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  • 1
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    Potential use of the N2/Ar ratio as a constraint on the oceanic fixed nitrogen loss (2016)
    Wiley
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    Publication Date: 2016-04-09
    Description: Using a global ocean biogeochemical model, we investigate the suitability of the N 2 /Ar supersaturation ratio (ΔN 2 /Ar) as a tracer of marine nitrogen fixation and denitrification, i.e., the main biological processes that add or remove fixed nitrogen from the ocean. In a series of factorial simulations, we demonstrate that in regions away from the oxygen minimum zones (OMZs) the ΔN 2 /Ar characteristics are mostly determined by benthic denitrification occurring in the deep ocean with minor contributions from benthic and water-column denitrification at shallower depths. In the OMZs, the subsurface maxima of ΔN 2 /Ar are mainly determined by water-column denitrification. In contrast, nitrogen fixation has little impact on ΔN 2 /Ar owing to the rapid loss of the N 2 supersaturation signal through air-sea exchange. We thus conclude that ΔN 2 /Ar can act as a powerful constraint on water column and benthic denitrification occurring in intermediate-to-deep waters, but it cannot be used to estimate nitrogen fixation. The comparison of the currently very limited observations of the ΔN 2 /Ar with our model results shows an acceptable level of agreement, suggesting that the model's prescribed rates and distribution of benthic and water-column denitrification (i.e., 140 and 52 TgN yr -1 , respectively) are reasonable and confirms the results derived from other constraints.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Temperature-induced marine export production during glacial period (2012)
    Wiley
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    Publication Date: 2012-11-08
    Description: Proxy records indicate that export production was enhanced at the onset of the last glaciation. We examine how glacial cooling affects marine export production through temperature-dependent phytoplankton productivity and organic carbon remineralization using glacial climate simulation. Compared with the standard assumption of no temperature dependence as applied in existing paleoclimate models, including temperature-dependence enhances export production globally under glacial climate conditions. The near freezing temperatures of Antarctic seawater significantly reduce organic carbon remineralization. Less remineralization than production results in increasing carbon export to the deep ocean. Nutrients remaining near the surface at high latitudes are advected to lower latitudes via Antarctic Intermediate Water, enhancing primary production, and hence export, in temperate and tropical regions as well. Including temperature-dependence improves the model's agreement with the glacial proxy records of export production and stable carbon isotopes even under stably stratified conditions with a weakening of North Atlantic Deep Water.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming (2015)
    Wiley
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    Publication Date: 2015-10-06
    Description: Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here, we simulate multi-millennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere–ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 4
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    The thermal threshold of the Atlantic meridional overturning circulation and its control by wind stress forcing during glacial climate (2012)
    Wiley
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    Publication Date: 2012-05-08
    Description: Paleo proxy data suggest that the Atlantic meridional overturning circulation (AMOC) was shallower and weaker at the Last Glacial Maximum (LGM) than at present. In this study, we have identified the existence of a thermal threshold of the AMOC which may explain why many coupled climate models fail to simulate the weaker AMOC during the LGM. By using results obtained from a coupled climate model and conducting sensitivity simulations with an ocean general circulation model, we found that the sudden transition from the present-day AMOC to the weaker glacial AMOC occurs when we gradually change the degree of surface cooling from present-day to glacial conditions. This result is related to response of deep convection in the northern North Atlantic Ocean; moderate cooling enhances deep convection whereas sufficient cooling results in total covering of sea ice there and suppression of deep convection. The findings indicate the existence of a thermal threshold controlling the AMOC, where the present-day-type AMOC suddenly shifts to the weaker glacial AMOC once the surface cooling exceeds this threshold. We also demonstrate that wind stress forcing plays a critical role in controlling the value of the thermal threshold. Our study suggests that slight differences in the degree of surface cooling or wind stress forcing for LGM simulations could lead to the very different response of the AMOC during the LGM as reported in previous LGM simulations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    A genome-wide association study of resistance to HIV infection in highly exposed uninfected individuals with hemophilia A (2013)
