History Museum, it was observed that a change of carbonate textures occurred at 26.4 m – from a fossil reef above
to strongly cemented facies below. The reef has grown
upward from 8,130 to $2,500 years BP at a growth rate
of 4.73 mm/year (26,400/[8,130–2,550]), much higher
than those recorded at Enewetak, Mururoa, and the Cook
Islands, but similar to that of Barbados (Fairbanks et al.,
1989). The reef growth of 26.4 m reflects the infill of
accommodation space for new reef growth made by the
glacial stage erosion of the last interglacial stage 5e, continuing subsidence and rising Holocene sea level.
Reef Island formation: higher sea-level or storm
impacts?
The Royal Society (1904) reported on the island morphology of Funafuti Atoll, declaring that the island ridges
($2 m altitude) were composed of unconsolidated coral
rubble and associated carbonate sand and corals in growth
position on top of reef flat. Such observations have been
used to infer that parts of the islets were formed during
a mid-Holocene highstand and a subsequent fall to
modern sea level (Schofield, 1977; Dickinson, 1999).
However, it is undeniable that Funafuti Atoll is low lying
and vulnerable to tropical storms (Maragos et al., 1973).
Unconsolidated materials on Funafuti islets may therefore
represent amalgamated rubble sheets deposited by
storm-wave washover of the islets and episodic formation
of rubble ridges on the reef platform (Dickison, 1999).
Radiocarbon dating of reef blocks (probable storm
deposits) together with historical records have been used
to compile a history of large tropical storms in Funafuti
Atoll, indicating major storms occurred in 2,000, 1,600,
1,450, 1,050, and 600 conventional radiocarbon years
ago (McLean, 1992, 2004). In October 1972, a huge rubble rampart 18-km long ($10% of the land area of the
atoll) was suddenly formed at Funafuti during cyclone
Bebe, the material derived from deeper water offshore.
Tropical cyclones therefore play potentially important role
in the land formation of atolls such as Funafuti (Maragos
et al., 1973). Radiocarbon dating of cores and surface samples (Schofield, 1977) show that the land area was estimated to form $2,000–1,000 years ago on the reef flat
when the sea level reached modern level (Schofield,
1977; Yamano et al., 2007). Prehistoric human settlement
of Funafuti was also assumed to be much more recent than
other traditionally populated islands like Majuro Atoll, the
Marshall Islands (Yamano et al., 2007). Low altitude atolls
are in future at risk from coastal damage caused by tropical
storms and sea-level rise associated with predicted global
warming by anthropogenic activities (Woodroffe, 2008).
Cyclone Bebe was called as the strongest cyclone these
100 years (Baines et al., 1974). However, the lowest barometric pressure of 954 mb recorded during the storm
(Maragos et al., 1973) is not too low compared to
typhoons occurring in the tropical western-north Pacific.
Therefore, Funafuti is in future at risk of flooding and
damage by projected stronger cyclones.
Funafuti and predicted sea-level rise
Recently, widespread floods in the interior of Fongafale
islet on Funafuti have frequently occurred during spring
high tides. Patel (2006) reported that Funafuti people feel
the floods are getting worse possibly associated with sealevel rise caused by global warming. The potentially huge
impact of sea-level rise on the people of Funafuti should
be evaluated from the best estimate of sea-level change
and its associated uncertainty from the available data.
Hunter (2002), using two sets of data, one from the University of Hawaii Sea Level Center and the other from
the Australian National Tidal Facility, predicted a rise of
0.8 (Æ1.9) mm/year. Rejecting data affected by Southern
Oscillation events, Hunter predicted a rise of 0.4 and
2 mm/year at a 68% probability level. This would represent a rise of 4–20 cm in 100 years and could significantly
increase the frequency and depth of saltwater flooding
and accelerate coastal erosion, threaten the local food
and housing, and could make the country simply
uninhabitable. Many Tuvaluans may become environmental refugees when the island is drowned by the sealevel rise (Mortreux and Barnett, 2009). Even greater
difficulties will arise as a consequence of rising sea levels
and increased intensity and/or frequency of high-energy
cyclonic events. Both will impact an atoll ecosystems
much changed by anthropogenic processes (e.g., construction of an airstrip over original mangroves).
In conclusion, low-lying islands such as Funafuti are, in
future, at risk of coastal damage including erosion, inundation, coral bleaching, changes in fishery resources, and
agricultural productivity (Woodroffe, 2008; Mortreux
and Barnett, 2009). Such risks are likely derived from
changes in the island ecosystems on which Funafuti people depend for their livelihoods and cultures. Short-term
scientific observations show little evidence of sea-level
rise in Funafuti (Patel, 2006), but the Government of
Tuvalu has argued that there is a visual evidence of sealevel rise, through such consequences as increased erosion, flooding, and salinity (Connell, 2003) and that Funafuti Atoll is in future at risk from coastal damage caused by
the sea-level rise associated with predicted global
warming by anthropogenic activities.
Summary
Funafuti Atoll was the site of the Royal Society Coral Reef
Expeditions in 1896–1898. The 339-m core was drilled into
the atoll (at 0-m altitude) on Fongafale islet to carry out the
experiment outlined by Charles Darwin to elucidate the origin and history of atoll formation. From the radiocarbon
dating, the top 26.4 m of the core records the history of
sea-level rise during the last 8,000 years. Sr isotope stratigraphy of the core indicates that during the past 1.5 million
years, more than 150 m of reef-lagoonal carbonate was
deposited through interaction between sea-level change
and plate subsidence. Dolomite in the lower core (196–
340 m) was formed through diagenesis between one and
two million years ago. Radiocarbon dates of the core-top
448
FUNAFUTI ATOLL
to strongly cemented facies below. The reef has grown
upward from 8,130 to $2,500 years BP at a growth rate
of 4.73 mm/year (26,400/[8,130–2,550]), much higher
than those recorded at Enewetak, Mururoa, and the Cook
Islands, but similar to that of Barbados (Fairbanks et al.,
1989). The reef growth of 26.4 m reflects the infill of
accommodation space for new reef growth made by the
glacial stage erosion of the last interglacial stage 5e, continuing subsidence and rising Holocene sea level.
