Straight from the source's mouth: Controls on field-constrained sediment export across the entire active Corinth Rift,central Greece

The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain-size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain-size increases westward along the southern coast of the Gulf of Corinth, with the coarse-fraction grain-sizes (84^th percentile of weighted grain-size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain-size export is primarily controlled by the input grain-size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain-size-specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain-size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics.     

An 11 000‐year record of driftwood delivery to the western Queen Elizabeth Islands,Arctic Canada

Fifty‐six new radiocarbon dates from driftwood (mainly Larix, Picea and Populus spp.) collected from the modern and raised shorelines of Melville and Eglinton islands (western Canadian High Arctic) are presented and compared to other driftwood collections from the Canadian Arctic Archipelago (CAA) and Greenland. By documenting the species (provenance) and spatio‐temporal distribution of driftwood at various sites across the Arctic, regional characterizations of former sea‐ice conditions and changes in Arctic Ocean circulation patterns may be deduced. The earliest postglacial invasion of the Canadian Arctic Archipelago by driftwood is recorded on central Melville Island at c. 11 cal. ka BP, suggesting that the modern circulation pattern of Arctic Ocean surface water southeast through the archipelago was established >1000 years earlier than previously proposed. Throughout most of the Holocene until c. 1.0 cal. ka BP, the rate of driftwood delivery to the western Arctic islands was low (~1 recorded stranding event per 200 years) and intermittent, with the longest break in the record occurring between c. 3.0 and 5.0 cal. ka BP. This 2000‐year hiatus is attributed to a period of colder temperatures causing severe sea‐ice conditions and effectively making the coasts of the western Arctic islands inaccessible. After c. 1.0 cal. ka BP, driftwood incursion increased to maximum Holocene levels (~1 recorded stranding event every 20 years). Driftwood identified to the genus level as Larix that was delivered at this time suggests that the Trans Polar Drift current was regularly in its most southwestern position, related to a dominantly positive Arctic Oscillation mode. The Little Ice Age appears to have had little impact on driftwood entry to the western Canadian Arctic Archipelago, indeed the general abundance in the latest Holocene may record infrequent landfast sea ice.     

Titan's prolific propane: The Cassini CIRS perspective

Although propane gas (C₃H₈) was first detected in the stratosphere of Titan by the Voyager IRIS infrared spectrometer in 1980, obtaining an accurate measurement of its abundance has proved difficult. All existing measurements have been made by modeling the ν₂₆ band at : however, different analyzes over time have yielded quite different results, and it also suffers from confusion with the strong nearby ν₅ band of acetylene. In this paper we select large spectral averages of data from the Cassini Composite Infrared Spectrometer (CIRS) obtained in limb-viewing mode at low latitudes (30^°S-30^°N), greatly increasing the path length and hence signal-to-noise ratio for optically thin trace species such as propane. By modeling and subtracting the emissions of other gas species, we demonstrate that at least six infrared bands of propane are detected by CIRS, including two not previously identified in Titan spectra. Using a new linelist for the range 1300-1400 cm^-1, along with an existing GEISA list, we retrieve propane abundances from two bands at 748 and 1376 cm^-1. At 748 cm^-1 we retrieve 4.2±0.5×10^-7 (1-σ error) at 2 mbar, in good agreement with previous studies, although lack of hotbands in the present spectral atlas remains a problem. We also determine 5.7±0.8×10^-7 at 2 mbar from the 1376 cm^-1 band — a value that is probably affected by systematic errors including continuum gradients due to haze and also an imperfect model of the ν₆ band of ethane. This study clearly shows for the first time the ubiquity of propane's emission bands across the thermal infrared spectrum of Titan, and points to an urgent need for further laboratory spectroscopy work, both to provide the line positions and intensities needed to model these bands, and also to further characterize haze spectral opacity. The present lack of accurate modeling capability for propane is an impediment not only for the measurement of propane itself, but also for the search for the emissions of new molecules in many spectral regions.     

