Calcium Carbonate Compensation Depth Research Articles

Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs

Systematic documentation of pteriomorph bivalves of the late Eocene–early Oligocene Keasey Formation in western Oregon follows previous monographic treatments of the anomalodesmatans and heteroconchs. It includes material from coeval Cascadia Margin strata in southwestern Washington in the context of major molluscan faunal turnover during the dramatic doubthouse climate transition from an ice-free tropical marine environment to the establishment of permanent polar ice caps and a cold temperate marine climate. The families represented are Crenellidae, Parallelodontidae, Glycymerididae, Limopsidae, Isognomonidae, Pectinidae, Propeamussiidae, and Limidae. New taxa include the genus Bathyisognomon and five new species: Limopsis squiresi, Bathyisognomon smithwickensis, Delectopecten kieli, Delectopecten keaseyorum, and Propeamussium (Parvamussium) mistensis. Small to minute mud pectens and glass scallops are among the most abundant and frequent taxa in the Keasey fauna, although they are poorly preserved and have been overlooked heretofore. Pteriomorphs are prominent elements of recurring associations of species in mudstone and fine-grained siltstone facies adjacent to three Keasey cold methane seeps. Previously described Keasey anomalodesmatans and heteroconchs in these seep-adjacent strata have living relatives adapted to dysoxia and toxic geochemistry. Because the unique macrofaunal associations in these settings are neither seep fauna nor part of the background fauna, this paper introduces and defines the concept of a transitional peri-seep biotope. Relationships, monophyly, systematic resolution within major pteriomorph groups, and global biogeographic distributions are reviewed in each systematic treatment. Recurring patterns include occurrences in active margin settings, inferred oscillatory deepening of the calcium carbonate compensation depth, late Eocene origin of two-layered oceans following establishment of the Antarctic Circumpolar Current, and biogeographic gateway changes that disrupted earlier Paleogene larval dispersal patterns.

Arcoid bivalve biodiversity during Eocene doubthouse cooling: Contrasting the active Cascadia Margin coldspot with the intracratonic Paris Basin hotspot

Response to the Eocene doubthouse interval of global climate cooling (53–33.5 Ma) is explored in arcoid bivalves of the families Parallelodontidae, Cucullaeidae, Arcidae, and Noetiidae. An anomalous biodiversity hotspot in the intracontinental Paris Basin of Northern Europe is contrasted with an equally anomalous coldspot at comparable latitude on the tectonically active Cascadia Margin of western North America. Reevaluation of arcoid shell morphology and an annotated glossary of shell features accompanies illustration and discussion of eight exemplar species, identifying new characters and distinguishing those with a strong phyletic signal from those representing functional convergence or developmental differences specific to size or age. Biodiversity anomalies cannot be attributed to any single factor. However, contributing factors include tectonic setting, correlates of bathymetric and sedimentary setting, sediment geochemistry, ocean gateway events, reorganization of current systems and water masses, deepening of the calcium carbonate compensation depth, patterns in the development of sea ice and polar ice storage, changes in sea level, and changes in atmospheric carbon dioxide and the carbon cycle. Opening of the Tasman Gateway and Drake Passage, thermal isolation of Antarctica, and evolution of a Pacific psychrosphere are correlated with the early appearance of cold-water molluscan taxa on the active Cascadia Margin along with the unrelated onset of arc volcanism, subduction, and geochemical changes associated with methane and sulfide seepage. Persistence of a shallow carbonate platform and proliferation of molluscan diversity in spite of global cooling is more difficult to explain, and understanding biogeographic anomalies requires additional climate proxy records. History of the western margin of North America includes an earlier Mesozoic volcanic arc and forearc basin in central and northern California with abundant basal arcoids, negating the need for westward migration out of the Tethyan region to the Cascadia Margin during the Paleogene.

