Study on the porosity of a metalliferous sediment core from the East Pacific Rise 13°N

研究了采自东太平洋海隆13°N（EPR13°N）的一个热液成因含金属箱式沉积物岩心E272的孔隙率变化特征。样品孔隙率在70．O％～85．2％之间,顶部层位比底部层位高14％左右。孔隙率随深度增加而指数式单调递减,平均递减梯度约为-0.31％／cm。该岩心上部层位呈红棕色,下部层位呈黄绿色,表明该岩心经历了显著的早期化学成岩作用。前人关于该岩心的元素地球化学,粒度和年代学数据,共同证明该岩心孔隙率随深度变化特征受稳态压缩过程控制。其孔隙率随深度的变化关系符合稳态压缩模型的经验拟合公式。E272顶部沉积物．水界面处溶解物质与海水的交换以离子扩散机制为主,而岩芯内部溶解物质的迁移则可能主要受自下而上的孔隙水流动机制控制,这与岩芯中活动元素含量上部高,下部低的分布模式一致。该研究对将来进一步讨论E272岩心在早期成岩作用中的化学过程具有指导意义。     

Morphotectonics, Volcanism and Hydrothermal Activity on the East Pacific Rise between 21°12′ S and 22°40′ S

The morphotectonic setting of the East Pacific Rise (EPR) between21°12 and 22°40 S and its recent and past hydrothermalactivity were the focus of the Russian R/V Geolog Fersmans expeditionin 1987–1988.The EPR axial zone in the study area is comprised of three segmentsseparated by overlapping spreading centers (OSCs) near 21°44 and22°08 S. The northern segment is the shallowest of three and hasa distinct massive axial ridge, trapeziodal in cross-section, toppedby a very wide flat summit surface and cut by a well-developedcentral graben. These features testify to intense magmatism and to avoluminous crustal magmatic chamber underlying the whole segment.Fine-scale segmentation is most clearly revealed in the structure ofthe central graben within which several 4th-order segments can bedistinguished. This scale of segmentation is also reflected on flanks of theaxis by variations in the character and intensity of faulting.According to structural and petrologic data, the magmatism is mostintense in the central part of the segment which is probably locateddirectly over a magmatic diapir supplying the melt to the whole segment.Magma migration at the subcrustal level from the center towards the ends ofthe segment with discrete injection into the crustal magmatic chamber ispresumed.The central segment is broken into two morphologically distinct partsseparated by a deval. In the subsided northern part, the wide summit of theaxial ridge is cut by a well-developed, intensely fractured axialgraben. In the southern part, the axial ridge is relatively elevated, butnarrow with an ephemeral graben along its crest. The character and intensityof faulting on the axial flanks are also considerably different in thenorthern and southern parts of the segment. Thus, the magmatic supply tothese two parts is thought to originate from two different sources. If so,then at present the magma chamber underlying the southern part of thesegment is probably at the stage of replenishment, while in the north it isat the stage of deep cooling.The southern segment is structurally similar to the central one. Howeverthere is considerably less intensive magmatic activity in this region,especially south of 22°30 S where the axial ridge is narrow, andtriangular in cross-section.Both OSCs studied are marked by abrupt narrowing and sharp subsidence ofthe tips of axial ridges within the northern limbs. The southern OSC limbsare morphologically similar to normal sections of axial ridges. In bothcases the flanks are structurally and morphologically disrupted adjacent tothe OSCs and oblique structures can be traced far southward of the OSCflanks. Due to the spatial position of oblique structures on the the flanksit is presumed that the OSC near 22°07 S is migrating northward.The 21°44 S OSC zone has apparently undergone small spatialoscillations. In spite of the small amplitude of lateral displacement, thiszone is marked by prominent bathymetric anomalies.Numerous massive sulfide deposits were discovered atop the axial ridgealong the entire length of the uplifted and hydrothermally active northernsegment. Ore metal concentrations in near-bottom waters are maximumover the southern part of the northern segment, while maximum concentrationsof the same metals in surficial sediments are confined to the central partof the same segment. We surmise that there has been a recentalong-axis shift of the zone of maximum hydrothermal activity fromthe middle of the segment to its present position in the southern part ofthe segment. Considering sedimentation rates, the age of this shift can beapproximately estimated to be 5 to 10 thousand years before the present.The relatively Mg-enriched basalts of the middle part of thenorthern segment represent a tike of a more primitive pattern, while therelatively Fe-rich rocks of its southern part probably reflect alarge degree of fractionation at shallow crustal levels. Considering thistrend, in addition to morphotectonic data we presume that subaxial magmaflow from the middle to the southern part of the segment is responsible forthe along-axis shift of hydrothermal activity.In the central segment of the study area, massive sulfides have only beendiscovered south of the 21°55 S deval, where the axial ridgeshoals and where the existence of a subjacent magma chamber is presumed.The very weak manifestations of recent volcanism within the southernsegment explain the absence of hydrothermal activity and sulfide depositswithin this segment.     

