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 - Jaccard, Samuel L. A1 - Kienast, Stephanie S. A1 - Haug, Gerald H. T1 - Change in dust seasonality as the primary driver for orbital-scale dust storm variability in East Asia JF - Geophysical research letters N2 - Glacial periods are recognized to be dustier than interglacials, but the conditions leading to greater dust mobilization are poorly defined. Here we present a new high-resolution dust record based on Th-230-normalized He-4 flux from Ocean Drilling Program site 882 in the Subarctic North Pacific covering the last 170,000years. By analogy with modern relationships, we infer the mechanisms controlling orbital-scale dust storm variability in East Asia. We propose that orbital-scale dust flux variability is the result of an expansion of the dust season into summer, in addition to more intense dust storms during spring and fall. The primary drivers influencing dust flux include summer insolation at subarctic latitudes and variable Siberian alpine glaciation, which together control the cold air reservoir in Siberia. Changes in the extent of the Northern Hemisphere ice sheets may be a secondary control. Y1 - 2017 U6 - https://doi.org/10.1002/2016GL072345 SN - 0094-8276 SN - 1944-8007 VL - 44 SP - 3796 EP - 3805 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Serno, Sascha A1 - Winckler, Gisela A1 - Anderson, Robert F. A1 - Maier, Edith A1 - Ren, Haojia A1 - Gersonde, Rainer A1 - Haug, Gerald H. T1 - Comparing dust flux records from the Subarctic North Pacific and Greenland: Implications for atmospheric transport to Greenland and for the application of dust as a chronostratigraphic tool JF - Paleoceanography N2 - We present a new record of eolian dust flux to the western Subarctic North Pacific (SNP) covering the past 27,000years based on a core from the Detroit Seamount. Comparing the SNP dust record to the North Greenland Ice Core Project (NGRIP) ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation, while the timing of abrupt changes is synchronous. If dust deposition in the SNP faithfully records its mobilization in East Asian source regions, then the difference in the relative amplitude must reflect climate-related changes in atmospheric dust transport to Greenland. Based on the synchronicity in the timing of dust changes in the SNP and Greenland, we tie abrupt deglacial transitions in the Th-230-normalized He-4 flux record to corresponding transitions in the well-dated NGRIP dust flux record to provide a new chronostratigraphic technique for marine sediments from the SNP. Results from this technique are complemented by radiocarbon dating, which allows us to independently constrain radiocarbon paleoreservoir ages. We find paleoreservoir ages of 745140years at 11,653year B.P., 680228years at 14,630year B.P., and 790498years at 23,290year B.P. Our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western SNP. Good temporal synchronicity between eolian dust records from the Subantarctic Atlantic and equatorial Pacific and the ice core record from Antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions. KW - Subarctic North Pacific KW - eolian dust KW - helium-4 KW - atmospheric circulation KW - chronostratigrapy KW - paleoreservoir age Y1 - 2015 U6 - https://doi.org/10.1002/2014PA002748 SN - 0883-8305 SN - 1944-9186 VL - 30 IS - 6 SP - 583 EP - 600 PB - American Geophysical Union CY - Washington 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 - Ren, Haojia A1 - Studer, Anja S. A1 - Serno, Sascha A1 - Sigman, Daniel M. A1 - Winckler, Gisela A1 - Anderson, Robert F. A1 - Oleynik, Sergey A1 - Gersonde, Rainer A1 - Haug, Gerald H. T1 - Glacial-to-interglacial changes in nitrate supply and consumption in the subarctic North Pacific from microfossil-bound N isotopes at two trophic levels JF - Paleoceanography N2 - Reduced nitrate supply to the subarctic North Pacific (SNP) surface during the last ice age has been inferred from coupled changes in diatom-bound delta N-15 (DB-delta N-15), bulk sedimentary delta N-15, and biogenic fluxes. However, the reliability of bulk sedimentary and DB-delta N-15 has been questioned, and a previously reported delta N-15 minimum during Heinrich Stadial 1 (HS1) has proven difficult to explain. In a core from the western SNP, we report the foraminifera-bound delta N-15 (FB-delta N-15) in Neogloboquadrina pachyderma and Globigerina bulloides, comparing them with DB-delta N-15 in the same core over the past 25 kyr. The delta N-15 of all recorders is higher during the Last Glacial Maximum (LGM) than in the Holocene, indicating