Preferential sinking export of biogenic silica during the spring and summer in the North Water Polynya (northern Baffin Bay): Temperature or biological control?

Abstract

in the North Water Polynya (northern Baffin Bay). The amount, composition, and vertical transformation of the organic material sinking out of the euphotic zone were assessed. Clear seasonal sedimentation patterns were apparent throughout the Polynya. Maximum sedimentation occurred during the month of June, at which time high sedimentation of intact diatom cells and empty frustules was observed. In July, abundant resting spores and zooplankton feces were sinking out of the euphotic zone. Vertical transformation of the sinking material, between 50 m and 100 m, revealed a consistent loss of $30-35% for particulate organic carbon and nitrogen and a loss of $10% for biogenic silica. A temperature model of silica dissolution was used to assess the role of temperature in controlling the low loss of biogenic silica observed in the upper water column. Model results show divergence of modeled rates from in situ loss rates at times when the biosiliceous fraction of the sinking material was high. This indicates that biological factors played a key role in reducing biogenic silica dissolution in the North Water Polynya. Sedimentation of intact cells, abundant resting spores, and feces all contributed to enhance preservation of silica in the sinking material. These results suggest that the North Water Polynya is a sink for biogenic silica and emphasize the significance of biological processes in controlling the silica pump in the marine environment.

Phytoplankton production in the North Water Polynya: size-fractions and carbon fluxes, April to July 1998

“…Our values are close to 2 independent estimates of phytoplankton production export from the euphotic zone of the NOW, i.e. 20% based on both nutrient budgets (Tremblay et al 2002b), and shortterm sediment traps (Michel et al 2002).…”

“…, Michel et al 2002). In June, these authors observed an increased chl flux (6.1 ± 5.8 mg chl m -2 d ) are close to the average of 1.1 ± 0.7 mg chl m -2 d -1 of Michel et al (2002).…”

“…In June, these authors observed an increased chl flux (6.1 ± 5.8 mg chl m -2 d ) are close to the average of 1.1 ± 0.7 mg chl m -2 d -1 of Michel et al (2002). The higher-settling flux from the drifting sediment trap than from the SETCOLs might have been caused by reduced turbulence in the latter.…”

Particulate organic carbon export in the upper twilight zone during the decline of the spring bloom

“…However, the cylindrical shape and aspect ratio (height:diameter = 7) of the traps used in the present study have been found to be effective as free-drifting particle interceptor traps (Baker et al 1988, Knauer & Asper 1989. Similar particle interceptor traps and mooring arrays have been used in other studies (Michel et al 2002, Caron et al 2004, and comparisons with flux estimates using 234 Th have shown close agreement in estimated carbon fluxes (Th-derived carbon flux = 0.68 + 1.05 drifting trap flux; n = 13, r 2 = 0.89, p < 0.001; Tremblay et al 2006). The average increase in DOC concentration within the particle interceptor traps during deployment intervals was 11 ± 6% below Z eu and 10 ± 5% at 150 m throughout the study period, reflecting the potential loss of particulate organic matter (POM) to the dissolved phase (solubilization; Buesseler et al 2007a) during trap deployments.…”

Vertical stability and the annual dynamics of nutrients and chlorophyll fluorescence in the coastal, southeast Beaufort Sea

“…Since the assimilatory reduction of NO 3 À is energetically disadvantageous at very low irradiance, a portion of the Si drawdown may also have been fueled by the recycling of reduced N sources (NH 4 + or DON) and P in the lower euphotic zone. The formation of highly silicified diatom resting spores at the SCM, which was documented elsewhere in the Arctic [Booth et al, 2002;Michel et al, 2002] may have played a secondary role during July and August. Although we cannot overrule any explanation for the elevated Si:NO 3 À drawdown ratio in Franklin Bay relative to Baffin Bay and the Barents Sea, a combination of high optimal Si requirements for the dominant diatoms and growth under low irradiance at the SCM appears most likely.…”