TY - JOUR T1 - Near constancy of the Pacific Ocean surface to mid-depth radiocarbon-age difference over the last 20 kyr JF - Earth and Planetary Science Letters Y1 - 2008 A1 - Broecker, W. A1 - Clark, E. A1 - Barker, S. AB - Although C-13 to C-12 and cadmium to calcium ratios provide information regarding the distribution of deep water masses during late glacial time and during the period of deglaciation, our knowledge of the rate at which these water masses were ventilated comes mainly from the difference in radiocarbon-age between coexisting bottom- and surface-dwelling foraminifera. Paired benthic/planktonic foraminiferal radiocarbonage differences covering last 20 kyr in a high-deposition-rate western equatorial Pacific core, MD01-2386, from a water depth of 2.8 km show no significant climate-related variations over this period. This result is surprising for we would have expected a change in this age difference between the last glacial maximum (LGM) and the Holocene and also during the Mystery Interval (17.5-14.5 kyr ago) when the waters in a radiocarbon-depleted abyssal reservoir were presumably being mixed back into the remainder of the ocean. (C) 2008 Elsevier B.V. All rights reserved. VL - 274 IS - 3-4 N1 - id: 770; 390GV Times Cited:2 Cited References Count:27Y JO - Near constancy of the Pacific Ocean surface to mid-depth radiocarbon-age difference over the last 20 kyr ER - TY - JOUR T1 - Radiocarbon age of late glacial deep water from the equatorial Pacific JF - Paleoceanography Y1 - 2007 A1 - Broecker, W. A1 - Clark, E. A1 - Barker, S. A1 - Hajdas, I. A1 - Bonani, G. A1 - Moreno, E. AB - Radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2.8 km in the western equatorial Pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater. This places a lower limit on the depth of the interface for the hypothetical radiocarbon-depleted glacial age seawater reservoir required to explain the 190% drop in the (14)C/C for atmospheric CO(2), which occurred during the mystery interval (17.5 to 14.5 calendar years ago). These measurements restrict the volume of this reservoir to be no more than 35% that of the ocean. Further, (14)C measurements on a single Last Glacial Maximum age sample from a central equatorial Pacific core from a depth of 4.4 km water fail to reveal evidence for the required 5- to 7-kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean. Nor does the (13)C record for benthic forams from this abyssal core yield any evidence for the excess respiration CO(2) expected to be produced during thousands of years of isolation. Nor, as indicated by the presence of benthic foraminifera, was the dissolved oxygen used up in this abyssal water. VL - 22 IS - 2 N1 - id: 413; 165MC Times Cited:10 Cited References Count:18 JO - Radiocarbon age of late glacial deep water from the equatorial Pacific ER - TY - JOUR T1 - Anomalous radiocarbon ages for foraminifera shells JF - Paleoceanography Y1 - 2006 A1 - Broecker, W. A1 - Barker, S. A1 - Clark, E. A1 - Hajdas, I. A1 - Bonani, G. AB - The causes for discordant radiocarbon results on multiple species of planktonic foraminifera from high-sedimentation-rate marine sediments are investigated. We have documented two causes for these anomalous results. One is the addition of secondary radiocarbon for which we have, to date, only one firm example. It involves an opal-rich sediment. The other is the incorporation of reworked material. Again, we have, to date, only one firm example. It involves a rapidly deposited ocean margin sediment. However, we have three other examples where reworking is the most likely explanation. On the basis of this study it is our conclusion that, where precise radiocarbon dating of high-deposition-rate marine sediment is required, a prerequisite is to demonstrate that concordant ages can be obtained on pairs of fragile and robust planktic shells. For sediment rich in opal, it is advisable to check for secondary calcite by comparing ages obtained on acid-leached samples with those on unleached samples. VL - 21 IS - 2 N1 - id: 980; 041JB Times Cited:7 Cited References Count:7 JO - Anomalous radiocarbon ages for foraminifera shells ER - TY - JOUR T1 - Ventilation of the glacial deep Pacific Ocean JF - Science Y1 - 2004 A1 - Broecker, W. A1 - Barker, S. A1 - Clark, E. A1 - Hajdas, I. A1 - Bonani, G. A1 - Stott, L. AB - Measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial Pacific deep-sea cores suggest that during peak glacial time the radiocarbon age of water at 2-kilometers depth was no greater than that of today. These results make unlikely suggestions that a slowdown in deep-ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon-14 (14C) to carbon in the atmosphere and surface ocean during glacial time. Comparison of 14C ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14C to C ratio difference was not substantially different from today's. VL - 306 IS - 5699 N1 - Broecker, WallaceBarker, StephenClark, ElizabethHajdas, IrkaBonani, GeorgesStott, Lowelleng2004/11/13 09:00Science. 2004 Nov 12;306(5699):1169-72. JO - Ventilation of the glacial deep Pacific Ocean ER -