Chloe Stanton, Julie Cosmidis, Lee Kump

Whiting events – the episodic precipitation of fine-grained suspended calcium cabonates in the water column – have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been proposed to explain the onset of these precipitation events, no consensus has been reached thus far. Fayetteville Green Lake (New York, USA), is a meromictic lake that experiences annual whitings. Materials suspended in the water column collected through the whiting season were characterized using scanning electron microscopy and scanning transmission X-ray microscopy. Whitings in Fayetteville Green Lake are initiated in the spring within the top few meters of the water column, by precipitation of fine amorphous calcium carbonate (ACC) phases nucleating on Synechococcus cells (cyanobacteria), as well as on extracellular polymeric substances (EPS), including abundant β-chitin fibrils exuded by centric diatoms. Whiting particles found in the summer consist of 5-7 µm calcite grains forming aggregates with diatoms and their EPS. Simple calculations demonstrate that calcite particles continuously grow over several days, then sink quickly through the water column. In the late summer, partial calcium carbonate dissolution is observed deeper in the water column. Settling whiting particles however reach the bottom of the lake, where they form a major constituent of the sediment, along with diatom frustules. The importance of diatoms and their EPS in whitings at Fayetteville Green Lake is described for the first time here, a largely overlooked mechanism for other whiting events in modern and ancient environments.