Phosphorus accumulation rates in metalliferous sediments on the East Pacific Rise

Based on phosphorus, iron and manganese analyses in 16 cores (5 dated) from the crest and flanks of the East Pacific Rise and the Bauer Deep we estimate that phosphorus is being deposited about 20 times faster in metalliferous sediments near the rise crest than in adjacent flank deposits, and about 40 times faster on the crest than in the Bauer Deep. Almost all of the phosphorus on the rise crest is contained in poorly crystallized hydrothermal iron oxyhydroxides, supporting Berner's (1973) proposal of phosphate sorption by these phases. The phosphate is probably derived from seawater, but some hydrothermal contribution cannot be excluded at this time. Flux estimates indicate that metalliferous sedimentation could remove 15–40% of the pre-agricultural river input of dissolved phosphate.     

Origin of metalliferous sediments from the East Pacific Rise

The distribution of several metals in East Pacific Rise sediments, when normalized to Al₂O₃, exhibit stronger maxima near the rise crest than when simply plotted on a carbonate-free basis. The similarity (1) between the distribution of metals in ridge sediments and previously measured mean heat flow values and (2) between the composition of crestal sediments and terrestrial ore bodies associated with greenstone belts, strongly supports a hydrothermal origin for rise crest sediments.     

Iron-rich metalliferous sediments on the East Pacific Rise: prototype of undifferentiated metalliferous sediments on divergent plate boundaries

Sediments in a zone on the East Pacific Rise with an especially high spreading rate were studied chemically, mineralogically, and microscopically. They consist of a mixture of metalliferous sediments and plankton tests. The metalliferous sediments were formed by an acidic, hydrothermal leaching of tholeiitic basalt with seawater and subsequent precipitation in contact with cold near-bottom seawater. We assume the precipitation from hydrothermal solutions in this part of the East Pacific rise to be undifferentiated due to the high spreading rate and the resulting rapid flow on the water through the basalt. Thus, these metalliferous sediments are an initial stage type that have not undergone differentiation.Mn, Mo, La, Cu, V, Ni, Fe, Zn, Co, and Y, all of which are leachable in acidic, hydrothermal solutions, are enriched in the metalliferous sediments in comparison to the tholeiitic basalts.Zr, Al, and Ti, on the other hand, which under the same conditions are not easily leached, are reduced in their concentrations.All components of the metalliferous sediments precipitated as hydroxides or as adsorbed ions on the hydroxides of other elements. This is due to the oxidizing conditions in the near-bottom seawater. The sedimentation rate is high; the almost 3-m-long cores reach only to the Late Pleistocene. The only distinctly observable diagenetic process for this period of time is the formation of goethite from amorphous iron oxides.Only for Na, K, and Rb does it seem possible that a distinct enrichment in the sediments by adsorption from the seawater could have taken place.Ca, Sr, Pb, and perhaps Sc, are primarily bound to the planktonic carbonate part of the sediments.     

Volcanogenic effects on the rates of deposition of sediments in the Northwest Pacific Ocean

Seven piston cores, 7–16 m long, taken between the Kuril Islands and Emperor Seamounts, have been dated using radiolarian and diatom extinction levels and correlated using volcanic ash layers. The average rate of deposition in the cores decreases from 6 cm/1000 years near the Kuril Trench to about 3.5 cm/1000 years near the seamounts. Dispersed volcanic ash is the main constituent of the cores and it comprises up to 80% of the sediments. The percentage of the ash in the sediments decreases eastward from the Kuril Islands as the rates of deposition decrease.The total thickness of the sediments in the same latitudinal belt also decreases eastward. The thickness of the sediment inferred from seismic data near the Kuril trench is about 600 m and rates of deposition are approximately 6 cm/1000 years in the Pleistocene cores. Sediment thickness near the seamounts is about 300 m, and rates of deposition are approximately 3 cm/1000 years in the Pleistocene cores. Extrapolated rates of deposition in these cores suggest that the age of the base of the sediment to the east of the Kurils is only about 10 m.y.The anomalously young age for the base of the sediments obtained by extrapolation of an assumed constant rate of deposition can be explained by Deep Sea Drilling Project data from the northwest Pacific. The sediment thickness at DSDP site 192 east of Kamchatka includes sediments from all the Cenozoic epochs except the Paleocene. Rates of deposition of sediment younger than Middle Miocene are an order of magnitude higher than those prior to this time. At DSDP sites east of Japan, either Late Miocene sediments lie directly on the basement, or sediments older than Late Miocene are very thin. Post-Middle Miocene sediments are composed primarily of glass shards. Thus, about 90% of the total thickness of sediments in the northwest Pacific is composed of sediments younger than Middle Miocene with volcanic ash as the main constituent. The volcanic ash results from the present phase of explosive volcanic activity which began in the Late Miocene in the northwest Pacific volcanic arcs.     

