Thematic Articles

The exploration of Mars has revealed that its ancient surface hosted lakes with a dazzling array of chemical and physical conditions and processes. The potential habitability of surface waters has driven studies aimed at understanding whether or not Mars once hosted life. High levels of atmospheric carbon dioxide are probable on early Mars, which means that lakes derived from weathering fluids could have contained substantial carbonate alkalinity. Recent studies show that lakes with high carbonate alkalinity are able to concentrate the phosphate and cyanide that are critical for molecular synthesis in the origin of life. While evidence for carbonate-rich Martian lakes remains limited, NASA’s Perseverance rover may reveal clues about the past existence of such waters in Jezero Crater.

Alkaline soda lakes are known as some of nature’s most biologically productive ecosystems. Vigorous production (photosynthetic conversion of inorganic carbon into biomass) is countered by incremental biomass degradation, which fuels and feeds a diverse microbial community. Learn here about key adaptations that help microbes survive and thrive in the extreme conditions of alkaline soda lakes. Dive into the interconnected microbial element cycles of alkaline soda lakes and discover how the geochemistry of these environments presents microbes with unique challenges and opportunities. Throughout this article, explore how the microbial inhabitants of alkaline soda lakes have been harnessed in biotechnological applications, including the production of protein-rich food, detergent enzymes, and the purification of biogas.

Alkaline lakes have some of the most unique and diverse known mineral assemblages as a result of their very high pH and dissolved inorganic carbon concentrations. In these closed-basin systems, aqueous geochemistry and mineralogy are intimately linked, whereby the removal of elements through mineral precipitation controls the lake water geochemistry. The resulting extreme water chemistry of alkaline lakes produces minerals that are rare in other environments, including low-temperature minerals that record valuable environmental information and that are commonly extracted as mineral resources. Alkaline lakes are also excellent environments to study various processes in mineral crystallization, growth, and transformation, including the formation of metastable phases, precipitation after extreme supersaturation, co-precipitation of minerals, and the influence of dynamic conditions.

Of all the surface environments on our planet, alkaline lakes are among the most distinctive and significant in terms of their biogeochemistry, climatic sensitivity, and associated mineral deposits. But how does the Earth produce alkaline lakes? Fifty years ago, Lawrence Hardie and Hans Eugster hypothesised that the bewildering complexity of non-marine evaporites could be explained by common successions of mineral precipitation events, or chemical divides. Since that time, the chemical divide concept has provided Earth scientists with an enduring framework within which to integrate new advances in mineral–water equilibria and kinetics, sedimentology, and paleoclimatology. These developments are painting an increasingly detailed picture of how alkaline waters form and interact with magmatic and atmospheric CO2, now and in the distant past.

Alkaline lakes are incredibly dynamic, unique, and fascinating biogeochemical environments that have remained distinctive features of Earth’s evolving surface over much of its history. Understanding these evaporative surface waters, their exceptionally productive ecosystems, and their rare sedimentary deposits requires an inherently interdisciplinary approach at the intersection of hydrology, geology, and biology. The discipline-spanning articles in this issue evaluate the diverse characteristics that make these dry, salty, and habitable environments so valuable in unraveling the history and evolution of Earth’s surface, and in following the arc of habitability on ancient Mars. Here, in this introductory article, we summarize the characteristics and importance of alkaline lakes with the hope of attracting you, too, to join in our fascination with them.