Quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in Lake Baikal, Siberia
Limnol. Oceanogr., 48(4), 2003, 1643-1661 | DOI: 10.4319/lo.2003.48.4.1643
ABSTRACT: Endemic planktonic diatoms are a major component of Lake Baikal sediments during interglacial periods. To investigate how these diatom assemblages are altered during sediment formation, quantitative plankton monitoring (1995-1998) was integrated with sediment trapping over 2 yr (1996-1997) in Baikals southern basin (depth ~1,400 m). The traps consisted of both open (~6 monthly) and sequential (~2 weekly) collectors deployed throughout the water column. Sedimentation was seasonal, with diatom species composition, valve abundance, and total dry massreflecting changes in the planktonic communities. Sedimented assemblages were transmitted largely intact to the deepest traps (~1,300-1,390 m); some compositional blurring occurred from differential sinking rates and dissolution of diatom valves. A rapid mass flux event of Aulacoseira skvortzowii and A. baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d-1 and dry mass fluxes >5 g m-2 d-1. Although dissolution was evident for all species, more delicate taxa were preferentially affected (e.g., A. skvortzowii vegetative cells and fine Synedra species), whereas Nitzschia acicularis valves were almost entirely dissolved within the water column. Comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment, with sedimentary diatom accumulation rates being only about 1% of trap deposition and plankton production rates. Dissolution was significant in explaining 5-30% of species variance between all taphonomic levels (plankton, trap samples, and surface sediments). Results indicate that diatom-based paleoclimatic records in Lake Baikal sediments could be improved and refined by taking taphonomic considerations into account.