Strong link found between Alaska's Yukon River and Meiji Drift
12 February 2009, by Matthew Aylott
The Bering Sea between Alaska and Siberia has long intrigued scientists, not least because it may be the route humans took when first migrating from Asia to North America.
The Yukon river, which carried sediment 1200 miles to the Meiji drift off the coast of Siberia.
Now researchers have traced the path of sediment particles across the same stretch of water, in a discovery that could greatly improve our understanding of the area's geological history.
During the last major ice age, glaciers locked up large amounts of water. This led to lower ocean levels which exposed a huge ridge of land beneath the sea now known as the Bering Strait that would have let humans walk from Siberia to Alaska and populate America thousands of years ago.
Now scientists have described how particles of sediment found in the Meiji Drift - a large sediment deposit in the north-western Pacific - made their own unique 1200-mile journey across the Bering Sea from the mountains of Alaska.
The findings, published in Earth and Planetary Science Letters, suggest up to 45% of the sediments in the Meiji Drift were carried there by ocean currents from the Yukon River in Alaska.
The Yukon basin drains over 300,000 square miles of Alaska and Canada but does not currently deposit sediment as far away as the Meiji Drift. The drift is thought to have formed as a result of deep water exiting the Bering Sea during the last major ice age, but no notable areas of deep water form there at the moment.
'Lowered sea level during glacial intervals moved all river mouths [in the Bering Sea] closer to the Meiji Drift, but this effect was greatest for the Alaskan sources such as the Yukon,' says Dr Sam VanLaningham at the University of Aberdeen, lead author of the research.
The large, deep ocean sediment deposit known as the Meiji Drift is constructed mostly during glacial times when sea-level is low and the Bering Land Bridge is exposed. Click to enlarge image.
The researchers drilled deep into the Meiji drift, sampling layers of material laid down over the past 140,000 years. They then traced and dated particles of sediment from the borehole by analysing the ratio between different isotopes of argon and neodymium.
These methods involve comparing the rate of decay of one isotope to another, and work like radiocarbon dating except over much longer periods. Carbon dating can only date objects up to 60,000 years old, while argon and neodymium can be used for samples dating back many millions of years.
Dating the particles of sediment from the drift means they can be compared to sediments released by various river basins in the area to reveal their origin. This can provide useful information about the historic direction of ocean currents and their speed. It also gives clues to how tectonic movement and large-scale climate events have shaped the region over its history.
'These sediment wash-out events might relate to bigger-scale climate phenomena that could have had, and still have, a huge impact on climate across the region,' VanLaningham explains.
It is still not certain whether this glacial-interglacial sediment transport varies in response to changes in temperature and salinity, or whether the closure of the Bering Strait alters the circulation patterns, velocities and resulting sediment dispersal. But application of Argon and Neodynium dating to map the origins of sediment samples acquired in Bering Sea coring expeditions in the near future promises more answers.
This research was carried out by an international team from the University of Aberdeen in the UK and Oregon State University in the US.
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