TY  - JOUR
A1  - Ren, Haojia
A1  - Sigman, Daniel M.
A1  - Meckler, Anna Nele
A1  - Plessen, Birgit
A1  - Robinson, Rebecca S.
A1  - Rosenthal, Yair
A1  - Haug, Gerald H.
T1  - Foraminiferal isotope evidence of reduced nitrogen fixation in the Ice Age Atlantic ocean
N2  - Fixed nitrogen ( N) is a limiting nutrient for algae in the low- latitude ocean, and its oceanic inventory may have been higher during ice ages, thus helping to lower atmospheric CO2 during those intervals. In organic matter within planktonic foraminifera shells in Caribbean Sea sediments, we found that the N-15/N-14 ratio from the last ice age is higher than that from the current interglacial, indicating a higher nitrate N-15/N-14 ratio in the Caribbean thermocline. This change and other species- specific differences are best explained by less N fixation in the Atlantic during the last ice age. The fixation decrease was most likely a response to a known ice age reduction in ocean N loss, and it would have worked to balance the ocean N budget and to curb ice age- interglacial change in the N inventory.
Y1  - 2009
UR  - http://www.sciencemag.org/
U6  - https://doi.org/10.1126/science.1165787
SN  - 0036-8075
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  - 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  -