The cold carbonate connection between Mono Lake, California and the Bransfield Strait, Antarctica

Ikaite is a rare form of carbonate - calcium carbonate hexahydrate (CaCO3. 6H(2)O) and is the precursor to thinolites. Metastable 'ikaite' crystals, d iscovered in unconsolidated marine sediments in the King George Basin in th e Bransfield Strait, Antarctica, are related to diagenetic remineralization reactions of organic matter. Stable C, O, and H-isotopes track the respons e of ikaite crystals, during growth, to changing interstitial fluid conditi ons as a result of bacterial sulphate reduction and methanogenesis. Ikaites form in preference over calcite or aragonite at the prevailing surface sed iment conditions of -1.6 degrees C and 200 bar in the King George Basin. The calcareous tufa towers of the terrestrial, hypersaline Mono Lake of nor thern California are CaCO3-precipitates formed by the influx of submerged s prings of calcium-rich freshwaters entering the alkaline lake (Sigma CO2 = 0.5 m, pH = 9.8). Under current climatic conditions the mineral calcite pre cipitates, but during the colder Tioga glacial period of Late Wisconsian ag e (12,000 to 9,000 years BP), and possibly present day during the winter se ason, the monoclinic calcium carbonate hexahydrate (ikaite) was the dominan t phase formed. These paleo-ikaites have since recrystallized to form the c alcitic pseudomorph 'thinolites'. They are found elsewhere in recent and an cient sediments of polar regions, e.g., as 'glendonites'. The environmental occurrence of ikaites and their pseudomorphs deem them as potential paleoc limatic indicators of cold environments. The larger crystals are typically restricted to colder, deeper organic-rich sediments or in moderately evapor itic basins. In these cases, the ikaite formation and decomposition may be influenced by additives such as phosphate or amino acids.