Quaternary environments and monsoonal climate off northwest Australia: Palynological evidence from Ocean Drilling Program Site 765

The bathyal Ocean Drilling Program Site 765 at 5725 m water depth, offshore northwest Australia at 16°S is directly under the influence of the Australian monsoon during the Austral summer and is the recipient of continental dust during the Austral winter. It is downstream of the Indonesian Throughflow, which is a major arm of the global thermohaline circulation. As such it is ideally situated to record the climate and oceanic consequences of Quaternary climate variability. Despite being over 400 km from northwest Australia, palynomorphs (pollen and spores) are relatively common in this section, sourced via aeolian (during the dry winter) and benthic transportation processes and sediment plumes (during the summer monsoon). Detailed palynological analyses of this flora in the upper part of this core reveals intermittent snap shots of environmental and climate change over the last 300 kyrs. Interglacial stages are interpreted to be characterised by palynomorph-rich turbidite and calcareous ooze deposition whereas palynomorph-poor slowly accumulating siliceous oozes (deposited below the Calcium Carbonate Compensation Depth) are present during glacials. The dominance of Poaceae sourced from the Australian mainland in interglacial periods suggests that vegetation during these periods was similar to today. Interglacial palynofloral assemblages suggest a more intense wet season (Australian monsoon) with higher rainfall that allowed more active erosion and deposition onto the shelf. The presence of Indonesian sourced pollen and fern spore taxa, as well as warm water dinoflagellate species suggest enhanced Leeuwin Current and monsoonal intensity during interglacials times. The youngest part of the core is dominated by siliceous ooze, likely deposited during the Last Glacial Maximum and the early Holocene. The lack of calcareous ooze near the top of the core is likely caused by Holocene to Recent erosive processes or core disturbance. The presence of common charcoal in all samples over the last 300 kyrs shows that fire was a constant feature of the landscape in northwest Australia prior to human occupation of the region 65,000 years ago.

Integrated Oceanographic Research of Discovery Gap (Eastern North Atlantic) during the Cruise 43 of the R/V Akademik Nikolaj Strakhov

During cruise 43 of the R/V Akademik Nikolaj Strakhov (September 21–October 9, 2019), new data were obtained on the bottom relief, sedimentation, and hydrological regime of the Discovery Gap (eastern North Atlantic). It was shown that the upper limit of the Antarctic Bottom Water in the study area follows the 2.05°C isotherm and 34.91 PSU isohaline at depths of 4400–4700 m. A digital elevation model of the Discovery Gap relief was obtained. Three acoustic facies have been identified, which characterize dense bottom sediments and low sedimentation rates. Sediment cores ANS-43003, ANS-43004, and ANS-43006 are represented by light brown silty clays with foraminiferal sands and bioturbation. Strong dissolution of foraminifera was found in core ANS-43006, which indicates the formation of sediments below the calcium carbonate compensation depth.

Paleocene Radiolarian Faunas in the Deep-Marine Sediments Near Zhongba County, southern Tibet

An upper Paleocene radiolarian-bearing succession (ZN1) located in the southern part of the north subzone of the Tethyan Himalaya is composed of siliceous siltstones and claystones. In this paper, 23 species belonging to 13 genera are reported. Three new species, Lychnocanium? pyramis Li and Matsuoka sp. nov., Lychnocanium? stypticum Li and Matsuoka sp. nov., and Pterocyrtidium sinense Li and Matsuoka sp. nov., are described. Radiolarian assemblages from this succession can be compared with the Bekoma campechensis Zone (RP6), indicating a time interval of 61.5–58.23 Ma, i.e., late Paleocene. The radiolarian assemblages from the Yamdrok melange, the Zheba section, and the Jiazhu section indicate that they are of the same age as those from the Zhinadibu 1 section. The lack of calcareous and coarse-grained terrestrial materials in the ZN1 section proves that the strata of this section were deposited in a relatively deep marine environment below the calcium carbonate compensation depth (CCD) and more distal to the continents during the late Paleocene. Coeval deepwater sediments near Saga were accumulated near the CCD.

