Papers on sea level in small island countries

This is a list of papers on sea level changes in small island countries such as Maldives. Emphasis is on the sea level observations, not its consequences. There are plenty of papers dealing with vulnerability of the island countries but so far only couple of such papers are included here. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (November 17, 2011): Merrifield (2011) and Becker et al. (2012) added.

Sea level variations at tropical Pacific islands since 1950 – Becker et al. (2012) “The western tropical Pacific is usually considered as one of the most vulnerable regions of the world under present-day and future global warming. It is often reported that some islands of the region already suffer significant sea level rise. To clarify the latter concern, in the present study we estimate sea level rise and variability since 1950 in the western tropical Pacific region (20°S–15°N; 120°E–135°W). We estimate the total rate of sea level change at selected individual islands, as a result of climate variability and change, plus vertical ground motion where available. For that purpose, we reconstruct a global sea level field from 1950 to 2009, combining long (over 1950–2009) good quality tide gauge records with 50-year-long (1958–2007) gridded sea surface heights from the Ocean General Circulation Model DRAKKAR. The results confirm that El Niño-Southern Oscillation (ENSO) events have a strong modulating effect on the interannual sea level variability of the western tropical Pacific, with lower/higher-than-average sea level during El Niño/La Niña events, of the order of ± 20–30 cm. Besides this sub-decadal ENSO signature, sea level of the studied region also shows low-frequency (multi decadal) variability which superimposes to, thus in some areas amplifies current global mean sea level rise due to ocean warming and land ice loss. We use GPS precise positioning records whenever possible to estimate the vertical ground motion component that is locally superimposed to the climate-related sea level components. Superposition of global mean sea level rise, low-frequency regional variability and vertical ground motion shows that some islands of the region suffered significant ‘total’ sea level rise (i.e., that felt by the population) during the past 60 years. This is especially the case for the Funafuti Island (Tuvalu) where the “total” rate of rise is found to be about 3 times larger than the global mean sea level rise over 1950–2009.” M. Becker, B. Meyssignac, C. Letetrel, W. Llovel, A. Cazenave, T. Delcroix, Global and Planetary Change, Volumes 80-81, January 2012, Pages 85-98, doi:10.1016/j.gloplacha.2011.09.004.

A Shift in Western Tropical Pacific Sea Level Trends during the 1990s – Merrifield (2011) “Pacific Ocean sea surface height trends from satellite altimeter observations for 1993–2009 are examined in the context of longer tide gauge records and wind stress patterns. The dominant regional trends are high rates in the western tropical Pacific and minimal to negative rates in the eastern Pacific, particularly off North America. Interannual sea level variations associated with El Niño–Southern Oscillation events do not account for these trends. In the western tropical Pacific, tide gauge records indicate that the recent high rates represent a significant trend increase in the early 1990s relative to the preceding 40 years. This sea level trend shift in the western Pacific corresponds to an intensification of the easterly trade winds across the tropical Pacific. The wind change appears to be distinct from climate variations centered in the North Pacific, such as the Pacific decadal oscillation. In the eastern Pacific, tide gauge records exhibit higher-amplitude decadal fluctuations than in the western tropical Pacific, and the recent negative sea level trends are indistinguishable from these fluctuations. The shifts in trade wind strength and western Pacific sea level rate resemble changes in dominant global modes of outgoing longwave radiation and sea surface temperature. It is speculated that the western Pacific sea level response indicates a general strengthening of the atmospheric circulation over the tropical Pacific since the early 1990s that has developed in concert with recent warming trends.” Merrifield, Mark A., 2011: A Shift in Western Tropical Pacific Sea Level Trends during the 1990s. J. Climate, 24, 4126–4138, doi: 10.1175/2011JCLI3932.1. [Full text]

