Prolonged diatom blooms and microbial food web dynamics: experimental results from an Arctic polynya
Bibliographic record
Abstract
Thalassiosira spp., large-chain forming centric diatoms, typically dominate the biomass during phytoplankton blooms in the North Water Polynya (76 to 79N, centred on ca. longitude 75W), which is the largest recurring polynya in the Canadian Arctic. We used an experimental method based on semi-continuous cultures to investigate mechanisms responsible for bloom maintenance and associated changes in microbial food web constituents. We compared 2 treatments: (1) a new nutrient system in which the cultures were partially enriched every 2 d with nutrient-rich seawater from depth to simulate horizontal or vertical advection, and (2) a recycled nutrient system in which large particles (> 2.0 m) were partially removed every 2 d to simulate grazing and sinking losses without nutrient replacement. The experiment lasted 8 d. In the new nutrient treatment, large diatoms, particularly Thalassiosira spp. and to a lesser extent Chaetoceros spp., consumed the added nutrients and continued to dominate production and biomass of the protist community. The total eukaryotic community production in the 'recycled' community shifted to one dominated by dinoflagellates and ciliates in the absence of diatom growth. These 2 end points corresponded to 2 types of communities observed in the North Water Polynya in June 1998. Net production rates for viruses and bacteria were not significantly different between treatments. These results demonstrate the importance of advective processes in maintaining a prolonged diatom bloom. An underlying microbial food web dominated by large (> 20 m) ciliates and dinoflagellates was able to maintain similar rates of net production respective of new versus recycled nutrient supply. Dominance of the protist communities by large cells under both conditions is likely to favour the sustained high productivity of zooplankton and megafauna that characterize the North Water Polynya.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".