Constraining modern‐day silicon cycling in Lake Baikal

Abstract

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 time scales. Silicon isotope data of dissolved silica (δ 30 Si DSi ) 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~92% of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river δ 30 Si DSi composition. The absence of a change in δ 30 Si DSi within the Selenga Delta, through which 62% of riverine flow passes, suggests a net balance between biogenic uptake and dissolution in this system. A key feature of this study is the use of δ 30 Si DSi to examine seasonal and spatial variations in DSi utilization and export across the lake. Using an open system model against deepwater δ 30 Si DSi values from the lake, we estimate that 20-24% of DSi entering Lake Baikal is exported into the sediment record. While highlighting the impact that lakes may have upon the sequestration of continental DSi, mixed layer δ 30 Si DSi values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilization with lower rates in the north relative to south basin.

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

“…Estimates for the Si fluxes were obtained from the following sources: Carey and Fulweiler (2012), Frings et al (2016), Laruelle et al (2009), Tréguer and De La Rocha (2013). Estimates for the range of δ 30 Si values were obtained from the following sources: Ehlert et al (2016); Figure 2 from Frings et al (2016) and references therein; Varela et al (2016) and Panizzo et al (2017). All data used to prepare this figure are available in Table S1.…”

“…Since the first data of DSi in freshwaters by De La Rocha (De La Rocha et al, 2000), δ 30 Si has been analyzed from a number of rivers (and lakes) across the world including the Congo River and tributaries Hughes et al, 2011), the Tana River (Hughes et al, 2012), the Yellow and Yangtze Rivers (Ding et al, 2004(Ding et al, , 2011, the Kalix River in Sweden (Engström et al, 2010), Swiss alpine rivers (Georg et al, 2006), and most recently from the Nile River (Cockerton et al, 2013), the Amazon river and tributaries , areas of central Siberia (Pokrovsky et al, 2013;Panizzo et al, 2017) and the Ganges (Fontorbe et al, 2013;Frings et al, 2015). The range in δ 30 Si from freshwaters, thus far analyzed, now stands at −0.17 to +4.66‰ (Figure 1).…”

“…As outlined above, there have been a handful of studies to date that have examined the application of δ 30 Si DSi in limnological settings Opfergelt et al, 2011;Panizzo et al, 2016Panizzo et al, , 2017. Lakes, in addition to the soil-vegetation system, play an important role in buffering continental DSi export to the oceans.…”

“…The potential of δ 30 Si is particularly evident in regions where climate change and anthropogenic lake catchment alteration (e.g., nutrient loading) are prompting limnological responses (e.g., increased duration of lake stratification and warmer surface water temperatures), which impact within lake biogeochemical cycling (Panizzo et al, 2017). For example, the approach has been demonstrated as a means to identify biogeochemical responses to climate change (Street-Perrott et al, 2008;Swann et al, 2010) and its value over more recent timescales is also stressed here as a means to address current pressures.…”

“…For example, the approach has been demonstrated as a means to identify biogeochemical responses to climate change (Street-Perrott et al, 2008;Swann et al, 2010) and its value over more recent timescales is also stressed here as a means to address current pressures. Comprehensive contemporary limnological monitoring is also emphasized (Opfergelt et al, 2011) to enable quantitative estimations of seasonal DSi and bSiO 2 cycling (via open or closed system modeling), by providing key constraints on deepsurface water δ 30 Si DSi exchange, Si residency times and Si uptake (Panizzo et al, 2016(Panizzo et al, , 2017. These data also serve to validate conventional palaeolimnological approaches, which can be applied to constrain continental bSiO 2 export from lake and reservoirs, particularly under a projected future of enhanced anthropogenic and climatic pressures on these systems.…”