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<p> Coastlines along the Arabian Sea are susceptible to marine inundation from Makran Subduction Zone (MSZ) earthquakes and tropical cyclones. Sediments deposited by these forms of inundation can expand the decadal instrumental record of events to include millennial timescales in regions without rich historical records (i.e., Oman). On November 28, 1945 a 8.1 M_w MSZ earthquake generated a tsunami that inundated coastlines of the Arabian sea with wave heights as high as 13m. The stratigraphic, sedimentological, foraminiferal, and geochemical signatures of deposit were examined from a small (12 km&sup2;), microtidal lagoon in Sur, Oman. The 1945 tsunami deposit contained distinctive taphonomic assemblages of foraminifera and bivalves. Below the 41cm thick 1945 shell-rich deposit at Sur Lagoon, seven additional anomalous sand (mean grain size of 3.73&phis; &plusmn; 1.66; very fine sand) layers, ranging in thickness from 7 to 32cm, were found preserved within fine-grained lagoonal sediment (mean grain size of 4.44&phis; &plusmn; 1.66; very coarse silt). The seven inferred overwash layers have features consistent with the 1945 tsunami deposit such as fining upward trends, marine foraminifera (e.g., <i> Amphistegina</i> spp., planktics) and increased concentrations of calcium and strontium. By contrast, the surrounding lagoon deposits contain finer grain sizes, intertidal and nearshore foraminifera (e.g., <i>Ammonia tepida</i>, miliolids), and increased concentrations of titanium and magnesium. Based on these data, the seven overwash layers found below the 1945 tsunami deposit have been attributed to marine inundation. Radiocarbon dating indicated an age of 3127 to 2515 cal yr BP for the deepest stratigraphic unit.</p><p>

The Atlantic Seaboard is an 18 km stretch of coastline located on the Cape Peninsula, South Africa, roughly between the Cape Town suburbs of Mouille Point in the north and Hout Bay in the south. It borders heavy shipping traffic and contains a mix of urban and natural environments including up-market seaside neighbourhoods and is part of the Table Mountain National Park. The predominantly rocky coastline has a northeast–southwest orientation with interspersed sandy pocket beaches. A narrow, low-lying coastal plain (marine terrace) in the north merges with coastal cliffs further south. The geomorphology and sedimentology of the coast are closely linked to the underlying geology, influencing the shape of coastal embayments and promontories, as well as the composition and distribution of sediment. Hydrographic, geophysical and sedimentological techniques were used to collect high-resolution bathymetry, seafloor geology and sediment distribution data to better understand modern coastal processes. The results indicate a low-relief seafloor consisting of Malmesbury Group rocks in the north. To the south the seafloor consists of high-relief Cape Granite reefs interspersed with fine to medium grain sand and bioclastic (shelly) gravel. Sediment transport is generally northward by longshore drift. In the south, the high-relief granite reef and headlands form sediment traps resulting in several large pocket beaches and offshore sediment deposits. In the north, the low-relief Malmesbury bedrock is largely free of sediment, except within narrow erosional gullies. Most sediment rapidly passes through to the north resulting in a sediment-starved rocky seafloor. The three principal sources of beach sand are aeolian fine sand transported by the Karbonkelberg headlands bypass dune entering the sea at Sandy Bay, biogenic carbonate production along the coast, and weathering of Table Mountain Group sandstone and granite bedrock. A fourth source is sediment entering the system via longshore drift from the south of Duiker Point. The water depth around the Duiker Point headland is presently too deep for sediment to be transported easily through longshore drift, other than during large storm events, but during past sea-level low stands this would have played an important part in supplying sediment to the coast. Changes in sea level play an important part in shaping the geomorphology of the coastline. Beach deposits, both sandy and boulder beaches have been left at various elevations along the coast, both offshore and onshore. Although today the Sea Point area is protected by sea walls and man-made structures, a higher sea level was responsible for shaping the narrow coastal plain. Increasing rates of global sea-level change are becoming an important issue all over the world and the Atlantic Seaboard coast is not immune to the effects of sea-level rise. The frequency and magnitude of storm events that breach the sea defences erode beaches and sea cliffs and cause damage to private and public property are likely to increase in the future

