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Systematics of Neodymium Isotopes and their Application to Paleoceanography

Literature: Frank, 2002, Reviews in Geophysics Goldstein & Hemming, 2003, Treatise on Geochemistry. http://www.ldeo.columbia.edu/~spk/Classes/G9802_PaleoProxies/paleo.html. Systematics of Neodymium Isotopes and their Application to Paleoceanography.

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Systematics of Neodymium Isotopes and their Application to Paleoceanography

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  1. Literature: Frank, 2002, Reviews in Geophysics Goldstein & Hemming, 2003, Treatise on Geochemistry http://www.ldeo.columbia.edu/~spk/Classes/G9802_PaleoProxies/paleo.html 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

  2. 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).

  3. 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).

  4. T-S curve at 9°S, Atlantic Ocean Open University Ocean Circulation Text Book

  5. Circulation of the Atlantic Ocean NADW = North Atlantic Deep Water AAIW = Antarctic Intermediate Water AABW = Antarctic Bottom Water

  6. 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 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.

  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 the amount of 143Nd in a rock increases with time

  9. 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) geological tracer parent daughter half-life 147Sm 143Nd 143Nd/144Nd 106 Ga 16Lu 176Hf 176Hf/177Hf 36 Ga 238U 206Pb 206Pb/204Pb 4.5 Ga 235U 207Pb 207Pb/204Pb 0.7 Ga 232Th 208Pb 208Pb/204Pb 14 Ga (143Nd/144Nd)measured - (143Nd/144Nd)CHUR e Nd = * 104 (143Nd/144Nd)CHUR

  10. 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 Why are Radiogenic Isotopes of Dissolved Trace Metals Useful in Paleoceanography ?

  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. Nd isotopes trace water mass mixing Residence Time of Nd:500 – 1000 yrs ocean inventory flux into the ocean = the time for which dissolved species stay in the water column before they are scavenged / precipitated t = Input Pathways and Water Mass Mixing • Nd isotopes trace provenance

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

  14. 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. 1 m Archives Ferromanganese Crusts • precipitates of • ambient seawater • grow only a few • mm per Myr  archives of past seawater isotope composition

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

  18. 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 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 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. 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)

  21. 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 Closure of the Indonesian Gateway for deep water: ~ 10 Ma (middle Miocene) (Frank, 2002)

  23. Indonesian Gateway (open in the early Miocene) Indonesian Gateway (closed around 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 Tasman Basin Record

  24. 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)

  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 Piotrowski et al., 2005, Science Piotrowski et al., 2005, Science

  27. 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

  28. 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)

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

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

  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 ?

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