Constraining modern‐day silicon cycling in Lake Baikal
Virginia N. PanizzoGeorge E. A. SwannAnson W. MackayE. G. VologinaL. AllemanLuc AndréVanessa PashleyMatthew Horstwood
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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.Keywords:
Biogenic silica
Dissolved silica
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Biogenic silica
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Concentrations of amorphous particulate silica (biogenic silica) in the uppermost layer of the inner Oslofjord, Norway, varied between 2 and 324 µ g Si·liter −1 over a 1‐year period in 1977–1978. Most of the silica was present in frustules of living or dead diatoms but there was always a certain amount (up to about 50 µ g Si·liter −1 ) in a form that could not be recognized under the microscope. Silica was produced mainly during three large blooms of Skeletonema costatum in February–March, May, and June. At the peak of the June bloom, there was up to 20 times more Si present as diatom silica than as dissolved orthosilicic acid. Uptake experiments in June indicated depletion times of dissolved Si as short as 3 h. Although the S. costatum cells were less heavily silicified in May and June than in February–March, they showed no morphological signs of a drastic Si shortage.
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Amorphous silica
Silicon dioxide
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Biogenic silica
Dissolved silica
Paleolimnology
Sediment core
Frustule
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Paleolimnology
Epilimnion
Dominance (genetics)
Dissolved silica
Biogenic silica
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Abstract A transfer function has been established to quantify the dissolution of diatom silica in Southern Ocean sediments. The relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box-core tops, each representative of a modern diatom species sediment assemblage. The amount of dissolved silica was measured for each experiment. The resulting data set of species abundances (42 samples containing 32 diatom species and 2 silicoflagellate genera) was added to the modern data base of diatom species distributed over the Southern Ocean (124 core tops). Q-mode factor analysis individualizes four factors explaining 83% of the variance. The first three factors are controlled by surface water properties (mostly temperature). The fourth factor is the only one correlated with loss of silica in the reference samples ( R = 0.900). We quantified the dissolution factor using this correlation: superficial sediments of the Southeast Indian Ocean are characterized, from low to high latitudes, by a decrease in silica loss by dissolution (from >50 to 10%) from the Subantarctic Zone (40°S) to around 55°S, followed by an increase of silica loss to values larger than 60% between 63° and 68°S. Application of the dissolution factor in two cores from the Southern Ocean (≈44° and 55°S) shows enhanced opal dissolution during the last glaciation, particularly during Emiliani's stage 3 (from 40,000 to 30,000 yr B.P.).
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Summary Diatom populations and silica concentrations were monitored at frequent intervals in the shallow, eutrophic Loch Leven over a 27‐day period (October 1972) and the influences of the inflows, outflow and the sediment were assessed. Changes in dissolved and particulate silica are accounted for by incorporating the results into a silica budget. During this period processes affecting silica within the loch were more important than those outside. The incorporation of diatom frustules into the sediments and the release of dissolved silica from the sediments appeared to be of particular importance. Evidence suggests that dissolution of the frustules of some planktonic diatom species was also important.
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