TY - JOUR T1 - Decreased influence of Antarctic intermediate water in the tropical Atlantic during North Atlantic cold events JF - Earth and Planetary Science Letters Y1 - 2014 A1 - Huang, Kuo-Fang A1 - Oppo, Delia W. A1 - Curry, William B. KW - antarctic intermediate water KW - Atlantic meridional overturning circulation KW - deglacial variability KW - Nd isotopes KW - North Atlantic cold events AB - Antarctic Intermediate Water (AAIW) is a key player in the global ocean circulation, contributing to the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and influencing interhemispheric heat exchange and the distribution of salinity, nutrients and carbon. However, the deglacial history of AAIW flow into the North Atlantic is controversial. Here we present a multicore-top neodymium isotope calibration, which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition () values in their authigenic coatings. We then present the first foraminifera-based reconstruction of from three sediment cores retrieved from within modern AAIW, in the western tropical North Atlantic. Our records reveal similar glacial and interglacial contributions of AAIW, and a pronounced decrease in the AAIW fraction during North Atlantic deglacial cold episodes, Heinrich Stadial 1 (HS1) and Younger Dryas (YD). Our results suggest two separate phases of reduced fraction of AAIW in the tropical Atlantic during HS1, with a greater reduction during early HS1. If a reduction in AAIW fraction also reflects reduced AMOC strength, this finding may explain why, in many regions, there are two phases of hydrologic change within HS1, and why atmospheric CO2 rose more rapidly during early than late HS1. Our result suggesting less flow of AAIW into the Atlantic during North Atlantic cold events contrasts with evidence from the Pacific, where intermediate-depth records may indicate increased flow of AAIW into the Pacific during the these same events. Antiphased behavior between intermediate depths of the North Atlantic and Pacific implies that the flow of AAIW into Atlantic and Pacific seesawed during the last deglaciation. VL - 389 UR - https://doi.org/10.1016/j.epsl.2013.12.037 ER - TY - JOUR T1 - The Passage of the Bomb Radiocarbon Pulse into the Pacific Ocean JF - Radiocarbon Y1 - 2010 A1 - Jenkins, W. J. A1 - Elder, K. L. A1 - McNichol, A. P. A1 - von Reden, K. KW - AMS KW - antarctic intermediate water KW - anthropogenic co2 KW - atlantic KW - c-14 data KW - carbon KW - distributions KW - graphite KW - south-pacific KW - tritium AB - We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150 degrees W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced (14)C into the oceanic thermocline. The changes over the 14 yr between occupations are demonstrably large relative to any possible drift in our analytical standardization. The computed difference field based on the gridded data in the upper 1600 m of the section exhibits a significant decrease over time (approaching 40 to 50 parts per thousand in Delta(14)C) in the upper 200-300 m, consistent with the decadal post-bomb decline in atmospheric (14)C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50-60 parts per thousand in Delta(14)C, a clear signature of the downstream evolution of the (14)C transient in this water mass. We use this observation to estimate the transit time of AAIW from its "source region" in the southeast South Pacific and to compute the effective reservoir age of this water mass. The 2 sections show small but significant changes in the abyssal (14)C distributions. Between 1991 and 2005, Delta(14)C has increased by 9 parts per thousand below 2000 m north of 55 degrees S. This change is accompanied overall by a modest increase in salinity and dissolved oxygen, as well as a slight decrease in dissolved silica. Such changes are indicative of greater ventilation. Calculation of "phosphate star" also indicates that this may be due to a shift from the Southern Ocean toward North Atlantic Deep Water as the ventilation source of the abyssal South Pacific. VL - 52 SN - 0033-8222 IS - 3 N1 - Sp. Iss. 2696jo Times Cited:7 Cited References Count:38 JO - Radiocarbon ER -