Wednesday, June 6, 2012

Exceptional Rise in Ancient Sea Levels Revealed

ScienceDaily (June 5, 2012) — Since the end of the last ice age 21,000 years ago, our planet has seen ocean levels rise by 120 meters to reach their current levels. This increase has not been constant, rather punctuated by rapid accelerations, linked to massive outburst floods from the ice caps. The largest increase, known by paleoclimatologists as 'Melt-Water Pulse 1A', proved to be enigmatic in many respects. A study recently published inNature by a team from the CEREGE laboratory in collaboration with the universities of Tokyo and Oxford has revealed the mysteries of this event, without doubt one of the most important in the last deglaciation.

A spectacular rise

The research has primarily confirmed the existence of this exceptional event, which had been controversial in some regards. Its chronology, amplitude and duration have now been defined. It began precisely 14,650 years ago and coincides with the start of the warm period known as the 'Bølling oscillation', which marked the end of the ice age. The rise in sea levels at that time was an average of 14m worldwide, over less than 350 years. This corresponds to a rate of 40mm per year -- compared to the 3mm per year we are currently experiencing.

Coral: a climate archive

To describe this remarkable event, researchers analysed cores taken from the coral reef surrounding Tahiti, Polynesia, during the international IODP 310 'Tahiti Sea Level'(4) expedition. The corals that built these reefs and atolls are excellent indicators of sea level variation* and also provide a virtual archive of previous climates(5).

Using reconstructions of sea levels from the fossilised corals as well as geophysical simulations, scientists have been able to identify the source of this accelerated rise in sea levels. They have demonstrated that the Antarctic ice cap was responsible for up to 50% of these increases. Experts had previously believed that only melting ice from the Northern hemisphere had contributed to Melt-Water Pulse 1A, particularly the Laurentide ice cap that covered a large part of North America. More