Regulation of the phytoplankton heme b iron pool during the North Atlantic spring bloom
Bibliographic record
Abstract
<p>Heme <i>b</i> is an iron-containing co-factor in hemoproteins. Heme <i>b</i> concentrations are low (<1 pmol L<sup>-1</sup>) in iron limited phytoplankton in cultures and in the field. Here, we determined heme <i>b</i> in marine particulate material (>0.7 μm) from the North Atlantic Ocean (GEOVIDE cruise – GEOTRACES section GA01), which spanned several biogeochemical regimes. We examined the relationship between heme <i>b</i> abundance and the microbial community composition, and its utility for mapping iron limited phytoplankton. Heme <i>b</i> concentrations ranged from 0.16 to 5.1 pmol L<sup>-1</sup> (median = 2.0 pmol L<sup>-1</sup>, <i>n</i> = 62) in the surface mixed layer (SML) along the cruise track, driven mainly by variability in biomass. However, in the Irminger Basin, the lowest heme <i>b</i> levels (SML: median = 0.53 pmol L<sup>-1</sup>, <i>n</i> = 12) were observed, whilst the biomass was highest (particulate organic carbon, median = 14.2 μmol L<sup>-1</sup>, <i>n</i> = 25; chlorophyll <i>a</i>: median = 2.0 nmol L<sup>-1</sup>, <i>n</i> = 23) pointing to regulatory mechanisms of the heme <i>b</i> pool for growth conservation. Dissolved iron (DFe) was not depleted (SML: median = 0.38 nmol L<sup>-1</sup>, <i>n</i> = 11) in the Irminger Basin, but large diatoms (<i>Rhizosolenia</i> sp.) dominated. Hence, heme <i>b</i> depletion and regulation is likely to occur during bloom progression when phytoplankton class-dependent absolute iron requirements exceed the available ambient concentration of DFe. Furthermore, high heme <i>b</i> concentrations found in the Iceland Basin and Labrador Sea (median = 3.4 pmol L<sup>-1</sup>, <i>n</i> = 20), despite having similar DFe concentrations to the Irminger Basin, were attributed to an earlier growth phase of the extant phytoplankton populations. Thus, heme <i>b</i> provides a snapshot of the cellular activity <i>in situ</i> and could both be used as indicator of iron limitation and contribute to understanding phytoplankton adaptation mechanisms to changing iron supplies.</p>
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 teacher head, 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".