Sources and Cycling of Neodymium and Rare Earth Elements in the Arctic Amerasian Basin and Bering Sea

• Main Author: Duggan, Brian D.
• Format: Text
• Language: English
• Published: Scholar Commons 2022
• Subjects: Arctic Ocean; Bering Sea; GEOTRACES; neodymium isotope composition; rare earth elements; seawater; Oceanography; Oceanography and Atmospheric Sciences and Meteorology; Arctic; Atlantic Arctic; Atlantic-Arctic; Bering Strait; Chukchi
• Online Access: https://scholarcommons.sc.edu/etd/7059; https://scholarcommons.sc.edu/context/etd/article/8023/viewcontent/Duggan_sc_0202A_18608.pdf

The isotopic composition of dissolved neodymium (143Nd/144Nd, expressed as εNd) behaves quasi-conservatively in the ocean and has been used as a palaeoceanographic tracer of ocean circulation. The εNd value of water masses is acquired—and often altered—during interaction with sediments along the margins; however, the processes involved in seawater εNd acquisition remains poorly characterized and quantified. Here we report the results of 349 Nd isotope and 354 rare earth element (REE) concentration measurements from 27 water column profiles across the Bering shelf and through the Arctic Amerasian Basin collected during U.S. Arctic GEOTRACES cruise HLY1502 (GEOTRACES section GN01). At the edge of the shelf (4 – 733 m), Bering Sea εNd is not appreciably altered from North Pacific endmember values despite transiting the Aleutian volcanic arc. The εNd values observed are then modified during transit across the eastern shelf; less radiogenic compositions accompany increases in the Nd concentration ([Nd]), particularly in samples below the pycnocline. The spatial pattern of [Nd] and less radiogenic εNd values point to benthic Nd additions to the water column, which is supported by a strong correlation between εNd values and 228Ra activities in sub-pycnocline samples and an enrichment of middle rare earth elements (MREE) The flux and the Nd isotope composition required to produce the observed changes was calculated by mass balance using a box model of the Bering Sea shelf. The results are consistent with Nd derived from the sedimentary authigenic ferromanganese component Near the Bering Strait, the εNd value is closer to the unaltered values at the southern Bering Shelf edge, reflecting the contribution of waters transiting the western shelf in a current system that moves faster and in deeper water compared to the eastern shelf, providing less opportunity for benthic driven alterations to the εNd value. Stations north of Bering Strait (on the Chukchi shelf) indicate the presence of Atlantic Arctic Water ...