Patterns of Indian Ocean sea-level change in a warming climate – Han et al. (2010) “Global sea level has risen during the past decades as a result of thermal expansion of the warming ocean and freshwater addition from melting continental ice. However, sea-level rise is not globally uniform. Regional sea levels can be affected by changes in atmospheric or oceanic circulation. As long-term observational records are scarce, regional changes in sea level in the Indian Ocean are poorly constrained. Yet estimates of future sea-level changes are essential for effective risk assessment. Here we combine in situ and satellite observations of Indian Ocean sea level with climate-model simulations, to identify a distinct spatial pattern of sea-level rise since the 1960s. We find that sea level has decreased substantially in the south tropical Indian Ocean whereas it has increased elsewhere. This pattern is driven by changing surface winds associated with a combined invigoration of the Indian Ocean Hadley and Walker cells, patterns of atmospheric overturning circulation in the north–south and east–west direction, respectively, which is partly attributable to rising levels of atmospheric greenhouse gases. We conclude that—if ongoing anthropogenic warming dominates natural variability—the pattern we detected is likely to persist and to increase the environmental stress on some coasts and islands in the Indian Ocean.” Weiqing Han, Gerald A. Meehl, Balaji Rajagopalan, John T. Fasullo, Aixue Hu, Jialin Lin, William G. Large, Jih-wang Wang, Xiao-Wei Quan, Laurie L. Trenary, Alan Wallcraft, Toshiaki Shinoda & Stephen Yeager, Nature Geoscience 3, 546 – 550 (2010), doi:10.1038/ngeo901. [Full text]

Wind Effects on Past and Future Regional Sea Level Trends in the Southern Indo-Pacific – Timmermann et al. (2010) “Global sea level rise due to the thermal expansion of the warming oceans and freshwater input from melting glaciers and ice sheets is threatening to inundate low-lying islands and coastlines worldwide. At present the global mean sea level rises at 3.1 ± 0.7 mm yr⁻¹ with an accelerating tendency. However, the magnitude of recent decadal sea level trends varies greatly spatially, attaining values of up to 10 mm yr⁻¹ in some areas of the western tropical Pacific. Identifying the causes of recent regional sea level trends and understanding the patterns of future projected sea level change is of crucial importance. Using a wind-forced simplified dynamical ocean model, the study shows that the regional features of recent decadal and multidecadal sea level trends in the tropical Indo-Pacific can be attributed to changes in the prevailing wind regimes. Furthermore, it is demonstrated that within an ensemble of 10 state-of-the-art coupled general circulation models, forced by increasing atmospheric CO₂ concentrations over the next century, wind-induced redistributions of upper-ocean water play a key role in establishing the spatial characteristics of projected regional sea level rise. Wind-related changes in near-surface mass and heat convergence near the Solomon Islands, Tuvalu, Kiribati, the Cook Islands, and French Polynesia oppose—but cannot cancel—the regional signal of global mean sea level rise.” Timmermann, Axel, Shayne McGregor, Fei-Fei Jin, 2010, J. Climate, 23, 4429–4437, doi: 10.1175/2010JCLI3519.1.

The dynamic response of reef islands to sea-level rise: Evidence from multi-decadal analysis of island change in the Central Pacific – Webb & Kench (2010) “Low-lying atoll islands are widely perceived to erode in response to measured and future sea-level rise. Using historical aerial photography and satellite images this study presents the first quantitative analysis of physical changes in 27 atoll islands in the central Pacific over a 19 to 61 yr period. This period of analysis corresponds with instrumental records that show a rate of sea-level rise of 2.0 mm yr⁻¹ in the Pacific. Results show that 86% of islands remained stable (43%) or increased in area (43%) over the timeframe of analysis. Largest decadal rates of increase in island area range between 0.1 to 5.6 ha. Only 14% of study islands exhibited a net reduction in island area. Despite small net changes in area, islands exhibited larger gross changes. This was expressed as changes in the planform configuration and position of islands on reef platforms. Modes of island change included: ocean shoreline displacement toward the lagoon; lagoon shoreline progradation; and, extension of the ends of elongate islands. Collectively these adjustments represent net lagoonward migration of islands in 65% of cases. Results contradict existing paradigms of island response and have significant implications for the consideration of island stability under ongoing sea-level rise in the central Pacific. First, islands are geomorphologically persistent features on atoll reef platforms and can increase in island area despite sea-level change. Second, islands are dynamic landforms that undergo a range of physical adjustments in responses to changing boundary conditions, of which sea level is just one factor. Third, erosion of island shorelines must be reconsidered in the context of physical adjustments of the entire island shoreline as erosion may be balanced by progradation on other sectors of shorelines. Results indicate that the style and magnitude of geomorphic change will vary between islands. Therefore, island nations must place a high priority on resolving the precise styles and rates of change that will occur over the next century and reconsider the implications for adaption.” Arthur P. Webb and Paul S. Kench, Global and Planetary Change, Volume 72, Issue 3, June 2010, Pages 234-246, doi:10.1016/j.gloplacha.2010.05.003. [Full text]

