Fossils reveal secrets of NZ history
A new study of New Zealand's climate 42 million years ago shows a greenhouse climate with warmer seas and little or no ice in Antarctica.
The study – based on analysis of fossilised micro-organisms at Hampden Beach, near the Moeraki Boulders in North Otago – suggests that Antarctica at that time was yet to develop extensive ice sheets.
Back then, New Zealand was about 1100km further south, closer to Antarctica, at the same latitude as the southern tip of South America.
But, the researchers found that the water temperature was 23degC - 25degC at the sea surface and 11degC-13degC at the bottom.
"This is too warm to be the Antarctic water we know today," said Dr Catherine Burgess from Cardiff University's School of Earth and Ocean Sciences.
She worked with Hugh Morgans of GNS Science to dig the fossils out of a cliff face at Hampden Beach.
The seawater chemistry revealed by the calcium carbonate shells of the exceptionally well-preserved fossils of marine micro-organisms called foraminifers, showed there was little or no ice on the planet, she said.
The rock sequence from the cliff face covered a time span of 70,000 years. A temperature oscillation seen in the fossils – with warming and cooling by approximately 1.5degC about every 18,000 years – was likely to be related to the Earth's orbital patterns around the Sun, known as Milankovitch cycles.
"Because the fossils are so well preserved, they provide more accurate temperature records," said Dr Burgess.
"Our findings demonstrate that the water temperature these creatures lived in was much warmer than previous records have shown".
Dr Burgess said she did not measure carbon dioxide, but several studies suggested that greenhouse gases forty million years ago were similar to those levels that are forecast for the end of this century and beyond.
"Our work provides another piece of evidence that, in a time period with relatively high carbon dioxide levels, temperatures were higher and ice sheets were much smaller and likely to have been completely absent," she said.