دانلود رایگان مقاله لاتین تغییر خط ساحل از سایت الزویر
عنوان فارسی مقاله:
تغییرات خط ساحلی چند دهه در واکنش به افزایش سطح آب اقیانوس در جزایر مارشال
عنوان انگلیسی مقاله:
Multi-decadal shoreline changes in response to sea level rise in the Marshall Islands
سال انتشار : 2015
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مقدمه انگلیسی مقاله:
1. Introduction
Atoll islands are coral reef associated sedimentary deposits found in subtropical and tropical oceans. The islands are comprised of unconsolidated or weakly lithified carbonate sediment derived from the skeletal remains of the reef framework and benthic organisms. Most chronologies of island development indicate islands are geologically young, having only formed in the mid-late Holocene, and were fully formed 5000–2000 years BP (Woodroffe et al., 1999, 2007; Woodroffe and Morrison, 2001; Kench et al., 2005; Kayanne et al., 2011; Kench et al., 2012, 2014a). However, recent chronologies and observations indicate some islands formed within the past 1000 years (Kench et al., 2014b; Ford and Kench, 2014). Once the islands have formed, reef island shorelines have been shown to be highly dynamic, with shoreline change driven by both local and distal storms (Stoddart 1963,1971; Maragos et al., 1973; Ford and Kench, 2014; Smithers and Hoeke, 2014), tsunami (Kench et al., 2006), as well as seasonal and decadal variations in wave climate (Flood, 1986; Kench et al., 2006; Kench and Brander, 2006). Despite their relatively recent formation, atoll islands have been sites of human habitation since the first few centuries AD (Weisler, 2001; Kayanne et al., 2011). Today, atoll islands provide the bulk of habitable land in the atoll nations of the Maldives, Tuvalu, Kiribati and the Marshall Islands. In addition, several other countries in the Pacific and Indian Oceans have substantial populations residing on atoll islands. Due to their limited land area, low elevation and limited economic and technical capacity atoll islands are considered vulnerable to the impacts of climate change, particularly sea level rise (SLR) (Barnett and Adger, 2003; Woodroffe, 2008). A suite of sea level rise impacts are considered likely to manifest on atoll islands including: increased marine inundation, increased groundwater salinity and chronic coastal erosion (Mimura, 1999; Barnett and Adger, 2003; Woodroffe, 2008). Sea level rise is commonly expected to destabilise island shorelines and lead to widespread loss of land as a result of erosion (Dickinson, 2009). Accounts and projections of islands being ‘washed away’ are a mainstay of political discussions and popular media reports of climate change impacts on atolls (Johnson, 2014; Lewis, 2015). Despite the widespread attention of the plight of atoll islands, there has been a paucity of evidence presented to underpin such assertions. Recently, the popular narrative of reef islands ‘disappearing’ has been considered overly simplistic and unhelpful for strengthening the resilience and adaptive capacity of island communities(Kelman, 2014; McCubbin et al., 2015). Likewise, evidence of the physical resilience of islands has emerged showing a notable absence of widespread chronic erosion (Webb and Kench, 2013; Yates et al., 2013). Relative to shorelines on continental landmasses, few studies have systematically examined changes to reef island shorelines over multi-decadal time scales, coincident with records of rising sea level (McLean and Kench, 2015). Pacific atolls are typically remote, and with the exception of a small number of densely populated urban islands, sparsely populated. As a result, fieldbased monitoring efforts of island erosion are limited (Kench and Harvey, 2003). Recently, remote sensing approaches, used for several decades along continental shorelines, have been applied in the study of reef island shoreline change (Webb and Kench, 2010; Ford, 2013; Yates et al., 2013). Within this recently emerging body of shoreline change studies on atoll islands there is little evidence of widespread reef island erosion. To the contrary, several studies have documented noteworthy shoreline progradation and positional changes of islands since the mid-20th century, resulting in a net increase in island area (Webb and Kench, 2010; Ford, 2013; Yates et al., 2013; Kench et al., 2015). Within densely populated urban atoll settings, such as Majuro in the Marshall Islands and Tarawa in Kiribati, human activities such as land reclamation and causeway construction have been recognised as a significant factor responsible for increasing island size (Ford, 2011; Biribo and Woodroffe, 2013; Duvat, 2013). A wide range of shoreline armouring strategies have been employed to effectively maintain a shoreline position within urban atoll settings. Likewise, land reclamation has led to the expansion of islands on both ocean and lagoon facing shorelines, while causeways have linked previously disconnected islands. In contrast, the sparsely populated “outer islands” have been subjected to few engineering interventions at the shoreline, with shoreline changes reflecting morphodynamic responses to changing boundary conditions. The use of remotely sensed imagery to study reef island change is still in its infancy, with an active phase of research only emerging since 2010 (Webb and Kench, 2010; Ford, 2011; Rankey, 2011; Yates et al., 2013). McLean and Kench (2015) provide a review of recent reef island change studies. To date, studies of shorelines along sparsely populated and uninhabited islands have revealed a prevalence of shoreline accretion compared to erosion, leading to an increase in island size (Webb and Kench, 2010; Ford, 2013; Yates et al., 2013). However, this limited set of observations has been derived from relatively small datasets and it is still unclear if accretion of reef-islands has been the prevalent mode of shoreline change over recent decades. Here we present analysis of shoreline change on 127 islands on six atolls and two mid-ocean platform islands within the Republic of the Marshall Islands.
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کلمات کلیدی:
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