Antarctic ice cores have recorded an impressive climatic history for us, spanning the past 800,000 years. But scientists are greedy, always looking to go back just a little further. Climate records based on things like seafloor sediment cores take us back much further, but ice cores can reveal unique details. Groups are currently looking for locations to drill new ice cores that could provide a continuous record going back more than a million years.
But another group has cheated, and this has enabled them to take a giant leap past everyone else. Instead of looking at places where the bottom ice might be the oldest, they looked at places where that oldest ice has been squeezed to the surface against high rock pinnacles. A few years ago, they published data from ice samples that were about 1 million years old. At a conference on Wednesday, the researchers unveiled the fruits of their second attempt: ice as old as 2.7 million years, blowing away their previous record.
The ice is quite squashed and convoluted, with pieces of ice less than 800,000 years old appearing among pieces of ice between 1 million and 2.7 million years old – the attempt to determine the age requires careful dating based on argon isotopes . But the researchers are able to measure greenhouse gas concentrations from trapped air bubbles and indicators of past ocean temperature.
One reason these samples are particularly interesting is that the rhythm of Earth’s ice age changed about 1.2 million years ago. The 800,000-year ice core record shows a succession of ice ages that were each about 100,000 years long. Prior to 1.2 million years ago, the cycle was slightly shallower and faster, with ice ages lasting only 40,000 years due to some interaction between the regular cycles in Earth’s orbit and our planet’s response.
According to a report in Scienceproject member Ed Brook is hopeful that the next trip to Antarctica may pay off even older ice that clears this latest find by a few million years.