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Cyanobacterial calcification, carbon dioxide concentrating mechanisms, and Proterozoic–Cambrian changes in atmospheric composition
Author(s) -
RIDING R.
Publication year - 2006
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/j.1472-4669.2006.00087.x
Subject(s) - carbonate , carbon dioxide , cyanobacteria , carbon dioxide in earth's atmosphere , photosynthesis , geology , carbonate minerals , environmental chemistry , total inorganic carbon , carbon fixation , mineralogy , chemistry , paleontology , bacteria , biochemistry , organic chemistry
Photosynthetic uptake of inorganic carbon can raise the pH adjacent to cyanobacterial cells, promoting CaCO 3 precipitation. This effect is enhanced by CO 2 concentrating mechanisms that actively transport into cells for carbon fixation. CO 2 concentrating mechanisms presumably developed in response to atmospheric decrease in CO 2 and increase in O 2 over geological timescales. In present‐day cyanobacteria, CO 2 concentrating mechanisms are induced when the atmospheric partial pressure of CO 2 (p CO2 ) falls below ∼0.4%. Reduction in p CO2 during the Proterozoic may have had two successive effects on cyanobacterial calcification. First, fall in p CO2 below ∼1% (33 times present atmospheric level, PAL) resulted in lower dissolved inorganic carbon (DIC) concentrations that reduced pH buffering sufficiently for isolated CaCO 3 crystals to begin to nucleate adjacent to cyanobacterial cells. As a result, blooms of planktic cyanobacteria induced precipitated ‘whitings’ of carbonate mud in the water column whose sedimentary accumulation began to dominate carbonate platforms ∼1400–1300 Ma. Second, fall in p CO2 below ∼0.4% (10 PAL) induced CO 2 ‐concentrating mechanisms that further increased pH rise adjacent to cells and promoted in vivo cyanobacterial sheath calcification. Crossing of this second threshold is indicated in the fossil record by the appearance of Girvanella 750–700 Ma. Coeval acquisition of CO 2 concentrating mechanisms by planktic cyanobacteria further stimulated whiting production. These inferences, that p CO2 fell below ∼1%∼1400–1300 Ma and below ∼0.4% 750–700 Ma, are consistent with empirical and modelled palaeo‐atmosphere estimates. Development of CO 2 concentrating mechanisms was probably temporarily slowed by global cooling ∼700–570 Ma that favoured diffusive entry of CO 2 into cells. Lower levels of temperature and DIC at this time would have reduced seawater carbonate saturation state, also hindering cyanobacterial calcification. It is suggested that as Earth emerged from ‘Snowball’ glaciations in the late Neoproterozoic, global warming and O 2 rise reactivated the development of CO 2 concentrating mechanisms. At the same time, rising levels of temperature, calcium ions and DIC increased seawater carbonate saturation state, stimulating widespread cyanobacterial in vivo sheath calcification in the Early Cambrian. This biocalcification event promoted rapid widespread development of calcified cyanobacterial reefs and transformed benthic microbial carbonate fabrics.