Role of silicon as a limiting nutrient to Antarctic diatoms: evidence from kinetic studies in the Ross Sea ice-edge zone

Abstract

During the austral summer of 1990 an intense, diatom-dominated, ice-edge phytoplankton bloom in the southwestern Ross Sea resulted in depletion of silicic acid, nitrate and phosphate to concentrations much lower than is typical for Antarctic surface waters. Silicic acid was depleted to <6 FM within the core of the meltwater field, where biogenic particulate silica concentrations exceeded 20 pm01 1-' Three Si uptake kinetic experiments were conducted on natural phytoplankton assemblages from the nutrient-depleted zone; 30Si-labeled Si(OH), was used to measure the uptake rate at concentrations ranging from 1 to 20 PM above ambient. Dependence of the spec~fic uptake rate ( V ) on silicic acid concentration conformed well to a Michaelis-Menten saturation model; maximum uptake rates (V,,,,,) ranged from 0.0022 to 0.0028 h-' which corresponds to maximum growth rates of 0.08 to 0.10 doublings d-l. Half-saturation constants (km) ranged from 1.1 to 4.6 PM, a range similar to values found in other areas of the ocean and considerably lower than those previously reported for several Antarctic d~atom species in culture studies. Results indicate detectable, but weak, substrate limitation of s~llcic acid uptake rate by the naturally occurring diatom assemblage in the western Ross Sea. Significant Si limitation in other subsystems of the Southern Ocean would be possible only if their resident diatom assemblages had much lower affinity for silicic acid than we observed.

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

“…Nitrate and phosphate concentrations were non-limiting to productivity within the whole of the survey area (Bowie et al, 2011). However, silicate was highly limiting (<5 µM) (Franck et al, 2000;Nelson and Treguer, 1992) within the mixed layer with average concentrations of 0.17 ± 0.06, 0.55 ± 0.07, and 0.65 ± 0.07 µM at P1 (SAZ-west), P2 (PFZ) and P3 (SAZ-east), respectively (P1 (∼45.82 • S, 141.69 • E), P2 (∼54.22 • S, 146.54 • E), P3 (∼45.53 • S, 153.51 • E); see Fig. 1).…”

Sources and fates of silicon in the ocean: the role of diatoms in the climate and glacial cycles

“…In our 1-D model for the EEP, we do not include Fe as a limiting nutrient explicitly, but rather consider it's role implicitly through the parameters that determine the growth rate of diatoms. There are two parameters in our current model reflecting Fe limitation, alpha, α, the slope of the photosynthetic rate over irradiance at low irradiance, and K Si(OH)4 , the halfsaturation for Si(OH) 4 uptake which varies considerably (Nelson and Brzezinski, 1990;Nelson and Treguer, 1992). When the model was run to mimic an Fe enrichment experiment ecological behaviors similar to these observed during the field Fe enrichment experiments (Martin et al, 1994;Coale et al, 1996;Boyd et al, 2000) resulted (Chai et al, in press).…”

Biogeochemistry and limnology in Antarctic subglacial weathering: molecular evidence of the linkage between subglacial silica input and primary producers in a perennially ice-covered lake

“…The subglacial water, which initially derives from melting caused by geothermal heat (heat flow rates, approximately 50 mW m −2 ; Siegert et al 2012), is involved in various water-rock interaction processes beneath the ice sheet, and these interactions play important roles in the supply of nutrients, including trace metals, to organisms in Antarctic environments. For example, silicon (Si) is one of the critical elements limiting the growth of Antarctic diatoms (e.g., Nelson and Treguer 1992), likewise nitrogen and other elements (e.g., Hutchins and Bruland 1998). Moreover, glacial input of particulate and dissolved Fe is essential to biological productivity in the Southern Ocean (Raiswell and Canfield 2012).…”