Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic

Abstract

Diatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the 'biological pump' than they have previously been attributed, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate, but northern Atlantic waters are richer in nitrate than silicate. Following the spring stratification, diatoms are the first phytoplankton to bloom. Once silicate is exhausted, diatom blooms subside in a major export event. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by 'mining' deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere.

Silicon isotopes indicate enhanced carbon export efficiency in the North Atlantic during deglaciation

“…Rapid sinking and sedimentation of the E. rex cells would then have been caused by deep mixing, which could have been caused by enhanced wind stress as observed for other HS pre-30 ka (ref. 36), turbulent mixing due to icebergs or upwelling at an unstable oceanic front 37 . A review of core descriptions reveals that the occurrence of E. rex during the deglacial appears to be limited to a region of B100-200 km diameter near the Bermuda Rise ( Supplementary Fig.…”

Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider

“…Fronts can be sites of high productivity through upwelling of nutrients and sites of downwelling of biomass, contributing to the biological pump (Flierl and Davis, 1993;Spall and Richards, 2000;Allen et al, 2005). This front is also a clear watermass boundary separating the deep boundary currents and the Labrador shelf current.…”

Optimizing models of the North Atlantic spring bloom using physical, chemical and bio-optical observations from a Lagrangian float

“…Diatoms depend on dissolved silicate to build their frustules and take it up in approximately similar molar quantities as nitrate. Since silicate concentrations in the North Atlantic are lower than nitrate concentrations, silicate is typically the first nutrient to become depleted and to start limiting diatom growth (Allen et al, 2005). Physiological stress resulting from silicate limitation is known to increase the sinking rates of diatoms (Bienfang et al, 1982).…”