Biogeosciences: Arctic (Svalbard islands) active and exported diatom stocks and cell health status

Susana Agustí1, Jeffrey W. Krause2,3, Israel A. Marquez2,3, Paul Wassmann4, Svein Kristiansen4, and Carlos M. Duarte1,5 are the authors of the paper “Arctic (Svalbard islands) active and exported diatom stocks and cell health status” published in the journal Biogeosciences. The article is based on data from the ARCEx cruise in 2016.

1Red Sea Research Center, King Abdullah University of Science and Technology, Kingdom of Saudi Arabia
2Dauphin Island Sea Lab, Dauphin Island, USA
3Department of Marine Sciences, University of South Alabama, USA
4Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Norway
5Arctic Research Centre, Department of Bioscience, Aarhus University, Denmark

Abstract: 

Diatoms tend to dominate the Arctic spring phytoplankton bloom, a key event in the ecosystem includinga rapid decline in surface-water pCO2. While a mass sedimentation event of diatoms at the bloom terminus is commonly observed, there are few reports on the status of diatoms’ health during Arctic blooms and its possible role on sedimentary fluxes. Thus, we examine the idea that the major
diatom-sinking event which occurs at the end of the regional bloom is driven by physiologically deteriorated cells. Here we quantify, using the Bottle-Net, Arctic diatom stocks below and above the photic zone and assess their cell health status. The communities were sampled around the Svalbard islands and encompassed pre- to post-bloom conditions. A mean of 24.2±6.7% SE (standard error) of the total water column (max. 415 m) diatom standing stock was found below the photic zone, indicating significant diatom sedimentation. The fraction of living diatom cells in the photic zone averaged 59.4±6.3% but showed the highest mean percentages (72.0 %) in stations supporting active blooms. In contrast, populations below the photic layer were dominated by dead cells (20.8±4.9% living cells). The percentage of diatoms’ standing stock found below the photic layer was negatively related to the percentage of living diatoms in the surface, indicating that healthy populations remained in the surface layer. Shipboard manipulation experiments demonstrated that (1) dead diatom cells sank faster than living cells, and (2) diatom cell mortality increased in darkness, showing an average half-life among diatom groups of 1.025±0.075 d. The results conform to a conceptual model where diatoms grow during the bloom until resources are depleted and supports a link between diatom cell health status (affected by multiple factors) and sedimentation fluxes in the Arctic. Healthy Arctic phytoplankton communities remained at the photic layer, whereas the physiologically compromised (e.g., dying) communities exported a large fraction of the biomass to the aphotic zone, fueling carbon sequestration to the mesopelagic and material to benthic ecosystems.

Reference:

Augusti, S.; Krause, J.W; Marquez, I.A.; Wassmann, P.; Kristiansen, S.; Duarte, C.M. (2020): Arctic (Svalbard islands) active and exported diatom stocks and cell health status. Biogeosciences, 17, 35–45, 2020. DOI: https://doi.org/10.5194/bg-17-35-2020. [intranet]