A series of well-developed submerged coral reefs are preserved in the Huon Gulf (Papua New Guinea) and around Hawaii. Despite different tectonics settings, both regions have experienced rapid subsidence (2-6 m/ka) over the last 500 ka. Rapid subsidence, combined with eustatic sea-level changes, is responsible for repeated drowning and backstepping of coral reefs over this period. Because we can place quantitative constraints on these systems (i.e., reef drowning age, eustatic sea-level changes, subsidence rates, accretion rates, basement substrates, and paleobathymetry), these areas represent unique natural laboratories for exploring the roles of tectonics, reef accretion, and eustatic sea-level changes in controlling the evolution of individual reefs, as well as backstepping of the entire system. A review of new and existing bathymetric, radiometric, sedimentary facies and numerical modeling data indicate that these reefs have had long, complex growth histories and that they are highly sensitive, recording drowning not only during major deglaciations, but also during high-frequency, small-amplitude interstadial and deglacial meltwater pulse events. Analysis of five generalized sedimentary facies shows that reef drowning is characterized by a distinct biological and sedimentary sequence. Observational and numerical modeling data indicate that on precessional (20 ka) and sub-orbital timescales, the rate and amplitude of eustatic sea-level changes are critical in controlling initiation, growth, drowning or sub-aerial exposure, subsequent re-initiation, and final drowning. However, over longer timescales (> 100-500 ka) continued tectonic subsidence and basement substrate morphology influence broad scale reef morphology and backstepping geometries. Drilling of these reefs will yield greatly expanded stratigraphic sections compared with similar reefs on slowly subsiding, stable and uplifting margins, and thus they represent a unique archive of sea-level and climate changes, as well as a record of the response of coral reefs to these changes over the last six glacial cycles.
Bibliographical noteFunding Information:
The work in PNG was funded by the US National Science Foundation grants OCE-9907153 to Silver and OCE-9907869 to Gallup. We also thank the captain and crew of the R/V Melville for their support during the cruise. For the work around Hawaii, we thank NOAA's Hawaiian Undersea Research Laboratory (HURL) for their work in the 1980s during the submersible dives that collected many samples used in the study. The most recent Hawaiian samples were collected during MBARI's expedition in 2001. The expedition, as well as the subsequent laboratory study of the samples by JMW and DAC was supported by the David and Lucile Packard Foundation through a grant to MBARI. We thank the captain and crew of the R/V Western Flyer , and the ROV Tiburon pilots for their outstanding work in collecting the samples.
- Papua New Guinea
- Pleistocene sea-level change
- carbonate platforms
- coral reefs
- meltwater pulse events
- sedimentary facies