<p> Recent research has proposed that an increase in sea surface temperatures (SSTs) interpreted to be caused by anthropogenic climate change has lead to an increase in the frequency of intense hurricanes. However, this theory has been challenged on the basis that the instrumental record is too short (approximately 160 years) and unreliable to reveal any long-term trends in intense hurricane activity. This limitation can be addressed by the means of paleotempestology, a field that studies past hurricane activity by means of geological and biological proxy techniques. Hurricane-induced overwash deposits that become preserved in the sediments of back-barrier lagoons, lakes and marshes can provide scientists a unique opportunity to study past hurricane landfalls. It also provides an opportunity to study their associated climate drivers over much longer time-scales (centuries to millennia). </p><p> This study investigates overwash deposits (paleo-tempestites) at 10 sites along the Southwest Florida coastline, focusing on two. The Sanibel Island marsh and Keewaydin Island lagoon have a high potential for recording hurricane-induced paleo-tempestites. The Sanibel Island marsh record was constructed using loss-on-ignition, grain size analysis, percent calcium carbonate, and chronologically dated using 210Pb analysis. Proxy and dating results of three sediment cores revealed two prominent paleo-tempestites&mdash;likely representing Hurricane Donna (1960) and the Great Miami Hurricane of 1926. These layers were deposited as both fine-grained sand and shell hash, and contribute to our understanding of storm overwash in the modern record. Three sediment cores were also extracted from a back-barrier lagoon (Island Bay), behind Keewaydin Island in Collier County, Florida. Core samples were analyzed for grain size, percent calcium carbonate, fossil shells species and dated using the ²¹⁰Pb and ¹⁴C dating methods. These methods revealed a 1 thousand year old record of hurricane overwash. Two prominent paleo-tempestites, deposited as both fine-grained sand and shell hash, were also observed at this site and may possibly replicate the most recent storm events documented on Sanibel Island. This suggests that only the most intense hurricanes are being recorded in the geologic record. </p><p> "Active" (1000-500 yrs. BP) and "inactive" (500-0 yrs. BP) periods of hurricane overwash were identified in the Island Bay record. These correlate well with the reconstructed SSTs from the Main Development Region in the North Atlantic Ocean during the Medieval Warm Period and Little Ice Age. Results from this initial Southwest Florida study point to SSTs of the North Atlantic Main Development Region as a potential climatic driver of hurricane landfalls in Southwest Florida over the past 1 thousand years. This is in opposition to SSTs in the Gulf of Mexico and El Ni&ntilde;o Southern Oscillation as hypothesized by other studies in the Gulf of Mexico and Caribbean regions. These results are the first proxy records of past hurricane strikes in Southwest Florida. </p>

<p> Porous media affect hydrate stability by forcing hydrate-liquid interfaces to form high curvature geometries and by forcing the molecules of the hydrate, liquid, and sedimentary particles that compose the medium to interact where they are in close proximity. To evaluate these effects we first create synthetic spherical packings to approximate pore space geometry. We use the synthetic pore space to calculate the perturbation to the chemical potential caused by the geometrical constraints. Our model predictions agree with published data for ice-water and water-vapor systems. When particles are well-approximated as spheres, our model fits the data with R-squared values that range between about 80% to over 99%. However, our model needs to be improved for porous media that contain a significant fraction of non-equant particles such as clay. Lastly, we demonstrate how our model can be used in predictions for the evolution of hydrate saturation. </p><p> This thesis includes unpublished co-authored material.</p>