Abundant seamounts of the Rano Rahi seamount field near the Southern East Pacific Rise, 15° S to 19° S

A widespread seamount province, the Rano Rahi Field, is located near the superfast spreading Southern East Pacific Rise (SEPR) between 15°–19° S. Particularly abundant volcanic edifices are found on Pacific Plate aged 0 to 6.5 Ma between 17°–19° S, an area greater than 100,000 km². The numbers of seamounts and their volume are several times greater than those of a comparablysurveyed area near the Northern East Pacific Rise (NEPR), 8°–17° N. Most of the Rano Rahi seamounts belong to chains, which vary in length from 25 km to >240 km and which are very nearly collinear with the Pacific absolute and relative plate motion directions. Bends of 10°–15° occur along a few of the chains, and some adjacent chains converge or diverge slightly. Many seamount chains have fluctuations in volume along their length, and statistical tests suggest that some adjacent chains trade-off in volume. Several seamount chains split into two lines of volcanoes approaching the axis. In general, seamount chains composed of individual circular volcanoes are found near the axis; the chains consist of variably-overlapping edifices in the central part of the survey; to the west, volcanic ridges predominate. Near the SEPR, the volume of nearaxis seamount edifices is generally reduced near areas of deflated cross-sectional area of the axial ridge. Fresh lava flows, as imaged by sidescan sonar and sampled by dredging, exist around some seamounts throughout the entire survey area, in sharp contrast to the absence of fresh flows beyond 30 km from the NEPR. Also, the increases in seamount abundance and volume extend to much greater crustal ages than near the NEPR. Seamount magnetization analysis is also consistent with this wider zone of seamount growth, and it demonstrates the asynchronous formation of most of the seamount chains and volcanic ridges. The variety of observations of the SEPR seamounts suggests that a number of factors and mechanisms might bring about their formation, including the mantle upwelling associated with superfast spreading, off-axis mantle heterogeneities, miniplumes and local upwelling, and the vulnerability of the lithosphere to penetration by volumes of magma. In particular, we note the association of extensive, recent volcanism with intermediate wavelength gravity lineaments lows on crust aged 6 Ma. This suggests that the lineaments and some of the seamounts share a common cause which may be related to ridge-perpendicular asthenospheric convection and/or some manner of extension in the lithosphere.     

Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N

A 43 cm long E271 sediment core collected near the East Pacific Rise(EPR) at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals(2 μm) were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils(diatoms or radiolarians), hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios(a proxy for overall REE/Fe ratio) in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.     

