![]() ![]() According to Tachikawa (2003), the ε Nd signature of continental Nd supply to the northern Pacific is +1.1 ± 2, originating from weathering of the surrounding volcanic landmasses. Where CHUR represents the Chondritic Uniform Reservoir ( Jacobsen and Wasserburg, 1980). The radiogenic Nd isotope compositions ( 143Nd/ 144Nd) are expressed in the ε Nd notation defined as: There are, however, still considerable gaps in data coverage and in our knowledge of North Pacific Ocean circulation and Nd isotope behavior in this region. In the West and North Pacific, dissolved Nd isotope compositions and concentrations have previously been applied to help constrain water mass distribution and mixing ( Piepgras and Jacobsen, 1988 Amakawa et al., 2004a, b, 2009 Zimmermann et al., 2009 Grenier et al., 2013 Haley et al., 2017 Behrens et al., 2018 Du et al., 2020). As a geochemical provenance tracer, radiogenic neodymium (Nd) isotopes add valuable independent information on the origin of water masses and present and past oceanic circulation ( Frank, 2002 Goldstein and Hemming, 2003 van de Flierdt et al., 2012 Tachikawa et al., 2017). This complicates the investigation of water mass advection and mixing applying standard hydrographic parameters such as salinity, temperature, and oxygen concentrations. Due to the lack of deep-water formation, strong stratification and low horizontal density gradients prevail resulting in very slow flow velocities and the absence of large differences in physical water properties with depth. The northern Pacific is the largest ocean basin on Earth, but its exact circulation and water mass mixing patterns, in particular at greater depth, are not well constrained. Moreover, comparison with previously reported data indicates that the Nd isotope signatures and concentrations below 100 m depth essentially remained stable over the past decades, which suggests constant impacts of water mass advection and mixing as well as of non-conservative vertical exchange and bottom release. The deep-water Nd isotope signatures indicate a southern Pacific origin and subsequent changes along its trajectory resulting from a combination of water mass mixing, vertical processes and Nd release from seafloor sediments, which precludes Nd isotopes as quantitative tracers of deep-water mass mixing. Further north in the open North Pacific, mixing calculations based on ε Nd, and salinity suggest that this modification of the AAIW composition has a strong impact on intermediate water ε Nd signatures of the entire region allowing for improved identification of the formation regions and pathways of North Pacific Intermediate Water (NPIW). Highly radiogenic weathering inputs from Papua-New-Guinea control the ε Nd signature of the equatorial surface waters and strongly alter the ε Nd signal of Antarctic Intermediate Water (AAIW) by sea water-particle interactions leading to an ε Nd shift from −5.3 to −1.7 and an increase in from 8.5 to 11.0 pmol/kg between 7°S and 15°N. The Nd isotope compositions of equatorial surface and subsurface waters are strongly influenced by regional inputs from the volcanic rocks surrounding the Pacific, which facilitates the identification of the source regions of these waters and seasonal changes in their advection along the equator. ![]() The strongest contrast in Nd isotope signatures is observed in equatorial regions between surface waters (ε Nd ∼0 at 4.5°N) and Lower Circumpolar Deep Water (LCDW) prevailing at 4500 m depth (ε Nd = −6.7 at 7.2°N). Here, we present dissolved neodymium (Nd) isotope compositions (ε Nd) and concentrations () obtained along a longitudinal transect at ∼180☎ from ∼7°S to ∼50°N. Geochemical tracers sensitive to water mass provenance and mixing allow to better characterize the origin and fate of the prevailing water masses. The sluggish water mass transport in the deeper North Pacific Ocean complicates the assessment of formation, spreading and mixing of surface, intermediate and deep-water masses based on standard hydrographic parameters alone. GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.Michael Fuhr *, Georgi Laukert, Yang Yu, Dirk Nürnberg and Martin Frank ![]()
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