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Article: Evaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: A modelling approach

TitleEvaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: A modelling approach
Authors
KeywordsAtoll Islands
Freshwater Lens
Salinisation
Sea-Level Rise
Tropical Cyclones
Issue Date2012
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/gloplacha
Citation
Global And Planetary Change, 2012, v. 88-89, p. 76-84 How to Cite?
AbstractDispersed human populations inhabiting remote atolls across the tropical Pacific Ocean are reliant on the viability of thin freshwater lenses (FWLs) contained within the island coralline sediments for their survival. Yet FWLs are uniquely fragile and easily damaged by saline intrusion. Eustatic sea-level rise (SLR) and sea flooding generated by intense tropical cyclones therefore pose special perils for continued existence on atolls. In this work, mathematical modelling is used to examine the effects on an atoll freshwater lens of various projected long-term SLR scenarios (10, 20, and 40. cm). A cyclone-driven wave washover event is then simulated in order to observe the responses and recovery of the FWL, subsequent to the SLR scenarios imposed. A key attribute of our model design is the inclusion of a topographic depression containing a low-lying fresh swamp in the atoll islet interior (which is often ignored), where seawater accumulates during inundation. Results indicate that a 40. cm SLR produces a major impact: the FWL decreases in thickness by approximately 50%, develops a brackish centre and contracts to a shrunken 'doughnut' morphology. Following cyclone inundation, observed salinity profiles are illuminating. Steep salinity gradients show how a strong saline plume forms at shallow depths, but also reveal the existence of an undisturbed fresh horizon beneath the salt plume under both present conditions and the modest 10. cm SLR scenario. Within the preserved fresh horizon, salt concentrations are maintained below 1.5. g/L (i.e. within usable limits) for at least a year. In contrast, the diminished freshwater lenses that exist after 20 and 40. cm SLR then exhibit far less resilience to saline damage over comparable post-cyclone timeframes. The findings point towards Pacific atolls becoming increasingly uninhabitable long before their complete submergence by sea-level rise, owing to irrecoverable groundwater salinisation seriously reducing the availability of freshwater. © 2012 Elsevier B.V.
Persistent Identifierhttp://hdl.handle.net/10722/180442
ISSN
2015 Impact Factor: 3.548
2015 SCImago Journal Rankings: 1.885
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorTerry, JPen_US
dc.contributor.authorChui, TFMen_US
dc.date.accessioned2013-01-28T01:37:58Z-
dc.date.available2013-01-28T01:37:58Z-
dc.date.issued2012en_US
dc.identifier.citationGlobal And Planetary Change, 2012, v. 88-89, p. 76-84en_US
dc.identifier.issn0921-8181en_US
dc.identifier.urihttp://hdl.handle.net/10722/180442-
dc.description.abstractDispersed human populations inhabiting remote atolls across the tropical Pacific Ocean are reliant on the viability of thin freshwater lenses (FWLs) contained within the island coralline sediments for their survival. Yet FWLs are uniquely fragile and easily damaged by saline intrusion. Eustatic sea-level rise (SLR) and sea flooding generated by intense tropical cyclones therefore pose special perils for continued existence on atolls. In this work, mathematical modelling is used to examine the effects on an atoll freshwater lens of various projected long-term SLR scenarios (10, 20, and 40. cm). A cyclone-driven wave washover event is then simulated in order to observe the responses and recovery of the FWL, subsequent to the SLR scenarios imposed. A key attribute of our model design is the inclusion of a topographic depression containing a low-lying fresh swamp in the atoll islet interior (which is often ignored), where seawater accumulates during inundation. Results indicate that a 40. cm SLR produces a major impact: the FWL decreases in thickness by approximately 50%, develops a brackish centre and contracts to a shrunken 'doughnut' morphology. Following cyclone inundation, observed salinity profiles are illuminating. Steep salinity gradients show how a strong saline plume forms at shallow depths, but also reveal the existence of an undisturbed fresh horizon beneath the salt plume under both present conditions and the modest 10. cm SLR scenario. Within the preserved fresh horizon, salt concentrations are maintained below 1.5. g/L (i.e. within usable limits) for at least a year. In contrast, the diminished freshwater lenses that exist after 20 and 40. cm SLR then exhibit far less resilience to saline damage over comparable post-cyclone timeframes. The findings point towards Pacific atolls becoming increasingly uninhabitable long before their complete submergence by sea-level rise, owing to irrecoverable groundwater salinisation seriously reducing the availability of freshwater. © 2012 Elsevier B.V.en_US
dc.languageengen_US
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/gloplachaen_US
dc.relation.ispartofGlobal and Planetary Changeen_US
dc.subjectAtoll Islandsen_US
dc.subjectFreshwater Lensen_US
dc.subjectSalinisationen_US
dc.subjectSea-Level Riseen_US
dc.subjectTropical Cyclonesen_US
dc.titleEvaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: A modelling approachen_US
dc.typeArticleen_US
dc.identifier.emailChui, TFM: maychui@hku.hken_US
dc.identifier.authorityChui, TFM=rp01696en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1016/j.gloplacha.2012.03.008en_US
dc.identifier.scopuseid_2-s2.0-84859928718en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-84859928718&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume88-89en_US
dc.identifier.spage76en_US
dc.identifier.epage84en_US
dc.identifier.isiWOS:000304848800008-
dc.publisher.placeNetherlandsen_US
dc.identifier.scopusauthoridTerry, JP=7103365580en_US
dc.identifier.scopusauthoridChui, TFM=24723787700en_US

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