通过第一性原理计算研究内地核的结构与成分

The determination of the composition and structure of the Earth’s inner core has long been the major subject in the study of the Earth’s deep interior. It’s widely believed that the Earth’s core is formed by iron with a fraction of nickel. However, light elements must exist in the inner core because the earth core is less dense than pure iron-nickel alloy (~2-3% in the solid inner core and ~6-7% in the liquid outer core). The questions are what and how much light element is there in the iron-nickel alloy. Besides the composition, the crystal structure of the iron with or without light element is also not well known. According to the seismological observations, the sound waves propagate 3-4% faster along the spin axis than in the equatorial plane. That means the inner core is anisotropic. The densest structure of iron-nickel alloy should be h.c.p structure under the very high pressures. However, the h,c,p structure does not propagate waves anisotropic ally. Then what is the structure of the iron-nickel alloy or the iron-nickle-light element alloy. In this study, we tried to predict the composition and the structure of the inner core through ab initio calculation of the Gibbs free energy, which is a function of internal energy, density and entropy. We conclude that the h.c.p structure is more stable than the b.c.c structure under high pressure and 0 K, but with the increase of temperature, the free energy of the b.c.c structure is decreasing much faster than the h.c.p structure caused by the vibration of the atomics, so the b.c.c structure is more stable at high temperatures. With the addition of light elements (S or Si or both), the free energy of b.c.c. decreases even faster, about 3at% of Si not only explains why the inner core is about 2-3 % lighter than the iron-nickle alloy, but also reasons why the inner core is anisotropic, since the b.c.c. structure becomes more stable than the h.c.p structure at 5500-6000K and b.c.c. is anisotropic in propagating seismic waves. Therefore, we infer that the inner core of the earth is formed by b.c.c iron and a fraction of nickel plus ~3at.% Si, with a temperature higher than 5500K, which is consistent with the studies from other approaches.

中国南方热带地区田洋玛珥湖24万年以来的气候变化及湖泊演变

A continuous long (224m) and high-resolution core TY2 was recovered from paleo-maar-lake Tianyang, tropical South China. Based on the diatom records of the upper 130-m core, this paper focuses on exploring climate change and the lake evolution history in tropical South China during the past 240ka. The most typical and unique characteristics of the diatom assemblages is that, Aulacoseira granulata was dominant or absolutely dominant species (80-90%) during most parts of the 130-m core, while Cyclotella stelligera var. tenuis and Fragilaria construens var. venter were subdominant species in only limited parts of the lower and upper core, respectively. Time scale is always the biggest problem for the study of TY2 core, so although diatom is seldom used for establishing time scale, here we attempt this by correlating the diatom-reconstructed temperature sequence with the time scale of ODP core 806B from Equatorial Western Pacific. Verified by the few most reliable ages from TY2 core and the parallel core TYl, a rather reasonable and reliable time scale was established. 01S 7/6 falls at the depth of 100m (ca. 194kaBP), OIS 6/5 at 75m (ca. 132kaBP), OIS 5/4 at 46m (ca. 75kaBP), OIS 4-3 at 35m (ca. 60kaBP). Qualitative and quantitative environmental reconstructions are made on the basis of diatom assemblage ecotype and EDDI dataset. Correlation of diatom-reconstructed temperature and moisture changes of Core TY2 with pollen-reconstructed temperature and rainfall sequence of Core TYl proves that the results are quite consistent in most periods. Thus the reconstruction results from diatom are quite reliable, and probably have a much higher resolution than pollen results. Combined with lithological and magnetic susceptibility variations, the diatom analysis reveals that, the general climate in tropical South China during the past 240ka was warm and wet. On the time scale of glacial-interglacial, warm and wet, cool and dry are not always synchronous. It was relatively warm-wet during the penultimate interglacial, cool-dry during the penultimate glacial, warm-dry during the last interglacial, and cooler-drier during the last glacial. In contrast, on the time scale of subglacial-subinterglacial scales, warm and dry, cool and wet corresponds very obviously, showing very clear 21-23 ka precession cycle. Analysis also shows that, the water of Tianyang paleo-maar-lake was generally warm, turbulent, turbid, meso-trophic, slightly alkaline, low conductivity and fresh during the past 240 kaBP, with small variations in some parts. Tianyang paleolake experienced shallow to semi-deep lake in OIS7d, open shallow lake in OIS7c-OIS5b, shallow coastal lake in OIS5a-OIS4c, swamp in OIS4b, and then completely dried up in OIS3c. The lake evolution was mainly controlled by temperature and precipitation changes in tropical China. While temperature and precipitation changes were probably controlled by the migrations of monsoon rainband and the evaporation rate, which was in turn controlled by the evolution of East Asian monsoon. Therefore, when the summer monsoon was strongest the climate was warm-dry, when stronger the climate was warm-wet; when the winter monsoon was strongest the climate was cool-dry, stronger cool-wet. This mechanism caused the warm-dry sub interglacial and cool-wet subglacial climate in the tropical South China.

