1. Systematics of Neodymium Isotopes
and their Application to Paleoceanography
EESC G9802, Spring 2006: Toward an improved understanding of paleoceanographic proxies: combining models with data
Samar Khatiwala, Tina van de Flierdt, Sidney Hemming
Literature: Frank, 2002, Reviews in Geophysics
Goldstein & Hemming, 2003, Treatise on Geochemistry

2. Global thermohaline circulation
The ocean is one of the main players of the climate system and affects climate in multiple ways.
71 % of the Earth surface are covered by the ocean and therefore most of the solar radiation received
at the Earth’s surface goes into the ocean. The ocean does not only store this heat, but also redistributes it
Before it is released again to the atmosphere. Additionally, the ocean can influence climate by its sea ice cover and by
Being part of the biogeochemical cycles and exchanging gases with the atmosphere.
Shown here is a simplified cartoon of the global thermohaline circulation, also called the “global conveyor belt” after Wally Broecker, which is responsible for the general overturning of the ocean, from the top to the bottom. Near surface waters (red lines) flow towards the main areas of deep water formation and recirculate at depth. While it is still argued , whether the thermohaline circulation can drive climate change, it is clear that it can act as an important amplifier.
Simplified on the basis of the two-layer conveyor belt model of Schmitz (1995). Modified after Frank (2002).
Original “global conveyor belt“ by Brocker (1991).

3. Deep water formation at high latitudes
= two main sites of deep water formation
= additional deep water formation
The driving force for the thermohaline circulation is deep water formation, which happens at present day in the North Atlantic and in the Southern Ocean. From the North Atlantic, the newly formed North Atlantic deep water is transported southward, into the Southern Ocean, and the deep Pacific. In the Pacific upwelling happens and surface waters are then carried back to the Atlantic via the Indian Ocean (warm water route) and across the Drake Passage (cold water route) and the cycle begins again.
Simplified on the basis of the two-layer conveyor belt model of Schmitz (1995). Modified after Frank (2002).

4. T-S curve at 9°S, Atlantic Ocean
The temperature-salinity properties of Atlantic water masses can be nicely observed at a water profile at 9 degrees south. Plotted on the x-axis is the salinity of the water, and on the y-axis the temperature. North Atlantic water is very saline, and that is because a lot of salt is transported to the North Atlantic from the subtropics by the Gulf Stream. Antarctic Bottom water on the other hand is not that salty, but colder than North Atlantic deep water. Both water masses are dense enough to form the deepest waters in the area’s where they are build. Shown is also the field for Antarctic Intermediate Water and you can see that this water mass has lower salinity and temperature than the other two and hence the water is not dense enough to form a deep water mass.
Open University Ocean Circulation Text Book

5. Circulation of the Atlantic Ocean
The observations from the conservative water mass tracers salinity and temperature and others translate in a simplified circulation pattern in the Atlantic Ocean as outlined in this diagram, which is adapted from Arnold Gordon. What you can see is a profile through the Atlantic basin from 80°N to 60°S. Simplified we have surface and Antarctic intermediate waters moving northward, North Atlantic deep water being build in the North Atlantic and moving southwards, and Antarctic Bottom Water being build in the south and moving northwards. All these water masses are at present day easy to identify because they have very distinct temperatures, salinity and other physical properties. If we, however, want to look at ocean circulation patterns back in the past and in order to understand the interaction of ocean circulation and climate we need other proxy records, since conservative water mass properties such as temperature and salinity are not preserved in the geological record.
NADW = North Atlantic Deep Water
AAIW = Antarctic Intermediate Water
AABW = Antarctic Bottom Water

6. a promising tracer for ocean circulation
Reconstruction of past deep water circulation patterns requires the use of proxy records, since conservative water mass properties such as temperature and salinity are not preserved.
neodymium isotopes -
a promising tracer for ocean circulation

7. Lanthanides The name neodymium is derived from the
Neodymium was first separated in 1885 from a material known as didymium.
The name neodymium is derived from the
Greek words neos = new and didymos = twin.
Lanthanides

8. What are Radiogenic Isotopes ?
= stable products of the natural decay
of radioactive parent nuclides
for example 147Sm decays to 143Nd by a decay:
147Sm  143Nd + a + Q (half-life: 106 billion years)
143Nd is therefore a radiogenic isotope
Before going into more detail, let’s do a small excursion to refresh your knowledge in radiogenic isotopes. What are radiogenic isotopes? Radiogenic isotopes are the stable products of the natural decay of radioactive parent nuclides. For example 147Sm decays to 143Nd by a decay with a half-life of 106 billion years. 143Nd is therefore a radiogenic isotope, the amount of which increases in a rock with time.
the amount of 143Nd in a rock increases with time

