Geochemistry of Tetrapyrrole, Tetraterpenoid, and Perylene Pigments in Sediments from the Gulf of California: Deep Sea Drilling Project Leg 64, Sites 474, 477, 479, and 481, and Scripps Institution of Oceanography Guaymas Basin Survey Cruise Leg 3, Sites 10G and 18G

Abstract

Results and discussion cover pigment analyses of 36 sediment samples recovered by Deep Sea Drilling Project Leg 64, and six samples from the Leg 64 site-survey cruise in the Guaymas Basin (Scripps Institution of Oceanography, Leg 3). Pigments investigated were tetrapyrroles, tetraterpenoids, and the PAH compound perylene.Traces of mixed nickel and copper ETIO-porphyrins were ubiquitous in all sediment samples, except for the very surface (i.e., <2 m sub-bottom), and their presence is taken as an indication of minor influxes of previously oxidized allochthonous (terrestrial) organic matter.Phorbides and chlorins isolated from Site 479 sediment samples (i.e., the oxygen-minimum locale, northeast of the Guaymas Basin) well represent the reductive diagenesis ("Treibs Scheme"; see Treibs, 1936) of chlorophyll derivatives. Three forms of pheophytin-a, plus a variety of phorbides, were found to give rise to freebase porphyrins, nickel phylloerythrin, and nickel porphyrins, with increasing depth of burial (increasing temperature).Sediments from Sites 481, 10G, and 18G yielded chlorophyll derivatives characteristic of early oxidative alterations. Included among these pigments are allomerized pheophytin-a, purpurin-18, and chlorin-p 6 .The high thermal gradient imposed upon the late Quaternary sediments of Site 477 greatly accelerated chlorophyll diagenesis in the adjacent overlying sediments, that is, the production of large quantities of free-base desoxophylloerythroetioporphyrin (DPEP) occurred in a section (477-7-5) presently only 49.8 meters sub-bottom. Present depth and age of these sediments are such that only chlorins and phorbides would be expected.Carotenoid (i.e., tetraterpenoids) concentrations were found to decrease rapidly with increasing sub-bottom depth. Less deeply buried sediments (e.g., 0-30 m) yielded mixtures of carotenes and oxygen-substituted carotenoids. Oxygencontaining (oxy-, oxo-, epoxy-) carotenoids were found to be lost preferentially with increased depth of burial.Early carotenoid diagenesis is suggested as involving interacting reductions and dehydrations whereby dehydro-, didehydro-, and retro-carotenes are generated. Destruction of carotenoids as pigments may involve oxidative cleavage of the isoprenoid chain through epoxy intermediates, akin to changes in the senescent cells of plants.Perylene was found to be a common component of the extractable organic matter from all sediments investigated. The generation of alkyl perylenes was found to parallel increases in the existing thermal regime at all sites. Igneous sills and sill complexes within the sediment profile of Site 481 altered (i.e., scrambled) the otherwise straightforward thermally induced alkylation of perylene.The degree of perylene alkylation is proposed as an indicator of geothermal stress for non-contemporaneous marine sediments.

Nitrogen isotopes in chlorophyll and the origin of Eastern Mediterranean sapropels

“…Furthermore, Chl686 is observed in three intervals from a Black Sea sapropel (e.g., Unit II), and in an Eastern Mediterranean sapropel (S7), each of which was soxhlet extracted in MeOH, then MeCl2. Finally, a chlorin with a virtually identical visible absorption spectrum, called "Phorbide-686.5," was reported in sediments from a sub-bottom depth of 31-35 min the Gulf of California (Baker and Louda, 1982;Louda and Baker, 1986).…”

“…Additional support for this interpretation comes from the high retention volume (7.29 mL) of the compound on size exclusion chromatography relative to PTNa (6.19 mL). Baker and Louda (1982) and Louda and Baker (1986) tentatively identified the chlorin they called Phorbide-686.5 as a 2-acetyl-2-desvinyl derivative of pyropheophytin a. They suggested, based on the 35.5 nm hypsochromic shift of the red band in the sodium borohydride-reduced product of Phorbide-686.5…”

Identification of carotenals in sediments

“…Repeta (1989) described the degradation of fucoxanthin to loliolide via an intramolecular rearrangement leading to fragmentation without the addition of oxygen. Degradation of bcarotene or diatoxanthin to loliolide according to this scheme requires oxidation of the molecule to an epoxide through microbially mediated fermentation reactions (Repeta, 1989;Baker and Louda, 1982). Perhaps such microbial fermentative processes in the anoxic parts of the water column could also play a role in the formation of the carotenals identified here.…”

Polystyrene‐Divinylbenzene (PS‐DVB), a Mild Stationary Phase for the Chromatographic Purification of the Unstable 132, 173‐Cyclopheophorbide a‐Enol

“…Previously, our group has isolated CPP from deep sea sediments, [7] though misidentified at the time, [6,7] using increasing percentages of acetone in petroleum ether (br 30-608C) to fractionate pigments in columns of microcrystalline cellulose. It was and remains unknown as to how many of the 'unknown' chlorins [7] in that sample were actually generated from the CPP (aka phorbide-686.5) during chromatography.…”

“…The synthesis of CPP, as well as other unusual dihydroporphyrins, has been reviewed. [4] CPP has been isolated from many natural sources including a sponge, [5] Pleistocene sediments from the Guaymas Basin in the Gulf of California, [6,7] the Black Sea, [8] and the highly sulfidic carbonate marls of Florida Bay. [9] In the later case, geochemical conversion of pyropheophorbide-a into CPP was traced downhole, mimicking the in vitro Dieckmann reaction.…”