1. 12.710 Intoduction to Marine Geology and Geophysics 11/1 Mid Term Sediments, Processes, and the Sedimentary Record 11/6 (McManus) Deep-sea sediments: composition, distribution 11/8 (McManus) Biological, chemical, and physical abyssal processes 11/13 (McManus)Dating methods and the sedimentary record 11/15 (McManus)Paleothermometry 11/20(McManus)Deep water chemistry and atmospheric p(CO 2 ) 11/22 Thanksgiving 11/27 (McManus)Ocean chemistry and continental weathering 11/29 (McManus)Astronomical climate theory 12/4 (McManus)Sedimentary records of abrupt climate change 12/6 Final Exam

2. Abyssal sedimentary processes I Early diagenesis Physical Chemical Addition Removal Sed.-water interaction II Abyssal reworking Nepheloid layers Syndepositional reworking Deep currents Sediment drift deposits III Bioturbation Discrete, episodic Modeled as diffusive process Varies with depth, age, size Environmental influence

3. Sediment traps and bottom sediments Composition of settling particles not reflected on the sea floor.

4. Case 1. No diagenesis Variable property preserved through time at increasing depth.

5. Case 2. Constant diagenesis Steady state profile preserved through time at migrating depth.

6. Process Compaction Cementation Authigenesis Recrystallization Inversion Replacement Dissolution Bioturbation

7. Sequence of chemical reactions Energy considerations yield predictable sequence.

10. CaCO 3 more soluble in the deep ocean: Pressure effect combines with lower [CO 3 = ].

11. The (“older”) deep Pacific is more corrosive. Pressure effect combines with lower [CO 3 = ]. “Delta carbonate” (  CO 3 = ) is defined as difference from saturation (after Broecker).

13. Nepheloid layer Turbidity increases toward the bottom due to resuspension.

15. McCave and Tucholke, 1986 Suspended load

16. Deep turbidity occurs where western boundary currents provide energy.

18. Sediment drift deposits Structure defined by sediment availability and bathymetry.

19. Sediment drift deposits Large features overlying basement structure.

20. Sediment drift deposits Large features overlying basement structure.

21. Sediment drift deposits Large features overlying basement structure.

22. Water masses and drifts Drift deposits follow deep currents and bathymetry.

23. Bioturbation Abundant, complex, benthic communities influence bottom sediments.

24. Bioturbation Instantaneous event (impact) distributed throughout the sediment column.

25. Modeling bioturbation Berger and Heath (1968) Observations suggest mixing in at least the top few centimeters, and an exponential decrease in concentration above boundaries and event horizons. Suggest a simple, useful model to explore.

26. Instantaneous mixing --------------------------- No mixing

28. Mixed layer influence Mixing is both upward and downward, influencing the overall sediment column.

30. Biodiffusivity Estimates for D b display a strong relationship to location.

31. Size-dependent bioturbation Different grain sizes mixed differently, give range of values for biodiffusivity. Wheatcroft, 1992

32. Size-dependent bioturbation Different grain sizes mixed differently, give range of values for biodiffusivity. Wheatcroft, 1992

33. Estimating D b A range of radioactive tracers can be used.

34. Age-dependent mixing Shorter-lived isotopes yield higher estimates for D b.

35. Subsurface maxima Not a simple 1=D process.

36. Influence of bioturbation May alter structure and timing of sedimentary signal. Original signalMixed record

37. Spectral influence of bioturbation May alter apparent frequency and amplitude of signal

38. Temporal influence of bioturbation May smooth appearance Of abrupt transitions.

39. Controls on mixing depth L In single region, strong influence of C org. Trauth et al.

40. Controls on biodiffusivity D b Globally, higher D b (mixing coeff.) follows higher sedimentation rate. Boudreau

41. Controls on mixing depth L Net result of com- peting influences is similar L. Boudreau