Deep-Tow magnetics near 20°S on the East Pacific Rise: A study of short wavelength anomalies at a very fast spreading center

Six Deep-Tow magnetic profiles across the axis of the East Pacific Rise [EPR] in two small areas between 19°25 and 20°10S were collected during the 1983 Protea 1 cruise of the R/V Melville. These near-bottom profiles are of extremely high resolution allowing the interpretation of very short wavelength features. We have inverted the magnetic field data to determine the rock magnetization distribution near the axis of this ultrafast speading center (162 mm yr^-1). The solutions reveal large amplitude (up to 35 A m^-1) short wavelength (1–3 km) variations in magnetization. Specifically all crossings show a narrow (0.5 to 1.5 km) low in magnetization superimposed on a broader (2.5 to 4 km) high directly over the ridge axis. Four profiles in the northern area (19°25 to 19°33S) also show symmetrical near-axis (within 4 km) lows which are remarkably continuous along strike. Explanations for the short-wavelength variations are discussed which fall into the following categories: (1) variations in the thickness of the magnetized layer, (2) variations in rock chemistry (e.g. alteration due to hydrothermal activity), and (3) paleofield intensity variations. None of the mechanisms discussed alone adequately explain the observed phenomena in the study area or on a world-wide scale. Further sampling and high resolution surveying will be required in order to accurately determine the relative importance of the mechanisms discussed.     

Sea Beam,SeaMARC II and ALVIN-based studies of faulting on the East Pacific Rise 9°20′ N–9°50′ N

A study of Sea Beam bathymetry and SeaMARC II side-scan sonar allows us to make quantitative measures of the contribution of faulting to the creation of abyssal hill topography on the East Pacific Rise (EPR) 9°15 N–9°50 N. We conclude that fault locations and throws can be confidently determined with just Sea Beam and SeaMARC II based on a number of in situ observations made from the ALVIN submersible. A compilation of 1026 fault scarp locations and scarp height measurements shows systematic variations both parallel and perpendicular to the ridge axis. Outward-facing fault scarps (facing away from the ridge axis), begin to develop within 2 km of the ridge and reach their final average height of 60 m at 5–7 km. Beyond these distances, outward-dipping faults appear to be locked, although there is some indication of continued lengthening of outward-facing fault scarps out to the edge of the survey area. Inward-facing fault scarps (facing toward the ridge axis), initiate 2 km off axis and increase in height and length out to the edge of our data at 30 km, where the average height of inward fault scarps is 60–70 m and the length is 30 km. Continued slip on inward faults at a greater distance off axis is probable, but based on fault lengths, 80% of the lengthening of inward fault scarps occurs within 30 km of the axis (>95% for outward faults). Along-strike propagation and linkage of these faults are common. Outward-dipping faults accommodate more apparent horizontal strain than inward ones within 10 km of the ridge. The net horizontal extension due to faulting at greater distances is estimated as 4.2–4.3%, and inward and outward faults contribute comparably. Both inward- and outward-facing fault scarps increase in height from north to south in our study area in the direction of decreasing inferred magma supply. Average fault spacing is 2 km for both inward-dipping and outward-dipping faults. The azimuths of fault scarps document the direction of ridge spreading, but they are sensitive to local changes in least compressive stress direction near discontinuities. Both the ridge trend and fault scarp azimuths show a clockwise change in trend of 3–5° from 9°50 N to 9°15 N approaching the 9° N overlapping spreading center.     

Morphology of a ‘superfast’ Mid-Ocean Ridge crest and flanks: The East Pacific Rise, 7°–9° S

Detailed bathymetric data from a Hydrosweep multibeam sonar survey of a 250 km-long portion of the superfast-spreading southern East Pacific Rise crest and flanks show that the along-axis variation in morphology and axial depth differs significantly from that observed at the fast-spreading northern East Pacific Rise. While the deep mantle upwelling pattern is similar under the northern and southern East Pacific Rise, our observations require that the connectivity of the shallow, subcrestal plumbing system be more efficient beneath the super-fast spreading southern East Pacific Rise than beneath the slower spreading northern East Pacific Rise.     

