Sedimentary chlorophyll

Sedimentary Chlorophyll Derivatives. In order to unravel the bio-geochemistry of chlorophyll, a variety of depositional environments, each representing potentially different fossilized counterparts, require study. Though the present investigation stresses marine sediments, collected well beneath the photic zone in order to divorce detrital from viable photoautotrophic material, photic zone sapropels and peats have also been examined. 

Seasonal inventories of sedimentary chloropigments indicated that there are differences in timing between the maximum chlorophyll and pheopigment inventories in Long Island Sound estuary (Sun et al., 1994). These differences in inventories likely reflect... 

Monobenzoporphyrins (139) were isolated from crude oil and their structure was assigned by H-NMR spectroscopy. It is clear from the substitution pattern that sedimentary porphyrins have arisen from chlorophylls rather than from tetrapyrroles, but the position of the benzene ring excludes an origin from any known chlorophyll either by a Diels-Alder... 

The rapid alteration of chlorophyll-a as phytoplankton leave the euphotic zone may well be expected to continue as passage through additional links in the food chain occurs. Thus, the detrital forms of chlorophyll-a, available to sedimentary diagenesis should contain a dominance of pheophorbide-a. 

The losses of magnesium and phytol through the combined effects of cellular senescence and predation (i.e. aerobic heterotrophy) in the water column lead to pheophytin-a and pheophorbide-a becoming the primary chlorophyll-a derivatives deposited in marine sedimentary environments. Though it is not known at present, the heterotrophic processes which cleave phytol more than likely also affect the 10-carbomethoxy group. Studies are underway to investigate the amounts of pyro-pheophorbides in water column detritus and surface sediments. 

Fig. 5. 6 Major early diagenetic (water column and very early sedimentary) pathways for chlorophyll- transformation (after Baker Louda 1986 Keely et al. 1990 Harradine et al. 1996 Louda et al. 1998 Louda et al. 2000).

Fig. 5. 9 Major anoxic sedimentary diagenetic routes for chlorophyll-a derivatives subsequent to those in Fig. 5.6 (after Barwise Roberts 1984 Baker Louda 1986 Louda et al. 1998, 2000).M= cations (e.g.Ni2+,V02+, Cu2+, GaOH2+).

Evidence for the biological origin of reduced carbon in sedimentary rocks comes from two sources. One is the existence of chemofossils, that is, characteristic remnants of biologically important compounds more resistant to chemical degradation than others. Notable examples are the isoprenoids pristane (2,4,6,10-tetramethyl pentadecane) and phytane (2,4,6,10-tetramethyl hexadecane), which arise from the decay of chlorophyll (Eglin-ton and Calvin, 1967 Didyk et al., 1978 McKirdy and Hahn, 1982 Hahn,... 

Quantitative relationships between Sp and 5 C values of organic matter that combine growth rates and carbon dioxide concentrations are being increasingly employed to evaluate sedimentary records of Sp values (e.g. Bentaleb 1996 Popp et al. 1997 Kump and Arthur 1999 Hofmann et al. 1999 Hayes et al. 1999 Rosenthal et al. 2000). Chlorophyll (e g. Sachs et al. 1999) and in ancient sediments, porphyrins (Hayes et al. 

---