The origins of rare earths in metalliferous sediments of the Troodos Massif. Cyprus

The ferromanganoan umbers which overlie the uppermost pillow lavas of the Troodos Massif, Cyprus, are strongly enriched in REE relative to normal pelagic clays. Together, the umbers, related ferruginous sediments, and the ochres which are associated with massive cupriferous sulphides located within the lavas, all show light REE enrichment. There is a marked negative Ce anomaly which is characteristic of seawater. Field and chemical data suggest that the REE were incorporated into ferruginous precipitates derived from deep leaching of tholeiitic lavas by seawater. All the metalliferous sediments can be interpreted as related events in the evolution of the Troodos ocean ridge. In contrast, REE patterns of bentonitic clays above the umbers indicate a predominantly continental derivation.     

Metal accumulation rates in the southeast pacific — errors introduced from assumed bulk densities

The common assumption that the in-situ dry bulk density of pelagic sediments is 0.7–0.75 g cm^?3 can produce errors as great as 300–400% in metal accumulation rates. The best approach to obtain accumulation rates is to measure wet bulk density and water content. We show in this paper that if this is not possible, reasonable density and water content estimates in southeast Pacific sediments can be obtained from the CaCO₃ content of the sample. Although the specific equations derived in this paper do not apply to all areas of the ocean, the technique shown here can be used to take into account the special characteristics of any given sedimentary province and produce reasonable accumulation rate estimates.     

Ferromanganoan sediments in the equatorial East Pacific

Ferromanganoan sediments containing little or no CaCO₃ have been found to occur extensively throughout the region between the East Pacific Rise and the Galapagos Rise. Concentrations of Fe and Mn of up to 18 and 6.5%, respectively, accompany low concentrations of Al and Ti. The concentrations of Cu, Ni, and Zn are also high relative to more typical pelagic sediments.While chemically similar to the non-carbonate fraction of metalliferous sediments previously described from the East Pacific Rise, the mineralogy is markedly different. A non-detrital smectite makes up the bulk of sediment (70 to 90%) and is the most important iron bearing phase. Fe and Mn oxides, occurring primarily as micro-nodules, comprise 10 to 20% of the sediment. Detrital material is relatively rare, amounting to less than 10% in all samples.     

Nutrients accumulation in drainage channel sediments

The drainage channel network in Vojvodina,northern part of the Republic of Serbia,in total length of around 20,000 km,transfers excessive(under)ground waters from around 2.15 million ha of lowlands.Channels are mostly in direct connection with the surrounding arable agricultural land and are exposed to different run-off,leaching and/or wind erosion processes.Close to urban areas,some channel sections serve as recipients of unrefined sewage and industrial waste waters.Water flows and velocities,as well as the transportable capacity of fluvial materials(sediments) are relatively low.This,in combination with other natural and anthropogenic impacts,contributes to sediment generation in the drainage channel network.Based on around 100 sediment samples from 46 channels,concentrations of primary nutrients(N,P and K) were elaborated in this study.Detected concentrations of macronutrients in the channel sediments(e.g.N 1-1.2%,P 100-265 and K 100-380 mg 100 g~(-1)) exceeded their content in surrounding arable land by a few fold.Also,significantly higher nutrient concentrations(in average by 50%) were detected in downstream(vs.upstream) channel sections.An excessive presence of observed elements in channel sediments,due to interactive processes between water and sediment material,can adversely influence the water quality and life conditions for channel biota and caused other negative environmental impacts such as eutrophication.These results clearly confirm that the processes of nutrient accumulation in channel sediments are greater than those in the surrounding,mostly intensively arable land areas.The erosion of unprotected agricultural areas and sediment transport as the most important pollution pathways from the drainage basin to channel network may be essential factors responsible for detected condition of nutrient accumulation.     

Metal accumulation in four molluscs

Specimens of mussels (Mytilus edulis), winkles (Littorina littorea), dogwhelks (Nucella lapillus) and limpets (Patella vulgata) were collected from the north-east coast of England in 1980–1981 in order to analyse the dried whole soft tissue for zinc, copper and iron. In each case, only a narrow size range of organisms was collected from a small environmentally homogeneous site and sex was taken into account. Most of the frequency distributions of metal concentrations obtained were found to show significant positive skewness. This skewness could not be explained either by the degree of mobility or type of feeding mechanism of the organisms or by any other known parameter, e.g. size, sex, habitat variation. Some individual mussels were found to be extremely good regulators of their zinc concentrations. On the other hand, other individual mussels had the ability to accumulate unusually high levels of zinc.     