Submerged reef terraces of the Maldives (Indian Ocean) – Fürstenau et al. (2009) “There is limited knowledge about the record of sea-level rise from the last glacial maximum (LGM) until the onset of Holocene reef growth in the Maldives archipelago. Multibeam data show that atoll slopes between 130 and 55 mbsl (meters below sea level) are characterized by a step-like morphology. In parts, these terraces show a raised rim and a crenate geometry. Atoll margin features can be interpreted as successive reef-growth and -drowning stages, which are attributable to changes in the rate of sea-level rise. These changes can tentatively be correlated to known records of global sea-level change since the LGM. In addition to terraces between 97 and 55 mbsl, which can be associated with the initiation of meltwater pulses MWP-1A and -1B, several reef-drowning stages between 94 and 68 mbsl are proposed. As the Maldives can be considered a tectonically stable, far-field site, the submerged reef terraces inferred from the first multibeam dataset for this region likely represent a valuable archive for global deglacial sea-level history in the Indian Ocean.” Jörn Fürstenau, Sebastian Lindhorst, Christian Betzler and Christian Hübscher, Geo-Marine Letters, Volume 30, Number 5, 511-515, DOI: 10.1007/s00367-009-0174-2.

Late Quaternary reef growth and sea level in the Maldives (Indian Ocean) – Gischler et al. (2008) “Based on rotary drilling and radiometric and U-series dating, we present the first comprehensive data on Holocene reef anatomy and sea-level rise as well as nature and age of underlying Pleistocene limestone in the Maldives. Holocene reefs in Rasdhoo Atoll, central Maldives, are composed of four facies including (1) robust-branching coral facies, (2) coralline algal facies, (3) domal coral facies, and (4) detrital sand and rubble facies. Branching coral and coralline algal facies predominate the marginal reefs and domal corals and detrital facies preferentially occur in a lagoon reef. In addition, microbialite crusts are found in lower core sections of marginal reefs. Microbialites formed during the early Holocene in reef cavities. Holocene reef thickness ranges from 14.5 m to > 22 m. Reef growth started as early as 8.5 kyr BP. Marginal reefs accreted in the keep-up mode with rates of > 15 m/kyr. Rate of sea-level rise significantly slowed down from 7–6 kyr BP and subsequently gradually rose with rates < 1 m/kyr. The lagoon reef accreted in the catch-up mode with rates of around 4 m/kyr. Even though no indications of a higher than present sea level were found during this study, it is not entirely clear from the data whether the sea gradually rose to or exceeded present level in the late Holocene. Submarine cementation in Holocene reefs studied is rather weak, presumably as a consequence of high accretion-rates, i.e., short time available for consolidation. Pleistocene coral grainstone was encountered in one core at 14.5 m below present level and three U-series dates indicate deposition during marine isotope stage 5e ca. 135 kyr BP.” Eberhard Gischler, J. Harold Hudson and Andrzej Pisera, Marine Geology, Volume 250, Issues 1-2, 21 April 2008, Pages 104-113, doi:10.1016/j.margeo.2008.01.004.

