The geochemical analysis of the Lake Magadi samples showed some of the greatest concentrations of aspects like vanadium, molybdenum, and arsenic ever reported in lake sediments. Hyperaccumulation of these elements has not formerly been observed in other East African lakes and generally needs euxinic conditions. Euxinic conditions happen when the lake water is both sulfidic and anoxic, generally triggered during negative water balance episodes like droughts.
Deocampo and co-authors found that euxinia became typical after about 700,000 years ago and consequently tended to occur throughout intervals when Earths orbit was more elliptical, which takes place over a 100,000-year cycle.
Lead author Dan Deocampo of Georgia State University and a group of global co-authors drilled Lake Magadi as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), which collected deep sediment cores from lake basins in the East African Rift.
Introduction of Lake Magadi from the western coast. Credit: Hominin Sites and Paleolakes Drilling Project
” Were trying to understand how the Earths surface environment has changed over the last a number of million years and how that has affected early hominin environments,” said Deocampo. “We are using various proxies of the ancient environments to comprehend how the environment has actually altered, how habitats have actually changed, and for that reason how the threats and resources for early hominins altered through time.”
The geochemical analysis of the Lake Magadi samples revealed a few of the greatest concentrations of elements like molybdenum, vanadium, and arsenic ever reported in lake sediments. Hyperaccumulation of these components has actually not previously been observed in other East African lakes and normally needs euxinic conditions. Euxinic conditions happen when the lake water is both anoxic and sulfidic, generally triggered throughout unfavorable water balance episodes like dry spells.
Drill core collection at the Lake Magadi site. Credit: Hominin Sites and Paleolakes Drilling Project
” The amount of molybdenum collected in a sulfide-rich sediment in the lake is not going to inform us habitat structure, where the hominins were living, but fluctuations between those euxinic conditions and fresher water conditions, that can inform us something about the speed of environmental modification,” stated Deocampo.
Deocampo and co-authors discovered that euxinia ended up being common after about 700,000 years back and consequently tended to occur during intervals when Earths orbit was more elliptical, which occurs over a 100,000-year cycle. As Earths orbit becomes more elliptical, Earth can end up being further away from the sun, which causes higher variations in seasonal environment. The episodes of euxinia offer a crucial sign of intense droughts in the area during periods of comprehensive glaciations.
Deocampo and colleagues collecting samples from the Lake Magadi drill core at the National Lacustrine Core Facility. Credit: Hominin Sites and Paleolakes Drilling Project
These high-amplitude ecological variations driving shifts in between euxinic and well-mixed lake conditions would have profoundly affected moisture accessibility and plant life over evolutionary timescales.
The ecological irregularity recommended by the geochemical record of Lake Magadi is associated in time with mammal types turnover and the very first appearance of Middle Stone Age technology in the southern Kenya Rift between 500,000 and 320,000 years ago.
” Now that is sort of a touching point with the paleoanthropologists who are thinking about changes in the amplitude of ecological change and how that connects to gene pool adjustments and changes in environment structure, first appearances, and last looks,” said Deocampo.
Referral: “Orbital control of Pleistocene euxinia in Lake Magadi, Kenya” by D.M. Deocampo; R.B. Owen; T.K. Lowenstein; R.W. Renaut; N.M. Rabideaux; A. Billingsley; A. Cohen; A.L. Deino; M.J. Sier; S. Luo; C.-C. Shen; D. Gebregiorgis; C. Campisano and A. Mbuthia, 20 September 2021, Geology.DOI: 10.1130/ G49140.1.
Rift Valley lakes within eastern Africa range from freshwater to highly alkaline systems and are homes to diverse ecosystems. These Rift Valley lakes are also sedimentary repositories, yielding a high-resolution ecological record that can be targeted to much better understand the environmental and climatic context of human development over the past few million years in eastern Africa.
A new study released just recently in Geology examines the geochemical record of drill core sediments collected from Lake Magadi– a saline, alkaline lake in the southern Kenya Rift– that provides a nearly one-million-year paleoenvironmental record from an unusual Rift Valley lake system.