Rates of nitrification along an estuarine gradient in Narragansett Bay

Rates of pelagic nitrification, measured using N-Serve-sensitive [¹⁴C]bicarbonate uptake, varied by as much as an order-of-magnitude among three sites along the salinity gradient of Narragansett Bay (Rhode Island, United States). Rates were always higher at the Providence River estuary site (0.04–11.2 μmol N I^?1 d^?1) than at either the lower Narragansett Bay site (0.02–0.98 μmol N I^?1d^?1) or the freshwater Blackstone River site (0.04–1.7 μmol N I^?1d^?1). Although temperature was the most important variable regulating the annual cycle of nitrification, ammonium concentrations were most likely responsible for the large differences in rates among the three sites in summer. At the levels found in this estuarine system, salinity and concentrations of oxygen or total suspended matter did not appear to have a direct measurable effect on nitrification and pH did only occasionally. Nitrification played an important role in the nitrogen cycle at all three sites. In Narragansett Bay, nitrification contributed 55% of the NO₂ ^? and NO₃ ^? entering annually, and was the major source during spring and summer. Water from offshore was the only other large source of NO₂ ^? and NO₃ ^?, contributing 34%. High summer rates of nitrification could support much of the phytoplankton uptake of NO₂ ^? and NO₃ ^?. In the Providence River estuary, the largest annual input of NO₂ ^? and NO₃ ^? was from rivers (54%), although nitrification (28%) and water from lower portions of the bay (11%) also made large contributions. Again, nitrification was most important in the summer. The high rates of nitrification in the Providence River estuary during summer were also likely to be important in terms of oxygen demand, and the production of nitric and nitrous oxides. In the Blackstone River, NO₂ ^? and NO₃ ^? concentrations increased as the river flowed through Rhode Island, and nitrification was a possible source.     

Using geolifespans to model dynamic geographic domains

Geographic objects are characterized by having different durations of existence, or geolifespans. A typology based on the concept of a geolifespan is developed to model variations in the longevity of entities that are stored in geographic information systems. The typology consists of two upper-level classes: Persistent and Ephemeral. The Ephemeral class is composed of three subclasses: Temporary, Transient and Brief. The set of possible transitions between classes in the typology is described, capturing how objects can change from one class to another, e.g., from Temporary to Brief or from Transient to Persistent. A transition sequence models the geolifespan class(es) to which an object belongs over a period of time and captures the evolution of dynamic geographic objects with respect to their longevity. Geolifespan classes are applied to scenarios of spatial change as well as a geosensor network to illustrate their role in modelling geographic dynamics.     

Increasing the spatial resolution of agricultural land cover maps using a Hopfield neural network

Land cover class composition of remotely sensed image pixels can be estimated using soft classification techniques increasingly available in many GIS packages. However, their output provides no indication of how such classes are distributed spatially within the instantaneous field of view represented by the pixel. Techniques that attempt to provide an improved spatial representation of land cover have been developed, but not tested on the difficult task of mapping from real satellite imagery. The authors investigated the use of a Hopfield neural network technique to map the spatial distributions of classes reliably using information of pixel composition determined from soft classification previously. The approach involved designing the energy function to produce a ‘best guess’ prediction of the spatial distribution of class components in each pixel. In previous studies, the authors described the application of the technique to target identification, pattern prediction and land cover mapping at the sub-pixel scale, but only for simulated imagery. We now show how the approach can be applied to Landsat Thematic Mapper (TM) agriculture imagery to derive accurate estimates of land cover and reduce the uncertainty inherent in such imagery. The technique was applied to Landsat TM imagery of small-scale agriculture in Greece and largescale agriculture near Leicester, UK. The resultant maps provided an accurate and improved representation of the land covers studied, with RMS errors for the Landsat imagery of the order of 0.1 in the new fine resolution map recorded. The results showed that the neural network represents a simple efficient tool for mapping land cover from operational satellite sensor imagery and can deliver requisite results and improvements over traditional techniques for the GIS analysis of practical remotely sensed imagery at the sub pixel scale.     

