Spatial differences in dissolved silicon utilisation in Lake Baikal, Siberia: examining the impact of high diatom biomass events and eutrophication

Recent research has highlighted how Lake Baikal, Siberia, has responded to the direct and indirect effects of climate change (e.g., ice-cover duration), nutrient loading, and pollution, manifesting as changes in phytoplankton/zooplankton populations, community structure, and seasonal succession. Here, we combine and compare= analyses of chlorophyll a (an estimate of total algal biomass), carotenoid pigments (biomarkers of algal groups), and lake water silicon isotope geochemistry (d30SiDSi) to differentiate spatial patterns in dissolved silicon (DSi) uptake at Lake Baikal. A total of 15 sites across the three basins (south, central, and north) of Lake Baikal were sampled in August 2013 along a depth gradient of 0–180 m. Strong, significant correlations were found between vertical profiles of photic zone DSi concentrations and d30SiDSi compositions (r 5 20.81, p < 0.001), although these are strongest in the central basin aphotic zone (r 5 20.98, p < 0.001). Data refute the hypothesis of DSi uptake by picocyanobacteria. Algal biomass profiles and high surface d30SiDSi compositions suggest greater productivity in the south basin and more oligotrophic conditions in the north basin. d30SiDSi signatures are highest at depth (20 m) in central basin sites, indicating greater (10–40%) DSi utilization at deep chlorophyll maxima. DSi limitation occurs in the pelagic central basin, probably reflecting a high diatom biomass bloom event (Aulacoseira baicalensis). Meanwhile in the more hydrologically restricted, shallow Maloe More region (central basin), both high d30SiDSi compositions and picocyanobacteria (zeaxanthin) concentrations, respectively point to the legacy of an “Aulacoseira bloom year” and continuous nutrient supply in summer months (e.g., localized eutrophication)

The nematode Caenorhabditis elegans survives subfreezing temperatures in an isochoric system

This study is the first experimental evidence showing that a living multicellular organism, the nematode Caenorhabditis elegans, can survive subfreezing temperatures in an isochoric (constant volume) thermodynamic system, while immersed in a simple isotonic solution, without the addition of cryoprotectants. Some of the test conditions were more extreme than those found at the ice/water interface of the Antarctic subglacial Vostok lake. On earth, life takes place in an isobaric (constant pressure) environment. In isobaric systems, subfreezing temperature survival of organisms in nature and subfreezing temperature preservation of living material for biotechnology and medicine, is made possible by use of cryoprotective chemicals additives. Our theoretical thermodynamic studies suggested that in an isochoric system, living biological material could survive subfreezing temperatures, without any cryoprotective chemicals. By confirming the theoretical predictions, this paper suggests a new technology for subfreezing preservation of cells, organs and organisms of possible value for biotechnology and medicine as well as new possible mechanisms of living organism survival in nature

Constraining modern day silicon cycling in Lake Baikal

Constraining the continental silicon cycle is a key requirement in attempts to understand both nutrient fluxes to the ocean and linkages between silicon and carbon cycling over different timescales. Silicon isotope data of dissolved silica (δ30SiDSi) are presented here from Lake Baikal and its catchment in central Siberia. As well as being the world's oldest and voluminous lake, Lake Baikal lies within the seventh largest drainage basin in the world and exports significant amounts of freshwater into the Arctic Ocean. Data from river waters accounting for c. 92% of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river δ30SiDSi composition. The absence of a change in δ30SiDSi within the Selenga Delta, through which 62% of riverine flow passes, suggest a net balance between biogenic uptake and dissolution in this system. A key feature of this study is the use of δ30SiDSi to examine seasonal and spatial variations in DSi utilisation and export across the lake. Using an open system model against deep water δ30SiDSi values from the lake, we estimate that 20-24% of DSi entering Lake Baikal is exported into the sediment record. Whilst highlighting the impact that lakes may have upon the sequestration of continental DSi, mixed layer δ30SiDSi values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilisation with lower rates in the north relative to south basin