
deposits of the Maltese Islands. These show deforestation from Pinus-Cupressaceae woodland in the early Neolithic, and then a long, but relatively stable history of agriculturally degraded environments to the present day. The major climate events which have affected the Italian and Balkan peninsulas to the
north, and Tunisia to the south, are not reflected in the pollen diagrams from the Maltese Islands because of the strong anthropogenic imprint on the Maltese vegetation from early in the Neolithic. Previous suggestions of environmentally-driven agricultural collapse at the end of the Neolithic appear, however,
to be substantiated and may be linked to regional aridification around 4300 cal. BP. Depopulation in early Medieval times is not supported by the current palynological evidence.