Cenozoic bathyal and abyssal ostracods beneath the oligotrophic South Pacific Gyre (IODP Expedition 329 Sites U1367, U1368 and U1370)

This study reports on Paleocene through Pleistocene deep sea ostracod assemblages from carbonate sequences recovered at Integrated Ocean Drilling Program (IODP) Sites U1367, U1368, and U1370 during Expedition 329 to the South Pacific Gyre (SPG). The SPG has the lowest surface primary productivity in the world oceans, and the sedimentary system beneath it has the lowest rates of organic matter flux to the seafloor in the ocean. Results show that this oligotrophic oceanic environment supported abundant and diverse ostracod faunas during the Oligocene, and the middle Miocene suggesting that ostracods are capable of exploiting low levels of food availability in the deep ocean. The SPG records revealed ostracod assemblages following major global climatic transitions: the Cretaceous/Paleocene (~65.5Ma) and the Eocene/Oligocene (~33.5Ma) transitions, and the middle Miocene climatic optimum (~14Ma). The Danian ostracod assemblage is scarce and characterized by Paraphysocythere spp. and Anebocythereis hostizea. High faunal turnover by the early Oligocene gives rise to an assemblage predominantly characterized by typical lower bathyal and abyssal genera Krithe, Poseidonamicus, Argilloecia, and Cytheropteron that are indicative of cold, moderately oxygenated conditions and signal the cooling of the deep ocean after the E/O transition. An increase in abundance of robust epifaunal taxa Bradleya, Henryhowella, Dutoitella, Pennyella, and Rugocythereis, and a pronounced decrease Argilloecia and Cytheropteron characterize the middle Miocene and Pleistocene assemblages, and indicate the presence of more corrosive bottom waters and enhanced oligotrophic conditions in the SPG. However, low variability in the ostracod assemblage taxonomic composition and stratigraphic distribution at Sites U1367 and U1368 suggest that mostly stable paleoceanographic conditions existed in the South Pacific Gyre during the early to the late Oligocene and from the middle to late Miocene (U1368). Declines in ostracod abundances toward the top of the sedimentary sequences at these sites are synchronous with the late Oligocene warming and the late Miocene carbonate crash in the equatorial Pacific, but they seem to also overlap the time when the site locations subsided below the calcium carbonate compensation depth (CCD) as they moved away from the East Pacific Rise.

Erosion and reworking of Pacific sediments near the Eocene‐Oligocene boundary

The Eocene‐Oligocene (E/O) boundary interval marks one of the largest and most rapid changes in climate during the last 50 Myr. Because of a very shallow calcium carbonate compensation depth in the Eocene, as well as the reworking of sediments and hiatuses in the boundary zone, it has also been one of the most difficult stratigraphic boundaries to study in deep water marine sections, especially in the Pacific Ocean. Recently, three drill sites have recovered complete sections of the E/O boundary interval in the tropical Pacific. A detailed study of these sections shows a series of pulses of reworked older radiolarians in the upper Eocene and lowermost Oligocene. The two largest pulses are coincident with the two sharp steps in carbon and oxygen isotope values that bracket the E/O boundary. Several smaller peaks in reworked material precede these two maxima. It is proposed that immixing of the older radiolarian species results from erosion and redeposition, possibly linked to pulses of new bottom water formation and the formation of a deep pycnocline.

A Cenozoic record of the equatorial Pacific carbonate compensation depth

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.

Vertical tectonics of the High Plateau region, Manihiki Plateau, Western Pacific, from seismic stratigraphy

The Manihiki Plateau is an elevated oceanic volcanic plateau that was formed mostly in Early Cretaceous time by hotspot activity. We analyze new seismic reflection data acquired on cruise KIWI 12 over the High Plateau region in the southeast of the plateau, to look for direct evidence of the location of the heat source and the timing of uplift, subsidence and faulting. These data are correlated with previous seismic reflection lines from cruise CATO 3, and with the results at DSDP Site 317 at the northern edge of the High Plateau. Seven key reflectors are identified from the seismic reflection profiles and the resulting isopach maps show local variations in thickness in the southeastern part of the High Plateau, suggesting a subsidence (cooling) event in this region during Late Cretaceous and up to Early Eocene time. We model this as a hotspot, active and centered on the High Plateau area during Early Cretaceous time in a near-ridge environment. The basement and Early Cretaceous volcaniclastic layers were formed by subaerial and shallow-water eruption due to the volcanic activity. After that, the plateau experienced erosion. The cessation of hotspot activity and subsequent heat loss by Late Cretaceous time caused the plateau to subside rapidly. The eastern and southern portions of the High Plateau were rifted away following the cessation of hot spot activity. As the southeastern portion of the High Plateau was originally higher and above the calcium carbonate compensation depth, it accumulated more sediments than the surrounding plateau regions. Apparently coeval with the rapid subsidence of the plateau are normal faults found at the SE edge of the plateau. Since Early Eocene time, the plateau subsided to its present depth without significant deformation.

