Algal-silica cycling and pigment diagenesis in recent alpine lake sediments: mechanisms and paleoecological implications |
| |
| Authors: | William O Hobbs Stefan V Lalonde Rolf D Vinebrooke Kurt O Konhauser R Paul Weidman Mark D Graham Alexander P Wolfe |
| |
| Institution: | (1) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada;(2) Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada;(3) St. Croix Watershed Research Station, Science Museum of Minnesota, 16910 152nd St. North, Marine on St. Croix, MN 55047, USA |
| |
| Abstract: | The quality and interpretability of the paleobiological record depends on the preservation of morphological and geochemical
fossils. Siliceous microfossils and sedimentary pigments are often cornerstones in paleoecology, although the microbial and
geochemical processes conducive to their preservation remain poorly constrained. We examined sediments from an alpine lake
in Banff National Park (Alberta, Canada) where diatom frustules are completely dissolved within 50 years of deposition. Diatom
dissolution, silica recycling, and diagenetic alteration of algal pigments were investigated, in conjunction with porewater
geochemistry and microelectrode profiling of the sediment–water interface. Analysis of sediment trap material showed ~90%
of biogenic silica (BSi) production is lost prior to burial. Silica flux calculations, based on dissolved silica (as H4SiO4) in pore-waters, show a further ~6% of total BSi is returned to the water column from the upper 4 cm of sediments, implying
that only ~4% of total BSi is permanently archived in sediments. In situ sediment pH and O2 profiles reveal that aerobic respiration by bacteria fully consumes oxygen by a depth of 4 mm into the sediment, with associated
strong pH and redox gradients. During sedimentation and early diagenesis, diatoms undergo loss of extracellular polymeric
substances that coat their frustules, promoting silica dissolution and leading to the loss of the microfossil record by a
depth of 3.25 cm. Sedimentary pigments similarly undergo rapid degradation, but diatom-related carotenoids persist below the
depth of silica dissolution. This work provides new insights on diagenetic processes in lakes, with broad implications for
the interpretation of sedimentary proxies for algal production. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