An estimate of the Nd isotopic composition of Iapetus seawater from ca. 490 Ma metalliferous sediments

Well-preserved metalliferous sediments and pillow basalts of Lower Ordovician age (ca. 490 Ma) have been studied in an attempt to specify the Nd isotopic composition of Iapetus seawater. Initial¹⁴³Nd/¹⁴⁴Nd ratios of the pillow basalts are indistinguishable from published initial ratios for the 505-Ma Bay of Islands ophiolite complex and are within the anticipated range for MORB-type basalts 500 Ma ago. Metalliferous sediments occur both interstitial to basalt pillows and as well-developed sedimentary accumulations. The initial¹⁴³Nd/¹⁴⁴Nd ratios for the non-interstitial variety range from 0.511851 to 0.511712 (ε_Nd = ?2.7to?5.4) and are considered to provide an estimate of¹⁴³Nd/¹⁴⁴Nd in Iapetus seawater. The interstitial metalliferous sediments show evidence for a significant basalt-derived Nd component. Although volcanic activity occurred at the margin of Iapetus essentially contemporaneous with the formation of the metalliferous sediments, it is clear that arc-type volcanic material was not a major source of Nd in Iapetus seawater. Rather the source of Nd was from continental regions with a similar average age to those supplying material to the present-day Atlantic Ocean.     

Radiolarian biogeography in surface sediments of the Northwest Pacific marginal seas

Overall abundance and species composition of radiolarian faunas were analyzed in surface sediment samples from representative areas of South China Sea,East China Sea,Sea of Japan,Sea of Okhotsk,Bering Sea,Philippine Sea,and the western boundary current regions of the NorthPacific,in order to understand the biogeographic distribution of radiolarians in the Northwest Pacific and explore its relationship with the main environmental factors and the North Pacific circulation.The results showed that radiolarians in the Northwest Pacific surface sediments can be divided into two large biogeographic provinces—cluster A and cluster B.Cluster A is characterized by the dominance of warm-water species and distributed primarily in tropical and subtropical seas with high radiolarian abundance and diversity;whereas cluster B is predominated by cold water species and distributed mainly in the Arctic and subarctic seas with comparably low abundance and diversity.Cluster A is further divided into five subclusters,Al to A5,which correspond to East China Sea,Philippine Sea,South China Sea,Sea of Japan,and Kuroshio Current,respectively;cluster B is divided into three subclusters,B1 to B3,which correspond to Sea of Okhotsk,Bering Sea,and subarctic gyre area,respectively.Based on the relationships between radiolarian faunas and major environment parameters in different biogeographic provinces,we suggest that the sea surface temperature(SST) and sea surface salinity(SSS) are primary factors that influence productivity,composition,and distribution pattern of the radiolarian fauna in the Northwest Pacific regions,while water depth is likely responsible for regional differences in the radiolarian fauna in each marginal sea.In addition,according to the distribution and abundance patterns of common radiolarian species in different areas,we identified five special radiolarian assemblages,which may be used as indicators for main Kuroshio Current,Kuroshio-East China Sea Branch,Kuroshio-South China Sea Branch,Tsushima Current,and Oyashio Current water masses.     

Helium flux through marine sediments of the northeast Pacific Ocean

Quantitative determinations of helium and other noble gas concentrations in pore waters of marine sediments permit the calculation of helium fluxes out of the sedimentary column. Values of 1.1 and 6.4 × 10⁴ atoms/cm² sec were found for two locations in the northeast Pacific. These fluxes are one to two orders of magnitude less than those based on theoretical degassing models of the earth or on measurements of excess helium in the deep ocean water.     

