The chronology of Funafuti Atoll: revisiting an old friend

Abstract

The drill core of Funafuti Atoll, collected by The Royal Society Coral Reef Expedition in 1896-1898, has been dated using high-precision 14 C and Sr isotope measurements determined by mass spectrometry. The core top is a Holocene reef deposit, reflecting 26.4 m of reef growth since 8 ka, and is underlaid by Pleistocene reef-lagoonal deposits separated by a series of inferred hiatuses at 26.4 m, ca. 30 m, ca. 65 m and ca. 80 m (ca. 0.1 Ma, ca. 0.2 Ma, ca. 0.3 Ma and ca. 0.6 Ma, respectively), reflecting atoll carbonate deposits associated with late Quaternary sea-level changes. In turn, the underlying sequence below ca. 80 m comprises an upper section of additional Pleistocene reef-lagoonal deposits, having a high accumulation rate greater than 100 m Ma −1 , and a heavily dolomitized lower section. Sr isotope data in the lower section provide maximum (oldest) ages for dolomite formation and, depending on the extent of the isotopic memory from precursor CaCO 3 , reflect ongoing diagenetic alteration from ca. 2.3 Ma (i.e. the oldest dolomite) or in one or more discrete diagenetic events at ca. 1 Ma, and possibly at ca. 2 Ma. This sequence reflects interaction between atoll carbonate sedimentation, tectonic subsidence and eustatic sea-level change.

Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu

“…2a;Hosking, 1991, 1992). According to radiocarbon dating of core and surface samples (Schofield, 1977;Kaplin, 1981;Ohde et al, 2002), the island formed approximately 2000 to 1000 yrs ago on a reef flat that reached sea level about 4000 yrs ago (McLean and Hosking, 1991). Both anthropogenic and natural phenomena have affected recent coastline changes.…”

Multidecadal Atoll Shoreline Change on Manihi and Manuae, French Polynesia

“…The reef growth is dependent on coral polyps that live near the surface of the water and excrete calcium carbonate to form skeletons. The solid base of the coral reef is composed of calcite and dolomite, which originate from coral skeletons, carbonate sediments created from their erosion, and direct precipitation of calcium carbonate from sea water (Ohde et al, 2002;Stoddart, 1969). Therefore, the geologic formation and longterm evolution (on scales of hundreds to thousands of years) of atolls is closely related to the relative sea level and the reef growth rate (e.g., Pirazzoli and Montaggioni, 1986;Pirazzoli et al, 1988;Stoddart, 1990).…”

“…Atoll islands are composed primarily of unlithified biodetrital sediments that are eroded from reefs and accumulate on atoll reef flats (Ohde et al, 2002). Atoll islands are highly dynamic environments in which the accumulation and retention of sedimentary deposits depends on the island elevation relative to sea level, as well as the tidal range, wind and wave energy and direction, and local currents (Stoddart, 1990).…”

Seismic evidence of glacial-age river incision into the Tahaa barrier reef, French Polynesia

“…The shallowest reflector is the last glacial subaerial exposure surface and overlays sediments that have been deposited since deglacial flooding, most probably during the mid-late Holocene (Toomey et al, 2013). By analogy, the deeper stratigraphic units likely represent older interglacial deposits separated by exposure horizons similar to stratigraphic sequences documented elsewhere in the Pacific including: Enewetak Atoll, Marshall Islands (Wardlaw and Quinn, 1991), Funafuti Atoll, Tuvalu (Ohde et al, 2002), and Mururoa Atoll (Buigues, 1997;Camoin et al, 2001).…”