Evolution of the East Pacific Rise at 16°–19° S since 5 Ma: Bisection of overlapping spreading centers by new,rapidly propagating ridge segments

Nearly complete side-scan, bathymetry and magnetic coverage documents the evolution of the geometry of the East Pacific Rise (EPR) between 16° and 19° S since 5 Ma. Lineaments visible in SeaMARC II, H-MR1 and Sea Beam 2000 side-scan data correspond dominantly to normal fault scarps which have developed in the axial region perpendicular to the least compressive stress. Except near overlapping spreading centers (OSCs), the lineament orientations are taken to represent the perpendicular to the instantaneous Pacific-Nazca spreading direction. Their dominant orientation in the axial region is 012°, in good agreement with the prediction of the current model of relative plate motion (DeMets et al., 1994). However, the variations of the lineament azimuths with age show that there has been a small (3°–5°) clockwise change in the Nazca-Pacific relative motion since 5 Ma. There is also a distinct population of lineaments which strike counterclockwise to the ambient orientation. These discordant lineaments form somewhat coherent patterns on the seafloor and represent the past migration tracks of several left-stepping OSCs. Concurrent analysis of these discordant zones and the magnetic anomalies, reveals that up to 1 Ma, the EPR was offset by a few large, left-stepping OSCs. These OSCs were bisected into smaller OSCs by new spreading segments forming within their overlap basins. The smaller OSCs proceeded to migrate rapidly and were further bisected by newly spawned ridge segments until the present staircase of small, left-stepping OSCs was achieved. By transferring lithosphere from one plate to the other, these migration events account remarkably well for the variable spreading asymmetry in the area. Between 16° and 19° S, the present EPR is magmatically very robust, as evidenced by its inflated morphology, the profuse volcanic and hydrothermal activity observed from submerisbles and towed cameras, the geochemistry of axial basalts, and seismic and gravity data. Since 1 Ma, all the OSCs have migrated away from the shallowest, most robust section of the ridge between 17° and 17°30 S, which was previously offset by a large OSC. We propose that the switch from a presumed starved magmatic regime typically associated with large OSCs to the presently robust magmatic regime occurred when the EPR overrode a melt anomaly during its westward migration relative to the asthenosphere. The resulting increase in melt supply at 17°–17°30 S has fed the migration of axial discontinuities for this section of the southern EPR since 1 Ma.     

Bottom fauna associated with mussel beds and alvinellid communities in the hydrothermal field at 9° N of the East Pacific Rise

Samples from mytilid mollusk and alvinellid polychaet communities and associated fauna were collected during cruise 49 of R/V Akademik Mstislav Keldysh at 9° N of the East Pacific Rise. The mytilids Bathymodiolus thermophylus occupied zones of diffuse releases of hydrothermal solutions with temperature anomalies a few degrees in amplitude. The alvinellid assemblages were located in the hottest parts of hydrothermal vents (～ 40°C) over sulfide mounds. The taxonomic compositions of these kinds of assemblages are different. The taxonomic richness of mytilid communities is almost twice higher. A comparison of the samples using Jaccard’s index showed a greater similarity among the alvinellid samples than that between the mytilid ones. With respect to the species number, polychaets formed the most diverse group, while gastropods were the second most diverse. The dominant species had greater proportions in alvinellid communities than in mytilid ones. This study showed great differences between the mytilid and alvinellid associations in their species composition and community structure.     

The geochemistry of deepwater particulate matter over the hydrothermal field at 9°d50′ N (the East Pacific Rise)

The results of geochemical studies of particulate matter in the water mass over the hydrothermal field at 9°50′ N on the East Pacific Rise are presented. The particulate matter was tested in background waters, in the buoyant plume, and in the near-bottom waters. The contents of Si, Al, P, C_org, Fe, Mn, Cu, Zn, Ni, Co, As, Cr, Cd, Pb, Ag, and Hg were determined. No definite correlations were found between the ele-ments in the background waters. Many of the chemical elements correlated with Fe and associated with its oxyhydroxides in the buoyant plume. In the near-bottom waters, microelements are associated with Fe, Zn, and Cu (probably, to their sulfides formed under fluid mixing with seawater). The matter precipitated in a sed-imentation trap was similar to the near-bottom particulate matter in the elemental composition.     