Reef-island topography and the vulnerability of atolls to sea-level rise – Woodroffe (2008) “Low-lying reef islands on the rim of atolls are perceived as particularly vulnerable to the impacts of sea-level rise. Three effects are inferred: erosion of the shoreline, inundation of low-lying areas, and saline intrusion into the freshwater lens. Regional reconstruction of sea-level trends, supplementing the short observational instrumental record, indicates that monthly mean sea level is rising in the eastern Indian and western Pacific Oceans. This paper reviews the morphology and substrate characteristics of reef islands on Indo-Pacific atolls, and summarises their topography. On most atolls across this region, there is an oceanward ridge built by waves to a height of around 3 m above MSL; in a few cases these are topped by wind-blown dunes. The prominence of these ridges, together with radiocarbon dating and multi-temporal studies of shoreline position, indicate net accretion rather than long-term erosion on most of these oceanward shores. Less prominent lagoonward ridges occur, but their morphology and continuity are atoll-specific, being a function of the processes operating in each lagoon. Low-lying central areas are a feature of many islands, often locally excavated for production of taro. These lower-lying areas are already subject to inundation, which seems certain to increase as the sea rises. Tropical storms play an important role in the geomorphology of reef islands in those regions where they are experienced. Topographical differences, as well as features such as emergence of the reef flat and the stability of the substrate, mean that islands differ in terms of their susceptibility to sea-level rise. Further assessment of variations in shoreline vulnerability based on topography and substrate could form the basis for enhancing the natural resilience of these islands.” Colin D. Woodroffe, Global and Planetary Change, Volume 62, Issues 1-2, May 2008, Pages 77-96, doi:10.1016/j.gloplacha.2007.11.001. [Full text]

Sea-level rise at tropical Pacific and Indian Ocean islands – Church et al. (2006) “Historical and projected sea-levels for islands in the tropical Pacific and Indian oceans are a subject of considerable interest and some controversy. The large variability (e.g. El Niño) signals and the shortness of many of the individual tide-gauge records contribute to uncertainty of historical rates of sea-level rise. Here, we determine rates of sea-level rise from tide gauges in the region. We also examine sea-level data from the TOPEX/Poseidon satellite altimeter and from a reconstruction of sea level in order to put the sparse (in space and time) tide-gauge data into context. For 1993 to 2001, all the data show large rates of sea-level rise over the western Pacific and eastern Indian Ocean (approaching 30 mm yr⁻¹) and sea-level falls in the eastern Pacific and western Indian Ocean (approaching − 10 mm yr⁻¹). Over the region 40°S to 40°N, 30°E to 120°W, the average rise is about 4 mm yr⁻¹. For 1950 to 2001, the average sea-level rise (relative to land) from the six longest tide-gauge records is 1.4 mm yr⁻¹. After correcting for glacial isostatic adjustment and atmospheric pressure effects, this rate is 2.0 mm yr⁻¹, close to estimates of the global average and regional average rate of rise. The long tide-gauge records in the equatorial Pacific indicate that the variance of monthly averaged sea-level after 1970 is about twice that before 1970. We find no evidence for the fall in sea level at the Maldives as postulated by Mörner et al. (2004). Our best estimate of relative sea-level rise at Funafuti, Tuvalu is 2 ± 1 mm yr⁻¹ over the period 1950 to 2001. The analysis clearly indicates that sea-level in this region is rising. We expect that the continued and increasing rate of sea-level rise and any resulting increase in the frequency or intensity of extreme sea-level events will cause serious problems for the inhabitants of some of these islands during the 21st century.” John A. Church, Neil J. White, and John R. Hunter, Global and Planetary Change, Volume 53, Issue 3, September 2006, Pages 155-168, doi:10.1016/j.gloplacha.2006.04.001. [Full text]

