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1 Your web browser (Safari 7) is out of date. For more security, comfort and the best experience on this site: Update your browser Ignore W EIRD WATERS Scientists explain Lake Turkana s unique chemistry For the complete article with media resources, visit: By Stuart Thornton Tuesday, April 17, 2012 Extending from northern Kenya into southern Ethiopia, Lake Turkana is a body of water with a handful of distinctions. Surrounded by arid, harsh terrain, Lake Turkana is the largest permanent desert lake in the world stretching almost 250 kilometers (155 miles) from north to south. The lake is also known for its striking turquoise color, leading to its nickname, the "Jade Sea." But it is Lake Turkana's unique chemistry that has drawn researchers to the region. Two of these scientists are Dr. Thure Cerling, a University of Utah geology and biology professor, and Dr. Richard Yuretich, who teaches geosciences at the University of Massachusetts-Amherst. Lake Turkana possesses water that is saline, which means it contains salt. The lake is also known for its high alkalinity. An alkaline liquid has a ph of higher than 7. According to Cerling, Lake Turkana's water is 9.3 to 9.4 on a ph scale. Lake Turkana is the largest alkaline lake in the world. Yuretich first traveled to Lake Turkana in the mid-1970s to study how sediments on the bottom of the lake were reacting with the chemistry of the lake water. He explains how the lake's position in a rift valley contributes to its salinity and alkalinity. 1 of 6

2 "It's in one of these geologic areas of the rift valley, and the rift valleys tend to have a lot of these volcanic rocks that have been spewed forth over the past several million years that are very rich in alkalis themselves," he says. "When they weather out, they form these naturally alkaline solutions, and then it gets even more alkaline as the water is concentrated by evaporation." Species of Lake Turkana Even though Lake Turkana is very alkaline, it is able to support a fish population. "The lake is in this interesting interval where it is too saline and alkaline for mollusks but not too saline and alkaline for fish," Cerling says. Mollusks, such as sea snails, do not thrive in Lake Turkana because they need calcium to build their calcium carbonate shells, and calcium is not prevalent in the African lake. "Lake Turkana is so low in calcium that today basically mollusks snails and those kind of things have a very difficult time making a living," Cerling says. "So they are basically all gone. It does not have some of the normal fauna of snails and clams and that sort of thing. The fresher lakes do, but Lake Turkana doesn't." Still, the lake supports a vibrant fishery. The most notable catch is probably the Nile perch, one of the largest freshwater fish in the world. Nile perch can grow up to 2 meters (6 feet) and can weigh up to 200 kilograms (440 pounds). Yuretich recalls being amazed by the size of Nile perch. "At the time I was there, the largest perch that I have ever seen existed in Lake Turkana," he says. Forming Lake Turkana 2 of 6

3 The Turkana Basin wasn't always filled with water. "The reason for Lake Turkana is because Mount Kulal at the south end of the lake is essentially a dam," Cerling says. "The Omo River used to flow all the way out to the Indian Ocean, and then this big volcano got in the way of things about 2 million years ago. "So since then the Omo is blocked from going to the Indian Ocean. Sometimes it goes into Lake Turkana. Sometimes it switches and runs over into the Nile [River]. Sometimes it fills up the lake basin and it flows out to the Nile. Other times, it is drier... like it is now." Like Yuretich, Cerling first started working in the Lake Turkana region as a graduate student in the 1970s. At that time, he was interested in learning about the chemistry of the modern lake in an attempt to understand the chemistry of the ancient lake known as a fossil lake. The Lake Turkana region is rich in fossil remains and has been the site of major discoveries that have helped scientists gain a greater understanding of human evolution. Cerling's focus has changed several times since the '70s. "Some of the questions have been answered, and I've moved on to work on other problems," he says. "I've been involved in things from the general mapping of the stratigraphy to the dating to the correlation of volcanic ashes to understanding the different environments. That's really what my main focus is. Just trying to use whatever geochemical footprints are left behind. How can we use those to understand what the environments for human evolution were like?" It's a project where he is collaborating with the Leakeys, a renowned family of paleontologists, and their Turkana Basin Institute. "I've been working with Richard and Meave Leakey on aspects of trying to 3 of 6

4 understand the environments of human evolution," Cerling says. "So what are the environments like that humans were evolving in? I've been involved in trying to understand the chemistry of the modern lake and the chemistry of the fossil lake. What modern soils are like and what fossil soils are like. And what modern animals eat and what fossil animals would eat. So I've had my foot in the modern lake and the fossil lake for quite a long time." Vocabulary alkali Term ancient arid basin Part of Speech Definition chemical compound often found as mineral salt in soils and bodies of water. adjectivevery old. adjectivedry. a dip or depression in the surface of the land or ocean floor. biology study of living things. calcium chemical element with the symbol Ca. calcium carbonate chemistry dam desert distinct environment chemical compound (CaCO3) found in most shells and many rocks. study of the atoms and molecules that make up different substances. structure built across a river or other waterway to control the flow of water. area of land that receives no more than 25 centimeters (10 inches) of precipitation a year. adjectiveunique or identifiable. conditions that surround and influence an organism or community. evaporation process by which liquid water becomes water vapor. evolution change in heritable traits of a population over time. 4 of 6

5 Term Part of Speech Definition family group of organisms that come from the same ancestors and share similar characteristics. Family is also a classification in chemistry and math. fauna animals associated with an area or time period. fishery industry or occupation of harvesting fish, either in the wild or through aquaculture. fossil remnant, impression, or trace of an ancient organism. fossil lake area that was a lake or lakebed thousands or even millions of years ago. freshwater water that is not salty. geology study of the physical history of the Earth, its composition, its structure, and the processes that form and change it. geoscience branches of study that focus on the origin and structure of the Earth. Also called Earth science. graduate person who pursues a college or university degree student program beyond the basic bachelor's degree. mollusk type of invertebrate animal. paleontologist person who studies fossils and life from early geologic periods. ph measure of a substance's acid or basic composition. Distilled water is neutral, a 7 on the ph scale. Acids are below 7, and bases are above. prevalent adjectivecommon or widespread. rift valley depression in the ground caused by the Earth's crust spreading apart. saline salt sediment adjectivesalty. (sodium chloride, NaCl) crystalline mineral often used as a seasoning or preservative for food. solid material transported and deposited by water, ice, and wind. 5 of 6

6 Term Part of Speech Definition soil top layer of the Earth's surface where plants can grow. stratigraphy study of rock layers and layering. terrain topographic features of an area. vibrant adjectivelively. volcanic ash fragments of lava less than 2 millimeters across. volcano an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions. Articles & Profiles Freshwater Ecoregions of the World: Lake Turkana UNESCO: World Heritage Lake Turkana National Parks Professor Richard Yuretich Dr. Thure Cerling Websites National Geographic Explorers-in-Residence: Meave and Louise Leakey National Geographic Society. All rights reserved. 6 of 6