1. Bioturbation The mixing of bulk sediments or sedimentary particles
by animals living in the sediments
Why worry about it?
The “classical” view: sediment mixing as a
quasi-diffusive process
Complications to quasi-diffusive mixing
“Non-diffusive” mixing and why it matters

5. c) “blurring” of signals in the sedimentary record
ML = 10 cm
Sed rate= cm’/y
No mixing
(from Broecker)

7. 3 cm

10. Mass Balance: F: flux e.g., mol/cm2sed/y C: concentration e.g., mol/gp
R: reaction rate e.g., mol/gp/y
X1,x2: depth (cmsed)
Mass Balance:

11. Diffusive flux: Burial flux: So: reaction Change in C in layer
over time
Diffusive
transport
Transport by
burial

12. Porosity and solid phase concentrations…
Craven et al.,1986, DSR 33,

13. Case 1: Only burial; steady state; , , w constant; R = -C
Case 2 : only quasi-diffusive mixing ; steady state;
, , w constant; R = -C

16. Xs Th-234 (24.1 days) Xs Pb-210 (22.3 years) C-14 (5730 years)
Browmawell, 1986
Xs Th-234 (24.1 days)
Xs Pb-210 (22.3 years)
C-14 (5730 years)

21. “Age-dependent mixing”… compare rates from 2 tracers

22. Mixing on the NW
Atlantic continental
margin

23. Size-selective mixing

27. xs Th-234 from the central equatorial Pacific
Pope et al., DSRII

29. How widespread
is this
“subductive
transport”?

30. Subductive transport is a factor in C cycling, too…

31. Time scales and steady state…