Marine dust identifies oldest ice 1.5 million years old near South America

Earth’s climate has undergone major changes over its billions of years of history, including numerous periods of ice growth across the planet. Today, ice cores can be a valuable resource for understanding these periods of Earth’s history because they capture a snapshot of the climate of that era, both through geochemical constituents and dust and debris. trained preserved over millennia.

Often, higher dust content in ice cores can be indicative of glacial periods, as exposure of the continental shelf, lower precipitation, increased aridity, and wind can all lead to greater dust transport.

The oldest known record of continuous ice in Antarctica (European Antarctic Dome C Ice Coring Project; Epica Dome C) dates back 800,000 years, but an international partnership of scientists is trying to increase that figure to 1.5 million ‘years.

Indeed, they capture the Earth’s climatic cycles (switching between glacial and interglacial periods) with a periodicity of approximately 41,000 years before 1.2 million years ago, irregular durations between 700,000 years and 1 .2 million years ago (known as the mid-Pleistocene transition), followed by cycles of approximately 100,000 years since 700,000 years ago.

Such an undertaking is challenging because topography can disrupt ice stratigraphy as glaciers move over land, and basal melting can eradicate records. Therefore, extensive reconnaissance is required to identify suitable sites for core drilling.

Once found, rapid core recovery involves melting upper layers of ice to reach basal ice more quickly, with optical logging (where a laser is lowered into the core and backscattered light measured as an indicator of dust content ) used to identify the oldest ice. .

New research, published in Climate of the pastsuggested that the International Ocean Discovery Program site U1537, near South America, is a viable candidate for dating the oldest ice based on its marine dust content.

Dr Jessica Ng, from the Scripps Institution of Oceanography, USA, and colleagues compared marine dust in southern Atlantic Ocean ice cores from the Ocean Drilling Project Site 1090 with those from the site U1537 to determine age correlation and provenance from South America, Australia and New Zealand. Site U1537 was considered the most suitable marine dust record to then be compared to ice dust from Epica Dome C in Antarctica.

The researchers generated artificial records of the oldest ice to match the marine dust records from site U1537 and experimented with manually clearing the records to determine the accuracy of the correlation. Although records from Sites 1090 and U1537 correspond up to 800,000 years ago, beyond this period their reduced correlation may indicate spatial variability in dust influx across the high-latitude Southern Hemisphere over the 40,000 year global scenario.

Another goal of establishing the oldest ice is to be able to understand why the mid-Pleistocene transition occurred and what its consequences were. Dr Ng and the team cite previous work identifying erosion of regolith (surface layer of dust and loose rock) allowing for thicker ice sheets and glacial cooling caused by tectonic activity as potential causes, but ultimately determined that further work is needed to establish a causal mechanism.

Overall, this research is important because climate cycles over ~40,000 years and ~100,000 years drive different feedback signals on Earth that have profound impacts on our ability to understand the regularity of change in systems. planetary issues and their consequences.

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