High variability of export fluxes along the North Atlantic GEOTRACES section GA01: Particulate organic carbon export deduced from the <sup>234</sup> Th method
Bibliographic record
Abstract
Abstract. In this study, we report Particulate Organic Carbon (POC) export fluxes estimated using the 234Th-based approach in different biogeochemical basins of the North Atlantic, as part of the GEOTRACES GA01 expedition (GEOVIDE, May–June 2014). Surface POC export fluxes were deduced by combining export fluxes of 234Th with the POC to 234Th ratio of sinking particles at the depth of export. Particles were collected in two size classes (> 53 µm and 1–53 µm) using in-situ pumps and the large size fraction was considered as representative of sinking material. Surface POC export fluxes revealed latitudinal variations between provinces ranging from 1.4 mmol C m−2 d−1 in the Irminger basin where the bloom was close to its maximum peak, to 12 mmol C m−2 d−1 near the Iberian Margin where the bloom had already declined. In addition to the bloom staging, the variations of POC export fluxes were also related to the phytoplankton community structure. In line with previous studies, the presence of coccolithophorids and diatoms appeared to increase the POC export flux while stations dominated by pico-phytoplankton cells, such as cyanobacteria, were characterized by lower fluxes. The surface POC export fluxes were then compared to in-situ and satellite primary production (PP) in order to assess the export efficiency. This ratio strongly varied regionally and was generally low (≤ 14 %), except at two stations located near the Iberian margin (35 %) and within the Labrador basin (38 %), which were characterized by unusual low in-situ PP. We thus conclude that the North Atlantic during this period was not as efficient in exporting carbon from the surface, as described in recent studies. Finally, we estimated the flux of POC exported 100 m below the surface export depth in order to investigate the transfer efficiency along the section. This parameter was also highly regional-dependent but the lowest attenuation of the POC flux was observed at stations where coccolithophorids dominated.
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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) | 0.001 | 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".