New production and mixed-layer physics     

Shubha Sathyendranath  Trevor Platt 《Journal of Earth System Science》1994,103(2):177-188

We treat the ocean carbon cycle as a coupled physical-biogeochemical process. The interactions between mixed-layer dynamics and growth of phytoplankton in the layer are discussed, and the formal relationship between phytoplankton accumulation and new production is examined. A coupled biological-physical model is presented for studying the classical spring bloom in the N. Atlantic, and possible differences in the mechanisms that drive the seasonal phytoplankton blooms in the N. Atlantic and the Arabian Sea are discussed. Finally, recommendations are made for observational programs to improve our understanding of the biologically-mediated carbon cycle in the Arabian Sea.  相似文献   

A synthesis of post-glacial diatom records from Lake Baikal     

J. Platt Bradbury  Ye. V. Bezrukova  G. P. Chernyaeva  S. M. Colman  G. Khursevich  J. W. King  Ye. V. Likoshway 《Journal of Paleolimnology》1994,10(3):213-252

The biostratigraphy of fossil diatoms contributes important chronologic, paleolimnologic, and paleoclimatic information from Lake Baikal in southeastern Siberia. Diatoms are the dominant and best preserved microfossils in the sediments, and distinctive assemblages and species provide inter-core correlations throughout the basin at millennial to centennial scales, in both high and low sedimentation-rate environments. Distributions of unique species, once dated by radiocarbon, allow diatoms to be used as dating tools for the Holocene history of the lake. Diatom, pollen, and organic geochemical records from site 305, at the foot of the Selenga Delta, provide a history of paleolimnologic and paleoclimatic changes from the late glacial (15 ka) through the Holocene. Before 14 ka diatoms were very rare, probably because excessive turbidity from glacial meltwater entering the lake impeded productivity. Between 14 and 12 ka, lake productivity increased, perhaps as strong winds promoted deep mixing and nutrient regeneration. Pollen evidence suggests a cold shrub — steppe landscape dominated the central Baikal depression at this time. As summer insolation increased, conifers replaced steppe taxa, but diatom productivity declined between 11 and 9 ka perhaps as a result of increased summer turbidity resulting from violent storm runoff entering the lake via short, steep drainages. After 8 ka, drier, but more continental climates prevailed, and the modern diatom flora of Lake Baikal came to prominence. On Academician Ridge, a site of slow sedimentation rates, Holocene diatom assemblages at the top of 10-m cores reappear at deeper levels suggesting that such cores record at least two previous interglacial (or interstadial?) periods. Nevertheless, distinctive species that developed prior to the last glacial period indicate that the dynamics of nutrient cycling in Baikal and the responsible regional climatic environments were not entirely analogous to Holocene conditions. During glacial periods, the deep basin sediments of Lake Baikal are dominated by rapidly deposited clastics entering from large rivers with possibly glaciated headwaters. On the sublacustrine Academician Ridge (depth = 300 m), however, detailed analysis of the diatom biostratigraphy indicates that diastems (hiatuses of minor duration) and (or) highly variable rates of accumulation complicate paleolimnologic and paleoclimatic reconstructions from these records.  相似文献   

Bicyclic sesquiterpenoids and diterpenoids in Australian crude oils     

R. Paul Philp  Trevor D. Gilbert  Jane Friedrich 《Geochimica et cosmochimica acta》1981,45(7):1173-1180

Bicyclanes previously reported only in heavily biodegraded Texas Gulf Coast crudes have been found to be ubiquitous in Australian crude oils of non-marine origin from four different basins. The compounds are present in oils, thought to be derived from the same or similar sources, that have undergone varying degrees of biodegradation. They are also found to be present in oils of different geological age. In addition a series of tricyclic diterpenoid hydrocarbons was common to four oils from the Gippsland Basin. Four of these compounds had the molecular formula C₂₀H₃₄ and mass spectral fragmentation patterns suggested they were mono-unsaturated diterpenoids. The presence of unsaturated diterpenoids in crude oils appears to be a unique observation. It is proposed that the diterpenoids may be the source of the bicyclanes also observed in these oils.  相似文献   

Geology of the continental margins: Boillot,G. 1981. Translated by A. Scarth,Longman, New York. 115 pp. 86 figs. Price: softcover £4.95     

J.P. Platt 《Journal of Structural Geology》1981,3(3):340-341

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Apatite/liquid partition coefficients for the rare earth elements and strontium     