more complete nitrate consumption. N. pachyderma FB-delta N-15 is similar to DB-delta N-15 in the Holocene but 2.2% higher during the LGM. This difference suggests a greater sensitivity of FB-delta(15)NZ to changes in summertime nitrate drawdown and delta N-15 rise, consistent with a lag of the foraminifera relative to diatoms in reaching their summertime production peak in this highly seasonal environment. Unlike DB-delta N-15, FB-delta N-15 does not decrease from the LGM into HS1, which supports a previous suggestion that the HS1 DB-delta N-15 minimum is due to contamination by sponge spicules. FB-delta N-15 drops in the latter half of the Bolling/Allerod warm period and rises briefly in the Younger Dryas cold period, followed by a decline into the mid-Holocene. The FB-delta N-15 records suggest that the coupling among cold climate, reduced nitrate supply, and more complete nitrate consumption that characterized the LGM also applied to the deglacial cold events. Y1 - 2015 U6 - https://doi.org/10.1002/2014PA002765 SN - 0883-8305 SN - 1944-9186 VL - 30 IS - 9 SP - 1217 EP - 1232 PB - American Geophysical Union CY - Washington 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 - 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 - McGee, David A1 - Winckler, Gisela A1 - Borunda, Alejandra A1 - Serno, Sascha A1 - Anderson, Robert F. A1 - Recasens, Cristina A1 - Bory, Aloys A1 - Gaiero, Diego A1 - Jaccard, Samuel L. A1 - Kaplan, Michael A1 - McManus, Jerry F. A1 - Revel, Marie A1 - Sun, Youbin T1 - Tracking eolian dust with helium and thorium: Impacts of grain size and provenance JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates. Dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples. More recently, dust fluxes have been estimated from measurements of helium and thorium, as rare isotopes of these elements (He-3 and Th-230) allow estimates of sediment flux, and the dominant isotopes (He-4 and Th-232) are uniquely associated with the lithogenic fraction of marine sediments. In order to improve the fidelity of dust flux reconstructions based on He and Th, we present a survey of He and Th concentrations in sediments from dust source areas in East Asia, Australia and South America. Our data show systematic relationships between He and Th concentrations and grain size, with He concentrations decreasing and Th concentrations increasing with decreasing grain size. We find consistent He and Th concentrations in the fine fraction (<5 mu m) of samples from East Asia, Australia and Central South America (Puna-Central West Argentina), with Th concentrations averaging 14 mu g/g and He concentrations averaging 2 mu cc STP/g. We recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine-grained, and suggest that previous studies may have systematically overestimated Th-based dust fluxes by 30%. Source areas in Patagonia appear to have lower He and Th contents than other regions, as fine fraction concentrations average 0.8 mu cc STP/g and 9 mu g/g for He-4 and Th-232, respectively. The impact of grain size on lithogenic He and Th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably. Our data also have important implications for the hosts of He in long-traveled dust and for the He-3/He-4 ratio used for terrigenous He in studies of extraterrestrial He in sediments and ice. We also investigate the use of He/Th ratios as a provenance tracer. Our results suggest differences in fine fraction He/Th ratios between East Asia, Australia, central South America and Patagonia, with ratios showing a positive relationship with the geological age of source rocks. He/Th ratios may thus provide useful provenance information, for example allowing separation of Patagonian sources from Puna-Central West Argentina or Australian dust sources. He/Th ratios in open-ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas. He/Th ratios in mid-latitude South Atlantic sediments suggest that dust in this region primarily derives from the Puna-Central West Argentina region (23-32 degrees S) rather than Patagonia (>38 degrees S). In the equatorial Pacific, He/Th ratios are much lower than in extratropical Pacific sediments or potential source areas measured as a part of this study (East Asia, South America, Australia) for reasons that are at present unclear, complicating their use as provenance tracers in this region. (C) 2015 Elsevier Ltd. All rights reserved. Y1 - 2016 U6 - https://doi.org/10.1016/j.gca.2015.11.023 SN - 0016-7037 SN - 1872-9533 VL - 175 SP - 47 EP - 67 PB - Elsevier CY - Oxford 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 -