<p> Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal (Core NGHP-01-19B; 18&deg;58'N, 85&deg;39'E; 1,422 m). Paired planktic foraminiferal Mg/Ca and &delta;¹⁸O_c of <i> G. ruber</i> constrain sea surface temperatures and isolate millennial-scale variations in the &delta;¹⁸O of surface waters (&delta;¹⁸O_sw) which resulted from changes in river runoff in the northwestern Bay. Concurrently with low &delta;¹⁸O_sw events, benthic foraminiferal &delta;¹³C of <i>Cibicidoides </i> spp. decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca of <i>H. elegans</i> supports the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.</p>

The effects of changes in relative sea-level on clastic shelf margins are examined utilizing two case studies, the passive Quaternary to Recent of Sable Island Bank, Nova Scotia, and the active Silurian shelf of Dyfed, southwest Wales. Within the overall transgressive systems tract of the Sable Island Sand and Gravel Formation, siliciclastic material is continually reworked in shallow water by modern storm-dominated, tidally-modulated flows in an attempt to reach equilibrium and textural grade with the bank-top hydrodynamics. Over the past 11,000 years marked transgressive marine ravinement of the bank-top has cannibalised considerable volumes of sediment into the dynamic realms of eustatically produced accommodation space. Sediment transport, together with bedform and grain-size variations reflect both progressive sorting and the depth dependent fluid power relationship. Bedload sediment transport is predominantly geostrophic, and is seen to be topographically steered at shelf-edge breaks in slope, a process related to the hydraulic fence concept. Through this process, sediment by-pass into deep water is hindered, and spatially significant upward coarsening/thickening sandbodies are developing, most notably at East Bar. Taken a stage further, shoal aggradation of this sediment supply dominated coastal system has enabled the emergence of the cuspate/elongate shelf-edge Sable Island. The effects of changes in relative sea-level on various scales is described from the Coralliferous and Gray Sandstone Groups of southwest Wales. Six Vailian sequences are recognised within a thick basinward prograding clastic wedge. During lowstands of relative sea-level, shelfal incision and sediment by-pass occurred, with sediment supplying deep water fan systems immediately to the north of the study area. Valley-fills vary in depositional environment from low sinuosity fluvial channels (Sequence I), estuarine tidal channels (Sequences II to V), and mixed estuarine/high sinuosity fluvial channels of Sequence VI.

Bibliography: pages 55-58. / The seafloor geology of Walker Bay on the southern Cape coastline is described by making use of geophysical information obtained over a period of 4 years, between 1986 and 1990. The data include side-scan sonar images, seismic profiles, seabed samples and observations by a Remotely Operated underwater Vehicle (ROV). Four sonograph facies were identified, based on their distinctly different reflectivity patterns. Using the seabed samples and R.O.V. observations, the physical characteristics of these facies are determined and presented in map format. Facies 1 consists of Bokkeveld Group rock outcrops with relatively high relief, occupying approximately 45 percent of the study area. Facies 2 represents similar outcrops but with low relief and partially covered by a thin veneer of unconsolidated sediment, including localized occurrences of loose cobbles and boulders. Facies 3 and 4 relate to sediment-covered areas displaying different bedform types. Facies 3 is dominated by well-defined patches of megarippled gravelly sand, whereas Facies 4 consists of small-scale rippled sand. The characteristics of the Facies 3 megarippled patches are discussed in detail and their relationships with the local wave pattern and nearby Facies 1 and 2 rock outcrops are investigated.