The origin and fate of mode water in the southern Pacific Ocean

Understanding the origin and fate of mode and intermediate waters (MW) in the subtropical Pacific Ocean is critical for climate, as MW store and export a large volume of CO₂, heat, nutrients and salinity to lower latitudes at depths isolated from the atmosphere. A realistic 4D simulation has been used to track and quantify the MW routes and their property characteristics at the last region of subduction. It also allows us to quantify the water transformation after subduction. The simulation has been compared to available observations using a collocation method that interpolated model data onto observations in time and space. The comprehensive comparisons gave us confidence in the model’s capacity to reproduce MW characteristics. A quantitative Lagrangian analysis was performed on the model output to depict the origin, the fate and the route of MW circulating in the southern Pacific Ocean, selected in the density range of 26.8–27.4 kg m⁻³. We found 18 Sv of MW were transported northward in patches through the 42° S section, mostly between 200 and 800 m depth. Of this transport, 8 Sv enters the Pacific Ocean in the upper layer south of Tasmania and subducts in the Pacific. The remainder is not ventilated in the Pacific sector: 4 Sv is advected from the Indian Ocean south of Tasmania at intermediate depth and finally 6 Sv is part of an intermediate depth recirculation within the Pacific Ocean. Particles take up to 30 years to travel northward through our domain before crossing the 42° S section. Southward transport branches also exist: 3 Sv flows southward following the eastern New Zealand coast and then exits through Drake Passage. An additional 4 Sv passes southward in the Tasman Sea, following the eastern Tasmanian coast and enters the Indian Ocean south of Tasmania, as part of the Tasman Leakage. Four different formation sites have been identified, where the MW are last ventilated. These formation sites have different water masses with specific salinity ranges. A study on the evolution of the physical characteristics of each of these water masses has been performed. All MW characteristics become more homogeneous at 42° S than they were when they left the mixed layer. This study confirms the homogenisation of mode waters at intermediate depth in the Pacific Ocean as previously revealed in the Indian Ocean using the same methodology. Transformations are shown to be mostly isopycnal in the Tasman Sea and diapycnal farther east.     

Distribution and composition of organic matter in surface sediments of coastal Southeast Alaska

Total organic carbon (TOC) and biogenic silica (opal) content, elemental (C/N) and isotopic (δ¹³C, δ¹⁵N) composition of organic matter and the content of lipid biomarkers derived from both marine and terrestrial sources constrain relative contributions from marine productivity and continental erosion to surface sediments throughout coastal SE Alaska (54°N to 61°N). TOC and opal content are very high (up to 8% and 33% by weight, respectively) in fjords and inlets south of Icy Strait (∼58°N) and uniformly low at offshore sites to the south, and at both offshore and inland sites to the north (averaging 0.6±0.3% and 2.3±1.8%, respectively). TOC and opal mass accumulation rates (MARs, based on bulk density and ²¹⁰Pb-derived sediment MAR) suggest dilution with terrigenous, inorganic detrital materials accounts for the low concentrations of both biogenic phases in sediments from the glacial tidewater fjords of Muir and Yakutat Bays but not elsewhere. C/N, δ¹³C, and δ¹⁵N indicate a dominant marine origin for organic matter deposited at most sites. This conclusion implicates elevated primary productivity in inland waters to the south with diatoms, based on opal results, being the dominant contributor. A very significant terrestrial organic fraction (25–50%) is contained in sediments deposited on the continental shelf to the north of 58°N. Hydrocarbon biomarkers indicate the terrestrial fraction in sediments from this region is represented by old organic matter (kerogen) likely contained within riverborne particles eroding from now heavily glaciated adjacent landscapes. In sediment to the south, the terrestrial fraction is traced to modern soil organic matter eroded from the now non-glaciated, heavily forested adjacent landscape. Our study provides a framework to guide future investigations of short- (anthropogenic) to long- (Holocene) term environmental and/or climate change in this region through down-core, stratigraphic analysis.     

The extension of the magnetic time scale in sediments of the Central Pacific Ocean

The extension of the magnetic reversal record back to the early Miocene is presented. This record is pieced together with the aid of microfloral analysis from three low sedimentation rate siliceous deep sea cores from the Equatorial Pacific.Nineteen Magnetic Epochs are now recognized from the earliest Miocene to the Present. By correlating the micropaleontological data in our cores with selected foraminiferal datums from DSDP Leg IX we correlate these datums with the following magnetic epochs: the Pulleniatina Datum occurs in the lower part of Epoch 5, the G. acostaensis Datum occurs in Epoch 11, the G. nepenthes Datum occurs in Epoch 12, the Orbulina Datum at the Epoch 15/16 boundary and the G. dissimilis Datum in the lower part of Epoch 16. The Early/Middle Miocene boundary (Orbulina Datum) is tentatively placed at the top of Epoch 16.     

Heavy metal accumulation in estuarine sediments in a historical mining of Cornwall

Sediments in the Hayle estuary in a historical mining area of Cornwall have been found to contain exceptionally high concentrations of tin, arsenic, copper, lead, tungsten and zinc. In this study, the distribution of these heavy metals is correlated with pollution from past mining activity through mine waste discharge into streams, and changes which took place at the time of the development of the Upton Towans.