The slanting property of semi-diurnal internal tide propagation in the Pacific Ocean at 1°45′S, 156°E

1Introduction DuringtheTOGA COARE,extensivejointin ternationaloceanicobservationswerecarriedoutin thewesternequatorialPacificOceanandavasta mountofvaluabledatawereobtained.Themaindata usedhereincludethedatafromasinglemooringin strumentarrayat1°45′S,156°E,deployedbythe WoodsHoleOceanographicInstitution(WHOI)and theCTD(profilerofconductivity-temperature-depth)datacollectedbytheChineseRVXiangy anghongNo.5.Fangetal.(2000)described brieflytheseobservationdataandanalyzedthedis persion…     

The slanting property of semi-diurnal internal tide propagation in the Pacific Ocean at 1°45′S, 156°E

By analyzing a data set collected using a moored instrument array and CTD during TOGA-COARE, it is found that there exist remarkable internal tides in the western equatorial Pacific Ocean around 1°45′S,156°E, whose horizontal wavenumber (wavelength), vertical wavenumber, h 156° orizontal propagation speed and vertical propagation speed are 3.3×10-2km-1(210 km),-1.6×10-3m, 2.0 m/s and -3.8 cm/s, respectively, that is, the waveform propagates downwards slantingly. Moreover, the propagating direction rotates statistically clockwise as the depth increases and its cause is unclear.     

Phylogenetic analysis of bacterial community in deep-sea sediment from the western Pacific “warm pool”

A depth profile of bacterial community structure in one deep-sea sediment core of the western Pacific ＂warm pool＂ （WP） was investigated and compared with that in a sediment sample from the eastern Pacific （EP） by phylogenetic analysis of 16S rDNA fragments. Five bacterial 16S rDNA clone libraries were constructed, and 133 clones with different restriction fragment length polymorphism （RFLP） patterns were sequenced. A phylogenetic analysis of these sequences revealed that the bacterial diversity in a sample from the WP was more abundant than that in the EP sample. The bacterial population in the sediment core of WP was composed of eight major lineages of the domain bacteria. Among them the γ-Proteobacteria was the predominant and most diverse group in each section of WP sediment core, followed by the α-Proteobacteria. The genus Colwellia belonging to γ-Proteobacteria was predominant in this sample. The shift of bacterial communities among different sections of the WP sediment core was δ-, ε-Proteobacteria, and Cytopahga-Flexibacteria-Bacteroides （CFB） group. The ratios between them in the bacterial communities all showed inversely proportional to the depth of sediment. The sequences related to sulphate reducing bacteria （SRB） were detected in every section. The bacterial community structure in this sediment core might be related to the environmental characteristics of the surface seawater of the western Pacific WP.     

Fifty years of the 137°E repeat hydrographic section in the western North Pacific Ocean

The 137°E repeat hydrographic section of the Japan Meteorological Agency across the western North Pacific was initiated in 1967 as part of the Cooperative Study of the Kuroshio and Adjacent Regions and has been continued biannually in winter and summer. The publicly available data from the section have been widely used to reveal seasonal to decadal variations and long-term changes of currents and water masses, biogeochemical and biological properties, and marine pollutants in relation to climate variability such as the El Niño-Southern Oscillation and the Pacific Decadal Oscillation. In commemoration of the 50th anniversary in 2016, this review summarizes the history and scientific achievements of the 137°E section during 1967–2016. Through the publication of more than 100 papers over this 50-year span, with the frequency and significance of the publication increasing in time, the 137°E section has demonstrated its importance for future investigations of physical–biogeochemical–biological interactions on various spatiotemporal scales, and thereby its utility in enhancing process understanding to aid projections of the impact of future climate change on ocean resources and ecosystems over the twenty-first century.     

