Olivier Marchal Woods Hole Oceanographic Institution Roger Francois Earth and Ocean Sciences, U....
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Transcript of Olivier Marchal Woods Hole Oceanographic Institution Roger Francois Earth and Ocean Sciences, U....
Olivier MarchalWoods Hole Oceanographic Institution
Roger FrancoisEarth and Ocean Sciences, U. British Columbia
Jan ScholtenMarine Environment Laboratory, Monaco
An Inverse Method to Combine of 230Th Data and a Circulation Model:
Application to the North Atlantic
Thanks to Carl Wunsch (MIT)
• Half-life = 76 kyr
• In ocean waters: 230Th/234U = O(10-4)
230Th
CENTRAL NORTH PACIFIC 23oN, 158oW
Data: Roy-Barman et al. (EPSL, 1996)
r2 = 0.99 (n=8)
unfiltered samples
filtered samples
SUBANTARCTIC ZONE 47oS, 142oE
r2 = 0.99 (n=12)
Data: R. Francois (pers. comm.)
filtered samples
SOME STATIONS WITH DISSOLVED 230Th MEASUREMENTS
Data: R. Francois (pers. comm.)
DISSOLVED 230Th IN NORTH ATLANTIC
Data: R. Francois (pers. comm.)
Can 230Th data complement physical oceanography data?
QUESTION
Use of an inverse method to assess dynamical information in 230Th data:
• Inversion # 1: Hydrographic data + circulation model
• Inversion # 2: Hydrographic data + circulation model + 230Th
STRATEGY
MODEL GRID
Total 230Th
Dissolved 230Th
HORIZONTAL SPACING:
3o x 3o
VERTICAL LEVELS:
1000 m2000 m3000 m4000 m5000 m
INVERSION # 1
HYDROGRAPHIC DATA + CIRCULATION MODEL
HYDROGRAPHIC DATA
CIRCULATION MODEL
= 0
Tarantola & Valette (1982)Mercier (1986)
HORIZONTAL FLOW BETWEEN 1000-4000 m
ERRORS IN (U,V)
Ui + Vj
HORIZONTAL FLOW BETWEEN 4000-5000 m
ERRORS IN (U,V)
Ui + Vj
INVERSION # 2
HYDROGRAPHIC DATA + CIRCULATION MODEL + 230Th
230Th MODEL
FRACTION OF 230Th IN PARTICULATE FORM (K = Cp/C)
SED.
SED.
SED.
Mean 01.015.0K (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 230Th IN ESTIMATION OF INTEGRATED TRANSPORTS
EFFECT OF 230Th IN ESTIMATION OF INTEGRATED TRANSPORTS
WHY DO 230Th LEAD TO HIGHER ESTIMATES OF VOLUME TRANSPORT?
IN SITU DENSITY AT 3000 m IN NORTH ATLANTIC
– 1000 (kg/m3)
< 41.66 41.66> 41.66
C.I. = 0.02 kg/m3
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 (230Th 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 230Th data:
- Addition of 230Th leads to the estimation of a larger amplitude of the integrated meridional transports below 1000 m (by 2-9 Sv)
- Correction by 230Th for a tendency of inverse geostrophic models to lead to the inference of a vanishing flow when horizontal gradients are insignificant
Yes, 230Th data can complement physical oceanography data
PENDING QUESTIONS
How comparable are 230Th data generated in different laboratories?
How do particle fluxes and composition influence Th scavenging?
- Need for 230Th 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: <C
2>1/2 = 0.75 x 105 dpm s-1
EFFECT OF 230Th 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 230Th
Dissolved 230Th
HORIZONTAL SPACING:
3o x 3o
VERTICAL LEVELS:
1000 m2000 m3000 m4000 m5000 m
DATA & MODEL RESIDUALS
i,o
i,oi
c
xx.r.n
i,f
i
c
)x(f.r.n
INVERSION # 2: DENSITY AND 230Th
• x0 extended to include 230Th
• C0 extended to include 230Th errors
DATA & MODEL RESIDUALS
i,o
i,oi
c
xx.r.n
i,f
i
c
)x(f.r.n
(w* = Kws = 115 m yr-1)