Chemical composition of manganese nodules and crusts from the Pacific and Indian Ocean and Loch Fyne, Scotland

The first part of this thesis includes some topics of a non-geochemical nature but which are of importance in interpreting the geochemistry of nodules. The points covered include their distribution, petrography, structure, mineralogy and internal compositional variations. Part Two includes the geochemistry of both nodules and that of their surrounding sediments, This geochemical study has been divided into firstly, a general geochemical study of both nodules and sediments using a statistical approach to the interpretation of the data, secondly, the regional geochemistry of Pacific and Indian Ocean nodules and sediments, the latter entirely uninvestigated in the past, and thirdly, local variations in the composition of nodules. Throughout, emphasis has been placed on the geochemistry of nodules in terms of their environment of formation.

Sediment core-top GDGT data from the Arctic, the North Pacific and the Southern Ocean

TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a sea surface temperature (SST) proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs). In this study, we appraise the applicability of TEX86 and TEX86L in subpolar and polar regions using surface sediments. We present TEX86 and TEX86L data from 160 surface sediment samples collected in the Arctic, the Southern Ocean and the North Pacific. Most of the SST estimates derived from both TEX86 and TEX86L are anomalously high in the Arctic, especially in the vicinity of Siberian river mouths and the sea ice margin, plausibly due to additional archaeal contributions linked to terrigenous input. We found unusual GDGT distributions at five sites in the North Pacific. High GDGT-0/crenarchaeol and GDGT-2/crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and/or methanotrophic archaea to the sedimentary GDGT pool here. Apart from these anomalous findings, TEX86 and TEX86L values in the surface sediments from the Southern Ocean and the North Pacific do usually vary with overlaying SSTs. In these regions, the sedimentary TEX86-SST relationship is similar to the global calibration, and the derived temperature estimates agree well with overlaying annual mean SSTs at the sites. However, there is a systematic offset between the regional TEX86L-SST relationships and the global calibration. At these sites, temperature estimates based on the global TEX86L calibration are closer to summer SSTs than annual mean SSTs. This finding suggests that in these subpolar settings a regional TEX86L calibration may be a more suitable equation for temperature reconstruction than the global calibration.

(Table, page 351-359) Chemical composition of manganese nodules and crusts from the Pacific and Indian Ocean

Chemical and mineralogical analyses of manganese nodules from a large number of widely spaced localities in the Pacific and Indian Oceans have shown that their mineralogy and chemical composition varies both areally and with depth of formation. This is considered to result from a number of factors, important among which are: (a) their proximity to continental or volcanic sources of elements; (b) the chemical environment of deposition, including the degree of oxygenation; and (c) local factors such as the upward migration of reduced manganese in sediments from certain areas. Sub-surface nodules appear to share the chemical characteristics of their surface counterparts, especially those from volcanic areas where sub-surface sources of elements are probably important.

Benthic foraminiferal stable isotope record from ODP Site 138-849 on the East Pacific Rise

