Source and Transport of Terrigenous Organic Matter In the Upper Yukon River: Evidence From Isotope (𝛿C-13, ΔC-14, and 𝛿N-15) Composition of Dissolved, Colloidal, and Particulate Phases
Bibliographic record
Abstract
Natural organic matter was collected from the upper Yukon River and size fractionated into the (LMW-DOC), colloidal (COC, 1 kDa to 0.45 mu m) and particulate organic carbon (POC, > 0.45 mu m) phases for characterization of elemental (C and N) and isotopic (C-13, C-14 and N-15) composition to examine their sources and transport. Concentrations of total organic carbon (TOC) decreased from 3010 mu M in mid-May to 608 mu M in September, accompanying an increase in river water delta O-18 from the snowmelt to summer and early fall. COC was the predominant OC species, comprising, on average, 63 +/- 8% of the TOC, with 23 +/- 5% partitioned in the LMW-DOC and 14 +/- 5% in the POC fraction. Annual riverine export flux to the ocean was 2.02 +/- 10(12) g-C for TOC, 7.66 x 10(10) g-N for total organic nitrogen (TON), and 3.53 x 10(12) g-C for dissolved inorganic carbon (DIC), respectively. The C/N molar ratios were distinctly different between colloidal organic matter (COM, 46 +/- 3) and particulate organic matter (POM, 15 +/- 1.4). Similar delta C-13 values were found for LMW-DOM (-27.9 +/- 0.5 parts per thousand), COM (-27.4 +/- 0.2 parts per thousand), and POM (-26.2 +/- 0.7 parts per thousand), although there was a general increase with increasing size, suggesting a common terrigenous organic source. In contrast, distinct D 14 C values were found for LMW-DOC (-155 to +91 parts per thousand), COC (40 to 140 parts per thousand), and POC (-467 to -253 parts per thousand) with a decreasing trend from snowmelt to ice-open season, suggesting that turnover pathways and transport mechanisms vary with organic matter size fractions. The high abundance of COC and its contemporary C-14 ages points to a predominant source from modern terrestrial primary production, likely from the leaching/decomposition of fresh plant litter in the upper soil horizon. The predominately old POC (average 3698 +/- 902 years B. P.), in contrast, was largely derived from riverbank erosion and melting of permafrost. These results imply that ice-opening Yukon River flows are dominated by snowmelt (low delta O-18) with high DOC (high Delta C-14) but low DIC and Si(OH)(4) concentrations, whereas late summer flows contain more products of permafrost or ice melt and rain (high delta O-18), with low DOC (low Delta C-14) but high DIC and Si(OH)(4) concentrations. A warming climate with a deeper permafrost active layer in the Yukon River watershed would enhance the mobilization and export of old terrestrial OC, but largely in the particulate form into the Bering Sea and Arctic Ocean.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 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 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".