Have there been large recent sea level changes in the Maldive Islands? – Woodworth (2005) “The Maldive Islands are often used as case studies within research into the impacts of potential future sea level change. Therefore, if such studies are to be realistic, it is important that the past and future variations of sea level in the islands are understood as well as possible. That objective led a fieldwork team to the Maldives, and resulted in a conclusion that sea level in the islands fell by approximately 30 cm during the past few decades. In the present paper, the suggestion of such a fall has been examined from meteorological and oceanographic perspectives and found to be implausible. A number of met-ocean data sets and regional climate indices have been examined, at least one of which would have been expected to reflect a large sea level fall, without any supporting evidence being found. In particular, a suggestion that an increase in evaporation could have caused the fall has been demonstrated to be incorrect. Without any real evidence for a hitherto-unrecognised process which could lead to a sea level change as significant as that proposed by the fieldwork team, one concludes that a rise in sea level of approximately half a metre during the 21st century, as suggested by the Intergovernmental Panel on Climate Change Third Assessment Report, remains the most reliable scenario to employ in future studies of the islands.” Philip L. Woodworth, Global and Planetary Change, Volume 49, Issues 1-2, November 2005, Pages 1-18, doi:10.1016/j.gloplacha.2005.04.001.

Late Quaternary sea-level highstands in the central and eastern Indian Ocean: A review – Woodroffe (2005) “The relative sea-level history of several atolls in the central and eastern Indian Ocean, including the Cocos (Keeling) Islands, Chagos Archipelago, and the Maldives–Laccadive Archipelagoes, has been debated for over a century but takes on a particular significance in the face of anticipated climate change. For each of these central and eastern Indian Ocean atolls Pleistocene limestone is encountered at depths of 6–20 m below sea level. On the Cocos (Keeling) Islands this has been dated to Last Interglacial age. Conglomerate platform underlies the reef islands on Cocos within which a sequence of fossil microatolls of massive and branching Porites records a gradual fall of sea level relative to the atoll. In the Maldives, the significance of outcrops of ‘reef rock’ has been vigorously debated without resolving sea-level history. Although in situ Heliopora occurs on the reef flat of Addu Atoll, dated at around 2700 radiocarbon yrs BP, other evidence for higher sea level remains poorly constrained. Conglomerates of a similar age have been described from the Chagos Archipelago, but it has not been unequivocally demonstrated that they formed under conditions of relatively higher sea level. In contrast to reefs further west in the Indian Ocean, each of these atolls has living microatolls of massive Porites that have been constrained in their upward growth by sea level. Interpretation of the upper surface of two such specimens from the Cocos (Keeling) Islands indicates broad fluctuations in the sea surface over the past century; similar microatolls are described from the Maldives implying little change in sea level over recent years. Regardless of minor past fluctuations, most reef islands in the Maldives are particularly low-lying and appear vulnerable to inundation, and extracting a more detailed sea-level history remains an important challenge.” Colin D. Woodroffe, Global and Planetary Change, Volume 49, Issues 1-2, November 2005, Pages 121-138, doi:10.1016/j.gloplacha.2005.06.002.

Holocene sea-level changes in the Indo-Pacific – Woodroffe & Horton (2005) “Holocene sea-level reconstructions exist from many locations in the Indo-Pacific region. Despite being a large geographical region, the nature of Holocene sea-level change is broadly similar in all locations. Differences do exist, however, in the timing and magnitude of the Mid-Holocene High Stand (MHHS) and the nature of late Holocene sea level fall across the region. When the Indo-Pacific is subdivided into smaller regions, these discrepancies do not disappear, and in some cases the discrepancies are large within a single coastline. It is clear from this analysis that the fundamental criteria to produce accurate local relative sea-level curves are hardly ever met. There are serious problems associated with the correct interpretation of sea-level indicators and their relationship to mean sea level, and with the quality of age determinations. A consistent methodology throughout the Indo-Pacific for the analysis of sea level data is lacking. Future sea-level analysis from far field locations must involve the application of a consistent methodology in order to allow meaningful comparison between studies. This should help to resolve the ongoing debate about the magnitude and timing of the Mid-Holocene High Stand, and the nature of late Holocene sea-level fall across the region.” S. A. Woodroffe and B. P. Horton, Journal of Asian Earth Sciences, Volume 25, Issue 1, April 2005, Pages 29-43, doi:10.1016/j.jseaes.2004.01.009.