The effect of environmental controls on the metal content in ferromanganese crusts and nodules from the Mozambique Ridge and in the Mozambique Basin, southwestern Indian Ocean

Major and minor element compositions of a suite of ferromanganese nodules and crusts dredged from the Mozambique Ridge on the RV Sonne cruise in 2005 are combined with previously published data from both the Mozambique Ridge and adjacent Mozambique Basin, in order to examine the relationship between regional variations in chemical composition and environmental controls on ferromanganese mineralisation. Three principal environmental controls on ferromanganese nodule and crust composition have previously been recognised: primary productivity in the surface waters, the oxygen minimum layer, and the calcium carbonate compensation depth. Of these three, the oxygen minimum layer is identified as having the greatest controlling influence on the composition of the ferromanganese deposits of the Mozambique Ridge and Basin, with primary productivity and the calcium carbonate compensation depth being secondary in importance. As a result, three different mineralisation zones can be defined in the study area: deepwater basin deposits, ridge flank deposits formed below the base of the oxygen minimum layer, and ridge crest deposits formed within the oxygen minimum layer. Nodules and crusts from these different zones display distinct variations in chemistry and mineralisation style.

Deep-Sea environments across the Cretaceous/Paleogene boundary in the eastern South Atlantic Ocean (ODP Leg 208, Walvis Ridge)

Sediments recovered at ODP Site 1262 on Walvis Ridge (eastern South Atlantic Ocean, paleodepth ∼ 2500–3000 m) offer an opportunity to look into the nature and cause(s) of the benthic foraminiferal turnover across the Cretaceous/Paleogene (K/Pg) boundary at abyssal depths at a location relatively remote from the location of the asteroid impact on the Yucatan peninsula. Late Maastrichtian assemblages were diverse and heterogeneous, reflecting oligo- to mesotrophic conditions at the sea floor. As at other locations, there was no significant extinction of benthic foraminiferal species at the K/Pg boundary, but the diversity and heterogeneity of the assemblages decreased precipitously. The percentage of infaunal buliminid taxa decreased rapidly, but the total percentage of infaunal taxa remained essentially unchanged. Benthic foraminiferal accumulation rates (BFAR) dropped at the boundary itself, and fluctuated strongly later in the Danian. After the K/Pg boundary, opportunistic taxa increased in relative abundance, and diversity and heterogeneity strongly fluctuated. There thus is no clear agreement between three proxies which have been used to indicate a high food supply to the sea floor: percentage buliminids, percentage infaunal taxa, and BFAR. This discrepancy might indicate that the food supply changed in character (e.g., type of food, temporal variability in flux), but did not show a long-term, large net change in total amount. The strong fluctuations in BFAR, heterogeneity and diversity indicate that environmental instability started at the K/Pg boundary, and persisted through planktic foraminiferal zones Pα and P1a. In lower planktic foraminiferal zone P1b, agglutinated species of the genera Spiroplectammina and Clavulinoides, thought to be infaunal and indicative of increasing levels of food supply, increased in relative abundance while the relative abundance of buliminids remained low. Possibly, agglutinated taxa took over at least part of the infaunal niche in the Paleocene, as a result of the rise in the calcium carbonate compensation depth. Towards the upper part of the studied interval (lower planktic foraminiferal Subzone 1c), benthic foraminiferal assemblages stabilized, with heterogeneity almost back to Maastrichtian values, although diversity and BFAR did not fully recover.