    Lane, J., McLaren, P. J., Dorrell, L., Shianna, K. V., Stemke, A., Pelak, K., Moore, S., Oldenburg, J., Alvarez-Roman, M. T., Angelillo-Scherrer, A., Boehlen, F., Bolton-Maggs, P. H. B., Brand, B., Brown, D., Chiang, E., Cid-Haro, A. R., Clotet, B., Collins, P., Colombo, S., Dalmau, J., Fogarty, P., Giangrande, P., Gringeri, A., Iyer, R., Katsarou, O., Kempton, C., Kuriakose, P., Lin, J., Makris, M., Manco-Johnson, M., Tsakiris, D. A., Martinez-Picado, J., Mauser-Bunschoten, E., Neff, A., Oka, S., Oyesiku, L., Parra, R., Peter-Salonen, K., Powell, J., Recht, M., Shapiro, A., Stine, K., Talks, K., Telenti, A., Wilde, J., Yee, T. T., Wolinsky, S. M., Martinson, J., Hussain, S. K., Bream, J. H., Jacobson, L. P., Carrington, M., Goedert, J. J., Haynes, B. F., McMichael, A. J., Goldstein, D. B., Fellay, J., for the NIAID Center for HIV/AIDS Vaccine Immunology (CHAVI)
    Oxford University Press
    Details
    Publication Date: 2013-04-02
    Description: Human genetic variation contributes to differences in susceptibility to HIV-1 infection. To search for novel host resistance factors, we performed a genome-wide association study (GWAS) in hemophilia patients highly exposed to potentially contaminated factor VIII infusions. Individuals with hemophilia A and a documented history of factor VIII infusions before the introduction of viral inactivation procedures (1979–1984) were recruited from 36 hemophilia treatment centers (HTCs), and their genome-wide genetic variants were compared with those from matched HIV-infected individuals. Homozygous carriers of known CCR5 resistance mutations were excluded. Single nucleotide polymorphisms (SNPs) and inferred copy number variants (CNVs) were tested using logistic regression. In addition, we performed a pathway enrichment analysis, a heritability analysis, and a search for epistatic interactions with CCR5 32 heterozygosity. A total of 560 HIV-uninfected cases were recruited: 36 (6.4%) were homozygous for CCR5 32 or m303. After quality control and SNP imputation, we tested 1 081 435 SNPs and 3686 CNVs for association with HIV-1 serostatus in 431 cases and 765 HIV-infected controls. No SNP or CNV reached genome-wide significance. The additional analyses did not reveal any strong genetic effect. Highly exposed, yet uninfected hemophiliacs form an ideal study group to investigate host resistance factors. Using a genome-wide approach, we did not detect any significant associations between SNPs and HIV-1 susceptibility, indicating that common genetic variants of major effect are unlikely to explain the observed resistance phenotype in this population.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 6
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    One possible uncertainty in CMIP5 projections of low-oxygen water volume in the Eastern Tropical Pacific (2017)
    Wiley
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    Publication Date: 2017-04-18
    Description: Using the results from nine Earth system models submitted to the Coupled Model Intercomparison Project Phase 5 (CMIP5), we identify the Eastern Tropical Pacific (ETP) as the region with the greatest uncertainty of future changes in oxygen-deficient (〈30 μM) water volumes since different models variously project both positive and negative changes in the oxygen-deficient volume and export flux there. We investigate the factors controlling future changes in oxygen-deficient volume in the ETP with global warming using a single offline biogeochemical model. Oxygen budget analysis clarifies that the Equatorial Undercurrent (EUC) is the key mechanism controlling future variations in the oxygen-deficient volume in the ETP in our model. From the outputs of all of the CMIP5 models, we identify a significant negative relationship between changes in the EUC volume transport and the oxygen-deficient water volume from the present to the end of the 21 st century, which indicates that the response of the EUC to global warming leads to one possible uncertainty in future projections of oxygen-deficient volume in the ETP.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    The post-2002 global surface warming slowdown caused by the subtropical Southern Ocean heating acceleration (2017)
    Wiley
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    Publication Date: 2017-03-29
    Description: The warming rate of global-mean surface temperature slowed down during 1998-2012. Previous studies pointed out role of increasing ocean heat uptake during this global warming slowdown , but its mechanism remains under discussion. Our numerical simulations, in which wind stress anomaly in the equatorial Pacific is imposed from reanalysis data, suggest sub-surface warming in the equatorial Pacific took place during initial phase of the global warming slowdown (1998–2002), as previously reported. It is newly clarified that the Ekman transport from tropics to subtropics is enhanced during the later phase of the slowdown (after 2002) and enhanced subtropical Ekman downwelling causes accelerated heat storage below depth of 700 m in the subtropical Southern Ocean, leading to the post-2002 global warming slowdown. Observational data of ocean temperature also support this scenario. This study provides clear evidence that deeper parts of the Southern Ocean play a critical role in the past-2002 warming slowdown.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Simultaneous constraints on the growth of structure and cosmic expansion from the multipole power spectra of the SDSS DR7 LRG sample (2014)