E. Bruce Watson  Trevor H. Green 《Earth and Planetary Science Letters》1981

Sixteen sets of apatite/liquid partition coefficients (D^ap/liq) for the rare earth elements (REE; La, Sm, Dy, Lu) and six values for Sr were experimentally determined in natural systems ranging from basanite to granite. The apatite + melt (glass) assemblages were obtained from starting glasses artificially enriched in REE, Sr and fluorapatite components; these were run under dry and hydrous conditions of 7.5–20 kbar and 950–1120°C in a solid-media, piston-cylinder apparatus. An SEM-equipped electron microprobe was used for subsequent measurement of REE and Sr concentrations in coexisting apatites and quenched glasses. The resulting partition coefficient patterns resemble previously determined apatite phenocryst/groundmass concentration ratios in the following respects: (1) the rare earth patterns are uniformly concave downward (i.e., the middle REE are more compatible in apatite than the light and heavy REE); (2) D_REE^ap/liq is much higher for silicic melts than for basic ones; and (3) strontium (and therefore Eu²⁺) is less concentrated by apatite than are the trivalent REE. The effects of both temperature and melt composition on D_REE^ap/liq are systematic and pronounced. At 950°C, for example, a change in melt SiO₂ content from 50 to 68 wt.% causes the average REE partition coefficient to increase from ～7 to ～30. A 130°C increase in temperature, on the other hand, results in a two-fold decrease in D_REE^ap/liq. Partitioning of Sr is insenstitive to changes in melt composition and temperature, and neither the Sr nor the REE partition coefficients appear to be affected by variations in pressure or H₂O content of the melt.The experimentally determined partition coefficients can be used not only in trace element modelling, but also to distinguish apatite phenocrysts from xenocrysts in rocks. Reported apatite megacryst/host basalt REE concentration ratios [12], for example, are considerably higher than the equilibrium partition coefficients, which suggest that in this particular case the apatite is actually xenocrystic.A reversal experiment incorporated in our study yielded diffusion profiles of REE in apatite, from which we extracted a REEαCa interdiffusion coefficient of 2–4×10^?14 cm²/s at 1120°C. Extrapolated downward to crustal temperatures, this low value suggests that complete REE equilibrium between felsic partial melts and residual apatite is rarely established.  相似文献   

Saudi Arabia     

Trevor R. Dixon  T.J. Dixon 《Marine pollution bulletin》1981,12(9):289-295

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Antarctic hydrocarbons     

Howard M. Platt  Peter R. Mackie 《Marine pollution bulletin》1982,13(1):32-33

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Paleoecological studies at Lake Patzcuaro on the west-central Mexican Plateau and at Chalco in the basin of Mexico     

W.A. Watts  J.Platt Bradbury 《Quaternary Research》1982,17(1):56-70

A 1520-cm sediment core from Lake Patzcuaro, Michoacan, Mexico, is 44,000 yr old at the base. All parts of the core have abundant pollen of Pinus (pine), Alnus (alder), and Quercus (oak) with frequent Abies (fir). The interval dated from 44,000 to 11,000 yr ago has a homogeneous flora characterized by abundant Juniperus (juniper) pollen and frequent Artemisia (sagebrush). It is believed to represent an appreciably drier and colder climate than at present. The Holocene at Lake Patzcuaro is characterized by a moderate increase in Pinus pollen and the loss of Juniperus pollen, as the modern type of climate succeeded. Alnus was abundant until about 5000 yr ago; its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake-shore and stream-course alder communities for agricultural purposes, or it may simply reflect a drying tendency in the climate. Pollen of Zea (corn) appears at Lake Patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr B.P. apparently recording a human population large enough to modify the natural environment, as well as the beginning of agriculture. A rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion. In the most recent period corn is absent from the sediments, perhaps reflecting a change in agricultural practices. The environment changes at Lake Patzcuaro are similar to and correlate with those in the Cuenca de Mexico, where diatom stratigraphy from the Chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture. Before 10,000 yr ago climates there were cool and dry, and the Chalco basin was occupied by a shallow freshwater marsh that drained north to Lake Texcoco, where saline water accumulated by evaporation. Increases in effective moisture and possible melting of glaciers during the Holocene caused lake levels to rise throughout the Cuenca de Mexico, and Lake Texcoco flooded the Chalco basin with brackish water. After 5000 yr ago such flooding decreased, and shallow freshwater ponds and marshes were restored in the Chalco basin. This environmental change coincides with the appearance of Zea pollen and suggests cultural control of lake levels and salinity.  相似文献   

The role of sphene as an accessory phase in the high-pressure partial melting of hydrous mafic compositions   总被引：1，自引：0，他引：1  

Phillip L. Hellman  Trevor H. Green 《Earth and Planetary Science Letters》1979,42(2):191-201

In a high-pressure experimental study of reactions and possible melt products occurring in the deep continental crust or in subducted oceanic crust, sphene has been identified over a pressure range of 10–18 kbar and to temperatures of 1020°C. Sphene may be a refractory phase with up to 60% partial melting for hydrous mafic compositions. Sphene breaks down at lower pressure than the maximum pressure stability of amphibole in hydrous mafic compositions, and rutile rather than sphene is the important Ti-bearing accessory phase at pressures greater than 16–18 kbar. Sphene and rutile coexist to pressures as low as 14 kbar. This implies that amphibole eclogites containing primary sphene and no rutile have most likely formed at depths less than 45 km.The presence of minor sphene as a residual phase in equilibrium with low-Ti silicic liquids may have a marked effect on the REE distribution in derivative liquids. Thus melts in equilibrium with a garnet and sphene-bearing residuum may have less light-REE-enriched patterns than those predicted when garnet is a residual phase without coexisting sphene. This effect is modelled using REE patterns for sphenes from high-grade metamorphic terrains of western Norway.Both the new REE data and the experimental study have important implications for the genesis of low-Ti magmas formed in continental margins and island arcs.  相似文献   

The high pressure experimental crystallization of staurolite in hydrous mafic compositions     

Phillip L. Hellman  Trevor H. Green 《Contributions to Mineralogy and Petrology》1979,68(4):369-372

The experimental crystallization of staurolite in two mafic compositions at high pressures (24–26 kb) and temperatures (740 °–760 ° C) is reported. This, together with a recent report of staurolite from metamorphosed basic igneous rocks from Fiordland, New Zealand, leads to the conclusion that Staurolite may be an important subordinate phase in the subducted lithosphere. The synthesized staurolites are more magnesian than those occuring in natural metapelitic assemblages and are characterized by relatively high Si, Ti, Mg, Ca, and low Al, Fe.  相似文献