Investigations to predict changes in sea levels and their impacts on coastal systems are a step closer, as a result of international collaboration between the University of Sydney and researchers from Japan, Spain, and the United States.
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| These are technical rebreather SCUBA divers collecting the fossil coral material used in this study from the submerged terrace off of Kawaihae [Credit: Association for Marine Exploration] |
Recent findings suggest that episodes of very rapid sea-level rise of about 20m in less than 500 years occurred in the last deglaciation, caused by periods of catastrophic ice-sheet collapse as Earth warmed after the last ice age about 20,000 years ago.
Lead author, PhD candidate at the University of Sydney, Kelsey Sanborn, has shown this sea-level rise event was associated with "drowning" or death of coral reefs in Hawaii.
The results are published in leading geosciences journal Quaternary Science Reviews.
The paper provides new evidence of a meltwater pulse (referred to as meltwater pulse 1-A), based on analysis of fossil coral reef samples from off the coast of Kawaihae, on the northwest of the Big Island of Hawaii.
Co-author Associate Professor Jody Webster, from the Geocoastal Research Group at the University of Sydney's School of Geosciences, said although this pulse was greater than current modelling predictions of sea-level rise over the next few hundred years, it provides an example of the risks rapid environmental change poses to our marine ecosystems.
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| This is a map showing the location of sample collection off of Kawaihae, Hawaii (blue sphere), and a slope profile (below) showing the backstepping younger and shallower terraces overlaying the targeted reef terrace 150m below sea level [Credit: Bathymetry data from Monterey Bay Aquarium Research Institute, and figure by Kelsey Sanborn, University of Sydney] |
The fossil corals used in this study were collected by a team of technical rebreather scuba divers who dove down to 150 m below present sea level to access the fossil reef. At this depth, more than 130m deeper than where you could dive along their living shallow counterparts today, the divers recovered targeted shallow reef species that were alive over 14,700 years ago.
Lead author Ms Sanborn said this coral reef had been growing for thousands of years, during the initially gradual sea-level rise as the ice sheets of the last ice age began to melt.
"During the meltwater pulse, sea level rose more rapidly than the reef could grow, preventing the photosynthetic algae living within the corals from receiving enough sunlight. This caused the previously thriving fringing reef system to drown, and left it to be overgrown by deep-water algae and other marine life," she said.
Although uncertainty remains regarding how quickly coastal areas could be inundated around the world, understanding how these events occurred in the past are key to understanding the risks we face in the future.
"The fact that this meltwater pulse was large enough to drown a large, active Hawaiian reef system implies that extreme climate change and associated sea-level rise occurred quite rapidly," Ms Sanborn said.