New perspectives for the future of the Maldives – Mörner et al. (2004) “Novel prospects for the Maldives do not include a condemnation to future flooding. The people of the Maldives have, in the past, survived a higher sea level of about 50–60 cm. The present trend lack signs of a sea level rise. On the contrary, there is firm morphological evidence of a significant sea level fall in the last 30 years. This sea level fall is likely to be the effect of increased evaporation and an intensification of the NE-monsoon over the central Indian Ocean.” Nils-Axel Mörner, Michael Tooley, and Göran Possnert, Global and Planetary Change, Volume 40, Issues 1-2, January 2004, Pages 177-182, doi:10.1016/S0921-8181(03)00108-5. [Full text]

Coral microatolls and 20th century sea level in the eastern Indian Ocean – Smithers & Woodroffe (2001) “Coral microatolls are discoid intertidal corals that are limited in their upward growth by subaerial exposure during low tides. Microatoll upper surface morphology preserves a filtered record of changes in the height of living coral (HLC), the upper limit to which corals can grow, and by proxy a historical record of former constraining water levels. Chronologies for these variations in HLC were established in this study using annual skeletal density bands revealed when skeletal slices were X-radiographed, supplemented by annual fluorescent bands visible when samples were illuminated with ultra-violet light. The upper surface morphologies of two large microatolls from separate reef-flat sites on the Cocos (Keeling) Islands are well correlated and indicate that the upper limit to coral growth has fluctuated by more than 5 cm since the early 1900s. The upper surfaces of these microatolls also indicate that there has been little net rise in sea level in the eastern Indian Ocean during the 20th century. Microatoll surface morphology suggests that average rates of sea-level rise in the eastern Indian Ocean over this period were less than 0.35 mm yr−1, a rate considerably lower than the rate of average global sea-level change determined from aggregated tide-gauge data. The broad surface undulations do not appear to correlate directly with either El Niño-Southern Oscillation events or occurrence of the Indian Ocean dipole mode of ocean-atmosphere circulation. Microatolls provide a simple and effective method for extrapolating broad variations in sea level beyond the tide-gauge record in remote mid-oceanic settings.” Scott G. Smithers and Colin D. Woodroffe, Earth and Planetary Science Letters, Volume 191, Issues 1-2, 30 August 2001, Pages 173-184, doi:10.1016/S0012-821X(01)00417-4.

Illuminating Sea-Level Fall around AD 1220–1510 (730-440 cal yr BP) in the Pacific Islands: Implications for Environmental Change and Cultural Transformation – Nunn (2000) “This paper focuses on the climatic transition between the Little Climatic Optimum (approximately AD 750–1300 or 1200-650 cal yr BP) and the Little Ice Age (approximately AD 1300–1800 or 650-150 cal yr BP) in the Pacific Islands. This transition was marked by rapid temperature and sea-level fall, and perhaps by sharply-increased precipitation associated with an increase in El Nino frequency. Examples from throughout the Pacific Islands demonstrate the possible and/or likely effects of sea-level fall at this time on inland horticulture through water-table fall; on coral reefs and lagoons through the emergence of reef surfaces and the consequent reduction of nearshore water circulation; on the emergence of reef islets and the conversion of tidal inlets to brackish lakes. The effects of such changes on human lifestyles are explored.” Patrick D. Nunn, New Zealand Geographer, Volume 56, Issue 1, pages 46–54, April 2000, DOI: 10.1111/j.1745-7939.2000.tb00559.x.