New constraints on the width of the zone of active faulting on the East Pacific Rise 8° 30′ N – 10° 00′ N from Sea Beam Bathymetry and SeaMARC II Side-scan Sonar

Sea Beam bathymetry and SeaMARC II side-scan sonar data are used to constrain the width of the zone of active faulting (plate boundary zone) to be 90 km (0.8 Ma) wide along the East Pacific Rise 8° 30N – 10° 00N. Fault scarps, identified on the basis of contoured, shaded relief and slope intensity maps of bathymetry, are measured. These scarp measurements, used in conjunction with data from a separate near-axis study, show that both inward- and outward-facing fault scarps increase in height away from the ridge axis, reaching average heights of 100 m at 0.8±0.2 Ma, 45±10 km from the ridge axis. Beyond this distance, there is no significant increase in scarp height. Earlier studies had suggested that the width of the zone of active faulting for outward-dipping faults might be significantly narrower than for inward-dipping faults. A lower crustal decoupling zone between brittle crust and strong upper mantle is predicted to exist out to 20–200 km from the ridge based on previously published lithospheric models. Such a decoupling zone may explain why outward-dipping faults continue to be active as far off-axis as inward-dipping faults. If the width of the zone of active faulting is controlled by the width of a lower crustal decoupling zone, our observations predict an 90 km wide decoupling zone in the lower oceanic crust at this location.     

Volcanic Morphology of the East Pacific Rise Crest 9°49′–52′: Implications for volcanic emplacement processes at fast-spreading mid-ocean ridges

Deep sea photographs were collected for several camera-tow transects along and across the axis at the East Pacific Rise crest between 9°49 and 9°52 N, covering terrain out to 2 km from the ridge axis. The objective of the surveys was to utilize fine-scale morphology and imagery of seafloor volcanic terrain to aid in interpreting eruptive history and lava emplacement processes along this fast-spreading mid-ocean ridge. The area surveyed corresponds to the region over which seismic layer 2A, believed to correspond to the extrusive oceanic layer, attains full thickness (Christeson et al., 1994a, b, 1996; Hooft et al., 1996; Carbotte et al., 1997). The photographic data are used to identify the different eruptive styles occurring along the ridge crest, map the distribution of the different morphologies, constrain the relative proportions of the three main morphologies and discuss the implications of these results. Morphologic distributions of lava for the area investigated are 66% lobate lava, 20% sheet lava, 10% pillow lava, and 4% transitional morphologies between the other three main types. There are variations in inferred relative lava ages among the different morphological types that do not conform to a simple increase in age versus distance relationship from the spreading axis, suggesting a model in which off-axis transport and volcanism contribute to the accumulation of the extrusive layer. Analysis of the data suggests this ridge crest has experienced three distinctly different types of volcanic emplacement processes: (1) axial summit eruptions within a 1 km wide zone centered on the axial summit collapse trough (ASCT); (2) off-axis transport of lava erupted at or near the ASCT through channelized surface flows; and (3) off-axis eruptions and local constructional volcanism at distances of 0.5-1.5 km from the axis. Major element analyses of basaltic glasses from lavas collected by Alvin, rock corer and dredging in this area indicate that the most recent magmatic event associated with the present ASCT erupted relatively homogeneous and mafic (>8.25 weight percent wt.% MgO) basalts compared to older, off-axis lavas which tend to be more chemically evolved (Perfit and Chadwick, 1998; Perfit and Fornari, unpublished data). The more primitive lavas have a more extensive distribution within and east of the ASCT. More evolved basalts (MgO <8.0wt.%) are concentrated in a broad area a few kilometers east of the axis, and in an oval-shaped area south of 9°50 N, west of the ASCT. Transitional and enriched (T- and E-) mid-ocean ridge basalts exist in relatively small areas (<1 km²) on the crestal plateau and correlate with scarps or fissures where pillow lavas were erupted. Mafic lavas in this area are primarily related to the youngest magmatic events. Geochemical analysis of samples collected at distances >500 m from the ASCT suggests that regions of off-axis volcanism may be sourced from older and cooler sections of the axial magma lens. Analysis of these data suggests that this portion of the EPR has not experienced large scale volcanic overprinting in the past 30 ka. The predominance of lobate flows (66%) throughout much of the crestal region, and subtle variations in sediment cover and apparent age between flows, suggest that eruptive volumes and effusion rates of individual eruptions have been similar over much of the last 30 ka and that most of the eruptions have been small, probably similar in volume to the 1991 EPR flow which had an estimated volume of 1×10⁶ m³ (Gregg et al., 1996).     

