Biogenic silica production and diatom dynamics in the Svalbard region during spring

Jeffrey W. Krause,Svein Kristiansen,Carlos M. Duarte,Susana Agustí,Israel A. Marquez,Ingrid Wiedmann,Philipp Assmy,Paul Wassmann,Mar Fernández-Méndez

doi:10.5194/bg-15-6503-2018

Abstract

Abstract. Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic since the early 1990s. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard, which reports the first concurrent data on biogenic silica production and export, export of diatom cells, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95 % of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low concentration, and at some stations during the present study, silicon kinetic limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. The diatom contribution to primary production was variable, ranging from <10 % to ∼100 % depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the export rate of diatom cells, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers. This study provides the most direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.

Highlights

Diatoms and the haptophyte Phaeocystis are the dominant contributors to the Arctic Ocean spring bloom, a cornerstone event supplying much of the annual net community production (Rat’kova and Wassmann, 2002; Vaquer-Sunyer et al, 2013; Wassmann et al, 1999) that fuels Arctic food webs (Degerlund and Eilertsen, 2010, and references therein)
Krause et al.: Biogenic silica production and diatom dynamics in the Svalbard region lates and picoautotrophs, which has been observed in certain sectors of the Arctic (Li et al, 2009; Lasternas and Agustí, 2010)
This repackaging is consistent with previous observation in the Barents Sea showing high potential for copepod fecal pellets to be exported in the Polar Front and Arctic-influenced regions during spring (Wexels Riser et al, 2002). It supports the general ideas for the importance of diatom organic matter in fueling secondary production regionally during this season (Degerlund and Eilertsen, 2010, and references therein). This is the first regional data set with contemporaneous measurements of diatom bSiO2 standing stock, production, and export and assessment of kinetic limitation by [Si(OH)4] in the European Arctic

Summary

Introduction

Diatoms and the haptophyte Phaeocystis are the dominant contributors to the Arctic Ocean spring bloom, a cornerstone event supplying much of the annual net community production (Rat’kova and Wassmann, 2002; Vaquer-Sunyer et al, 2013; Wassmann et al, 1999) that fuels Arctic food webs (Degerlund and Eilertsen, 2010, and references therein). Because the spring diatom bloom is arguably the single most important productivity event for the Arctic Ocean ecosystem (Degerlund and Eilertsen, 2010; Holding et al, 2015; Vaquer-Sunyer et al, 2013), understanding how diatoms’ ecological and biogeochemical importance changes in response to system-wide physical or chemical shifts is important to predict future food web alterations. There is a current knowledge gap in regional silicon cycling, which precludes robust assessments of the spring bloom in future scenarios, e.g., Tréguer et al (2018)

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Discussion

Conclusion