Influence of Ocean Circulation and Benthic Exchange on Deep Northwest Atlantic Nd Isotope Records During the Past 30,000 Years

Abstract

Neodymium (Nd) isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance. To better constrain the controls of water mass provenance and nonconservative effects on the archived Nd isotope signal, we present a new depth transect of Nd isotope reconstructions from the Blake Bahama Outer

Constraints on the Northwestern Atlantic Deep Water Circulation From 231Pa/230Th During the Last 30,000 Years

“…Accordingly, when considering the depth structure of 231 Pa/ 230 Th (Figure ), our new records are in line with the hypothesis of the northwestern Atlantic basin predominantly bathed by NSW rather than SSW during the LGM as inferred from Nd isotope records (Howe et al, ; Pöppelmeier et al, ).…”

“… 231 Pa/ 230 Th (diamonds) and biogenic opal (black dots) records from this study complemented by Nd isotope records (downward triangles) denoted as εNd ( 143 Nd/ 144 Nd normalized to the Chondritic Uniform Reservoir in parts per ten thousand) of the BBOR cores (Pöppelmeier et al, ). For all panels, the gray background lines depict 231 Pa/ 230 Th and Nd isotope records from the Bermuda Rise for comparison (Gutjahr & Lippold, ; Lippold et al, ; McManus et al, ; Roberts et al, ).…”

“…While the latter records display deglacial millennial‐scale features, these are missing in the 12JPC record exhibiting a small plateau during the B/A only. Similarly, the Nd isotope record of 12JPC also shows only a gradual glacial‐interglacial shift (Pöppelmeier et al, ). Sedimentary depositional processes (e.g., winnowing or sediment redistribution; Gutjahr et al, ; Pöppelmeier et al, ) may have played a role in smoothing out the original oceanographic signal at this site.…”

“…From these findings it is difficult to maintain the notion of SSW predominantly bathing the BBOR and the Bermuda Rise during the LGM. Analyses from all these sites provide very similar Nd isotope signatures indicating that the complete depth transect at the BBOR was bathed in the same water mass during the LGM (Gutjahr et al, ; Gutjahr & Lippold, ; Pöppelmeier et al, ; Roberts et al, ). In contrast to the uniform picture in Nd isotope signatures, 231 Pa/ 230 Th ratios at the Bermuda Rise (~4,500‐m water depth; McManus et al, ; Lippold et al, ) were significantly lower than at the BBOR during the LGM nearly reaching Holocene levels (Figures and a; note the different color at ~4,500 m between ~20 and ~24 ka compared to the predominant color of the water column above and below in Figure ).…”

“…In addition, we improved the 231 Pa/ 230 Th records (partly reanalyzed and recalibrated, see Table S5 in the supporting information) of KNR140 12JPC (hereafter 12JPC) on the BBOR and cores GeoB1515‐1 and GeoB1523‐1 from the Ceara Rise in the equatorial western Atlantic (Lippold et al, ). Age models for Sites 1059 to 1062 are provided by Pöppelmeier et al () and are based on the correlation of carbonate concentration for Sites 1059 and 1062 (Grützner et al, ) to neighboring cores KNR140 GGC39 (Keigwin & Schlegel, ) and KNR31‐GPC9 (Keigwin & Jones, ), respectively. Additionally, the age model consists of 12 14 C dates on Site 1060, two dates on Site 1062, and four recalibrated 14 C dates on Site 1059 (Hagen & Keigwin, ; Pöppelmeier et al, ).…”