In:
Paleoceanography, American Geophysical Union (AGU), Vol. 15, No. 6 ( 2000-12), p. 625-641
Abstract:
Holocene sediments from the Atlantic are characterized by 231 Pa/ 230 Th ratios below the production ratio of the two radionuclides in the water column (0.093), whereas Holocene sediments from the Southern Ocean have 231 Pa/ 230 Th 〉 0.093. This pattern of 231 Pa deficit and excess was ascribed to southward 231 Pa export from the Atlantic by the Atlantic thermohaline circulation (THC) as Pa is scavenged less efficiently by marine particles and more effectively transported by the THC than Th. The same pattern is observed in deposits of the Last Glacial Maximum (LGM), which led to a previous contention that the THC strength did not vary markedly through the last glacial termination. Here we embed a description of trace metal scavenging into a zonally averaged, circulation‐biogeochemistry ocean model to explore the sensitivity of 231 Pa/ 230 Th in Atlantic and Southern Ocean sediments to THC changes. Our results show that the production of biogenic opal (which, unlike other marine particles, poorly fractionates Th and Pa) in the Southern Ocean water column determines the spatial pattern of the sensitivity. Also, 231 Pa/ 230 Th increases in the North Atlantic but changes little in the South Atlantic and decreases in the Southern Ocean as THC is reduced. The mean 231 Pa/ 230 Th of the whole Atlantic is therefore less sensitive to THC changes than the mean 231 Pa/ 230 Th of the North Atlantic. The current uncertainties in Atlantic mean 231 Pa/ 230 Th are too large to rule out a twofold reduction of the THC at the LGM. However, the increase in North Atlantic mean 231 Pa/ 230 Th simulated in response to a twofold THC reduction is larger than the observed change in the North Atlantic mean 231 Pa/ 230 Th from the LGM to Holocene. Comparing this change with the modeled sensitivity of North Atlantic 231 Pa/ 230 Th to THC variations indicates that the THC at the LGM could not have been reduced by 〉 30% of its present strength. Experiments of transient THC changes indicate that high‐resolution 231 Pa/ 230 Th records from North Atlantic sediments could also document thermohaline oscillations on century‐to‐millennial timescales.
Type of Medium:
Online Resource
ISSN:
0883-8305
,
1944-9186
DOI:
10.1029/2000PA000496
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
2000
detail.hit.zdb_id:
637876-6
detail.hit.zdb_id:
2015231-0
detail.hit.zdb_id:
2916554-4
SSG:
16,13
SSG:
13
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