Paleocirculation: Neodymium

1
Paleocirculation Neodymium

• Paleoproxy Seminar
• Alison Hartman
• April 2, 2005

2
Notation
3
Background 147Sm 143Nd
REEs , low water solubility, existing in 3 ox
state
4
Long-Lived Isotope System

• Decay rates slow compared to age of Earth (4.56
  Gyr)
• 147Sm 143Nd
• t1/2 1.06 x 1011
• Measure by referencing abundance of
• relatively stable isotope of Nd
• We use 144Nd

5
Element Fractionation

• Nd is preferred in magma over Sm
• Continents have lower Sm/Nd
• Smaller 143Nd/ 144Nd
• More negative ?Nd signal for continental crust.

6
Nd as Water Mass Tracer

• ?Nd values preserved in Fe-Mn crusts and fossil
  fish teeth for bottom water
• Water masses have distinctive ?Nd based on
  surrounding source areas
• Short residence time (500-1000 years)

7
(No Transcript)
8
Nd and Salinity
9
?Nd Signal for Water Masses
Seawater eNd
AAIW
-5 to -7
NADW
-13.5
AABW
-6 to -9
various sources, mainly Wasserburg, Piepgras,
Jeandel, Lacan
NADW North Atlantic Deep Water AAIW
Antarctic Intermediate Water AABW Antarctic
Bottom Water
10
(No Transcript)
11
Nd Paradox

12
Nd Paradox
Nd concentrations not as well-behaved as ?Nd
13
(No Transcript)
14
Summary

• Some unknown relationships between Nd
  concentration and Nd- isotopic ratios
• Nd acts as conservative water mass tracer by
  imprinting water masses with ?Nd values
  indicative of their source regions
• Less uncertainty than other isotopes systems and
  not impacted by biological variances
• Works as paleoproxy by recording source of deep
  water in specific regions such as S. Atlantic