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535 results on '"Blaauw M"'

4. SISALv2: A comprehensive speleothem isotope database with multiple age-depth models

Author

Comas-Bru, L, Rehfeld, K, Roesch, C, Amirnezhad-Mozhdehi, S, Harrison, SP, Atsawawaranunt, K, Ahmad, SM, Brahim, YA, Baker, A, Bosomworth, M, Breitenbach, SFM, Burstyn, Y, Columbu, A, Deininger, M, Demény, A, Dixon, B, Fohlmeister, J, Hatvani, IG, Hu, J, Kaushal, N, Kern, Z, Labuhn, I, Lechleitner, FA, Lorrey, A, Martrat, B, Novello, VF, Oster, J, Pérez-Mejías, C, Scholz, D, Scroxton, N, Sinha, N, Ward, BM, Warken, S, Zhang, H, Apaéstegui, J, Baldini, LM, Band, S, Blaauw, M, Boch, R, Borsato, A, Budsky, A, Rosell, MGB, Chawchai, S, Constantin, S, Denniston, R, Dragusin, V, Drysdale, R, Dumitru, O, Frappier, A, Gandhi, N, Gautam, P, Hanying, L, Isola, I, Jiang, X, Jingyao, Z, Johnson, K, Vanessa Johnston, Kathayat, G, Klose, J, Krause, C, Lachniet, M, Laskar, A, Lauritzen, SE, Lončar, N, Moseley, G, Narayana, AC, Onac, BP, Racovitǎ, E, Pawlak, J, Ramsey, CB, Rivera-Collazo, I, Rossi, C, Rowe, PJ, Stríkis, NM, Tan, L, Verheyden, S, Vonhof, H, Weber, M, Wendt, K, Wilcox, P, Winter, A, Wu, J, Wynn, P, and Yadava, MG

Subjects
Atmospheric Sciences, Geochemistry, Physical Geography and Environmental Geoscience
Abstract

Characterizing the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, correlating climate events between records, assessing climate periodicities, identifying potential triggers and evaluating climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) working group showed that age model uncertainties are not systematically reported in the published literature, and these are only available for a limited number of records (ca. 15 %, n = 107/691). To improve the usefulness of the SISAL database, we have (i) improved the database's spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age- depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age models and their uncertainties as well as the expansion of the database to include new records and the qualitycontrol measures applied. This paper also documents the age-depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age-depth models, including age-depth temporal uncertainties for 512 speleothems.

Published
2020

7. A Lake Record of Geomagnetic Secular Variations for the Last 23 ka From Lake Chala : Toward a Composite Directional Lake Record of the Earth's Magnetic Field for Equatorial East Africa

Author

Di Chiara, A., Hounslow, M. W., Maher, B. A., Karloukovski, V., Van Daele, M., Blaauw, M., Verschuren, D., Di Chiara, A., Hounslow, M. W., Maher, B. A., Karloukovski, V., Van Daele, M., Blaauw, M., and Verschuren, D.

Abstract

The documentation and understanding of variations in the Earth's magnetic field through time is fundamental for several disciplines, but current geomagnetic models rely on datasets heavily biased toward the mid‐ and high northern latitudes. The African continent and surrounding islands and oceans are particularly underrepresented. Here, we present a new record of paleo‐secular variation (PSV) of the inclinations over the last 23 ka from Lake Chala, situated at 3°S near Mt Kilimanjaro in eastern equatorial Africa. This groundwater‐fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well‐constrained age model based on 210Pb and 14C dating. The magnetic mineralogy of the sediments is tested with rock magnetic analyses. The Lake Chala inclination record shows four highs and lows over 20 ka and compares well with that of Lake Malawi (10°S) between 20 and 16.2 ka, and from 9.8 to 2.6 ka. This record is linked to PSV records at Lakes Victoria and Malawi using a sequence slotting technique to generate a composite PSV model for east Africa. Analyzed at best‐possible resolutions up to 200 years, the Lake Chala PSV record not only represents an important contribution to improve our understanding of local and global features of the Earth's magnetic field. It also expands the utility of paleomagnetism as a key tool for dating and correlation both for archeological sites throughout East Africa and the many volcanoes, active or dormant, of the East African Rift System.