High population connectivity and Pleistocene range expansion in the direct-developing plough shell Bullia rhodostoma along the South African coast

Pleistocene climatic and oceanographic changes have influenced the distribution of marine biodiversity in southern Africa. Most evidence, however, has been derived from rocky shore or demersal taxa; data on sandy shore species are limited, despite severe threats to many sandy beach ecosystems. To test the effects of past climatic changes on sandy shore species, we sampled 140 smooth plough shell Bullia rhodostoma individuals from eight localities and generated phylogeographic data derived from the mtDNA cytochrome c oxidase subunit 1 (COI) marker. Nuclear markers (ATPSα, ATPSβ, ANT, SRPS4, TBP, LTRS and ZMP) showed no sequence variation. Bullia rhodostoma exhibited shallow genetic differentiation (Φ_ST = 0.07, p < 0.05) across its range. Isolation-by-distance suggests a stepping-stone model of migration, which is expected given the species’ direct-development life-history strategy. Demographic reconstruction suggests a post-LGM (Last Glacial Maximum) range expansion, concordant with the signal of shallow genetic differentiation. Phylogeographic patterns obtained suggest that, during lower sea levels than current, B. rhodostoma could have been restricted to the South-West Coast, the central Agulhas Bioregion and probably also the East Coast. When climatic conditions changed and temperatures began to rise after the LGM, the species began a rapid westward range expansion from these refugial regions.     

Foraminifera and tidal notches: Dating neotectonic events at Korphos,Greece

Fossil assemblages of foraminifera and thecamoebians from three salt-marsh cores recovered at Korphos, Greece, provided evidence for five transgression events since the mid Holocene. Marsh accretion rates based on radiocarbon-dated peat and geomorphic evidence from a series of discrete, v-shaped, submerged tidal notches indicated that these transgression events were rapid and episodic. Correlation of the tidal notches with the transgression horizons in the salt-marsh stratigraphy revealed a stepwise pattern of relative sea-level change at Korphos, which is best explained by coseismic subsidence related to fault displacement (earthquakes) associated with the Hellenic subduction zone. A comparison between the Korphos data and a model of Holocene sea-level change for the Peloponnesus reinforces this interpretation as sea-level rose in a series of jumps by amounts greater than accounted for by eustatic and glacio-hydro-isostatic factors (up to ~ 2.0 m). This study illustrates that by combining microfossil, sedimentary and geomorphic records of past sea-level change, problems frequently encountered with each record individually (e.g. dating submerged notches and autocompaction of marsh sediments) may be overcome.     

Responses of coastal lagoon plant communities to levels of nutrient enrichment: A mesocosm study

An experiment was conducted to quantify the effects of different levels of nutrient enrichment on the plant communities of temperate coastal lagoons, specifically the lagoons of the northeast U.S. Ten mesocosms, each containing coastal water, lagoon sediments, and plants and animals found in natural lagoons, were subjected to five levels of enrichment. Two mesocosms served as controls, and received no experimental nutrient additions. The remaining 8 mesocosms were enriched in duplicate with ammonium plus phosphate at 1.0 and 0.11 mmol N or P m^?2 d^?1, 2.0 and 0.19 mmol N or P m^?2 d^?1, 4.0 and 0.35 mmol N or P m^?2 d^?1, and 8.0 and 0.67 N or P mmol m^?2 d^?1. At all levels of enrichment, and through much of the experiment, water column concentrations of dissolved inorganic nitrogen (DIN) were drawn down to background levels. Despite the efficient drawdown of added DIN even at the highest loadings, differences in plant biomass among the 5 treatments were difficult to detect. Enrichment at the highest loadings increased standing stocks of phytoplankton for one month mid-experiment. No significant effect of loading could be detected for dry biomass of eelgrass (Zostera marina), epiphytic material, drift macroalgae, or for all plant components combined. The experiment has demonstrated that the enrichment responses of coastal lagoons can be diverse, especially at intermediate loadings.