Earth's Climatic History Was Written In Dust
January 25, 2014

Scientific Treasure Trove From South Polar Sea Sediment Cores

April Flowers for - Your Universe Online

Polarstern, a research icebreaker, returned from the South Pacific in 2010 with a scientific treasure. The treasure, described in a recent issue of Science, consisted of ocean sediments from a previously almost unexplored part of the South Polar Sea. To geological history researchers, these inconspicuous mud samples are a valuable archive from which they can reconstruct the climatic history of the polar areas over many years of analysis. This archive is fundamentally important for understanding global climatic development.

The researchers report that these sediment cores will make it possible to provide complete evidence of how dust has had a major influence on the natural exchange between cold and warm periods in the southern hemisphere. Using the cores, an international team of researchers under the management of the Alfred Wegener Institute in Bremerhaven proved that dust infiltrations in the Southern Ocean were 2 to 3 times higher during all the ice ages in the last million years than in the warm phases in climatic history.

"High large-area dust supply can have an effect on the climate for two major reasons", explained Dr. Frank Lamy, geoscientist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, about the findings. "Trace substances such as iron, which are essential for life, can be incorporated into the ocean through dust. This stimulates biological production and increases the sea's capacity to bind carbon. The result is that the greenhouse gas carbon dioxide is taken out of the atmosphere. In the atmosphere itself, dust reflects the sun's radiation and purely due to this it reduces the heat input into the Earth's system. Both effects lead to the fact that the Earth cools down."

Scientists have long suspected the influence of dust supply on the climate changes between ice ages and warm periods. Particularly high dust content containing iron has always been found by climatologists in both Antarctic ice cores and sediment cores from the Atlantic part of the Southern Ocean when the planet was going through an ice age. Up until now, however, no data was available for the Pacific section, which covers 50 percent of the Southern Ocean. "We can now close this central gap" is how Lamy underlines the importance of the new study. "The result is that we are now finding the same patterns in the South Pacific that we found in cores from the South Atlantic and the Antarctic ice. Therefore, the increased dust input was a phenomenon affecting the southern hemisphere during colder periods. This means that they now have to be considered differently when assessing the complex mechanisms which control natural climate changes."

Although this sounds like a minor discovery, it is considerably relevant for climate research. Prior to these findings, scientists were convinced that dust supply to the Pacific area could not have been higher during the ice ages than during warmer periods of the Earth's climate history. Until now, South Patagonia has been the suspected culprit for supplying large quantities of geologic dust, since it is the only landmass in the Southern Ocean. The predominating wind in this part of the world comes from the West, however, so any dust particles in the air originating from South America mostly drift towards the Atlantic. Because of this, core sediment data from the South Pacific has been on a scientific wish list for a long time.

Despite modern technology, the Pacific section of the Southern Ocean has remained something of a "terra incognita" because it is one of the most remote parts of the world's oceans. "The region is influenced by extreme storms and swells in which wave heights of 10 m or more are not uncommon. The area is also complicated from a logistic point of view due to the huge distance between larger harbors," explains AWI scientist Dr. Rainer Gersonde, leader of the Polarstern expedition at the time of the study, speaking about the extraordinary challenges faced by the research voyage. In order to obtain these high quality and sufficiently long sediment cores, the Polarstern made a voyage of 10,000 nautical miles through this particularly inhospitable part of the Antarctic Ocean.

The question still remains, however, as to where the historic dust freight towards the South Pacific came from, and why did the phases of increased output take place at all? One of the causes, according to Lamy, could be the relocation or extension of the exceptionally strong wind belts prevalent in this region towards the Equator. The powerful westerly winds of this region — the "Roaring Forties" and the "Furious Fifties" — have made the Southern Ocean notorious amongst sailors. The researchers hypothesize that a relocation or extension of this powerful westerly wind belt towards the North could have caused stronger wind erosion on the extended dry areas of Australia. This would result in higher dust infiltration into the Pacific Ocean, causing the consequences described above. New Zealand was an additional source of dust, as the extended glaciation of the mountains in New Zealand during the ice age provided considerable quantities of dust. This dust was blown far out into the South Pacific by the winds.

"Our investigations have now proved without a doubt that colder periods in the southern hemisphere over a period of 1 million years always and almost everywhere coincided, with lower carbon dioxide content in the atmosphere and higher dust supply from the air. The climatic history of the Earth was, therefore, written in dust."