Published
2024

8. The >250-kyr Lake Chala record : A tephrostratotype correlating archaeological, palaeoenvironmental and volcanic sequences across eastern Africa

Author

Martin-Jones, C., Lane, C.S., Blaauw, M., Mark, D.F., Verschuren, D., Van der Meeren, T., Van Daele, M., Wynton, H., Blegen, N., Kisaka, M., Leng, M.J., Barker, P., Martin-Jones, C., Lane, C.S., Blaauw, M., Mark, D.F., Verschuren, D., Van der Meeren, T., Van Daele, M., Wynton, H., Blegen, N., Kisaka, M., Leng, M.J., and Barker, P.

Abstract

Regional tephrostratigraphic frameworks connect palaeoclimate, archaeological and volcanological records preserved in soils or lake sediments via shared volcanic ash (tephra) layers. In eastern Africa, tracing of tephra isochrons between geoarchaeological sequences is an established chronostratigraphic approach. However, to date, few long tephra records exist from sites with continuous depositional sequences, such as lake sediments, which offer the potential to connect local and discontinuous sequences at the regional scale. Long lake sediment sequences may also capture more complete eruptive histories of understudied volcanic centres. Here, we present and date the tephrostratigraphic record of a >250,000-year (>250-kyr) continuous sediment sequence extracted from Lake Chala, a crater lake on the Kenya-Tanzania border near Mt Kilimanjaro. Single-grain glass major and minor element analyses of visible and six cryptotephra layers reveal compositions ranging from mafic foidites and basanites to more evolved tephri-phonolites, phonolites, trachytes and a single rhyolite. Of these, nine are correlated to scoria cone eruptions of neighbouring Mt Kilimanjaro or the Chyulu volcanic field ∼60 km to the north; seven are correlated to phonolitic eruptions of Mt Meru, ∼100 km to the west; and four to voluminous trachytic eruptions of Central Kenyan Rift (CKR) volcanoes located ∼350 km to the north. The only rhyolitic tephra layer, a cryptotephra, correlates to the 73.7-ka BP (before present, taken as 1950 CE) Younger Toba Tuff (YTT) from Sumatra. Two of the CKR tephra layers provide direct ties with terrestrial sequences relevant to Middle Stone Age archaeology of the eastern Lake Victoria basin in Kenya. Absolute age estimates obtained by direct 40Ar/39Ar dating of 10 tephra layers are combined with six 210Pb and 162 14C dates covering the last 25-kyr and the well-constrained known age of the YTT to build a first absolute chronology for the full Lake Chala sediment sequence. T

Published
2024

10. Summary of the Snowmastodon Project Special Volume. A high-elevation, multi-proxy biotic and environmental record of MIS 6-4 from the Ziegler Reservoir fossil site, Snowmass Village, Colorado, USA

Author

Miller, IM, Pigati, JS, Scott Anderson, R, Johnson, KR, Mahan, SA, Ager, TA, Baker, RG, Blaauw, M, Bright, J, Brown, PM, Bryant, B, Calamari, ZT, Carrara, PE, Cherney, MD, Demboski, JR, Elias, SA, Fisher, DC, Gray, HJ, Haskett, DR, Honke, JS, Jackson, ST, Jiménez-Moreno, G, Kline, D, Leonard, EM, Lifton, NA, Lucking, C, Gregory McDonald, H, Miller, DM, Muhs, DR, Nash, SE, Newton, C, Paces, JB, Petrie, L, Plummer, MA, Porinchu, DF, Rountrey, AN, Scott, E, Sertich, JJW, Sharpe, SE, Skipp, GL, Strickland, LE, Stucky, RK, Thompson, RS, and Wilson, J

