Dust Measurements in an Antarctic Ice Core Reveal Abrupt Changes in Last Ice Age Westerly Winds

Abhijith U. Venugopal, the lead author of the study, examines a section of the RICE ice core. Photo: GNS Science / Victoria University of Wellington / Roosevelt Island Climate Evolution (RICE) Project

The westerly winds that traverse the region between the mid-latitudes and Antarctica hold significant importance in shaping both regional and global climates. These winds are key players in regulating the upwelling of carbon-rich deep water in the Southern Ocean, a process that profoundly affects the global carbon cycle. When these winds shift poleward, they can enhance upwelling and the release of carbon into the atmosphere, whereas an equatorward shift has the opposite effect. These wind shifts also wield considerable influence over the climate of mid-latitude regions, impacting temperature and precipitation patterns. Mountain glaciers, sensitive to changes in temperature and precipitation, respond to these wind movements, influencing their growth and retreat.

The transportation of dust by these westerly winds from mid-latitude regions like South America, Australia, or New Zealand to Antarctica is a well-documented phenomenon. The measurement of dust concentrations in Antarctic ice provides vital insights into environmental conditions in these mid-latitude source regions, helping to distinguish between wet and dry conditions and shedding light on wind transport patterns. Elevated dust concentrations suggest winds positioned closer to the source regions, while reduced dust levels indicate winds located further away.

 Roosevelt Island Climate Evolution (RICE) Ice Core

The Roosevelt Island Climate Evolution (RICE) ice core was obtained from Roosevelt Island in West Antarctica, between 2011-2013, as part of a collaborative effort involving nine nations. A New Zealand led project, headed by Prof. Nancy Bertler, aims to determine the stability of the Ross Ice Shelf in a warming world, thus improving estimates of contributions of the West Antarctic Ice Sheet to future sea level rise. This 764-meter-long core spans approximately 80,000 years and offers valuable insights due to its unique location near the Ross Sea, making it particularly sensitive to Southern Ocean and westerly wind dynamics.

Antarctica's Abrupt Increase in Dust 32,000 Years Ago

 One intriguing finding from the RICE ice core analysis is an abrupt surge in dust concentration around 32,000 years ago, a period corresponding to a pronounced cooling phase often referred to as an ice age. This sudden increase in dust levels aligns with observations in other Antarctic ice cores, indicating a continent-wide phenomenon. Our study links this rise in dust supply to Antarctica with a shift in the westerly winds closer to the mid-latitude source regions. Simultaneous with this wind shift, the Southern Ocean's upwelling weakened, and atmospheric CO2 levels declined, signifying a significant impact on the global carbon cycle.

The study's Implications

 The implications of this research are substantial. The abrupt nature of the wind shift highlights critical thresholds within the climate system. Once crossed, these thresholds can trigger rapid climate changes over a span of years or decades, a timescale relevant to human lifetimes. Such non-linear and abrupt climate transitions remain a challenge for climate models to capture accurately. Insights from studies like this one help bridge our understanding of rapid changes within the climate system.

 Furthermore, climate models indicate that the future position of westerly winds depends on the levels of anthropogenic CO2 emissions into the atmosphere. Lower emissions would push the winds equatorward, while higher emissions would drive them further south. Since shifts in the Southern Hemisphere Westerly Winds can have substantial impacts on both global and regional climates, understanding these shifts in the past is essential for predicting their consequences under future climate scenarios.

The drilling site for RICE - a nine-nation collaborative science venture led by New Zealand. Photo: Nancy Bertler / Roosevelt Island Climate Evolution (RICE) Project

The paper has been published in "Nature Communications," and you can access it through the following link: https://www.nature.com/articles/s41467-023-40951-1

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