Holocene Sea-Level Record on Funafuti and Potential Impact of Global Warming on Central Pacific Atolls – Dickinson (1999) “Geomorphic features inherited from the mid-Holocene glacio-hydro-isostatic sea-level highstand that affected the central Pacific region influence the susceptibility of atoll islets to potentially enhanced wave erosion associated with rise in sea level from global warming. Shoreline morphology on multiple islets of Funafuti atoll in central Tuvalu reflects a relative mid-Holocene sea-level highstand 2.2–2.4 m above modern sea level. Typical islets are composed of unconsolidated post-mid-Holocene sediment resting disconformably on cemented coral rubble formed beneath now-emergent mid-Holocene reef flats. Exposed remnants of the lithified islet foundations serve as resistant buttresses protecting the flanks of atoll islets from wave attack. Islets lacking cemented mid-Holocene deposits as part of their internal structure are migratory sand cays with unstable shorelines. Any future sea-level rise ≥0.75 m, bringing high tide above the elevation of mid-Holocene low tide, might trigger enhanced wave erosion of stable atoll islets by overtopping the indurated mid-Holocene reef platforms. As analogous threshold relations are inferred for other central Pacific atolls, the risk of future inundation of island nations cannot be evaluated solely in terms of expected sea-level rise with respect to gross islet elevations.” William R. Dickinson, Quaternary Research, Volume 51, Issue 2, March 1999, Pages 124-132, doi:10.1006/qres.1998.2029.

Submarine topography of Maldivian atolls suggests a sea level of 130 metres below present at the last glacial maximum – Anderson (1998) “This present study reports the results of an echo sounding survey around four Maldivian atolls which suggests that local sea level was reduced to about 130 m below current levels during the last glacial maximum. At that time present-day atolls would have been exposed as large, steeply clifted islands.” R. C. Anderson, Coral Reefs, Volume 17, Number 4, 339-341, DOI: 10.1007/s003380050135.

Morphology and evolution of reef islands in the Maldives – Woodroffe (1992). From Mörner et al. (2004): “More recently, Woodroffe (1992) presented the first sea level curve for the Maldives. He claimed that the islands were predominantly formed by catch-up coral reef growth.” Woodroffe, C.D., 1992, Proc. 7th Int. Coral Reef Symp., Gaum 2, 1217– 1226.

Microatolls and recent sea level change on coral atolls – Woodroffe & McLean (1990) “MICROATOLLS are colonies of corals, commonly Porties, which are dead on top but living around their perimeter, and are found in intertidal environments on coral atolls. They can grow to several metres in diameter. Their upward growth is constrained by sea level through prolonged exposure at the lowest spring tides, and their dead upper surfaces have been limited by past sea levels. They act as natural recorders of sea level, which is of particular significance for coral atolls thought to be susceptible to inundation and erosion if sea level rises in response to global warming. X-radiographs of vertical slices through microatolls from the Maldives and Cocos (Keeling) Islands (Indian Ocean) and Kiribati (Pacific Ocean) record sea-level fluctuations over the past few decades. There is a high degree of reproducibility between adjacent corals, although on Cocos we noted geographical variation in the pattern of change around the atoll. The majority of microatolls sampled on these atolls record a slight fall in sea level over the past ten years.” Colin Woodroffe & Roger McLean, Nature 344, 531 – 534 (05 April 1990); doi:10.1038/344531a0.

Sea level rise: Some implications for Tuvalu – Lewis (1989) “Much current evidence suggests that global temperatures are slowly increasing. It is believed that this increase will be associated with a sea level rise. Tuvalu, approximately 1000 km north of Fiji in the South Pacific Ocean, is one of six countries, all of them island states, that could face total destruction when sea levels rise. If sea level rises occur anywhere near the extreme projections that have been made, we can write these nations off the map. (Pernetta, 1988). This paper examines possible implications to the people of Tuvalu.” James Lewis, The Environmentalist, Volume 9, Number 4, 269-275, DOI: 10.1007/BF02241827.