Abstract

© 2014 University of Washington. In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean-atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010-2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA) revealed a nearly continuous, lacustrine/wetland sedimentary sequence that preserved evidence of past plant communities between ~. 140 and 55. ka, including all of MIS 5. At an elevation of 2705. m, the Ziegler Reservoir fossil site also contained thousands of well-preserved bones of late Pleistocene megafauna, including mastodons, mammoths, ground sloths, horses, camels, deer, bison, black bear, coyotes, and bighorn sheep. In addition, the site contained more than 26,000 bones from at least 30 species of small animals including salamanders, otters, muskrats, minks, rabbits, beavers, frogs, lizards, snakes, fish, and birds. The combination of macro- and micro-vertebrates, invertebrates, terrestrial and aquatic plant macrofossils, a detailed pollen record, and a robust, directly dated stratigraphic framework shows that high-elevation ecosystems in the Rocky Mountains of Colorado are climatically sensitive and varied dramatically throughout MIS 5.

Published
2014

14. Psychiatric symptoms in people living with HIV: prevalences, interactions and consequences

Author

Meeder, E. M., primary, Blaauw, M., additional, van Eekeren, L. E., additional, Groenendijk, A., additional, Vos, W. A., additional, de Mast, Q., additional, Blok, W. L., additional, Verbon, A., additional, Berrevoets, M. A., additional, van Lunzen, J., additional, Joosten, L., additional, Netea, M., additional, Matzaraki, V., additional, van der Ven, A. J., additional, and Schellekens, A. F., additional

Published
2023
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27. Defining "kf-factors" for threshold reactions.

Author

van Sluijs, R. and Blaauw, M.

Subjects
ACTIVATION energy, NEUTRON flux, HEAT flux, NUCLEAR reactions, NUCLEAR activation analysis
Abstract

The k0-method (De Corte in The k0-standardization method: move to the optimization of neutron activation analysis. Habil. Thesis, Ghent University, Belgium, 1987) was developed solely for the use of (n, γ) nuclear reactions in neutron activation analysis. For this, a definition of only the thermal and epi-thermal flux was needed. The fast flux of the fission neutrons was not taken into account although it was considered for primary interferences by De Corte0. The energy distribution of the fission neutrons can be rather well described by a Watt distribution but is reactor dependent. To complicate things, the activation cross-section behaviour is nuclide dependent. In order to incorporate threshold reactions in the k0-method we propose to use predefined kf-factors, measuring the fast flux using a Ni-58 monitor, and to introduce an h-factor that accounts for all deviations for a specific reaction and irradiation facility. It is shown, based on data from Verheijke, that there are useful correlations for Ni-58, Ti-47 and Ti-48. Activation cross section functions indicate that there are possible more relations that might allow h-factors to be predicted. [ABSTRACT FROM AUTHOR]

Published
2023
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30. Identifying host genetic determinants of HIV-1 reservoir markers reveals PTDSS2 and IRF7 as potential modifying factors in HIV-1 patients

Author

Trypsteen, W., Zhang, Z., Blaauw, M., dos Santos, J.C., Chu, X., Rutsaert, S., Vandekerckhove, L., Xu, C-J., Swertz, M.A., Li, Y., and van der Ven, A.

Subjects
Drug therapy, Development and progression, Genetic aspects, Patient outcomes, Health aspects, Host-virus relationships, HIV infections -- Genetic aspects -- Development and progression -- Drug therapy, Antiretroviral agents -- Patient outcomes, Gene expression -- Health aspects, Antiviral agents -- Patient outcomes, HIV infection -- Genetic aspects -- Development and progression -- Drug therapy
Abstract

Background: Combination antiretroviral treatment (cART) cannot eradicate HIV-1 from the body due to the establishment of persisting viral reservoirs which reinitiate new rounds of HIV-1 replication after treatment interruption. These [...]

Published
2021
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