Radiometrically determined sedimentary fluxes in the sub-polar North Atlantic during the last 140,000 years

McManus, Jerry F; Anderson, Robert F.; Broecker, Wallace S.; Fleisher, Martin Q.; Higgins, Sean M.

doi:10.1016/s0012-821x(97)00201-x

Cited by 124 publications

(90 citation statements)

References 43 publications

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“…Excess activities were calculated using a correction for the supported detrital portion of the total 230 Th and 231 Pa measured. The detrital fraction of 238 U was calculated assuming a detrital source for all 232 Th, and a detrital 238 U/ 232 Th activity ratio of 0.5±0.2, within error of the value (0.57-0.6 ± 0.2) estimated in previous studies of North Atlantic sediments 5,16,38 . Each sample was also corrected for radioactive decay of excess nuclides since the time of deposition.…”

Section: Discussionsupporting

confidence: 75%

“…The 231 Pa flux approach relies on the robustness of the assumption that the burial rate of 230 Th in the sediment is equal to its production in the water column. This assumption is widely believed to be accurate to ±30% over most of the ocean 3 , and is likely to be more accurate in the relatively particle-rich Atlantic, where B90% of 230 Th production is buried in the basin today 1,6 , and possibly more in our older study intervals 16,38 . Figure 4 shows 231 Pa fluxes from the 25 cores in our depth survey during the Holocene, HS1 and LGM time slices compared with total water-column production of 231 Pa.…”

Section: Discussionmentioning

confidence: 88%

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231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1

2014

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The strength of Atlantic meridional overturning circulation is believed to affect the climate over glacial-interglacial and millennial timescales. The marine sedimentary 231 Pa/ 230 Th ratio is a promising paleocirculation proxy, but local particle effects may bias individual reconstructions. Here we present new Atlantic sedimentary 231 Pa/ 230 Th data from the Holocene, the last glacial maximum and Heinrich Stadial 1, a period of abrupt cooling ca. 17,500 years ago. We combine our results with published data from these intervals to create a spatially distributed sedimentary 231 Pa/ 230 Th database. The data reveal a net 231 Pa deficit during each period, consistent with persistent 231 Pa export. In highly resolved cores, Heinrich 231 Pa/ 230 Th ratios exceed glacial ratios at nearly all depths, indicating a significant reduction, although not cessation, of overturning during Heinrich Stadial 1. These results support the inference that weakened overturning was a driver of Heinrich cooling, while suggesting that abrupt climate oscillations do not necessarily require a complete shutdown of overturning.

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Section: Discussionsupporting

confidence: 75%

Section: Discussionmentioning

confidence: 88%

231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1

2014

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“…2), at the same time as the occurrence of a peak in IRD related to a major iceberg discharge, Heinrich event 11 (H11) (49). This oldest of the events identified by Heinrich (49) is evident throughout the North Atlantic (16,17,40,(50)(51)(52), and is recognized in associated changes globally (14,53,54). Immediately thereafter, NpS and IRD abundances decrease sharply, as the benthic δ 18 O reaches its peak interglacial level and the subpolar NpD abundance rises to its maximum.…”

Section: Our Investigations Are Based On New Results From Oceanmentioning

confidence: 97%

Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic

Mokeddem

McManus

Oppo

2014

Proc. Natl. Acad. Sci. U.S.A.

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The last interglacial interval was terminated by the inception of a long, progressive glaciation that is attributed to astronomically influenced changes in the seasonal distribution of sunlight over the earth. However, the feedbacks, internal dynamics, and global teleconnections associated with declining northern summer insolation remain incompletely understood. Here we show that a crucial early step in glacial inception involves the weakening of the subpolar gyre (SPG) circulation of the North Atlantic Ocean. Detailed new records of microfossil foraminifera abundance and stable isotope ratios in deep sea sediments from Ocean Drilling Program site 984 south of Iceland reveal repeated, progressive cold water-mass expansions into subpolar latitudes during the last peak interglacial interval, marine isotope substage 5e. These movements are expressed as a sequence of progressively extensive southward advances and subsequent retreats of a hydrographic boundary that may have been analogous to the modern Arctic front, and associated with rapid changes in the strength of the SPG. This persistent millennial-scale oceanographic oscillation accompanied a long-term cooling trend at a time of slowly declining northern summer insolation, providing an early link in the propagation of those insolation changes globally, and resulting in a rapid transition from extensive regional warmth to the dramatic instability of the subsequent ∼100 ka.gyre systems | cold anomalies | frontal zone | ocean circulation

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“…Contour lines on map are ∆T from Benthien & Müller (2000). Th ratio of R=0.6 was assumed (McManus et al, 1998). Errors given for focusing factor and flux estimates are based on R=0.6 ± 0.1.…”

mentioning

confidence: 99%

Rapid lateral particle transport in the Argentine Basin: Molecular 14C and 230Thxs evidence

Mollenhauer

McManus

Benthien

et al. 2006

Deep Sea Research Part I: Oceanographic Research Papers

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Recent studies have revealed that lateral transport and focusing of particles strongly influences the depositional patterns of organic matter in marine sediments. Transport can occur in the water column prior to initial deposition or following sediment re-suspension. In both cases, fine-grained particles and organic-rich aggregates are more susceptible to lateral transport than coarse-grained particles (e.g. foraminiferal tests) because of the slower sinking velocities of the former. This may lead to spatial and, in the case of redistribution of resuspended sediments, temporal decoupling of organic matter from coarser sediment constituents. Prior studies from the Argentine Basin have yielded evidence that suspended particles are displaced significant distances (100 -1000 km) northward and downslope by strong surface and/or bottom currents. These transport processes result in anomalously cold alkenone-derived sea surface temperature (SST) estimates (up to 6°C colder than measured SST) and in the presence of frustules of Antarctic diatom species in surface sediments from Thxs-based focusing factors of 1.4 to 3.2 at sites where alkenone-based SST estimates were 4 -6 °C colder than measured values. In contrast, alkenone radiocarbon data suggest coeval deposition of marine biomarkers and planktic foraminifera, as alkenones in core-tops were younger than, or similar in age to, foraminifera. We therefore infer that the transport processes leading to the lateral displacement of these sediment components are rapid, and hence probably occur in the upper water column (< 1500 m).

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Radiometrically determined sedimentary fluxes in the sub-polar North Atlantic during the last 140,000 years

Cited by 124 publications

References 43 publications

231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1

231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1

Oceanographic dynamics and the end of the last interglacial in the subpolar North Atlantic

Rapid lateral particle transport in the Argentine Basin: Molecular 14C and 230Thxs evidence

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