4.7 Article

Rapid changes in meridional advection of Southern Ocean intermediate waters to the tropical Pacific during the last 30 kyr

Journal

EARTH AND PLANETARY SCIENCE LETTERS
Volume 368, Issue -, Pages 20-32

Publisher

ELSEVIER
DOI: 10.1016/j.epsl.2013.02.028

Keywords

neodymium isotopes; planktonic foraminifera; intermediate water masses; Eastern Equatorial Pacific; Equatorial Undercurrent; Southern Ocean

Funding

  1. US National Science Foundation (NSF) [OCE-10-31198]
  2. LDEO Climate Center
  3. Spanish Ministerio de Ciencia e Innovacion [CTM2006-01957/MAR, CTM2009-08849/MAR]
  4. Generalitat de Catalunya (Catalan Government) [2009SGR142]
  5. Ramon y Cajal Contract
  6. Storke Endowment of the Columbia University Department of Earth and Environmental Sciences
  7. LDEO
  8. US NSF
  9. Division Of Ocean Sciences
  10. Directorate For Geosciences [1031198] Funding Source: National Science Foundation
  11. ICREA Funding Source: Custom

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The Southern Ocean is increasingly recognized as a key player in the general ocean thermohaline circulation and the global climate system during glacial interglacial transitions. In particular, the advection of Southern Ocean intermediate waters (SOIW), like Antarctic Intermediate Water and Sub-Antarctic Mode Water, to the Eastern Equatorial Pacific (EEP), through a so-called oceanic tunnelling mechanism, is an important means for rapid transfer of climatic signals (such as heat, fresh water, salt, and chemical species) from high-to-low latitudes. However, information on how intermediate water advection rates changed in the past, and particularly during deglaciations, is fragmentary. We present new results for Nd isotopes (epsilon(Nd)) in cleaned foraminifera shells (Neogloboquadrina dutertrei) for the last 30 kyr at ODP Site 1240 in the EEP. N. dutertrei preferentially dwells in the lower thermocline, at the core of the Equatorial Undercurrent (EUC), and the epsilon(Nd) variability over time provides a record of the changes in the epsilon(Nd) of the EUC. Through mixing models we show that the EUC record is primarily controlled by changes in the volume transport of intermediate waters and not by Southern Ocean epsilon(Nd) changes. Southern Ocean signals in the EUC are stronger during colder intervals (Younger Dryas, last glacial maximum and Heinrich stadials 1 and 2), in agreement with tropical Atlantic intermediate water records. In addition, covariations between N. dutertrei delta C-13, molecular biomarkers, and diatom productivity at Site 1240 confirm the intermediate water route as an important mechanism for the transfer of climate signals from high-to-low latitudes. Changes in the SOIW chemistry during the deglaciation are likely linked to the upwelling of 'old' deep waters in the Southern Ocean and subsequent export as intermediate waters, which are coeval with the atmospheric CO2 rise. Moreover, a comparison of multiple proxy records for the last 30 kyr indicates a latitudinal shift and/or a change in the convection depth of intermediate waters in the Southern Ocean prior to the onset of the deglaciation. (C) 2013 Elsevier B.V. All rights reserved.

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