Ancient ‘Great Barrier’ Fossil Reef Discovered

3032119126_f33cb8965d_z An ancient reef up to 169,000 years old has been discovered.600 meters from Australia's Great Barrier Reef.
The first awareness of its existence came in 2007, when seismic and
sonar measurements revealed odd ridges and lagoons on the seabed.
Confirmation arrived in February this year, when an international team
extracted 34 sediment cores from three sites on the seabed, revealing a
fossilized coral reef that extends 110 meters down to the sea floor. 

"This is the great-grandmother of the Great Barrier Reef," says
John Pandolfi of the University of Queensland, who was not on the
mission. It is "a very important discovery", he said in an interview with New Scientist. The prevailing theory has been that the Great Barrier Reef sits atop an older, dead
reef, but 110 meters beneath the live reef, the team hit rock. Corals
need light to live, and Pandolfi now thinks that when rising sea levels
at the end of the last ice age threatened to put the lights out on the
ancient reef, some larvae travelled to shallower waters and seeded the
modern one.

Since early July, 28 scientists from nine countries have been analyzing fossil coral reef cores that were recovered during an expedition to the shelf edge of the Great Barrier Reef to determine the relationship of past sea-level rise, and the response of the Great Barrier Reef to climate changes.

“Fossil coral reefs are very difficult to core due to the great variability of rock and sediment types”, says Dr Yokoyama of the University of Tokyo.
“Moreover we had to cope with very bad weather conditions”, adds Dr
Webster. “In spite of these challenges, we have recovered fantastic
fossil coral reef samples ranging from more than 30,000 to 9,000 years
in age.”

“Initial observations of the cores confirm the presence of the
shallow fossil reef biota needed to construct a new and robust sea
level curve”, says Dr Jody Webster of Sydney University . Because the
Great Barrier Reef is on a tectonically stable portion of the Earth`s
crust, and is far from the confounding influence of vast-ice sheets
that existed in the northern hemisphere during the last ice age, this
region represents a prime location to investigate global sea-level
changes over the last 20,000 years including the final phase of the
last ice age.

Climate variations based on information such as
ocean temperature, salinity and chemistry can also be reconstructed.
“The coldest time in recent Earth history was 20,000 years ago”
explains Dr Yokoyama. “Accurate sea surface temperature records from
equatorial regions are a key constraint needed to improve future global
climate models”

The cores are also being studied to see how
the reef ecosystem responded to rapid rises of sea level and changes in
climate. Scientists currently believe that there may have been at least
three such periods of accelerated sea-level rise about 19,000, 13,800,
and 11,300 years ago. “From previous studies, we know that the last
deglacial sea-level rise was not smooth and continuous but may have
been characterized by several rapid jumps in sea level”, the Co-chief
scientists point out. “The new cores from the Great Barrier Reef will
help to greatly refine the timing and magnitude of these events as well
as the ecological response of the reef to environmental changes.”

Although the investigations deal with past events in Earth history they
can be very important to our understanding of how the modern Great
Barrier Reef, a World Heritage Site since 1980, will respond to future
changes. Analysis of the cores will provide important insights into how
robust the reef is over different timescales and under different
environmental conditions and stresses such as changing sea level and
sea-surface temperatures, changing sediment input and ocean chemistry.
Says Dr Webster: “The expedition has provided us with a truly unique
opportunity to test ecologic theories about coral reef resilience and
the vulnerability of the Great Barrier Reef to future climate change.”

During the offshore phase of the expedition, the team acquired cores from 34 holes at three key geographic locations on the outer edge of the Great Barrier Reef in water depths of 42 to 167 meters. The expedition team recovered more than 225 metres of material, including 191 meters of fossil coral reef, which were investigated during the so-called Onshore Science Party that ended on July 16th.

Casey Kazan


Image Credit: Giovanni Paccolini Flickr Photostream

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