Impact of hydrothermal activity on the Si cycle in Yellowstone Lake

Diatoms (unicellular algae forming siliceous tests) are a significant component of the linked carbon-silicon (Si) cycles in that they consume Si released from the weathering of silicate rocks and subsequently sequester carbon and silica when buried in sediments. Thus, regions of diatom-rich sediment yield a window into the conditions that favor high carbon export rates and burial. We studied the Si sources (tributaries, hydrothermal vents) and sinks (diatomaceous sediment) of Yellowstone Lake, which is situated on silicate rich volcanic rocks, to elucidate Si cycling dynamics in the present and during the Holocene. 

Recent lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake were analyzed for their dissolved Si (DSi) concentration and stable silicon isotopes (δ³⁰Si) to aid in evaluating the sources of variability in the lake’s Si cycle. In addition, elemental composition (XRF), biogenic silica (BSi) content, and the diatom δ³⁰Si were analyzed in two sedimentary core records spanning the Holocene from a hydrothermally influenced area and an undisturbed deep portion of the lake to identify whether past hydrothermal explosions and disturbance by Mazama ash deposition affected Si cycling.

Combinations of the Si and δ³⁰Si mass balance, sedimentary BSi, diatom δ³⁰Si with XRF, and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system influenced by consistently high hydrothermal input throughout the Holocene. Several of the hydrothermal explosions identified in the lithology had no identifiable long-term impact on BSi accumulation or the diatom δ³⁰Si signature. Both cores show similarities that suggest a stable and homogeneous DSi source across the entire lake. Thus, the diatom δ³⁰Si values record changes in the relative proportion of DSi sources, diatom production connected with changes in climate, and hydrothermal inputs.