Olivier Marchal Woods Hole Oceanographic Institution Roger Francois Earth and Ocean Sciences, U. British Columbia Jan Scholten Marine Environment Laboratory, Monaco An Inverse Method to Combine of 230 Th Data and a Circulation Model: Application to the North Atlantic Thanks to Carl Wunsch (MIT)

Half-life = 76 kyr In ocean waters: 230 Th/ 234 U = O(10 -4 ) 230 Th

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CENTRAL NORTH PACIFIC 23 o N, 158 o W Data: Roy-Barman et al. (EPSL, 1996) r 2 = 0.99 (n=8) unfiltered samples filtered samples

SUBANTARCTIC ZONE 47 o S, 142 o E r 2 = 0.99 (n=12) Data: R. Francois (pers. comm.) filtered samples

SOME STATIONS WITH DISSOLVED 230 Th MEASUREMENTS Data: R. Francois (pers. comm.)

DISSOLVED 230 Th IN NORTH ATLANTIC Data: R. Francois (pers. comm.)

Can 230 Th data complement physical oceanography data? QUESTION

Use of an inverse method to assess dynamical information in 230 Th data: Inversion # 1: Hydrographic data + circulation model Inversion # 2: Hydrographic data + circulation model Th STRATEGY

MODEL GRID Total 230 Th Dissolved 230 Th HORIZONTAL SPACING: 3 o x 3 o VERTICAL LEVELS: 1000 m 2000 m 3000 m 4000 m 5000 m

INVERSION # 1 HYDROGRAPHIC DATA + CIRCULATION MODEL

HYDROGRAPHIC DATA

CIRCULATION MODEL

= 0 Tarantola & Valette (1982) Mercier (1986)

HORIZONTAL FLOW BETWEEN m ERRORS IN (U,V) Ui + Vj

HORIZONTAL FLOW BETWEEN m ERRORS IN (U,V) Ui + Vj

INVERSION # 2 HYDROGRAPHIC DATA + CIRCULATION MODEL Th

230 Th MODEL

FRACTION OF 230 Th IN PARTICULATE FORM (K = C p /C) SED. Mean (n = 75) Cochran et al. (EPSL, 1987) Colley et al. (DSR, 1995) Moran et al. (EPSL, 1997, 2002) Vogler et al. (EPSL, 1998)

EFFECT OF 230 Th IN ESTIMATION OF INTEGRATED TRANSPORTS

WHY DO 230 Th LEAD TO HIGHER ESTIMATES OF VOLUME TRANSPORT?

IN SITU DENSITY AT 3000 m IN NORTH ATLANTIC  – 1000 (kg/m 3 ) < > C.I. = 0.02 kg/m 3 Data: HydroBase2 (R. Curry)

u = 0 is a possible solution

u = 0 is NOT a possible solution unless C(z) is linear

CONCLUSIONS In 1st inversion ( 230 Th data not considered), the flow displays a WBC and coherent structures in the interior with low statistical significance In 2nd inversion, the flow is further constrained by 230 Th data: - Addition of 230 Th leads to the estimation of a larger amplitude of the integrated meridional transports below 1000 m (by 2-9 Sv) - Correction by 230 Th for a tendency of inverse geostrophic models to lead to the inference of a vanishing flow when horizontal  gradients are insignificant Yes, 230 Th data can complement physical oceanography data

PENDING QUESTIONS How comparable are 230 Th data generated in different laboratories? How do particle fluxes and composition influence Th scavenging? - Need for 230 Th measurements on both dissolved and particulate phases (K) - Need for Th scavenging experiments with various particle types (e.g., Chase et al., 2002) Should we aim for more sophisticated scavenging models?

COMPARISON BETWEEN INTEGRATED TRANSPORTS Roemmich & Wunsch (1985) Bryden et al. (2005) Roemmich & Wunsch (1985)

Error in radiochemical balance: 1/2 = 0.75 x 10 5 dpm s -1 EFFECT OF 230 Th IN ESTIMATION OF INTEGRATED TRANSPORTS

FLOAT TRAJECTORIES Data from Hogg and Owens (1999)

Marchal and Nycander (J. Phys. Oceanogr., 2004) Floats Theory

MODEL GRID Total 230 Th Dissolved 230 Th HORIZONTAL SPACING: 3 o x 3 o VERTICAL LEVELS: 1000 m 2000 m 3000 m 4000 m 5000 m

DATA & MODEL RESIDUALS

INVERSION # 2: DENSITY AND 230 Th x 0 extended to include 230 Th C 0 extended to include 230 Th errors

DATA & MODEL RESIDUALS

(w * = Kw s = 115 m yr -1 )