Phytoplankton Dynamics in the Subarctic Northeast Pacific Ocean During the 2019 Marine Heatwave
Bibliographic record
Abstract
Marine phytoplankton are responsible for nearly 50% of all the primary productivity on Earth, and their response to climate change and anomalous climatic events impacts biogeochemical cycling. During the summer of 2019, the NE Pacific Ocean experienced a warming event that caused sea surface temperature anomalies of up to 4 °C. These types of events, called marine heatwaves (MHW), are becoming more common globally but their effects on pelagic primary producers are not yet well understood. In September 2018 and August-September 2019, temperature, salinity, nutrient concentrations, primary producer biomass, and uptake rates of carbon (ρC) and nitrogen (ρNO3) were measured along the Line P transect in the NE Pacific. Additionally, in August-September 2019, nitrate (NO3) and silicon (Si) uptake kinetic experiments were performed at five Line P stations in addition to five stations on the west coast of Vancouver Island to assess potential physiological limitation in phytoplankton from NO3 and Si. In 2019, temperatures in the euphotic zone along Line P were higher and the water column was more stratified at all stations than in 2018. Concentrations of dissolved NO3 and silicic acid (Si(OH)4) were anomalously low in 2019 and nutrient depletion extended approximately 500 km further offshore than in 2018. The Line P station closer to the shelf (P4) had a considerable reduction in chlorophyll-a (chl-a), biogenic silica (bSiO2) and the contribution of diatoms to the entire phytoplankton assemblage. From P4 to P20, the assemblage was dominated by small-celled phytoplankton (<5 um) in both years, but there was a relative increase in 2019. There were particularly unusual observations at the most oceanic station (P26) where the contribution of diatoms, concentrations of chl-a and bSiO2, and ρC, and ρNO3 were anomalously high in 2019 compared to regional averages. In 2019, the uptake of Si(OH)4 appeared to be substrate limited at the majority of stations while only station CS02 on the west coast of Vancouver Island appeared to have physiological limitation by NO3. Based on Michaelis-Menten uptake kinetics, half saturation constants (Km) ranged from 0.01-0.13 for NO3 and 2.33-18.3 for Si(OH)4, suggesting that assemblages are less efficient at Si uptake than NO3 uptake in the NE Pacific. Results from this study are consistent with observations from the other warming anomalies including the 2015 “blob” and the 1997/1998 ENSO event in the NE Pacific Ocean. The similarities observed during these ocean warming events suggest that phytoplankton in the NE subarctic Pacific may become increasingly susceptible to nutrient limitation, particularly from Si(OH)4, with increased stratification. Future investigations should focus on co-limitation studies of Fe and Si(OH)4, uptake rates of regenerated nitrogen sources, timing of bloom onsets, total annual biomass and trophic interactions with zooplankton during MHW events.
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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 | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".