Marine dust identifies 1.5 million year Oldest Ice near South America

Earth’s climate has experienced major shifts over its billions of years of history, including numerous periods where ice proliferated across the planet. Today, ice cores can be a valuable resource for understanding these periods of Earth’s history as they capture a snapshot of the climate at that time, both through geochemical constituents and entrained dust and debris preserved through millennia.

Often, higher dust content in the ice cores can be indicative of glacial periods as continental shelf exposure, weaker rainfall, increased aridity and wind can all drive higher dust transport.

The oldest known continuous ice record from Antarctica (European Project for Ice Coring in Antarctica Dome C; Epica Dome C) extends back 800,000 years, but an international partnership of scientists is attempting to increase this to 1.5 million years.

This is because they capture Earth’s climate cycles (swapping between glacial and interglacial periods) with a periodicity of ~41,000 years prior to 1.2 million years ago, irregular lengths between 700,000 years and 1.2 million years ago (known as the mid-Pleistocene transition), followed by ~100,000 year cycles since 700,000 years ago.

Such an endeavor is challenging as topography can disturb the ice stratigraphy as glaciers move across land, and basal melting can eradicate records. Therefore, extensive reconnaissance is required to identify suitable sites for drilling cores.

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

New research, published in Climate of the Past, has suggested International Ocean Discovery Program Site U1537 near South America is a viable candidate for dating Oldest Ice based upon its marine dust content.

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

The researchers generated artificial Oldest Ice records to pattern-match with the Site U1537 marine dust record and experimented with manually offsetting the records to determine accuracy of correlation. While the records for Sites 1090 and U1537 match up to 800,000 years ago, beyond that their reduced correlation may indicate spatial variability of dust influx across the high-latitude southern hemisphere during the 40,000 year world scenario.

A further goal of establishing Oldest Ice is to be able to understand why the mid-Pleistocene transition happened and what the consequences were. Dr. Ng and the team cite previous work identifying eroding regolith (surface layer of loose dust and rock) permitting thicker ice sheets and glacial cooling caused by tectonic activity as potential causes, but ultimately determined that further work is required to establish a causal mechanism.

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

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