Truncated dunes as evidence of the 2004 tsunami in North Sumatra and environmental recovery post‐tsunami

The 2004 tsunami transformed the coast of Indonesia. This research investigates a sand dune area in Lampuuk, Sumatra, that was scoured by tsunami flow. We assessed geomorphology one‐year post‐event and examine the timescale of vegetation recovery. Ground Penetrating Radar (GPR) evidence shows an eroded succession of thin dipping units, overlain by aeolian layers 0 to 50 cm thick. Incipient dunes were absent, indicating limited dune rebuilding at one‐year post‐tsunami, possibly resulting from channelised airflow and the absence of vegetation. Recolonisation by vegetation was initially limited but progressed rapidly between 2005 and 2011, highlighting the temporal non‐linearity of recovery processes.     

Vertical Stacking Statistics of Multi-facies Object-Based Models

Mathematical Geosciences - Equations describing facies proportions and amalgamation ratios are derived for randomly placed objects belonging to two or three foreground facies embedded in a...     

Are toxic contaminants accumulating in Massachusetts coastal sediments following startup of the Massachusetts Bay outfall: a comprehensive comparison of baseline and post-diversion periods

The Massachusetts Water Resources Authority (MWRA) conducts monitoring to address concerns related to the 2000 diversion of secondarily treated effluent discharge into Massachusetts Bay. Baseline data (1992-2000) showed multiple regions defined by physical and chemical composition. Near the Massachusetts Bay outfall, there is a series of heterogeneous sediments in relatively close proximity to the primary historic source of contaminants (Boston Harbor). Farfield sediments exhibited greater compositional definition from one another, which was attributed to the greater spatial separation of the sampling locations. Factors that influence contaminant variability include local and distributed sources, and are primarily related to gradients in depositional environments. Post-diversion sediment data suggest that 4 years of treated effluent discharge has not increased contaminant concentrations to the bay system. However, abundance of the sewage tracer, Clostridium perfringens, has increased variably in sediments located within 2 km of the outfall, providing a distinct effluent signal near the outfall.     

Bottom pressure tides along a line in the southeast Atlantic Ocean and comparisons with satellite altimetry

Seafloor pressure records, collected at 11 stations aligned along a single ground track of the Topex/Poseidon and Jason satellites, are analyzed for their tidal content. With very low background noise levels and approximately 27 months of high-quality records, tidal constituents can be estimated with unusually high precision. This includes many high-frequency lines up through the seventh-diurnal band. The station deployment provides a unique opportunity to compare with tides estimated from satellite altimetry, point by point along the satellite track, in a region of moderately high mesoscale variability. That variability can significantly corrupt altimeter-based tide estimates, even with 17 years of data. A method to improve the along-track altimeter estimates by correcting the data for non-tidal variability is found to yield much better agreement with the bottom-pressure data. The technique should prove useful in certain demanding applications, such as altimetric studies of internal tides.     

DISTRIBUTION AND CHEMICAL COMPOSITION OF MICROCOLONIAL FUNGI AND ROCK COATINGS FROM ARID AUSTRALIA

Microcolonial fungi are found on rock coatings at various sites throughout the arid regions of Australia. Fungi tend to concentrate in depressions, although it is uncertain whether they contribute to enlargement of microhollows. As determined by SEM-EDAX, the chemical characteristics of microcolonial fungi are variable but do not reflect those of the surfaces on which they are found. Most fungi contain calcium, sulfur, chlorine and sometimes phosphorus, but not manganese, in quantities greater than those of adjacent rock coatings. Major sources for accumulated elements may be rainfall or dust. Some elements, especially calcium, are apparently concentrated temporarily in microcolonial fungi, with amounts present in dead organisms being relatively low. The incorporation of some dead microcolonial fungi into developing rock coatings is therefore unlikely to lead to anomalously high calcium levels for cation ratio dating. As rock coatings contain trace or undetectable amounts of some other elements concentrated within active microcolonial fungi, the presence of an accumulator organism on coating surfaces does not necessarily result in these elements being incorporated within the coating. [Key words: microcolonial fungi, rock coatings, arid Australia.]     

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

Beach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore-normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back-barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post-seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo-storm initially created a washover fan into the back-barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern-day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern-day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.     

On Robust Multi-Year Tidal Prediction Using T_TIDE

Ocean Science Journal - A minimum 19 year tidal prediction dataset covering nodal (satellite) modulation effects is required to determine the Lowest Astronomical Tide (LAT) and Highest Astronomical...