On sources and sinks of bioavailable nitrogen on the Scotian Shelf: Insights from nutrient distributions and nitrate isotope ratios
Bibliographic record
Abstract
The northwestern North Atlantic, and the extensive Northwest Atlantic Shelf in particular, are among the areas of the world’s ocean most dramatically affected by ongoing climate change. Profound alterations of nitrogen (N) cycling both in the water column and in the sediment are expected in response to rapidly changing ocean and biogeochemical conditions. Despite the importance of bioavailable nitrogen in shaping this marine environment and ultimately sustaining large commercial fisheries, significant uncertainties remain regarding the main sources and sinks of this key macronutrient. In this study, we use hydrographic data (T, S, O2) and nutrient concentrations collected during the Atlantic Zone Monitoring Program (AZMP) in an extended Optimum Multiparameter Analysis (eOMPA) to quantify the fractional contribution of nearshore versus slope waters on the Scotian Shelf. In combination with nitrate N and O isotope ratios (δ15NNO3 and δ18ONO3) these results will help to constrain the relationship between physical forcing (on-shelf nutrient transport) and biologically mediated sources and sinks of bioavailable N on the Scotian Shelf. Tracer distributions indicate different hydrographic sources between coastal and offshore slope stations. Nearshore subsurface (> 50 m) waters are characterized by low temperatures and a pronounced deficit in nitrate relative to phosphate (-4 µmol/L; assuming Redfield stoichiometry), highlighting the dominance of cold, fresh water from the Gulf of St. Lawrence along the inner shelf. Off-shelf, higher temperatures along with higher salinity and lower O2 concentrations indicate the presence of nutrient-rich slope waters, with contributions from both the Labrador Sea and the Gulf Stream. N and O isotope ratios show lower δ18ONO3 (0.0 – 0.4‰) and higher δ15NNO3 (~5.0‰) near the coast relative to stations further offshore (> 2.0‰ and ~4.0‰, respectively). Increased temperatures along with higher values of δ18ONO3 (~2.0‰) and a surplus in nitrate over phosphate (4 µmol/L) reflect the intrusion of warm slope waters into deep basins on the shelf. Tracer distributions further show an imprint of remineralization on bottom water properties along the shelf. These new data and results from the eOMPA will be discussed in the context of the regional circulation and N biogeochemistry.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".