Chemistry of Late Early Triassic Siliceous Claystone (‘Toishi-type’ Shale) from the Oritate Area, Sambosan Belt, Kyushu, Southwest Japan

. Inorganic chemical compositions are determined for late Early Triassic siliceous claystone (‘Toishi-type’ shale) and associated chert from Oritate area, Sambosan Belt, Kyushu, southwest Japan. The siliceous claystone is similar in chemical composition to Post-Archean Australian Shale (PAAS), but is depleted in Ca, Sr, Mn, and Fe and slightly enriched in Cu, Zn, P, and rare earth elements (REEs). The siliceous claystone and associated chert have flat REE patterns with positive Eu anomalies and no distinct Ce anomaly. The siliceous claystone and associated chert have largely constant Ti/Al, Th/Al, and Nb/Al ratios compared to the variable ratios found in siliceous shale and sandstone deposited close to land in a trench setting. This suggests that the claystone and chert were deposited in a deep-sea pelagic environment and were derived mainly from the suspended fraction, including eolian dust and material transported from distant lands, rather than from turbidity currents that occurred close to land. The low Ca contents of the analyzed rocks indicate deposition below the calcium-carbonate compensation depth. The depletion of Mn and Fe, and no distinct Ce anomaly in the Oritate siliceous claystone are also evident, being similar to those in samples from the Sasayama and Kinkazan sections in the Mino-Tanba Belt, where oceanic anoxia developed during the Late Permian to earliest Triassic. This might suggest that oceanic anoxia prevailed through to the late Early Triassic.

A comparative analysis of compositional variations in and between marine ferromanganese nodules and crusts in the South Pacific and their environmental controls

Regional variation of Mn, Fe, Co, Ni and Cu in ferromanganese oxides (nodules and crusts) in the central south Pacific is related to primary productivity, oxygen minimum layer, and calcium carbonate compensation depth. The largely latitudinal influence of these environmental parameters on nodule and crust composition reflects their predominantly latitudinal variation. Primary productivity is the principal regional environmental control, influencing diagenetic enrichment of these elements in nodules through its effect, mediated by the CCD, on supply and concentration of labile organic matter vs. carbonate remains to the sediments. It influences hydrogenetic enrichment of these elements in nodules and crusts through its effect, mediated by the oxygen minimum layer (mainly in the case of crusts), on their export from surface waters. The elements’ varying susceptibility to being scavenged or organically bound influences the contrasting composition of diagenetic vs. hydrogenetic ferromanganese oxides, which is further influenced by depth. Hydrogenesis is the fundamental process governing nodule and crust formation, superimposed on which is diagenesis under specific circumstances; both are subject to intermittent interruption, diminution and augmentation by changes in environmental parameters. Application of regionally operative environmental controls locally explains local compositional variations and helps refine exploration criteria for economically viable nodules and crusts.

Radiolarian biozonation for the upper Quaternary in the Japan Sea.

Rapid and drastic changes in radiolarian assemblages during the last 33 kyr were revealed in three sediment cores from the eastern and northeastern Japan Sea. Such changes occurred synchronously over the Sea according to the correlation by TL layers and AMS14C dating. On the basis of these bio-events, four radiolarian biozones were established : Ceratospyris borealis Interval Biozone (33 to 1514C kyr BP), Stylochlamydium venustum Interval Biozone (15 to 1214C kyr BP), Cycladophora davisiana Interval Biozone (12 to 10.514C kyr BP), and Larcopyle butschlii Interval Biozone (10.514C kyr BP to Present) . These radiolarian biozones are useful for correlating the upper Quaternary sediments in the Japan Sea, where carbonate fossils are poorly preserved below the calcium carbonate compensation depth (CCD) .