Benthic foraminifer and delta13C data from Site 849, on the west flank of the East Pacific Rise (0°11 'N, 110°31'W; 3851 m), give relatively continuous records of deep Pacific Ocean stable isotope variations between 0 and 5 Ma. The mean sample spacing is 4 k.y. Most analyses are from Cibicides wuellerstorfi, but isotopic offsets relative to Uvigerina peregrina appear roughly constant. Because of its location west of the East Pacific Rise, Site 849 yields a suitable record of mean Pacific Ocean delta13C, which approximates a global oceanic signal. The ~100-k.y.-period climate cycle, which is prevalent in delta18O does not dominate the long-term delta13C record. For delta13C, variations in the ~400- and 41-k.y. periods are more important. Phase lags of delta13C relative to ice volume in the 41- and 23-k.y. bands are consistent with delta13C as a measure of organic biomass. A model-calculated exponential response time of 1-2 k.y. is appropriate for carbon stored in soils and shallow sediments responding to glacial-interglacial climate change. Oceanic delta13C leads ice volume slightly in the 100-k.y. band, and this suggests another process such as changes in continental weathering to modulate mean river delta13C at long periods. The delta13C record from Site 849 diverges from that of Site 677 in the Panama Basin mostly because of decay of 13C-depleted organic carbon in the relatively isolated Panama Basin. North Atlantic to Pacific delta13C differences calculated using published data from Sites 607 and 849 reveal variations in Pliocene deep water within the range of those of the late Quaternary. Maximum delta13C contrast between these sites, which presumably reflects maximum influx of high-delta13C northern source water into the deep North Atlantic Ocean, occurred between 1.3 and 2.1 Ma, well after the initiation of Northern Hemisphere glaciation. Export of high-delta13C North Atlantic Deep Water from the Atlantic to the circumpolar Antarctic, as recorded by published delta13C data from Subantarctic Site 704, appears unrelated to the North Atlantic-Pacific delta13C contrast. To account for this observation, we suggest that deep-water formation in the North Atlantic reflects northern source characteristics, whereas export of this water into the circumpolar Antarctic reflects Southern Hemisphere wind forcing. Neither process appears directly linked to ice-volume variations.

Neogene calcareous nannofossils in the Caribbean and the eastern equatorial Pacific

Principal components analysis of nannofossil assemblages in five ODP sites in the Caribbean and the eastern equatorial Pacific was used to monitor Neogene surface water circulation changes. In 15.83-10.71 Ma, floral distributions clearly show the existence of the Circum-tropical Current between the Caribbean and the eastern equatorial Pacific and no surface water communication between the northern and southern Caribbean. In 10.71-9.36 Ma, the Circum-tropical Current weakened and the northward intra-Caribbean current had been initiated. Northern and southern Caribbean surface waters again became separated in 8.35-3.65 Ma and the Circum-tropical Current was regenerated. After 2.76 Ma, the northward intra-Caribbean current has completely been established and the Circum-tropical Current disappeared. This suggests that a barrier to the Circum-tropical Current had formed, indicating the final closure of the Isthmus of Panama.

(Table 11-I, page 338) Metal contents (%) of a representative sampling of manganese nodules from the North Pacific high-grade region

Two types of deep-sea dredges are currently under development for the mining of the manganese nodules, a deep-sea hydraulic dredge and a mechanical cable-bucket system. Both systems offer some advantages with the hydraulic system appearing to be advantageous in themining of a specific deposit for which it is designed while the cable-bucket system appears to be somewhat more flexible in working in a variety of deposits, topographic environments, and water depths. Environmental studies conducted in conjunction with deep-sea tests of the two types of mining systems currently indicate that substantially no environmental damage will be done in the mining of the deep-sea nodules. Because of the nature of the deposits and the way in which they can be mined, the manganese nodules appear to be a relatively pollution free and energy-saving source of a number of industrially important metals.

Geochemical composition of a representative collection of manganese nodules and slabs collected in the Western Pacific

Chemical analyses were performed on seveteen manganese nodules collected from the Pacific Ocean floor. The results were discussed compared with the previous data on the manganese nodules. Minerals were found to be todorokite, delta-MnO2 and other silicates, montmorillonite, illite, phillipsite and alpha-SiO2. Average composition shows that copper is concentrated on the deep sea nodules more than the shallow ones, and that the todorokite rich nodules contain more copper and nickel than the delta-MnO2 rich ones.

Protein and organic phosphorus in particulate matter and mesoplankton fraction in waters of the East Pacific

Vertical distribution of organic phosphorus and phosphatase activity was studied in the Southeast Pacific Ocean. The average rate of mineralization of organic phosphorus in the 0-200 m layer was shown to differ by a factor of 5-10 in oligotrophic and eutrophic areas, while residence time of phosphorus in production-destruction cycles differed by a factor of only 2-5, apparently because of both concentration of organic phosphorus and phosphorolysis rate increased simultaneously in the areas.