Variation of sulfate aerosol concentrations over the western Pacific and their effect on clouds, radiation and precipitation

Under bilateral cooperation between the United States of America and the People's Republic of China, a series of research cruises were conducted over the western Pacific Ocean. It was found that a) the non-sea-salt sulfate aerosol particles are the major source of cloud condensation nuclei, b) the population of clouds and the total albedo are proportional to the concentration of condensation nuclei and consequently to the concentration of the non-sea-salt aerosol particles, and c) the amount of rainfall is inversely proportional to the concentration of non-sea-salt sulfate aerosol particles. It seems that anthropogenic sulfate aerosol particles affect the regional planetary albedo and climate and that the contribution from biogenically derived sulfate aerosol particles is of lesser importance.     

Island mass effect in the Juan Fernández Archipelago (33°S), Southeastern Pacific

Spatial and temporal variability of the island mass effect (IME; defined as local increases of phytoplankton associated with the presence of islands) at the Juan Fernández Archipelago (JFA) is analyzed using chlorophyll-a (Chl-a) satellite data, altimetry, sea surface temperature, wind, geostrophic currents and net heat flux over a ten year period (2002–2012). The the JFA islands (Robinson Crusoe-Santa Clara (RC-SC) and Alejandro Selkirk (AS)) present wakes with significant Chl-a increases, mainly during spring time. These wakes can reach Chl-a values of one order of magnitude higher (~1 mg m⁻³) than the surrounding oligotrophic waters (<0.1 mg m⁻³). The wakes are similar to von Kármán vortex streets which have been used to explain the impact of IME on Chl-a increases in numerical models. The wakes are formed from a high productivity area in the lee of the island, extending to the oceanic region as high Chl-a patches associated with submesoscale eddies that are detached from the islands and connected by less-productive zones. This pattern coincides with previous models that predict the effects of island-generated flow perturbations on biological production variability. The IME is a recurrent feature of islands that has even been observed in decadal average fields. In such average fields, the Chl-a values in RC-SC and AS islands can exceed values found in a Control Zone (a zone without islands) by ~50% and 30%, respectively. Seasonal and interannual variability reveals that, as a consequence of the IME, the winter Chl-a maximum associated with the development of winter convection and mesoscale eddies that propagate from the continental zone, promote that the Chl-a maximum extends towards spring. The IME has an impact on the island on both a local as well as a more regional scale that affects an area of ~40,000 km² (1°Latitude×4°Longitude) centered on the islands. The transport of high productivity patches associated with submesoscale eddies may be responsible for IME propagation at a regional scale. Around the islands, the presence of a weak oceanic incident flow and strong and recurrent wind-wakes, suggest that the generation of Chl-a wakes result from a combined effect between both forcings.     

Abnormality of thermal structure and current in the upper western tropical Pacific Ocean and its effect on subtropical high

-Mainly on the basis of the data obtained during PRC/US bilateral TOGA cruises, abnormal variation occurred during the 1986/1987 El Nino is shown in this paper about the thermal structure and circulation of the upper western tropical Pacific Ocean. The effects of the abmormal variation on the subtropical high over the Northwest Pacific Ocean are discussed. During the El Nino: (1) In the east part of the western tropical Pacific Ocean (the subsurface temperature data on the 165° E section are taken as an example), the water wanner than 29 C in the upper layer spread on the longitudinal section and positive temperature anormalies appeared in a large area of the sea surface. (2) In the west part of the western tropical Pacific Ocean (the subsurface temperature data on the 137°E section are representative ), the cross section occupied by the upper layer warmer water ( T >28 ℃ ) became shrunk, and the sea surface temperature showed negative amomalies. (3) The eastward flows in the upper layer of the 165°