UNIVERSITE TOULOUSE III - PAUL SABATIER Ecole ... - LEGOS

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DENMARK STRAIT WATER HETEROGENEITY: CIRCULATION
TRACED BY NEODYMIUM ISOTOPES AND RARE EARTH
ELEMENTS
Francois Lacan ∗ and Catherine Jeandel
LEGOS, Observatoire Midi-Pyrénées, 18 av Edouard Belin, 31401 Toulouse Cedex 4, France
ABSTRACT
Seawater Neodymium isotopic composition and Rare Earth Elements concentrations
were measured along four hydrologic sections within the East Greenland Current, between the
Fram and the Denmark Straits, during summer 1999. East Greenland Current intermediate
waters, between 77°N and 70°N, displaying similar hydrological characteristics as Denmark
Strait Overflow Water, have very constant REE characteristics and ε Nd value of –11.2. This
constancy reveals the absence of lithogenic input, from the East Greenland margin, into
intermediate waters in this area, corroborating previous dissolved aluminum data (Measures
and Edmond, 1992). The Denmark Strait Overflow Water was characterized by ε Nd = -8.7 ±
1.4. This value (which is in very good agreement with one previous data; Piepgras and
Wasserburg, 1987) can be explained by the imprint of basaltic formations bordering the
Denmark Strait on the intermediate waters described above. The heterogeneity of the DSOW
Nd signature revealed the resuspension of Precambrian particles in the Strait. The presence of
Atlantic Water is observed at a station located at the mouth of Nansen Fjord, on the western
side of Denmark Strait. We suggest that this water reaches the fjord from the Irminger current
within eddy structures. These results provide a better understanding of the DSOW Nd
signature, which will allow a better use of this tracer in the study of modern and paleo North
Atlantic Deep Water dynamic.
Keywords: Denmark Strait, circulation, neodymium, water masses, weathering, isotopic
tracer.
1. Introduction
Neodymium (Nd) is a Rare Earth Element (REE). It mainly occurs at the earth surface
in the solid phase. Its Isotopic Composition (Nd IC) is the 143 Nd/ 144 Nd ratio, expressed as ε Nd ,
which is the deviation of this ratio in the sample from a reference value (CHUR, Chondritic
Uniform Reservoir, 143 Nd/ 144 Nd = 0.512638, which represents the present day average earth
value):
143
⎛ ⎛ Nd ⎞ ⎞
⎜ ⎜ ⎟ ⎟
144
⎜ ⎝ Nd⎠
measured ⎟ 4
ε Nd
= ⎜
− 1
⎛ Nd ⎞
⎟ × 10
143
⎜ ⎜ ⎟
144
⎝ ⎝ Nd⎠
⎟
⎠
CHUR
∗
Corresponding author. Fax: +33 5.61.25.32.05. Phone: +33 5.61.33.30.03. Email address:
francois.Lacan@cnes.fr
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