Profiles of ocean island coral reefs controlled by sea-level history and carbonate accumulation rates

Abstract

Modern and preserved coral reefs on islands exhibit a broad range of forms, from actively accreting fringing and barrier reefs to terraces preserved by drowning or subaerial exposure. Darwin's canonical model of reef development proposes an evolutionary sequence of reef forms as a volcanic island ages and subsides, from fringing reef to lagoon-bounding barrier reef to atoll. Compiled data from modern systems show, however, that many islands do not follow this sequence, implying that reefs are shaped by more than island subsidence alone. We show that the diversity of modern reef morphology arises from the combined effects of island subsidence, coral growth, and glacial sea-level cycles. A model for the evolution of a reef elevation profi le over the past 400 k.y. reveals that different combinations of reef accretion rate and island vertical motion produce a variety of forms that matches the observed distribution of modern reefs. This match occurs only if the model is driven by Pleistocene sea-level oscillations-few modern environments have the right combination of conditions to produce the Darwinian atoll progression.

Late Cenozoic sea level and the rise of modern rimmed atolls

“…This model is similar to, but simpler than, previous models used to study the evolution of island atoll systems (e.g., Montaggioni et al, 2015;Quinn, 1991a;Toomey et al, 2013;Warrlich et al, 2002). …”

Coastal evolution on volcanic oceanic islands: A complex interplay between volcanism, erosion, sedimentation, sea-level change and biogenic production

“…The Darwinian model is still generally accepted as a valid framework for reef evolution, and the classification of reef morphologies is still useful. However, at a finer scale, subsidence alone cannot explain the entire variety of modern and preserved reef morphologies present in the oceans (Toomey et al, 2013). These morphologies range from actively accreting fringing and barrier reefs to terraces preserved by drowning or subaerial exposure, and other effects need to be considered in order to fully explain their differences (Scott and Rotondo, 1983;Toomey et al, 2013).…”

“…Second, vertical movements also have a direct effect on the erosional, sedimentary and biological processes acting upon shores due to changes in relative sea level. The growth and morphology of coral reefs, for example, is strongly influenced by vertical movements affecting the island edifices (Chappell and Veeh, 1978;Scott and Rotondo, 1983;Toomey et al, 2013). In fact, very large reefs such as those in ring atolls are only possible if an optimal subsidence rate is met (Chappell and Veeh, 1978).…”

“…Local uplift -whose origins are still poorly understood or are the focus of hot debate (see Scott and Rotondo, 1983;McNutt and Menard, 1978;McMurtry et al, 2010;Ramalho et al, 2010b) -may further contribute to the variability in reef morphology. It is now perceived that the diversity of modern reef morphology essentially arises from the combined effects of island subsidence (or sometimes uplift), coral accretion rates, and Pleistocene glacioeustatic cycles (Woodroffe et al, 1999;Toomey et al, 2013). This modern perspective somewhat reconciles the competing models proposed by Daly and Darwin, in that reef profiles and the formation of barrier reefs are controlled by subsidence and vertical coral accretion (Darwin's hypothesis), yet the morphology of modern reefs bears the strong imprint of Pleistocene eustatic variations (Daly's hypothesis) (Toomey et al, 2013).…”

“…It is now perceived that the diversity of modern reef morphology essentially arises from the combined effects of island subsidence (or sometimes uplift), coral accretion rates, and Pleistocene glacioeustatic cycles (Woodroffe et al, 1999;Toomey et al, 2013). This modern perspective somewhat reconciles the competing models proposed by Daly and Darwin, in that reef profiles and the formation of barrier reefs are controlled by subsidence and vertical coral accretion (Darwin's hypothesis), yet the morphology of modern reefs bears the strong imprint of Pleistocene eustatic variations (Daly's hypothesis) (Toomey et al, 2013). At an even finer scale, wave energy may also contribute to shape reef morphology (Storlazzi et al, 2003).…”