Tracing the Nd isotope evolution of North Atlantic Deep and Intermediate Waters in the western North Atlantic since the Last Glacial Maximum from Blake Ridge sediments
Stirling, Claudine H.
Keigwin, Lloyd D.
Halliday, Alex N.
MetadataShow full item record
A high-resolution authigenic Nd isotope record has been extracted from the Fe-Mn oxyhydroxide fraction of drift sediments along the Blake Ridge in the North Atlantic. These sediments facilitate reconstruction of the timing and extent of major hydrographic changes in the western North Atlantic since the Last Glacial Maximum (LGM). This is one of the few locations where sediments were deposited in the major flow path of the Western Boundary Undercurrent (WBUC), which transports North Atlantic Deep Water (NADW) southward at the present day. The hydrodynamic setting, however, also causes problems. Authigenic Nd isotope compositions similar to the typical present-day NADW εNd value of –13.5 ± 0.5 were only extracted from sediments located within the main water body of the WBUC coinciding with the highest along slope current velocity below 3200 m water depth. Above this depth the authigenic Nd isotopic composition is more radiogenic than measured in a nearby seawater profile and appears to be influenced by downslope and lateral sediment redistribution. Our data suggest that these radiogenic signals were formed at shallow depths in Florida current waters, compromising the recorded ambient deep water Nd isotope signal in the Blake Ridge Fe-Mn oxyhydroxide coatings from intermediate depths during the Holocene and the deglaciation. The unradiogenic Nd isotopic composition typical of present-day NADW is not detectable along the Blake Ridge for any water depth during the LGM. Unlike the deglacial and Holocene sections, the intermediate core from 1790 m water depth did not experience significant sediment focussing during the LGM, in accord with the higher current velocities at this depth, suggesting that at this site an ambient LGM bottom water Nd isotope signal was recorded. Assuming this to be correct, our results indicate that the εNd of the shallower glacial equivalent of NADW, the Glacial North Atlantic Intermediate Water (GNAIW) may have been as radiogenic as –9.7 ± 0.4. Since the authigenic Nd isotope compositions of the Holocene and the deglacial sections of the intermediate depth sediment core were biased towards a shallow water signal, this first determination of a GNAIW εNd for the LGM will have to be corroborated by results from other locations and archives. The LGM and deglacial sediments below 3400 m water depth bear no evidence of an ambient deep water εNd as unradiogenic as -13.5. Although the deep core sites also experienced enhanced degrees of sediment focusing before the Younger Dryas, the εNd values of between -11 and – 10 are more readily explained in terms of increased presence of Southern Source Waters. If this is the case, the change to Nd isotopic compositions that reflect a modern circulation pattern, including the presence of Lower NADW, only occurred after the Younger Dryas.
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 266 (2008): 61-77, doi:10.1016/j.epsl.2007.10.037.
Showing items related by title, author, creator and subject.
Changes in the North Atlantic Oscillation influence CO2 uptake in the North Atlantic over the past 2 decades Thomas, Helmuth; Prowe, A. E. Friederike; Lima, Ivan D.; Doney, Scott C.; Wanninkhof, Rik; Greatbatch, Richard J.; Schuster, Ute; Corbiere, Antoine (American Geophysical Union, 2008-12-31)Observational studies report a rapid decline of ocean CO2 uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physical-biological numerical simulations forced with interannually ...
The impact of the North Atlantic Oscillation on the uptake and accumulation of anthropogenic CO2 by North Atlantic Ocean mode waters Levine, Naomi M.; Doney, Scott C.; Lima, Ivan D.; Wanninkhof, Rik; Bates, Nicholas R.; Feely, Richard A. (American Geophysical Union, 2011-09-21)The North Atlantic Ocean accounts for about 25% of the global oceanic anthropogenic carbon sink. This basin experiences significant interannual variability primarily driven by the North Atlantic Oscillation (NAO). A suite ...
A science plan for a collaborative international research program on the coupled North Atlantic-Arctic system, a report of a Planning Workshop for an International Research Program on the Coupled North Atlantic-Arctic System developed from a workshop held in Arlington, VA 14-16 April 2014 Hofmann, Eileen E.; St. John, Mike; Benway, Heather M. (Ocean Carbon & Biogeochemistry Program, 2015)This North Atlantic-Arctic science plan is derived from an international workshop held in April 2014 with support from the National Science Foundation Division of Ocean Sciences and the European Union (EU). The workshop ...