岱海岩芯沉积的粒度组成与湖区全新世降水变化历史

Sediment cores DH99a and DH99b recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4-crn intervals for grain-size distribution. Grain-size distributions of the lake sediments are inferred to be a proxy for past changes in East Asian monsoon precipitation, such that greater silt-size percentage and higher median grain size reflect increased monsoonal precipitation rates. The grain-size record of Daihai Lake sediments spanning the last ca 11,000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages: the Early, Middle and Late Holocene. During the Early Holocene before ca 7900 cal yr BP, the median grain size (Md) and the silt-fraction content were relatively low and constant, suggesting relatively low precipitation over the lake region. The Middle Holocene between ca 7900 and 3100 cal yr BP was marked by intensified and highly variable monsoonal precipitation, as indicated by high and variable Md values and silt contents of the lake sediments. During this period, average precipitation rate gradually increased from ca 7900 to 6900 cal yr BP, displayed intense oscillations between ca 6900 and 4400 cal yr BP, and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr BP Although generally high during the Middle Holocene, both the Md and the silt content assumed distinctly low values at the short intervals of ca 6500-6400, 6000-5900, 5700-5600, 4400-4200 cal yr BP, implying that monsoonal precipitation might have been significantly reduced during these intervals. During the Late Holocene since ca 3100 cal yr BP, grain-size values suggest that precipitation decreased. However, during the Late Holocene, relatively higher Md values and silt contents occurring between ca 1700 to 1000 cal yr BP may denote an intensification of hydrological cycles in the lake area. Changes in the East Asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the Earth's orbital parameters, but also may have been closely related to variations in the temperature and size of the Western Pacific Warm Pool, in the intensity of the El Nino-Southern Oscillation, and in the path and strength of the North Equatorial Current in the western Pacific.

Radio tomography: A new experimental technique

Pryse, Sian, 'Radio tomography: A new experimental technique', Surveys in Geophysics (2003) 24 pp.1-38 RAE2008

Large-scale structure of the fast solar wind

Breen, Andrew; Bisi, M.M.; Fallows, R.A.; Habbal, S.R., (2007) 'Large-scale structure of the fast solar wind', Journal of Geophysical Research 112(A6) pp.A06101 RAE2008

Contrasting the efficiency of radiation belt losses caused by ducted and nonducted whistler-mode waves from ground-based transmitters

It has long been recognized that whistler-mode waves can be trapped in plasmaspheric whistler ducts which guide the waves. For nonguided cases these waves are said to be "nonducted", which is dominant for L < 1.6. Wave-particle interactions are affected by the wave being ducted or nonducted. In the field-aligned ducted case, first-order cyclotron resonance is dominant, whereas nonducted interactions open up a much wider range of energies through equatorial and off-equatorial resonance. There is conflicting information as to whether the most significant particle loss processes are driven by ducted or nonducted waves. In this study we use loss cone observations from the DEMETER and POES low-altitude satellites to focus on electron losses driven by powerful VLF communications transmitters. Both satellites confirm that there are well-defined enhancements in the flux of electrons in the drift loss cone due to ducted transmissions from the powerful transmitter with call sign NWC. Typically, ∼80% of DEMETER nighttime orbits to the east of NWC show electron flux enhancements in the drift loss cone, spanning a L range consistent with first-order cyclotron theory, and inconsistent with nonducted resonances. In contrast, ∼1% or less of nonducted transmissions originate from NPM-generated electron flux enhancements. While the waves originating from these two transmitters have been predicted to lead to similar levels of pitch angle scattering, we find that the enhancements from NPM are at least 50 times smaller than those from NWC. This suggests that lower-latitude, nonducted VLF waves are much less effective in driving radiation belt pitch angle scattering. Copyright 2010 by the American Geophysical Union.

