Colman, Albert

Voelker, Antje H. L.

Repositório do LNEG

  Oxygen and deuterium stable isotope signals in Northeast Atlantic waters ANTJE H. L. VOELKER1* AND ALBERT COLMAN2  1LNEG, Unidade Geologia Marinha, Amadora, Portugal, antje.voelker@lneg.pt (* presenting author) 2The University of Chicago, Dept. of Geophysical Sciences, Chicago, USA, asc25@uchicago.edu  Material and Methods A comprehensive study of seawater stable isotope properties in the mid-latitude North Atlantic is still missing [1], especially for the intermediate and deep water masses. To fill this gap seawater samples were collected along various transects in the Northeast Atlantic. During the Atlantic Meridional Transect (AMT) 18 expedition the upper 300 m were sampled between 46.6 and 24.7°N. RV Poseidon cruises P334, P349, P377, and P383 to the Azores Front region (38.3–30°N; 22–20°W) generally yielded samples down to 2000 m. High resolution sampling over the whole water column was performed during the OVIDE 2010 (Portugal to Reykjanes ridge) and KN199-4 cruises. Cruise KN199-4 implemented the section from Lisbon to the Cape Verde Islands of the US GEOTRACES North Atlantic transect. AMT 18 and P cruise samples were analyzed for δ18O using the Delta E mass spectrometer at the Leibniz Laboratory (Kiel, Germany). Analysis of δ18O and dD in the OVIDE 2010 and KN199-4 samples was done at the Godwin Laboratory (Cambridge, UK) using the PICARRO L2120 water isotope analyzer. Splits of some of the KN199-4 samples were also analyzed for both isotope ratios at the University of Chicago using a GasBench II linked to a Delta V Plus mass spectrometer.  Results and Conclusions  Along the AMT 18 transect, i.e. in the central basin, a clear boundary is visible with δ18O values in the upper 100 m of 0.75–1.15 permil north of 38°N and 1.3–1.5 permil south of it. The range narrows in the North Atlantic Central Water (NACW) to 0.9–1.2 permil with the stations in the subtropical gyre, as expected, showing the higher values. In the eastern basin variability in the upper mixed layer (<300 m) is much larger with values ranging from 0.4 to 1.6 permil. The high variability can be attributed to seasonal mixing processes at the Azores Front, upwelling along the Iberian margin and the influence of riverine water at KN199-4 station 1 positioned in the Setubal canyon. Below 300 m the subpolar and subtropical NACW can clearly be distinguished in the isotope profiles. Along with temperature, δ18O values decrease with depth to generally less than 0.7 permil below 2000 m. Along the Iberian margin this trend is, however, interrupted between 500 and 1500 m due to the Mediterranean Outflow Water (MOW). The different cores of the MOW are clearly visible in the δ18O and dD (which is highly correlated to salinity) profiles, especially those close to the Iberian margin. Results for many of the OVIDE and GEOTRACES stations are pending and when they are available it will be possible to better define the isotopic properties of the subsurface water masses, especially the North Atlantic Deep Water and the Antarctic Bottom Water.  [1] LeGrande & Schmidt (2006) Geophys. Res. Lett. 33, L12604.  

Oxygen and deuterium stable isotope signals in Northeast Atlantic waters

Laboratório Nacional de Energia e Geologia Repository

http://repositorio.lneg.pt/bitstream/10400.9/1817/1/35544.pdf

Oxygen and deuterium stable isotope signals in Northeast Atlantic waters

Abstract

Similar works

Full text

Available Versions

Repositório do LNEG

Laboratório Nacional de Energia e Geologia Repository