9. (143Nd/144Nd)measured - (143Nd/144Nd)CHUR
radiogenic isotopes are normalized to non-radiogenic
isotopes of the same element (e.g. 143Nd to 144Nd)
143Nd/ 144Nd varies in natural rocks dependent on their
age and their composition (lithology)
parent
daughter
half-life
geological tracer
147Sm
143Nd
106 Ga
143Nd/144Nd
16Lu
176Hf
36 Ga
176Hf/177Hf
238U
206Pb
4.5 Ga
206Pb/204Pb
235U
207Pb
0.7 Ga
207Pb/204Pb
Instead of using this radioactive clock to date rocks we can also use it to identify certain rock types. If we normalize the radiogenic isotopes to another non-radiogenically build stable isotope of the same element, we end up with a ratio (e.g 143/144), which is very different for different rock types. To trace rock types and ultimately geological processes radiogenic isotopes are normalized to non-radiogenic isotopes of the same element. 144Nd is such a non-radiogenic isotope of Nd, the amount of which does not change with time. Therefore the ratios of 143Nd to 144Nd increases with time, since 143 is continuously build by the decay of Sm. Besides the age, however, the composition of the rock is important, means how much Sm there is initially (if there is not a lot, there is not a lot which can decay) and this varies between different rock types in the earth crust and mantle. In summary the ratios shown here for different isotope systems of Pb, Nd, and Hf are different for different rocks. In some of the following slides you will see Nd or Hf isotopes expressed in e units. This is just a way to make the numbers easier to read, because the 143/144 and 176/177 sometimes only show deviations in the 5th digit.
232Th
208Pb
14 Ga
208Pb/204Pb
(143Nd/144Nd)measured - (143Nd/144Nd)CHUR
e Nd =
* 104
(143Nd/144Nd)CHUR

10. Why are Radiogenic Isotopes of Dissolved
Trace Metals Useful in Paleoceanography ?
Impact of hydrothermal inputs:
• Nd isotopes: no effect
Impact of eolian inputs:
• distinct isotopic compo-
sition of the source area
is delivered to the ocean
Impact of riverine inputs:
• different lithologies and ages of
source rocks result in different
radiogenic isotope compositions

11. Boundary
Exchange
Lacan and Jeandel, 2005, EPSL
Tachikawa et al., 2003, JGR
continental margins can be sources and sinks for elements in the ocean by means of particulate / dissolved exchange processes

12. Input Pathways and Water Mass Mixing
Nd isotopes trace
water mass mixing
Nd isotopes
trace provenance
Let‘s start with some basics on dissolved radiogenic isotopes in the ocean, and why we think they are useful tracers in paleoceanography. Well, first of all, we know that dissolved trace metals in the oceans are derived from three main sources, which are riverine inputs from the continents, eolian dust transported by winds and hydrothermal activity. For Nd, we can cancel out hydrothermal contribution, since Nd is scavenged very efficiently at hydrothermal vent sites. Instead, boundary exchange, meaning additon of Nd to the water column from interatction with the ocean‘s margin seems to be important in some areas. All of these inputs do implement a typical Nd isotopic signature to the water column, and therefore dissolved Nd isotopes can fingerprint the provenance of material. However, the Nd isotopic composition of a particular water mass is not only dependent on its input sources but also whether it has had exchange with another water mass, which may alter its isotopic composition. This is, however, only true if the residence time for the element of interest is in the order of or shorter than the global turn-over time of the ocean. The residence time of Nd is between 500 and 1000 years and is therefore perfectly suited to apply Nd isotopes as circulation and water mass tracer.
Residence Time of Nd: 500 – 1000 yrs
= the time for which dissolved
species stay in the water column
before they are scavenged / precipitated
ocean inventory
flux into the ocean
t =

13.  Two Water Mass Tracers Antarctic Intermediate Water (AAIW)
North Atlantic Deep
Water (NADW) 
Antarctic
Intermediate
Water (AAIW)
Bottom
Water (AABW)
von Blanckenburg (1999)
Nd isotope profiles match the present-day
salinity distribution in the Atlantic Ocean.
(von Blanckenburg, 1999, Science)

