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.
|Original language||English (US)|
|Number of pages||15|
|State||Published - Nov 6 2018|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors thank the science team and crew of the RV Helmer Hanssen. We also thank Sigrid Øygarden, Emma Kube, Angelika Renner, Daniel Vogedes, Hanne Foshaug, Sydney Acton, David Wiik, Britt Vaaja, and William Dobbins for logistic support. We also thank two anonymous reviewers for constructive feedback. Primary data analysis was supported by the Dauphin Island Sea Lab. Vessel time, ancillary data, and Ingrid Wiedmann’s and Paul Wassmann’s contribution was supported by ARCEx, funded by industry partners and the Research Council of Norway (project no. 228107). Philipp Assmy was supported by the Research Council of Norway (project no. 244646). Philipp Assmy and Mar Fernández-Méndez were funded by Norwegian Ministries of Foreign Affairs and Climate and Environment through the Arktis 2030 programme (project ID Arctic). Jeffrey W. Krause, Carlos M. Duarte, and Susana Agustí were supported by internal funding sources at their respective institutions.