Intensification of summer rainfall variability in the southeastern United States during recent decades

The variability of summer precipitation in the southeastern United States is examined in this study using 60-yr (1948-2007) rainfall data. The Southeast summer rainfalls exhibited higher interannual variability with more intense summer droughts and anomalous wetness in the recent 30 years (1978-2007) than in the prior 30 years (1948-77). Such intensification of summer rainfall variability was consistent with a decrease of light (0.1-1 mm day-1) and medium (1-10 mm day-1) rainfall events during extremely dry summers and an increase of heavy (.10 mm day-1) rainfall events in extremely wet summers. Changes in rainfall variability were also accompanied by a southward shift of the region of maximum zonal wind variability at the jet stream level in the latter period. The covariability between the Southeast summer precipitation and sea surface temperatures (SSTs) is also analyzed using the singular value decomposition (SVD) method. It is shown that the increase of Southeast summer precipitation variability is primarily associated with a higher SST variability across the equatorial Atlantic and also SST warming in the Atlantic. © 2010 American Meteorological Society.

Epipelagic mesozooplankton distribution and abundance over the Mascarene Plateau and Basin, south-western Indian Ocean

The crescent shaped Mascarene Plateau (southwestern Indian Ocean), some 2200 km in length, forms a partial barrier to the (predominantly westward) flow of the South Equatorial Current. Shallow areas of the Mascarene Plateau effectively form a large shelf sea without an associated coastline. Zooplankton sampling transects were made across the plateau and also the basin to the west, to investigate the role the partial interruption of flow has on zooplankton biomass and community structure over the region. Biomass data from Optical Plankton Counter (OPC) analysis, and variability in community structure from taxonomic analysis, appear to indicate that the obstruction by the plateau causes upwelling, nutrient enrichment and enhanced chlorophyll and secondary production levels downstream. The Mascarene Basin is clearly distinguishable from the ridge itself, and from the waters to the south and north, both in terms of size-distributed zooplankton biomass and community structure. Satellite remote sensing data, particularly remotely-sensed ocean colour imagery and the sea surface height anomaly (SSHA), indicate support for this hypothesis. A correlation was found between OPC biovolume and SSHA and sea surface temperature (SST), which may indicate the physical processes driving mesozooplankton variability in this area. Biomass values away from the influence of the ridge averaged 24 mg m-3, but downstream if the ridge biomass averaged 263 mg m-3. Copepods comprised 60% of the mean total organisms. Calanoid copepods varied considerably between regions, being lowest away from the influence of the plateau, where higher numbers of the cyclopoid copepods Oithona spp., Corycaeus spp. and Oncaea spp., and the harpacticoid Microsetella spp. were found.

Can the subtropical North Atlantic permanent thermocline be observed from space?

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for similar to 2/3 of the temperature variance or vertical displacement of isotherms at a depth of similar to 550 m in the Subtropical North Atlantic Ocean near 32.5 degree N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for similar to 3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as - x650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data tie series in the Subtropical North Atlantic at 32.5 degree N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25 degree W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

Phytoplankton carbon fixation chlorophyll-biomass and diagnostic pigments in the Atlantic Ocean

