South Pacific dissolved Nd isotope compositions, rare earth element and nutrient concentrations from SONNE cruise SO213

Despite its enormous extent and importance for global climate, the South Pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography. Here we present the first detailed analysis of dissolved radiogenic Nd isotopes (epsilon-Nd) and rare earth elements (REEs) in intermediate and deep waters of the mid-latitude (~40°S) South Pacific along a meridional transect between South America and New Zealand. The goal of our study is to gain better insight into the distribution and mixing of water masses in the South Pacific and to evaluate the validity of Nd isotopes as a water mass tracer in this remote region of the ocean. The results demonstrate that biogeochemical cycling (scavenging processes in the Eastern Equatorial Pacific) and release of LREEs from the sediment clearly influence the distribution of the dissolved REE concentrations at certain locations. Nevertheless, the Nd isotope signatures clearly trace water masses including AAIW (Antarctic Intermediate Water) (average epsilon-Nd = -8.2 ± 0.3), LCDW (Lower Circumpolar Deep Water) (average epsilon-Nd = -8.3 ± 0.3), NPDW (North Pacific Deep Water) (average epsilon-Nd = -5.9 ± 0.3), and the remnants of NADW (North Atlantic Deep Water) (average epsilon-Nd = -9.7 ± 0.3). Filtered water samples taken from the sediment-water interface under the deep western boundary current off New Zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process. These data will serve as a basis for the paleoceanographic application of Nd isotopes in the South Pacific.

Composition of recent pelagic sediments from the South Pacific

Lithologic, grain size, chemical and mineral compositions of recent bottom sediments from the South Pacific are reported in the paper.

Benthic foraminifera stable isotope data from the South Pacific sediment cores PS75/059-2 and PS75/056-1

Investigating the inter-basin deep water exchange between the Pacific and Atlantic Oceans over glacial-interglacial climate cycles is important for understanding circum-Antarctic Southern Ocean circulation changes and their impact on the global Meridional Overturning Circulation. We use benthic foraminiferal d13C records from the southern East Pacific Rise to characterize the d13C composition of Circumpolar Deep Water in the South Pacific, prior to its transit through the Drake Passage into the South Atlantic. A comparison with published South Atlantic deep water records from the northern Cape Basin suggests a continuous water mass exchange throughout the past 500 ka. Almost identical glacial-interglacial d13C variations imply a common deep water evolution in both basins suggesting persistent Circumpolar Deep Water exchange and homogenization. By contrast, deeper abyssal waters occupying the more southern Cape Basin and the southernmost South Atlantic have lower d13C values during most, but not all, stadial periods. We conclude that these values represent the influence of a more southern water mass, perhaps AABW. During many interglacials and some glacial periods, the gradient between Circumpolar Deep Water and the deeper southern Cape Basin bottom water disappears suggesting either no presence of AABW or indistinguishable d13C values of both water masses.