Carbonate dissolution in the South Atlantic Ocean: evidence from ultrastructure breakdown in Globigerina bulloides

Ultrastructure dissolution susceptibility of the planktic foraminifer Globigerina bulloides, carbonate ion content of the water column, calcium carbonate content of the sediment surface, and carbonate/carbon weight percentage ratio derived from sediment surface samples were investigated in order to reconstruct the position of the calcite saturation horizon, the sedimentary calcite lysocline, and the calcium carbonate compensation depth (CCD) in the modern South Atlantic Ocean. Carbonate ion data from the water column refer to the GEOSECS locations 48, 103, and 109 and calcium carbonate data come from 19 GeoB sediment surface samples of 4 transects into the Brazil, the Guinea, and the Cape Basins. We present a new (paleo-) oceanographic tool, namely the Globigerina bulloides dissolution index (BDX). Further, we give evidence (a) for progressive G. bulloides ultrastructural breakdown with increasing carbonate dissolution even above the lysocline; (b) for a sharp BDX increase at the sedimentary lysocline; and (c) for the total absence of this species at the CCD. BDX puts us in the position to distinguish the upper open ocean and the upwelling influenced continental margin above from the deep ocean below the sedimentary lysocline. Carbonate ion data from water column samples, calcite weight percentage data from surface sediment samples, and carbonate/carbon weight percentage ratio appear to be good proxies to confirm BDX. As shown by BDX both the calcite saturation horizon (in the water column) and the sedimentary lysocline (at the sediment–water interface) mark the boundary between the carbonate ion undersaturated and highly corrosive Antarctic Bottom Water and the carbonate ion saturated North Atlantic Deep Water (NADW) of the modern South Atlantic.

Biostratigraphic and paleoclimatic significance of a new Pliocene foraminiferal fauna from the central Arctic Ocean

A Pliocene benthic foraminiferal fauna containing a previously unknown species association was found in the basal section of a piston core collected from the crest of Northwind Ridge (NWR) in the central Arctic Ocean. The fauna is dominated by Epistominella exigua, Cassidulina reniforme, Eponides tumidulus, Cibicides scaldisiensis, Lagena spp., Cassidulina teretis, Eponides weddellensis, Bolivina arctica, and Patellina corrugata. The presence of Cibicides scaldisiensis in the assemblage and the occurrence of Cibicides grossus higher in the core are indicative of an early Pliocene age. The morphologically distinctive species Cibicidoides sp. 795 of McNeil (in press) which occurs in the NWR core sample was previously known only from Oligocene through Miocene deposits in the Beaufort-Mackenzie Basin of Arctic Canada. Ehrenbergina sp. A and Cibicidoides aff. C. sp. 795, also present in the core, are new and endemic to the Arctic late Miocene and early Pliocene. These species, and possibly others, are survivors of the late Miocene (Messinian) sea-level crisis, which caused a significant faunal turnover in the Arctic Ocean. The predominantly calcareous assemblage indicates deposition above the calcium carbonate compensation depth in an upper bathyal environment. Paleogeographic affinities for the bulk of the assemblage indicate probable connections between the Arctic and the North Atlantic Oceans, but the endemic species identify environmental differences or partial isolation of the western Arctic Ocean. The species association suggests a cold but milder paleoclimate than that which existed during Pleistocene glacial intervals.

Deep-water agglutinated foraminifera from the Lower Cretaceous (Neocomian) ‘Complex à Aptychus’ Formation (Corridor de Boyar, Betic Cordillera, southern Spain)

Abstract. The oldest deep-water sediments of the flysch units in the western part of the Betic Cordillera (southern Spain) arc red and green pelagic claystones with intercalated siliciclastic and carbonate turbidites, ranging from Berriasian to Barremian in age. Autochthonous and redeposited benthic foraminiferal assemblages were studied in outcrops of this ‘Complex à Aptychus’ Formation in the ‘Corridor de Boyar’ near Grazalema. The assemblage of the autochthonous red and green claystones is wholly comprised of agglutinated forms, reflecting deposition beneath the calcium carbonate compensation depth (CCD). Compared to coeval abyssal and deep bathyal assemblages from the NW Australian Margin (Eastern Tethys), the Polish Outer Carpathians and the North Atlantic, the assemblage from the Betic Flysch Zone is more related to its Tethyan equivalents and may represent a truly abyssal Early Cretaceous sub-CCD environment.

