Neodymium and hafnium boundary contributions to seawater along the West Antarctic continental margin

Abstract

30Neodymium and hafnium isotopes and elemental concentrations (Sm, Nd, Hf, Zr) 31 have been measured in three water column profiles south of the Antarctic 32 Circumpolar Current in, and to the east of the Ross Sea, in conjunction with five 33 bottom water samples from the Amundsen Sea Embayment. 34Neodymium and hafnium both appear to be released from sediments in the 35Embayment. In the case of Nd, this is reflected in radiogenic isotope 36 compositions (εNd up to -5.4) and highly elevated concentrations (up to 41 37 pmol/kg). Hafnium isotopes, on the other hand, are only very slightly altered 38relative to the open ocean sites, and boundary release is most prominently 39 indicated by elevated concentrations (> 1 pmol/kg versus ~0.7 pmol/kg). There 40 is also a local input of both Hf and Nd at the Marie Byrd Seamounts, which leads 41 to Nd isotope compositions as radiogenic as -3.1, and hafnium shifted to less 42 radiogenic compositions in local bottom water.

Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific

“…Closer to the Antarctic continent, CDW signatures are modified to more radiogenic values due to exchange with the margins (Carter et al, 2012). The same mechanism was inferred for the isotopic signature of Antarctic Bottom Water (AABW) formed in the Ross Sea (Rickli et al, 2014). At depth, AABW actively forms along the Antarctic shelf in the Weddell Sea, Ross Sea, Adélie Coast, and Prydz Bay (Orsi et al, 1999).…”

“…. Red symbols plotted together with station PS75/052 and PS75/088 are ε Nd (empty red circles) and [Nd] (empty red squares) from adjacent open ocean station 022 (Carter et al, 2012) and 116-1 (Rickli et al, 2014). Error bars for ε Nd are typically 2σ external reproducibility of JNdi-1 analyzed during the analytical sessions.…”

“…Simple mixing of these waters in the Southern Ocean are thought to dominantly determine the isotopic composition of Circumpolar Deep Water (CDW) with an intermediate ε Nd value of −8 to −9 (Goldstein and Hemming, 2003;Stichel et al, 2012;Garcia-Solsona et al, 2014) but weathering contributions from Antarctica to the Southern Ocean ε Nd have also recently been reported to play some role (Carter et al, 2012;Stichel et al, 2012;Rickli et al, 2014). In contrast to the Nd isotope distributions in the ocean, which appear to be dominated by advection and mixing of water masses, Nd concentrations generally show a nutrient-like behavior with increasing [Nd] with water depth, indicating a dominant vertical control (Elderfield and Greaves, 1982).…”

“…Only a limited number of dissolved Nd isotope data is available from the South Pacific sector of the Southern Ocean; these are located around the southern boundary of the ACC and one station immediately north of the APF (Carter et al, 2012;Rickli et al, 2014), leaving data gaps across the high latitude South Pacific that have so far prevented a comprehensive understanding of the ε Nd and [Nd] behavior in this region. Carter et al (2012) reported that Nd isotopes in the middle of the water column behave conservatively at open ocean stations.…”

Authigenic Neodymium Isotope Record of Past Ocean Circulation

“…Slightly modified from (A) Arsouze et al (2007) and (B), (C) Lacan et al (2012). Additional data from Rutberg et al (2000), Singh et al (2012), Stichel et al (2012), Jang et al (2013), Rickli et al (2014) and Garcia-Solsona et al (2014).…”