TY - JOUR A1 - Hayes, Christopher T. A1 - Anderson, Robert F. A1 - Fleisher, Martin Q. A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Gersonde, Rainer T1 - Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes JF - Earth & planetary science letters N2 - Dissolved Th-232 is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as Fe. Oceanic Th-230, on the other hand, is sourced primarily from the highly predictable decay of dissolved U-234. The rate at which dissolved Th-232 is released by mineral dissolution can be constrained by a Th removal rate derived from Th-230:U-234 disequilibria, assuming steady-state. Calculated fluxes of dissolved Th-232 can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies, such as aerosol dust deposition, given the concentration and fractional solubility of Th (or other metals) in the lithogenic material. This method is applied to 7 water column profiles from the Innovative North Pacific Experiment (INOPEX) cruise of 2009 and 2 sites from the subtropical North Pacific. The structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved Th-232 at 100-200 m depth. This rapid cycling could involve colloidal Th generated during mineral dissolution, which may not be subject to the same removal rates as the more truly dissolved Th-230. An additional deep source of Th-232 was revealed in deep waters, most likely dissolution of seafloor sediments, and offers a constraint on dissolved trace element supply due to boundary exchange. (C) 2013 Elsevier B.V. All rights reserved. KW - dust KW - aerosols KW - thorium KW - boundary exchange KW - North Pacific Ocean KW - GEOTRACES compliant Y1 - 2013 U6 - https://doi.org/10.1016/j.epsl.2013.09.025 SN - 0012-821X SN - 1385-013X VL - 383 IS - 12 SP - 16 EP - 25 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Anderson, Robert F. A1 - Hayes, Christopher T. A1 - McGee, David A1 - Machalett, Bjoern A1 - Ren, Haojia A1 - Straub, Susanne M. A1 - Gersonde, Rainer A1 - Haug, Gerald H. T1 - Eolian dust input to the Subarctic North Pacific JF - Earth & planetary science letters N2 - Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, He-4, Th-232 and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at similar to 4 mu m. Applying the Th-230-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1-2 g/m(2)/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2-4 g/m(2)/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45 degrees N and west of 165 degrees E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5-1 g/m(2)/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific. KW - eolian dust KW - Subarctic North Pacific KW - INOPEX KW - helium-4 KW - Th-232 KW - REE Y1 - 2014 U6 - https://doi.org/10.1016/j.epsl.2013.11.008 SN - 0012-821X SN - 1385-013X VL - 387 SP - 252 EP - 263 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hayes, Christopher T. A1 - Anderson, Robert F. A1 - Fleisher, Martin Q. A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Gersonde, Rainer T1 - Biogeography in Pa-231/Th-230 ratios and a balanced Pa-231 budget for the Pacific Ocean JF - Earth & planetary science letters N2 - The ratio of unsupported protactinium-231 to thorium-230 in marine sediments, (Pa/Th)(xs), is potentially sensitive to several processes of oceanographic and climatological interest: deep ocean circulation, marine biological productivity (as it relates to total particle flux) and particle composition (specifically, biogenic opal and authigenic Mn). In order to attribute variations in (Pa/Th)(xs) observed in sediment records to changes in specific processes through time, a better understanding of the chemical cycling of these elements in the modern ocean is necessary. To this end, a survey was undertaken of (Pa/Th)(xs) in surface sediments from the subarctic Pacific (SO202-INOPEX expedition) in combination with a Pacific-wide compilation of published data. Throughout the Pacific, (Pa/Th)(xs) is robustly correlated with the opal content of sediments. In the North and equatorial Pacific, simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of Pa in the eastern equatorial Pacific and subarctic Pacific. Deep ocean water mass ageing (>3.5 km) associated with the Pacific overturning appears to play a secondary role in determining the basin scale distribution of (Pa/Th)(xs). A basin-wide extrapolation of Pa removal is performed which suggests that the Pacific Pa budget is nearly in balance. We hypothesize that through time (Pa/Th)(xs) distributions in the Pacific could define the evolving boundaries of contrasting biogeographic provinces in the North Pacific, while the influence of hydrothermal scavenging of Pa potentially confounds this approach in the South Pacific. KW - thorium KW - protactinium KW - biogeographic provinces KW - boundary scavenging KW - INOPEX Y1 - 2014 U6 - https://doi.org/10.1016/j.epsl.2014.02.001 SN - 0012-821X SN - 1385-013X VL - 391 SP - 307 EP - 318 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Anderson, Robert F. A1 - Hayes, Christopher T. A1 - Ren, Haojia A1 - Gersonde, Rainer A1 - Haug, Gerald H. T1 - Using the natural spatial pattern of marine productivity in the Subarctic North Pacific to evaluate paleoproductivity proxies JF - Paleoceanography N2 - Sedimentary proxies used to reconstruct marine productivity suffer from variable preservation and are sensitive to factors other than productivity. Therefore, proxy calibration is warranted. Here we map the spatial patterns of two paleoproductivity proxies, biogenic opal and barium fluxes, from a set of core-top sediments recovered in the Subarctic North Pacific. Comparisons of the proxy data with independent estimates of primary and export production, surface water macronutrient concentrations, and biological pCO(2) drawdown indicate that neither proxy shows a significant correlation with primary or export productivity for the entire region. Biogenic opal fluxes, when corrected for preservation using Th-230-normalized accumulation rates, show a good correlation with primary productivity along the volcanic arcs (tau = 0.71, p = 0.0024) and with export productivity throughout the western Subarctic North Pacific (tau = 0.71, p = 0.0107). Moderate and good correlations of biogenic barium flux with export production (tau = 0.57, p = 0.0022) and with surface water silicate concentrations (tau = 0.70, p = 0.0002) are observed for the central and eastern Subarctic North Pacific. For reasons unknown, however, no correlation is found in the western Subarctic North Pacific between biogenic barium flux and the reference data. Nonetheless, we show that barite saturation, uncertainty in the lithogenic barium corrections, and problems with the reference data sets are not responsible for the lack of a significant correlation between biogenic barium flux and the reference data. Further studies evaluating the factors controlling the variability of the biogenic constituents in the sediments are desirable in this region. Y1 - 2014 U6 - https://doi.org/10.1002/2013PA002594 SN - 0883-8305 SN - 1944-9186 VL - 29 IS - 5 SP - 438 EP - 453 PB - American Geophysical Union CY - Washington ER -