Reef Island formation: higher sea-level or storm
impacts?
The Royal Society (1904) reported on the island morphology of Funafuti Atoll, declaring that the island ridges
($2 m altitude) were composed of unconsolidated coral
rubble and associated carbonate sand and corals in growth
position on top of reef flat. Such observations have been
used to infer that parts of the islets were formed during
a mid-Holocene highstand and a subsequent fall to
modern sea level (Schofield, 1977; Dickinson, 1999).
However, it is undeniable that Funafuti Atoll is low lying
and vulnerable to tropical storms (Maragos et al., 1973).
Unconsolidated materials on Funafuti islets may therefore
represent amalgamated rubble sheets deposited by
storm-wave washover of the islets and episodic formation
of rubble ridges on the reef platform (Dickison, 1999).
Radiocarbon dating of reef blocks (probable storm
deposits) together with historical records have been used
to compile a history of large tropical storms in Funafuti
Atoll, indicating major storms occurred in 2,000, 1,600,
1,450, 1,050, and 600 conventional radiocarbon years
ago (McLean, 1992, 2004). In October 1972, a huge rubble rampart 18-km long ($10% of the land area of the
atoll) was suddenly formed at Funafuti during cyclone
Bebe, the material derived from deeper water offshore.
Tropical cyclones therefore play potentially important role
in the land formation of atolls such as Funafuti (Maragos
et al., 1973). Radiocarbon dating of cores and surface samples (Schofield, 1977) show that the land area was estimated to form $2,000–1,000 years ago on the reef flat
when the sea level reached modern level (Schofield,
1977; Yamano et al., 2007). Prehistoric human settlement
of Funafuti was also assumed to be much more recent than
other traditionally populated islands like Majuro Atoll, the
Marshall Islands (Yamano et al., 2007). Low altitude atolls
are in future at risk from coastal damage caused by tropical
storms and sea-level rise associated with predicted global
warming by anthropogenic activities (Woodroffe, 2008).
Cyclone Bebe was called as the strongest cyclone these
100 years (Baines et al., 1974). However, the lowest barometric pressure of 954 mb recorded during the storm
(Maragos et al., 1973) is not too low compared to
typhoons occurring in the tropical western-north Pacific.
Therefore, Funafuti is in future at risk of flooding and
damage by projected stronger cyclones.
Funafuti and predicted sea-level rise
Recently, widespread floods in the interior of Fongafale
islet on Funafuti have frequently occurred during spring
high tides. Patel (2006) reported that Funafuti people feel
the floods are getting worse possibly associated with sealevel rise caused by global warming. The potentially huge
impact of sea-level rise on the people of Funafuti should
be evaluated from the best estimate of sea-level change
and its associated uncertainty from the available data.
Hunter (2002), using two sets of data, one from the University of Hawaii Sea Level Center and the other from
the Australian National Tidal Facility, predicted a rise of
0.8 (Æ1.9) mm/year. Rejecting data affected by Southern
Oscillation events, Hunter predicted a rise of 0.4 and
2 mm/year at a 68% probability level. This would represent a rise of 4–20 cm in 100 years and could significantly
increase the frequency and depth of saltwater flooding
and accelerate coastal erosion, threaten the local food
and housing, and could make the country simply
uninhabitable. Many Tuvaluans may become environmental refugees when the island is drowned by the sealevel rise (Mortreux and Barnett, 2009). Even greater
difficulties will arise as a consequence of rising sea levels
and increased intensity and/or frequency of high-energy
cyclonic events. Both will impact an atoll ecosystems
much changed by anthropogenic processes (e.g., construction of an airstrip over original mangroves).
In conclusion, low-lying islands such as Funafuti are, in
future, at risk of coastal damage including erosion, inundation, coral bleaching, changes in fishery resources, and
agricultural productivity (Woodroffe, 2008; Mortreux
and Barnett, 2009). Such risks are likely derived from
changes in the island ecosystems on which Funafuti people depend for their livelihoods and cultures. Short-term
scientific observations show little evidence of sea-level
rise in Funafuti (Patel, 2006), but the Government of
Tuvalu has argued that there is a visual evidence of sealevel rise, through such consequences as increased erosion, flooding, and salinity (Connell, 2003) and that Funafuti Atoll is in future at risk from coastal damage caused by
the sea-level rise associated with predicted global
warming by anthropogenic activities.
Summary
Funafuti Atoll was the site of the Royal Society Coral Reef
Expeditions in 1896–1898. The 339-m core was drilled into
the atoll (at 0-m altitude) on Fongafale islet to carry out the
experiment outlined by Charles Darwin to elucidate the origin and history of atoll formation. From the radiocarbon
dating, the top 26.4 m of the core records the history of
sea-level rise during the last 8,000 years. Sr isotope stratigraphy of the core indicates that during the past 1.5 million
years, more than 150 m of reef-lagoonal carbonate was
deposited through interaction between sea-level change
and plate subsidence. Dolomite in the lower core (196–
340 m) was formed through diagenesis between one and
two million years ago. Radiocarbon dates of the core-top
448
FUNAFUTI ATOLL