Documentation of novel diatom-associated calcification in a lacustrine whiting event at Fayetteville Green Lake, New York, USA

Open Access
- Author:
- Stanton, Chloe
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 18, 2019
- Committee Members:
- Lee Kump, Thesis Advisor/Co-Advisor
Julie Genevieve Cosmidis, Thesis Advisor/Co-Advisor
Katherine Haines Freeman, Committee Member
Mark E Patzkowsky, Program Head/Chair - Keywords:
- calcium carbonate
biomineralization
diatom
cyanobacteria
whiting
carbonate muds - Abstract:
- Whiting events – the episodic precipitation of fine-grained CaCO3 minerals suspended in the water column – have been documented across a variety of environments, including both marine and lacustrine settings. Whitings could be a dominant source of shallow water carbonate muds, especially in the Precambrian, before the rise of green algae, which were a major source in the Phanerozoic. While several biological hypotheses have been proposed to explain the onset of these precipitation events, no consensus has been reached so far, and it is still unclear which process dominates in which environments. Carbonate muds are important archives for geochemical proxies of Earth history, thus, building greater understanding of these mechanisms is crucial to our understanding of the geological record. Proposed models for biological CaCO3 precipitation involving cyanobacteria, diatoms and organic byproducts as possible mechanisms for whiting events were explored using a variety of techniques. Field studies were conducted at Green Lake in Fayetteville (NY), which experiences a whiting every year initiated in the spring and persisting through the summer. Relevant geochemical parameters were analyzed in the water column, while suspended minerals, cells, and extracellular materials were collected and visualized using scanning and transmission electron microscopy and scanning transmission X-ray microscopy. Results indicate that the development of a seasonal wind-mixed surface layer is important to the distribution of microorganisms in the lake. Importantly, results show that two plankton groups are involved in whiting events at Green Lake. Synechococcus cells are associated with organic films coated by early nucleation of nano-scale amorphous calcium grains, which likely grow into larger calcite grains. A new finding is the role of diatoms: chitin fibers extruded from the siliceous tests adsorb calcium and provide surfaces on which to nucleate large calcite grains. Additionally, mineral phases are found coated across cyanobacterial and diatom cells themselves. Amorphous minerals continuously nucleating on cells or organic microbial byproducts grow to calcite grains 5-7 µm in size over several days, which sink quickly through the column as they grow.