14. Goldstein and Hemming (2003)
Nd Isotopes vs. Silicate in Atlantic Deep Waters
Goldstein and Hemming (2003)
 remarkable co-variation between dissolved eNd and SiO2
 Nd isotopes = quasi conservative water mass tracer

15. Water Profile Stations Only (at least 3 points)
Global Seawater Stations for Nd Isotopes

16. Archives Ferromanganese Crusts precipitates of ambient seawater
grow only a few
mm per Myr
 archives of past seawater isotope composition

17. Nd Isotope Composition of Seafloor
Mn-Fe Deposits (Deep and Bottom Water)
-20 -8
-13
-11 -7 -4 -8
Albarède and Goldstein, 1992

18. Extraction of Nd From Foraminiferal Shells Extraction of Nd From
The Nd isotopic composition of
planktic foraminifera reflects the
surface seawater composition.
(e.g., Vance et al., 2004, Paleoceanography)
Ellen E. Martin/University of Florida
Fossil fish teeth, about one-fortieth of an inch long.
New York Times, January 22, 2002
Extraction of Nd From
Fossil Fish Teeth
Fish teeth acquire their Nd signal post-
mortem (early diagenesis) while still in
contact with ambient bottom water.
(e.g., Martin and Scher, 2004, EPSL 220)

19. Extraction of Nd From Bulk Sediments Extraction of Nd From
Extraction of dispersed FeMn fraction from
bulk sediments by sequential leaching allows
high-resolution records of Nd isotopes.
(e.g., Rutberg et al., 2000; Bayon et al., 2002)
Deep-sea core repository
at Lamont
Extraction of Nd From
Deep-Sea Corals
Deep-sea corals offer the potential to
achieve past seawater Nd from
absolutely (U-Th) dated archives.
(e.g., van de Flierdt et al., submitted)
Solitary coral Desmophyllum Dianthus from the New England seamounts

20. tracing the closure of the Indonesian Gateway and
Case Studies
tracing the closure of the
Indonesian Gateway and
associated changes in deep
water circulation with Nd isotopes
Archive:
ferromanganese crusts
(van de Flierdt et al., 2003, Paleoceanography)
The second case study is addressing what happens to the deep water isotope composition at the onset of the Northern Hemisphere glaciation. In other words: Is the associated change in the style of weathering from normal chemical weathering to predominantly physical weathering manifested in the deep water record.

21. Latitudinal Variability in the Pacific Ocean
What happened in the SW Pacific around 10 Ma ?
Latitudinal Variability
in the Pacific Ocean
eNd = - 7
Nd isotopes become progressively more radiogenic from the South to the North
continuous dilution of
Southern Ocean water
with overlying Pacific
Deep Water (PDW)
Neodymium isotopes
monitor circulation patterns !
Equatorial Pacific data: Ling et al. (1997) and Lee et al. (1999)

22. Major paleogeographic changes of the past 60 Myr
Acutally around that time the Indonesian Gateway, which was allowing deep water communication between the Pacific and Indian Ocean closed for deep waters. This is because the Australian plate continuously drifts northwards as indicated by this red arrow, and hence leads to a merging of the plate fragements in the Indonesian area. One effect is for example the large orogeny on Papua New Guinea.
Closure of the Indonesian Gateway for deep water:
~ 10 Ma (middle Miocene)
(Frank, 2002)

23. (open in the early Miocene)
 from 10 Ma onwards:
increased „Pacific-like“ signature due to increased southward deflection of water
Indonesian Gateway
between the Pacific
and Indian Oceans
closed around 10 Ma
(closed around 10Ma)
Indonesian Gateway
(open in the early Miocene)
Tasman Basin
Record

24. (2) The First High-Resolution Nd Record
Case Studies
(2) The First High-Resolution Nd Record
Covering the Last Glacial Cycle
Archive:
Dispersed FeMn
Fraction Extracted
From Bulk Sediments
(Piotrowski et al., 2004, EPSL & 2005, Science)
The second case study is addressing what happens to the deep water isotope composition at the onset of the Northern Hemisphere glaciation. In other words: Is the associated change in the style of weathering from normal chemical weathering to predominantly physical weathering manifested in the deep water record.