Neogene oceanographic variations recorded in manganese nodules from the Somali Basin

A detailed study of a nodule from the Somali Basin dated by 230Th excess was correlated with the paleoceanographic events recorded in Site 236 (Leg 24) Deep Sea Drilling Project (DSDP) cores. Tentative indications are that the phase of nodule accretion starting with the development of pillar structure at a depth of 20 mm in the nodule around 13 Ma coincides with increased Antarctic Bottom Water (AABW) flow and an elevated calciumcarbonate compensation depth (CCD). The Late Miocene lowering of the CCD is represented by the mottled zones between 8 and 18 mm in the nodule is characterised by an abundant silicate component (>20%) of aeolian origin. The Miocene/Pliocene boundary (5 Ma) occurs at a depth of about 8 mm and is represented by the development of pillar structure and a minimum of aeolian dust (10.3%). The increased biological productivity of the Somali surface water since the Middle Miocene is demonstrated by the increasing C org content of the nodule (from 0.11 to 0.19%) towards its surface.

Manganese nodules in the EEZ's of island countries in the southwestern equatorial Pacific

Studies on polymetallic manganese nodules in south equatorial Pacific EEZ's between 0 and 20°S show that Ni and Cu reach their greatest combined abundances of over 2% between 2° and 8°S on the southern margin of the equatorial zone of high biological productivity in the Cook, Line and Phoenix Island areas, as a result of biological fluxing of Ni and Cu to the nodules at and just below the calcium carbonate compensation depth (CCD). By contrast, Co reaches its greatest abundance of 0.6% south of 8°S in the Cook Islands area in what are believed to be slowly growing nodules on non-biogenic clays well below the CCD where little biological Co supply is likely. Nodule abundances are greatest (up to 30 kg/m 2) in the Co-rich area, in part due to Antarctic Bottom Water (AABW) flow, giving highest overall metal quantities per square metre in the nodules there, particularly of Co. Ellice Islands nodules are different from those found in the other island groups studied in that they show features more typical of hydrogenetic ferromanganese oxide crusts than of diagenetically influenced nodules. There are approximately 110 × 10 6t of combined Ni+Cu+Co expressed as Ni equivalent in the Cook Islands EEZ nodules, approximately 12 × 10 6t in Phoenix Islands nodules and approximately 1.4 × 10 6t in Ellice Islands nodules, in areas of 5kg/m 2 nodule abundance.

Provenance and accumulation rates of Pliocene and Quaternary sediments from the western Coral Sea

Seven sediment cores were investigated from areas in the western Coral Sea where a thin sediment cover above acoustic basement, or above marked unconformities, was visible in reflection seismic records, implying low accumulation rates. Consequently in five of the cores Pliocene strata were reached in less than 4 meters depth subbottom. The remaining cores reached Pleistocene strata at similar shallow depths. Cores from the Queensland Plateau and the Coral Sea Abyssal Plain are composed of mainly calcareous nannofossil and foraminiferal oozes, indicating a calcareous biological primary production in the western Coral Sea at least since the Pliocene. The younger Quaternary sections of two cores from the northeastern slope of the Queensland Plateau show a high abundance of siliceous microfossils resulting from the influence of silica-rich seawater of the eastern Coral Sea. Sediments cored in the Moresby Canyon are terrigenous muds. The carbonate content of the Quaternary sediments depends strongly on the waterdepth and on the input of terrigenous material. The Quaternary calcium carbonate compensation depth of the western Coral Sea was estimated to be at 4600 m, which is close to that of the equatorial Pacific Ocean. The sediments from the Moresby Canyon, the Coral Sea Abyssal Plain, and the northeastern slope of the Queensland Plateau have received their terrigenous components, mainly quartz, feldspar, chlorite and muscovite-illite from mainland New Guinea. The western slope of the Queensland Plateau and the western Coral Sea Abyssal Plain very likely have received terrigenous components also from mainland Australia as indicated by admixed kaolinite. The frequent fine-grained volcanic glass in the sediments probably was provided by drift-pumice rafts, which derived from volcanic eruptions in the southwestern Pacific region.