Kröpelin is still assembling the final details of his work. When he is finished, he and his colleagues plan to publish the fruits of their backbreaking work in the journal Nature. Climate modelers from around the world are already waiting for the results. "Stefan's drilling core will enable us to precisely tracks how the African monsoon system has shifted," says Martin Claußen of the Max Planck Institute for Meteorology in Hamburg, one of the leading experts on simulation of the Sahara climate.
Kröpelin is already thinking about his next step. For him, the drilling core from Lac Yoa is much more than a chronicle of climate in the region. He is convinced that analyzing the sediments will also offer a glimpse into an entire chapter of human history. In a place now covered by the largest desert on earth, human settlers once ruled the savannah.
Until the end of the ice age, about 11,000 years ago, Kröpelin explains, the Sahara constituted the northern border of the areas settled by Homo sapiens. The wasteland was too inhospitable for humans to traverse it.
But when the glaciers melted in Europe, the monsoon system shifted in North Africa, and rain clouds were driven inland from the Gulf of Guinea. As the East African savannah continued to expand northward, a path was opened up to Homo sapiens to travel to more distant lands.
Various traces of settlements show that man took advantage of this opportunity. The Sahara became a center of cultural development, where ceramics were created at a very early stage, nomads domesticated cattle and goats, and humans documented their daily lives in spectacular scenes painted on cliff walls.
Only when the life-bringing monsoon slowly diminished about 5,000 years ago did the desert gradually return. The grass withered, the rivers ran dry and the animal herds disappeared, making it difficult for humans to survive. A portion of the Sahara population moved south to the more fertile Sahel zone, while the rest settled along the Nile River. This migration away from the desert, says Kröpelin, probably paved the way for the advanced civilization of ancient Egypt.
The 'Man of the Desert' Kröpelin is a wiry, hands-on man with seemingly inexhaustible energy, whoseems youthful despite his 61 years. In an article titled "Man of the Desert," the journal Nature describes him as "one of the most devoted Sahara explorers of our time." Some see him as part of a tradition established by predecessors like Heinrich Barth and Gustav Nachtigal.
Kröpelin, like these great scholars of the 19th century, is a universalist. He is equally at home with such diverse subjects as stone-age settlements, the ecological importance of solitary wasps and the angles of sickle-shaped migrating dunes.
In Sudan, Kröpelin explored Wadi Howar, a dry valley that was once filled with a large desert tributary of the Nile. He has retraced the trading routes of caravans from the days of the pharaohs, and he has documented climate change on the basis of tentatively sprouting camel grass in the desert.