Potential Paleocirculation Implications By Coupling Pb and Nd Isotope Analyses On Different Grain-Size Fractions From Labrador Sea Sediments
Bibliographic record
Abstract
The production of deep water in the North Atlantic is one of the puzzle in understanding oceanic influence in climate changes. In this work, Nd and Pb isotopes were measured on the fine fraction of Labrador Sea sediments. Our aim is to record the relative contribution of fine particle supplies carried by the North Atlantic deep components into Labrador Sea. Based on characterization of potential geographical sources of particles, three main sources contribute to sediment mixture at core location: an old Precambrian crustal material from Canada, Greenland and Scandinavia (NAS), a Paleozoic or younger crustal material from East Greenland, Europa, and Scandinavia (YC) and a volcanic source from Iceland, Faeroe and Reykjanes Ridge (MAR). For the last 12 kyr, clay isotope signatures indicate two mixtures of sediment sources. The first mixture is composed of proximal material from Labrador Sea margins and distal deep current-driven crustal source. From 6.5 kyr onward, the mixture is characterized by the crustal and volcanic components. Since the significant decrease in proximal deglacial supplies, the evolution of the relative contributions of sediment sources suggests major changes in relative contributions of the deep water masses carried by the Western Boundary Undercurrent (WBUC) over the past 8.4 kyr. The progressive intensification of WBUC was associated mainly with the transport of North East Atlantic Deep Water mass until 6.5 kyr and with Denmark Strait Overflow Water thereafter. The establishment of the modern circulation at 3 kyr suggests a reduced influence of the Denmark Strait Overflow Water, synchronous with the full appearance of the Labrador Sea Water mass. Our isotopic dataset emphasizes several changes in the relative contribution of the two major components of North Atlantic Deep Water throughout the Holocene. However, if the clay-size fraction gives informations about the inception and presence of a deep current, it does tell nothing about the strength of this current. Moreover, clays are not likely to be deposited in case of high-strength deep current, resulting in an uncomplete and/or biased reconstruction of deep current evolution. To overcome this problem, it is necessary to look also at coarser fractions. Pb and Nd isotope compositions were thus analysed by MC-ICP-MS on different grain-size fractions (clay-size < 2 `µm, cohesive silt 2-10 µm, fine silt 10-30 µm and coarse silt 30-60 µm) on Late Glacial and Holocene sediments. Four grain-size fractions were investigated for a set of 12 samples from core MD99-2227:. Our results show a clear variation of Pb concentration and isotopic signatures according to grain-size (Nd data still in progress). The observed shifts are interpreted in terms of changes in deep current strength. This approach allows to monitor deep current changes through time, whatever the strength of paleocurrent.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".