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- Title
Fossil Reefs Reveal Temporally Distinct Late Holocene Lagoonal Reef Shutdown Episodes at Kiritimati Island, Central Pacific.
- Authors
Ryan, E. J.; Morgan, K. M.; Kench, P. S.; Owen, S. D.; Carvajal, C. P.; Turner, T.
- Abstract
An extremely rare example of well‐preserved emergent Holocene fossil reefs exists at Kiritimati Island, central Pacific. Fossil reefs are rich geological archives of paleoenvironmental change. The first paleoecological surveys of two fossil reefs are presented, revealing high coral cover (40–50%) and low diversity (6 genera). Fossil coral ages suggest reefs exhibited disparity in the timing of reef development (4,113 and 1,915 cal yBP) and ecological surveys show different coral compositions (Acropora or Porites dominant), between reefs. Results constrain two discrete episodes of reef shutdown (at 2,905 and 1,705 cal yBP) as lagoonal reefs thrived, and subsequently died off, through the late Holocene. Shifts in physio‐chemical conditions associated with reduced lagoon flushing following storm‐driven changes in atoll rim morphology are argued as the driver for the staged reef die‐off. The findings have implications for interpreting past and future eco‐morphological change on atolls, given projected increases in storminess with climate change. Plain Language Summary: Fossil coral reefs include the skeletal remains of corals and are rarely preserved in good condition above modern sea level. Such reefs are rich archives that hold information about past environmental and ecological conditions at the time of reef development. A rare and expansive example of fossil reefs grew during the period 7,000 to 1,000 years ago at Kiritimati Island, Kiribati. Surveys and radiometric dating were used to reveal, for the first time, the age, elevation, and coral ecology of two of the most well‐preserved fossil reefs on Kiritimati Island (between 4,000 and 2,000 years ago). Results show that the reefs flourished during different time periods and were dominated by different coral taxa, before dying off. We argue that reef die‐off is attributed to changing lagoon seawater conditions that became intolerable for coral growth. These changing water conditions were the result of storm‐induced changes at the atoll rim that enclosed the lagoon and reduced flushing. As tropical cyclones are projected to increase in frequency and severity under global climate change, our results are critical for understanding the future responses of mid‐oceanic atolls and their supporting ecologies. Key Points: Reef condition at two emergent fossil reticulate reefs in Kiribati was reconstructed using paleoecological surveys and radiometric datingTemporally distinct episodes of reef growth, followed by reef shutdown, were observed through the late HoloceneReef shutdown was likely associated with storm‐deposited ridges on the atoll rim, driving changes in lagoon water, restricting coral growth
- Subjects
KIRIBATI; CORAL reef conservation; CORAL reefs &; islands; REEFS; FOSSIL corals; CORAL bleaching; ECOLOGICAL surveys; HOLOCENE Epoch; CLIMATE change
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 8, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2020GL092113