25. Study Location – South Atlantic
high
sedimentation rate: 20 cm/kyr
high-resolution
record possible
water depth:
3700 – 4700 m
mixing front
between NADW
and AABW

26. Nd isotopes NADW AABW  weaker NADW during full glacials
and during cold
stadial events
 stronger NADW
during warm periods
The motivation for this study is as old as is the interest in Nd isotopes as a tracer for past ocean circulation. This diagram shows the very first high resolution record of authigenic Nd isotopes over the past glacial cycle produced by Alex Piotrowski, and co-workers here at Lamont. The record is based on the extraction of seawater-derived authigenic Nd from bulk sediments from the Cape Basin. Nd isotopes in red and carbon isotopes in blue and black show a remarkable close correspondence, which has been interpreted to reflect waxing and waning amounts of North Atlantic Deep Water in the South Atlantic. For example, the low Nd isotopic compositions in the Holocene are interpreted to reflect large contributions of NADW, and high values at the Last Glacial Maximum are interpreted to reflect reduced amounts of NADW in the Cape Basin. The validity of this interpretation however heavily depends on the assumption of constant end-member compositions.
Therefore one of the key concerns in applying Nd isotopes to unravel the intensity of global overturning circulation is whether the Nd isotopic composition of NADW has changed on glacial-interglacial time-scale and this is the question I will try to answer today.
Piotrowski et al.,
2005, Science
Piotrowski et al.,
2005, Science

27. Deglacial Record Large deglacial changes with
Piotrowski et al., 2004, EPSL
intensification of NADW from kyr onwards
millennial excursions seem to be linked to changes in sea ice cover
in the North Atlantic
Large deglacial changes with
millennial-scale variability
are superimposed on the long-term trend.

28. (3) Quantifying and Identifying Nd Fluxes in the North Pacific –
Case Studies
(3) Quantifying and Identifying Nd
Fluxes in the North Pacific –
a Very Simple Box Model
Archive:
ferromanganese crusts
(van de Flierdt et al., 2004, GCA)
The second case study is addressing what happens to the deep water isotope composition at the onset of the Northern Hemisphere glaciation. In other words: Is the associated change in the style of weathering from normal chemical weathering to predominantly physical weathering manifested in the deep water record.

29. Dust Input From Asia – Important for the Nd budget ? Importance of
North Pacific
Island Arcs
modified
AABW
Importance of
Circum Pacific
Island Arcs ?

30. Simple Box Model for the North Pacific
(van de Flierdt et al., 2004a)
OUTPUTS: (1)
FNPDW = flux of Nd in deep
water leaving the N-Pacific
eNPDW = Nd isotope compo-
sition of North Pacific Deep
Water (NPDW)
(1)
INPUTS: (3)
FAABW* = advected flux of Nd
eAABW* = Nd isotope
composition of modified
Antarctic Bottom Water
(AABW*)
(3)
g x Fdust x e dust
Farc x e arc
INPUTS: (1)
= fraction of dust that
dissolves in seawater
Fdust = dust-derived Nd-flux
edust = Nd isotope
composition of dust
(1)
OUTPUTS (2)
Fscav = flux of Nd scavenged
out of the water column
eNPDW = Nd isotope
composition of NPDW
(2)
INPUTS: (2)
Farc = arc-derived Nd-flux
earc = Nd isotope
composition of arcs
(2)
Assuming steady state
Farc can be modelled as
a function of the dust
dissolution rate g .
g Fdust edust + Farc earc + FAABW* eAABW* = FNPDW eNPDW + Fscav eNPDW
FAABW* x e AABW*
North Pacific
FNPDW x e NPDW
Inventory: ~ 1.3 x 1012 g Nd
Fscav x e NPDW
g Fdust edust + Farc earc + FAABW* eAABW* = FNPDW eNPDW + Fscav eNPDW
g Fdust + Farc + FAABW* = FNPDW + Fscav
Fscav = g Fdust + Farc

31. Results / Implications of the Box Model for the Nd Budget in the North Pacific
 dust has been a minor component for the dissolved Nd
budget indicated by dissolution rates of less than 3.4 %
 island arcs supply at least 4 x 108 g Nd / year
in the North Pacific
• this is in the order of the global dissolved riverine Nd flux
• but no big rivers with an arc-like composition
discharge into the North Pacific ...
 supply mechanism of arc-like Nd:
small rivers and / or particle – seawater interaction

32. Lacan and Jeandel, 2005, EPSL
„[...] modeling studies should help better
understanding the precise processes
involved and the global significance [...]
of boundary exchange.“

33. Questions ?
I could give you many more examples about how we can use radiogenic isotopes to trace different processes in the past ocean, but I guess I better stop here to allow some time for questions…