@article {1958, title = {Sediment Cd and Mo accumulation in the oxygen-minimum zone off western Baja California linked to global climate over the past 52 kyr}, journal = {Paleoceanography}, volume = {21}, year = {2006}, note = {110idTimes Cited:34 Cited References Count:68 }, month = {Nov 25}, abstract = {[ 1] Concentrations of organic carbon (orgC), cadmium (Cd), and molybdenum (Mo) were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen-minimum zone (OMZ) off southern Baja California at a temporal resolution of similar to 0.5 kyr over the past 52 kyr. These records are supplemented with diffuse spectral reflectance (DSR) measurements obtained on board ship soon after collection at a resolution of similar to 0.05 kyr. In the core from 700 m depth, a component extracted from the DSR data and the three geochemical proxies generally vary in concert with each other and over a wide range ( 4 - 22\% orgC; 1 - 40 mg/kg Cd; 5 120 mg/kg Mo). Intervals of increased orgC, Cd, and Mo accumulation generally correspond to warm periods recorded in the oxygen-isotopic composition of Greenland ice, with the exception of the Bolling/Allerod which is only weakly expressed off Baja California. Concentrations of the biogenic proxies are higher in the core from 430 m depth, but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgC, Cd, and Mo concentrations. The new data provide further evidence of an intimate teleconnection between global climate and the intensity of the OMZ and/or productivity along the western margin of North America. On the basis of a comparison with Cd and Mo records collected elsewhere in the region, we conclude that productivity may actually have varied off southern Baja California by no more than a factor of 2 over the past 52 kyr.}, keywords = {continental-margin, enhanced preservation, late pleistocene, marine-sediments, nitrogen isotope, northeast pacific waters, organic-carbon preservation, productivity variations, santa-barbara basin, suboxic sediments}, isbn = {0883-8305}, doi = {10.1029/2005PA001239}, author = {Dean, W. E. and Zheng, Y. and Ortiz, J. D. and van Geen, A.} } @article {493, title = {Geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of Araihazar, Bangladesh: Implications for deeper aquifers as drinking water sources}, journal = {Geochimica et Cosmochimica Acta}, volume = {69}, year = {2005}, note = {id: 604; 999UZ Times Cited:59 Cited References Count:49}, pages = {5203-5218}, abstract = {Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers ( 50 ka ago and a groundwater age of thousands of years. In the other village (Bay), the sediment is}, issn = {0016-7037}, doi = {10.1016/J.Gca.2005.06.001}, author = {Zheng, Y. and van Geen, A. and Stute, M. and Dhar, R. and Mo, Z. and Cheng, Z. and Horneman, A. and Gavrieli, I. and Simpson, H. J. and Versteeg, R. and Steckler, M. and Grazioli-Venier, A. and Goodbred, S. and Shahnewaz, M. and Shamsudduha, M. and Hoque, M. A. and Ahmed, K. M.} } @article {2032, title = {Enhanced marine productivity off western North America during warm climate intervals of the past 52 kyr}, journal = {Geology}, volume = {32}, year = {2004}, note = {id: 603}, month = {2004}, pages = {521-524}, author = {Ortiz, J. D. and O{\textquoteright}Connell, S. and DelViscio, J. and Dean, W. E. and Carriquiry, J. and Marchitto, T. M. and Zheng, Y. and van Geen, A.} } @article {2061, title = {1999 RV Melville Baja California cruise, on the preservation of laminated sediments along the western margin of North America}, journal = {Paleoceanography}, volume = {18}, year = {2003}, note = {id: 1102}, month = {2003}, author = {van Geen, A. and Zheng, Y. and Bernhard, J. M. and Cannariato, K. G. and Carriquiry, J. and Dean, E. and Eakins, B. W. and Ortiz, J. D. and Pike, J.} } @article {2060, title = {On the preservation of laminated sediments along the western margin of North America}, journal = {Paleoceanography}, volume = {18}, year = {2003}, note = {id: 1128}, month = {2003}, author = {van Geen, A. and Zheng, Y. and Bernhard, J. M. and Cannariato, K. G. and Carriquiry, J. and Dean, W. E. and Eakins, B. W. and Ortiz, J. D. and Pike, J.} } @article {903, title = {Challenges in radiocarbon dating organic carbon in opal-rich marine sediments}, journal = {Radiocarbon}, volume = {44}, year = {2002}, note = {591keTimes Cited:13Cited References Count:28}, pages = {123-136}, abstract = {We explored the reliability of radiocarbon ages obtained on organic carbon phases in opal-rich Southern Ocean sediments. Paired biogenic carbonate and total organic carbon (TOC) C-14 analyses for three Southern Ocean cores showed that the TOC ages were systematically younger than the carbonate ages. Carbonate ages were consistent with oxygen isotopic and bio-stratigraphy, indicating error in TOC ages that could be explained by 5-24\% of modern carbon contamination of TOC samples. Two possible sources of contamination are: 1) adsorption of atmospheric CO2 or volatile organic compounds to reactive opal surface sites, and 2) fixation of atmospheric CO2 by chemosynthetic bacteria during core storage. In an effort to reduce the modem carbon contamination, diatoms were separated from sediments, purified, and pre-oxidized by concentrated nitric and perchloric acids to permit dating of opal-intrinsic organic carbon (similar to0.1-0.3\% by weight). C-14 ages of chemically pre-oxidized opal showed a significant amount of modem carbon contamination, from 11 to 32\%, indicating adsorption from the atmosphere of modem carbon onto opal surfaces that were previously cleaned by acid oxidation. Several experiments designed to eliminate the modern C contamination were attempted, but so far we have not been able to obtain a radiocarbon age on C-14-dead Southern Ocean opal-rich sediments, either bulk TOC or purified diatom opal samples, as old as our procedural blank.}, issn = {0033-8222}, url = {https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/4084/3509}, author = {Zheng, Y. and Anderson, R. F. and Froelich, P. N. and Beck, W. and McNichol, A. P. and Guilderson, T.} } @article {2246, title = {Challenges in application of radiocarbon dating of organic carbon phases in opal-rich marine sediments from the Southern Ocean}, journal = {Trans. AGU 79}, year = {1998}, note = {id: 266}, month = {1998}, author = {Zheng, Y. and Anderson, R. F. and Froelich, P. N. and Beck, W. and McNichol, A. P. and Guilderson, T.} } @article {2262, title = {Microscale AMS 14C measurements at NOSAMS}, journal = {Radiocarbon}, volume = {40}, year = {1998}, note = {id: 1621}, month = {1998}, pages = {61-75}, author = {Pearson, A. and McNichol, A. P. and Schneider, R. J. and von Reden, K. F. and Zheng, Y.} } @article {2261, title = {Microscale AMS 14C measurements at NOSAMS: (Proceedings of the 16th International Radiocarbon Conference, 1997)}, journal = {Radiocarbon}, volume = {40}, year = {1998}, note = {id: 1814}, month = {1998}, pages = {61-75}, author = {Pearson, A. and McNichol, A. P. and Schneider, R. J. and von Reden, K. F. and Zheng, Y.} }