    Oxford University Press
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    Publication Date: 2014-03-21
    Description: The anisotropic galaxy clustering on large scales provides us with a unique opportunity to probe into the gravity theory through the redshift-space distortions (RSDs) and the Alcock–Paczynski effect. Using the multipole power spectra up to hexadecapole ( = 4), of the luminous red galaxy (LRG) sample in the Data Release 7 (DR7) of the Sloan Digital Sky Survey II (SDSS-II), we obtain simultaneous constraints on the linear growth rate f , angular diameter distance D A , and Hubble parameter H at redshift z  = 0.3. For this purpose, we first extensively examine the validity of a theoretical model for the non-linear RSDs using mock subhalo catalogues from N -body simulations, which are constructed to match with the observed multipole power spectra. We show that the input cosmological parameters of the simulations can be recovered well within the error bars by comparing the multipole power spectra of our theoretical model and those of the mock subhalo catalogues. We also carefully examine systematic uncertainties in our analysis by testing the dependence on prior assumption of the theoretical model and the range of wavenumbers to be used in the fitting. These investigations validate that the theoretical model can be safely applied to the real data. Thus, our results from the SDSS DR7 LRG sample are robust including systematics of theoretical modelling; f ( z  = 0.3) 8 ( z  = 0.3) = 0.49 ± stat. 0.08 ± sys. 0.04, D A ( z  = 0.3) = 968 ± stat. 42 ± sys. 17 (Mpc), H ( z  = 0.3) = 81.7 ± stat. 5.0 ± sys. 3.7 (km s –1  Mpc –1 ). We believe that our method to constrain the cosmological parameters using subhaloes catalogues will be useful for more refined samples like CMASS and LOWZ catalogues in the Baryon Oscillation Spectroscopic Survey in SDSS-III.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Divergence of East Asians and Europeans Estimated Using Male- and Female-Specific Genetic Markers (2014)
    Oxford University Press
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    Publication Date: 2014-03-05
    Description: To study the male and female lineages of East Asian and European humans, we have sequenced 25 short tandem repeat markers on 453 Y-chromosomes and collected sequences of 72 complete mitochondrial genomes to construct independent phylogenetic trees for male and female lineages. The results indicate that East Asian individuals fall into two clades, one that includes East Asian individuals only and a second that contains East Asian and European individuals. Surprisingly, the European individuals did not form an independent clade, but branched within in the East Asians. We then estimated the divergence time of the root of the European clade as ~41,000 years ago. These data indicate that, contrary to traditional views, Europeans diverged from East Asians around that time. We also address the origin of the Ainu lineage in northern Japan.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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  • 10
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    Simulating the anisotropic clustering of luminous red galaxies with subhaloes: a direct confrontation with observation and cosmological implications (2014)
    Oxford University Press
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    Publication Date: 2014-08-30
    Description: We model the apparent clustering anisotropy of luminous red galaxies (LRGs) in the Sloan Digital Sky Survey using subhaloes identified in cosmological N -body simulations. We first conduct a Markov chain Monte Carlo analysis on the parameters characterizing subhaloes hosting LRGs assuming a specific cold dark matter cosmology on which we run the simulations. We show that simple models with central and satellite subhaloes can explain the observed multipole moments of the power spectrum up to hexadecapole on large scales ( k 0.3 h Mpc –1 ). A satellite fraction of 20–30 per cent is favoured weakly depending on the detail of the model. The fraction is shown to be robust when we adopt a more refined model based on the halo occupation number from the literature. We then vary cosmological parameters controlling the anisotropy in redshift space effectively by deforming the simulation box (the Alcock–Paczynski effect) and changing the amplitude of the velocities (the redshift-space distortions). We demonstrate that we can constrain the geometry of the Universe, the structure growth rate and the parameters characterizing LRGs simultaneously. This is a step towards cosmological analysis with realistic bias description beyond empirical bias functions with nuisance parameters.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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