Dredging operations carried out on the Agulhas Bank have proved the existence of a widespread phosphorite nodule deposit, considered to be essentially in situ. The pebble to boulder sized nodules recovered have been classified into two conglomeratic and three non-conglomeratic classes. The latter classes comprise (i) phosphatized microfossiliferous limestones (N I class); (ii) phosphatized highly ferruginous microfossiliferous limestones (N II class); and (iii) nodules composed of a poorly sorted mixture of quartz, glauconite and microfossil grains set in a micrite/collophane cement (N III class). Surface to centre phosphatization effects have been observed in some N I nodules. The first conglomeratic variety (C I class) is noted for abundant, often highly irregularly shaped, enclosed N I class phosphorite pebbles set in a matrix that is similar to the N III phosphorite type. The second conglomeratic variety (C II class) is similar to the first, but it is characterised by the inclusion of pebble sized microfossiliferous internal cast of macrofossils, as well as the presence of macrofossil shell debris. X-Ray diffraction studies have shown that the prime phosphate mineral present is francolite, a carbonate fluorapatite, while optically this mineral has been identified as cellophane. An X-Ray diffraction peak-pair technique has indicated an average 5.5% CO₂ concentration in the apatite phase of the phosphorites. Studies on the major element geochemistry of the various phosphorite classes has shown that the bulk geochemistry of the nodules corresponds to the dominant mineralogy and that variations in the bulk geochemistry of the nodules from within a given group reflects variations in the concentration of diluent allogenic minerals. A sympathetic relationship exists between the Na and S concentrations in the phosphorites, and this has been related to substitution effects in the phosphate mineral phase. The average P₂O₅ concentration determined for the Agulhas Bank phosphorites is 16.18%. The N I and N II phosphorite classes are considered to have originated as a result of limestone phosphatization involving a calcite-to-francolite replacement process. Many of the sedimentological features exhibited by the texturally heterogenous N III, C I and C II class nodules are incompatible under normal hydrodynamic conditions, suggesting an unusual depositional environment. In order to explain these features it has been proposed that the nodules were originally lime mud rich sediments and that the conglomeratic varieties were deposited by submarine transporting agencies such as mud-flows, turbidity currents and/or tidal/storm wave surges. Bioturbation may have been responsible for the mixing of lime mud and coarser material to produce the poorly sorted non-conglomeratic N III phosphorite class. Replacement of the calcitic lime mud by francolite .s considered to be the prime mechanism responsible for the phosphate mineralization and lithification of these N III, C I and C II class phosphorites.

<p> Sand levels were monitored at five southern California beaches for periods of 3 to 15 years, spanning a total of 18 km alongshore. Every 3 months, GPS equipped vehicles measured sand elevations on cross-shore transects from the backbeach to 8 m depth, with 100 m alongshore resolution. Subaerial observations were collected monthly above the spring low-tide line. Wave buoys and a numerical model provided hourly wave estimates in 10 m depth at each site. </p><p> These observations show that beach profile shapes (depth versus cross-shore distance) evolve consistent with the equilibrium hypothesis: under steady wave conditions, evolution is toward a unique, wave condition dependent, equilibrium beach profile. Beaches far out of equilibrium change rapidly, and as equilibrium is approached they change ever more slowly. At the sandy regions, a simple equilibrium beach state model has skill >0.5 (Chapter 2, [Ludka et al., 2015]). </p><p> Repeated nourishments over multiple decades, costing hundreds of thousands of dollars, are a primary beach management strategy worldwide, but the wave-driven redistribution of nourishment sand is poorly understood. At four survey sites, 50,000-300,000 m</p><p>3 of imported sand was placed on the subaerial beach overalongshore spans between 300-1300 m. Wave conditions in the months after placement were similar at all sites, but the subaerial nourishment pads eroded and retreated landward at different rates. A pad built with native-sized sand washed offshore in the first few storms. In contrast, nourishments with coarser than native sand remained on the beach face for several years and protected shorelines during the significant wave attack of the 2015&ndash;16 El Ni&ntilde;o (Chapter 3, [Ludka et al., 2016]). These relatively resilient and coarse subaerial pads stretched alongshore in a pattern consistent with seasonally shifting, wave-driven alongshore currents. Natural gains and losses in the total sand volume budget, integrated spatially over each site, are sometimes larger than the nourishment contributions (Chapter 4, in prep for Coastal Engineering). </p>