It has been known since Rhodes Fairbridge's first attempt to establish a global pattern of Holocene sea-level change by combining evidence from Western Australia and from sites in the northern hemisphere that the details of sea-level history since the Last Glacial Maximum vary considerably across the globe. The Australian region is relatively stable tectonically and is situated in the 'far-field' of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. The broader Australasian region has provided critical information on the nature of post-glacial sea level, including the termination of the Last Glacial Maximum when sea level was approximately 125 m lower than present around 21,000-19,000 years BP, and insights into meltwater pulse 1A between 14,600 and 14,300 cal. yr BP. Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin. This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes). Several seminal studies in the early 1980s produced important data sets from the Australasian region that have provided a solid foundation for more recent palaeo-sea-level research. This review revisits these key studies emphasising their continuing influence on Quaternary research and incorporates relatively recent investigations to interpret the nature of post-glacial sea-level change around Australia. These include a synthesis of research from the Northern Territory, Queensland, New South Wales, South Australia and Western Australia. A focus of these more recent studies has been the re-examination of: (1) the accuracy and reliability of different proxy sea-level indicators; (2) the rate and nature of post-glacial sea-level rise; (3) the evidence for timing, elevation, and duration of mid-Holocene highstands; and, (4) the notion of mid-to late Holocene sea-level oscillations, and their basis. Based on this synthesis of previous research, it is clear that estimates of past sea-surface elevation are a function of eustatic factors as well as morphodynamics of individual sites, the wide variety of proxy sea-level indicators used, their wide geographical range, and their indicative meaning. Some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level, the inter-comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years. These issues need to be thoroughly understood befor...
Mangroves occur on upper intertidal shorelines in the tropics and subtropics. Complex hydrodynamic and salinity conditions, related primarily to elevation and hydroperiod, influence mangrove distributions; this review considers how these distributions change over time. Accumulation rates of allochthonous and autochthonous sediment, both inorganic and organic, vary between and within different settings. Abundant terrigenous sediment can form dynamic mudbanks, and tides redistribute sediment, contrasting with mangrove peat in sediment-starved carbonate settings. Sediments underlying mangroves sequester carbon but also contain paleoenvironmental records of adjustments to past sea-level changes. Radiometric dating indicates long-term sedimentation, whereas measurements made using surface elevation tables and marker horizons provide shorter perspectives, indicating shallow subsurface processes of root growth and substrate autocompaction. Many tropical deltas also experience deep subsidence, which augments relative sea-level rise. The persistence of mangroves implies an ability to cope with moderately high rates of relative sea-level rise. However, many human pressures threaten mangroves, resulting in a continuing decline in their extent throughout the tropics.
The response of mangroves to high rates of relative sea level rise (RSLR) is poorly understood. We explore the limits of mangrove vertical accretion to sustained periods of RSLR in the final stages of deglaciation. The timing of initiation and rate of mangrove vertical accretion were compared with independently modeled rates of RSLR for 78 locations. Mangrove forests expanded between 9800 and 7500 years ago, vertically accreting thick sequences of organic sediments at a rate principally driven by the rate of RSLR, representing an important carbon sink. We found it very likely (>90% probability) that mangroves were unable to initiate sustained accretion when RSLR rates exceeded 6.1 millimeters per year. This threshold is likely to be surpassed on tropical coastlines within 30 years under high-emissions scenarios.
The growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction, and coastlines are at the forefront of such confrontation. In this paper, we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes, and how these processes evolve throughout the islands' lifetime. Volcanic constructional processes dominate during the emergent island and subaerial shield-building stages. During the emergent island stage, surtseyan activity prevails and hydroclastic and pyroclastic structures form; these structures are generally ephemeral because they can be rapidly obliterated by marine erosion. With the onset of the subaerial shield-building stage, coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas, largely expanding the coastlines until they, typically, reach their maximum extension. With the post-shield quiescence in volcanic activity, destructive processes gradually take over and coastlines retreat, adopting a more prominent profile; mass wasting and marine and fluvial erosion reshape the landscape and, if conditions are favorable, biogenic processes assume a prominent role. Posterosional volcanic activity may temporarily reverse the balance by renewing coastline expansion, but islands inexorably enter in a long battle for survival above sea level. Reef growth and/or uplift may also prolong the island's lifetime above the waves. The ultimate fate of most islands, however, is to be drowned through subsidence and/or truncation by marine erosion.Keywords complex, interplay, between, volcanism, erosion, sedimentation, sea, level, islands, change, coastal, biogenic, production, oceanic, evolution, volcanic, GeoQuest Disciplines Medicine and Health Sciences | Social and Behavioral Sciences Publication DetailsRamalho, R. S., Quartau, R., Trenhaile, A. S., Mitchell, N. C., Woodroffe, C. D. & Avila, S. P. (2013). Coastal evolution on volcanic oceanic islands: a complex interplay between volcanism, erosion, sedimentation, sealevel change and biogenic production. Earth-Science Reviews, 127 140-170. AbstractThe growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction, and coastlines are at the forefront of such confrontation. In this paper, we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes, and how these processes evolve throughout the islands' lifetime. Volcanic constructional processes dominate during the emergent island and subaerial shield-building stages. During the emergent island stage, surtseyan activity prevails and hydroclastic and pyroclastic structures form; these structures are generally ephemeral because they can be rapidly obliterated by marine erosion. With the onset of the subaerial shield-building stage, coastal evolution is essentially ch...
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