Bestimmung des 'endmembers' der Nd-Isotopie von nordatlantischem Tiefenwasser über den letzten glazialen Zyklus
Mineralogie, Petrologie und Geochemie
Zusammenfassung der Projektergebnisse
In order to reconstruct past variations in the Atlantic Meridional Overturning Circulation many studies interpreted Nd isotope records under the assumption of invariable end members. However, during recent investigations it emerged that this assumption does not hold for all times. To investigate this a good spatio-temporal resolution with welldefined Nd end members is required. Until this study no Nd isotope record from the North Atlantic, representing the northern end member, existed that spans the entire glacial cycle. This study aimed to close this critical data gap in the North Atlantic. In this project we generated new authigenic Nd data of North Atlantic site U1313. Supported by a comparison to the shallower site SU90-03 it is demonstrated that site U1313 was not bathed by significant amounts of SSW over the past 100 kyr, and hence faithfully represents the northern εNd end-member. Combining these new northern Nd isotope end-member constraints with previously published εNd reconstructions from the Southeast Atlantic Cape Basin, representing the southern end-member, allows for binary mixing calculations. These suggest high proportions of NSW bathing the equatorial and Northeast Atlantic continuously over the entire last glacial cycle. This is largely attributed to the concurrent evolutions of both end-members as well as the intra-basin records over the past ~100 kyr, generally exhibiting more radiogenic signatures during colder climates and less radiogenic ones during warm periods. The only major exception is glacial MIS4 when NSW contributions at both intra-basin sites appear to have been ~15% higher than the baseline during the last glacial cycle. These findings are corroborated by δ 13C records from the same locations also evolving predominantly in tandem over the past 100 kyr indicating similar large and concurrent glacial-interglacial swings in endmember compositions. Hence, this result contradicts the notion that colder climates promoted the expansion of SSW in the deep Atlantic. If confirmed, this suggests that the increased glacial carbon storage was not a result of changes in deep ocean water mass provenance in the Atlantic but instead was more closely related to (more sluggish) deep ocean advection, enhanced export productivity, and/or changes in airsea gas exchange/disequilibrium due to increased sea-ice extent.
Projektbezogene Publikationen (Auswahl)
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Stable Atlantic Deep Water Mass Sourcing on Glacial‐Interglacial Timescales. Geophysical Research Letters, 48(15).
Pöppelmeier, Frerk; Gutjahr, Marcus; Blaser, Patrick; Schulz, Hartmut; Süfke, Finn & Lippold, Jörg
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Neodymium isotopes as a paleo-water mass tracer: A model-data reassessment. Quaternary Science Reviews, 279(c(2022, 3)), 107404.
Pöppelmeier, Frerk; Lippold, Jörg; Blaser, Patrick; Gutjahr, Marcus; Frank, Martin & Stocker, Thomas F.
