Seasonal Sea Ice Might Have Formed in Arctic before Antarctic
17.07.2009 - Land & Geology, Ice & Snow, Other, Arctic
A new study suggests that significant sea ice formation started occurring in the Arctic 47.5 million years ago, which suggests sea ice formation might have started in the Arctic before it did in the Antarctic. An international research team came to these conclusions through analysing oceanic sediment cores collected from the Lomonosov Ridge in the central Arctic during the Integrated Ocean Drilling Program Expedition 302 ("ACEX").
Previous research had discovered ice-rafted debris dating back to the middle Eocene epoch, indicating that ice first appeared in the Arctic 46 million years ago. However these ice-rafted debris records do not differentiate sea ice from glacial (land) ice. This distinction is important because sea ice influences climate by directly affecting ocean-atmosphere exchanges, whereas land-based ice influences sea level and ocean acidity.
The scientists working in ACEX who took sediment cores on the Lomonosov Ridge had a look at fossilised remains of diatoms in the sediment cores. The remains of these diatoms, which come from the genus Synedropsis, are an important indicator of what was going on during the middle Eocene. Synedropsis diatoms, like the various species of the same genus today, are known for being adapted to surviving long periods of darkness and freezing temperatures. Their presence led the team to believe that it is likely that sea ice formed in autumn and winter and melted in spring and summer, just like seasonal sea ice does today. Their presence also suggests that episodic sea ice formation in marginal shelf areas of the Arctic began 47.5 million years ago and that seasonal sea-ice formation in offshore areas of the central Arctic followed half a million years later, 24 million years before major ice-sheet expansion in the region occurred.
The implications for climate are important. Spring sea ice and summer cloud formation that would have occurred at the time would have reduced oceanic heat loss to the atmosphere and increased the amount of solar radiation reflected back into space. Having a stable sea ice regime would also suggest that glacial ice also existed at the same time, and independent evidence supports this hypothesis.
Their findings also indicate that sea ice formed in the Arctic before it did in Antarctica. Levels of CO2 all over the planet were declining during the middle Eocene; however now it seems as if the threshold for sea ice formation was crossed in the Arctic sooner in the Arctic than in the Antarctic.
