Highly dealkylated copper and nickel etioporpyfrins in marine sediments

Copper porphyrins have been recognized as natural constituents of marine sediments only within the past 5 years (Palmer and Baker, 1978, Science201, 49-51). In that report it was suggested that these pigments may derive from and be markers for oxidized terrestrial organic matter redeposited in the marine environment. In the present study we describe the distribution of copper porphyrins in sediments from several north Pacific and Gulf of California DSDP/IPQD sites (Legs 56,63,64). These allochthonous pigments have now been found to be accompanied by identical arrays of highly dealkylated nickel etioporphyrins. Evaluation of data from this and past studies clearly reveals that there is a strong carbon-number distribution similarity betweeen coincident Cu and Ni etioporphyrins. This homology match is taken as reflecting a common source for the tetrapyrrole ligands of this population of Cu and Ni chelates. Predepositional generation of these highly dealkylated etioporphyrins is concluded from the occurrence of these pigments in sediments continuing essentially all stages of in situ chlorophyll diagenesis (cf. Baker and Louda, 1983). That is, their presence is not regulated by the in situ diagenetic continuum. Thus, the highly dealkylated Cu and Ni etioporphyrins represent an 'allochthonous' background over which 'autochthonous' (viz. marine produced) chlorophyll derivatives are deposited and are undergoing in situ diagenesis.

Paleointensity of various DSDP sites (Table 3)

The existing database for paleointensity estimates of the ancient geomagnetic field contains more than 1500 data points collected through decades of effort. Despite the huge amount of work put into obtaining these data, there remains a strong bias in the age and global distribution of the data toward very young results from a few locations. Also, few of the data meet strict criteria for reliability and most are of unknown quality. In order to improve the age and spatial distribution of the paleointensity database, we have carried out paleointensity experiments on submarine basaltic glasses from a number of DSDP sites. Of particular interest are the sites that provide paleointensity data spanning the time period 0.3-5 Ma, a time of relatively few high quality published data points. Our new data are concordant with contemporaneous data from the published literature that meet minimum acceptance criteria, and the combined data set yields an average dipole moment of 5.49 +/- 2.36*10**22 Am**2. This average value is comparable to the average paleofield for the period 5-160 Ma (4.2 +/- 2.3*10**22 Am**2) (Juarez et al., 1998, doi:10.1038/29746) and is substantially less than the value of approximately 8*10**22 Am**2 often quoted for the last 5 Myr (e.g. McFadden and McElhinny (1982) J. Geomagn. Geoelectr. 34, 163-189; Goguitchaichvili et al., 1999, doi:10.1016/S0012-821X(99)00010-2).

(Table 1) Counts and ratios of microfossils at DSDP Hole 64-480

We examined the relative abundance of various components in the coarse fraction (> 150 µm) from a selected portion of the DSDP Site 480 piston core. The components consist mainly of diatoms, radiolarians, benthic and planktonic foraminifers with minor amounts of sponge spicules, terrigenous material, volcanic glass(?), dehydrated gypsum crystals, and spines of unknown biological origin. The examination shows that the siliceous organisms abound in the laminated sediments and that the calcareous organisms are more abundant in the nonlaminated sediments. Seasonal upwelling is responsible for the deposition of laminated sediments. The upwelling creates a strong oxygen-minimum zone, restricting the occurrence of burrowing benthic organisms and benthic foraminifers.