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
http://www.ldeo.columbia.edu/~spk/Classes/G9802_PaleoProxies/paleo.html
Global thermohaline circulation
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).
Deep water formation at high latitudes
= two main sites of deep water formation
= additional deep water formation
Simplified on the basis of the two-layer conveyor belt model of Schmitz (1995). Modified after Frank (2002).
T-S curve at 9°S, Atlantic Ocean
Open University Ocean Circulation Text Book
Circulation of the Atlantic Ocean
NADW = North Atlantic Deep Water
AAIW = Antarctic Intermediate Water
AABW = Antarctic Bottom Water
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
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
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
the amount of 143Nd in a rock increases with time
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)
daughter
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
232Th
208Pb
14 Ga
208Pb/204Pb
e Nd =
half-life
geological tracer
parent
(143Nd/144Nd)measured - (143Nd/144Nd)CHUR
(143Nd/144Nd)CHUR
* 104
Why are Radiogenic Isotopes of Dissolved
Trace Metals Useful in Paleoceanography ?
Impact of hydrothermal inputs:
Impact of eolian inputs:
• Nd isotopes: no effect
Impact of•riverine
inputs:
distinct isotopic composition of the
source
• different lithologies
and
ages area
of
is delivered
the ocean
source rocks
result in to
different
radiogenic isotope compositions
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
Input Pathways and Water Mass Mixing
 Nd isotopes
trace provenance
 Nd isotopes trace
water mass mixing
Residence Time of Nd: 500 – 1000 yrs
ocean inventory
= the time for which dissolved
t=
flux into the ocean
species stay in the water column
before they are scavenged / precipitated
Two Water Mass Tracers
Antarctic
Intermediate
Water (AAIW)


Antarctic
Bottom
Water (AABW)
North Atlantic Deep
Water (NADW)

von Blanckenburg (1999)
Nd isotope profiles match the present-day
salinity distribution in the Atlantic Ocean.
(von Blanckenburg, 1999, Science)
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
Water Profile
Stations
Only (at
points)
Global
Seawater
Stations
forleast
Nd 3Isotopes
Archives
Ferromanganese Crusts
- precipitates of
ambient seawater
- grow only a few
mm per Myr
1m
 archives of past seawater isotope composition
Nd Isotope Composition of Seafloor
Mn-Fe Deposits (Deep and Bottom Water)
-20
-4
-8
-13
-4
-11
-7
-7
-8
Albarède and Goldstein, 1992
Extraction of Nd From
Foraminiferal Shells
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 postmortem (early diagenesis) while still in
contact with ambient bottom water.
(e.g., Martin and Scher, 2004, EPSL 220)
Extraction of Nd From
Bulk Sediments
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
Case Studies
(1) 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)
Latitudinal Variability
happened in the SW
inWhat
the
Pacific
Ocean
Pacific around 10 Ma ?
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)
Major paleogeographic changes of the past 60 Myr
Closure of the Indonesian Gateway for deep water:
~ 10 Ma (middle Miocene)
(Frank, 2002)
Indonesian Gateway
Tasman Basin
Record
(open
(closed
in the
around
early Miocene)
10Ma)
Indonesian Gateway
between the Pacific
and Indian Oceans
closed around 10 Ma
 from 10 Ma onwards:
increased „Pacific-like“ signature due to
increased southward deflection of water
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)
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
Nd isotopes
NADW
AABW
 weaker NADW
during full glacials
and during cold
stadial events
 stronger NADW
during warm periods
Piotrowski et al.,
2005, Science
Piotrowski et al.,
2005, Science
Deglacial Record
Large deglacial changes with
millennial-scale variability
are superimposed on the
long-term trend.
 intensification of NADW
from 17-18 kyr onwards
 millennial excursions
seem to be linked to
changes in sea ice cover
in the North Atlantic
Piotrowski et al., 2004, EPSL
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)
Dust Input
From Asia –
Important for
the Nd budget ?
North Pacific
Island Arcs
modified
AABW
Importance of
Circum Pacific
Island Arcs ?
Simple Box Model for the North Pacific
(van de Flierdt et al., 2004a)
 x Fdust x e dust
Farc x e arc
(1)
(3)
FAABW* x e AABW*
North Pacific
FNPDW x e NPDW
(1)
OUTPUTS:
OUTPUTS
INPUTS:
INPUTS: (3)
(2)
(2)
(1)
(2)
Inventory: ~ 1.3 x 1012 g Nd
(1)
(2)
scav
=Assuming
fraction
dust
that
FFF
==*=flux
arc-derived
=flux
advected
ofofNd
Nd
scavenged
in
Nd-flux
flux
deep
of Nd
steady
state
NPDW
AABW
arc
in
seawater
out
water
of
leaving
the
water
the
column
N-Pacific
Fdissolves
can
be
modelled
as
arc
eeAABW
=
*
Nd
=
Nd
isotope
isotope
arc
a =function
of
dust
Fdust
dust-derived
Nd-flux
eNPDW
composition
composition
Nd isotope
of the
modified
of
compoarcs
dissolution
rate
Deep
.
sition
composition
Antarctic
of
North
Bottom
of
Pacific
NPDW
Water
edust = Nd isotope
*)
Water
(AABW
(NPDW)
composition of dust
Fscav x e NPDW
 Fdust edust + Farc earc + FAABW* eAABW* = FNPDW eNPDW + Fscav eNPDW
 Fdust + Farc + FAABW* = FNPDW + Fscav
Fscav =  Fdust + Farc
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
Lacan and Jeandel, 2005, EPSL
„[...] modeling studies should help better
understanding the precise processes
involved and the global significance [...]
of boundary exchange.“
Questions ?