We have made daily measurements of phytoplankton pigments, size-fractionated (<2 and >2-μm) carbon fixation and chlorophyll-a concentration during four Atlantic Meridional Transect (AMT) cruises in 2003–04. Surface rates of carbon fixation ranged from <0.2-mmol C m−3 d−1 in the subtropical gyres to 0.2–0.5-mmol C m−3 d−1 in the tropical equatorial Atlantic. Significant intercruise variability was restricted to the subtropical gyres, with higher chlorophyll-a concentrations and carbon fixation in the subsurface chlorophyll maximum during spring in either hemisphere. In surface waters, although picoplankton (<2-μm) represented the dominant fraction in terms of both carbon fixation (50–70%) and chlorophyll-a (80–90%), nanoplankton (>2-μm) contributions to total carbon fixation (30–50%) were higher than to total chlorophyll-a (10–20%). However, in the subsurface chlorophyll maximum picoplankton dominated both carbon fixation (70–90%) and chlorophyll-a (70–90%). Thus, in surface waters chlorophyll-normalised carbon fixation was 2–3 times higher for nanoplankton and differences in picoplankton and nanoplankton carbon to chlorophyll-a ratios may lead to either higher or similar growth rates. These low chlorophyll-normalised carbon fixation rates for picoplankton may also reflect losses of fixed carbon (cell leakage or respiration), decreases in photosynthetic efficiency, grazing losses during the incubations, or some combination of all these. Comparison of nitrate concentrations in the subsurface chlorophyll maximum with estimates of those required to support the observed rates of carbon fixation (assuming Redfield stoichiometry) indicate that primary production in the chlorophyll maximum may be light rather than nutrient limited.

Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide

Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt (Halocarbons in the Ocean and Atmosphere) database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1 degrees x 1 degrees grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global sea-to-air concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr(-1) for CHBr3, 0.78/0.98 Gmol Br yr(-1) for CH2Br2 and 1.24/1.45 Gmol Br yr(-1) for CH3I (robust fit/ordinary least squares regression techniques). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic regions. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our flux calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An under-representation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom-up emission estimate and top-down approaches.

Joint distributions of waves and rain

The transfer of gases between the atmosphere and ocean is affected by a number of processes, of which wave action and rainfall are two of potential significance. Efforts have been made to quantify separately their contributions; however such assessments neglect the interaction of these phenomena. Here we look at the correlation statistics of waves and rain to note which regions display a strong association between rainfall and the local sea state. The conditional probability of rain varies from ~0.5% to ~15%, with most of the equatorial belt (which contains the ITCZ) showing a greater likelihood of rain at the lowest sea states. In contrast the occurrence of rain is independent of wave height in the Southern Ocean. The 1997/98 El Niño enhances the frequency of rain in some Pacific regions, with this change showing some association with wave conditions.

Genetic and migratory evidence for sympatric spawning of tropical Pacific eels from Vanuatu

The spawning areas of tropical anguillid eels in the South Pacific are poorly known, and more information about their life histories is needed to facilitate conservation. We genetically characterized 83 out of 84 eels caught on Gaua Island (Vanuatu) and tagged 8 eels with pop-up satellite transmitters. Based on morphological evidence, 32 eels were identified as Anguilla marmorata, 45 as A. megastoma and 7 as A. obscura. Thirteen of these eels possessed a mitochondrial DNA sequence (control region, 527 bp) or nuclear haplotype (GTH2b, 268 bp) conflicting with their species designation. These individuals also had multi-locus genotypes (6 microsatellite loci) intermediate between the species, and 9 of these eels further possessed heterozygote genotypes at species-diagnostic nuclear single nucleotide polymorphisms (SNPs). We classified these individuals as possibly admixed between A. marmorata and A. megastoma. One A. marmorata and 1 A. megastoma migrated 634 and 874 km, respectively, towards the border between the South Equatorial Current and the South Equatorial Counter Current. Both species descended from around 200 m depth at night to 750 m during the day. Lunar cycle affected the upper limit of migration depths of both species. The tags remained attached for 3 and 5 mo and surfaced <300 km from the pop-up location of a previously tagged A. marmorata pop-up location. A salinity maximum at the pop-up locations corresponding to the upper nighttime eel migration depths may serve as a seamark of the spawning area. The similar pop-up locations of both species and the evidence for admixture suggest that these tropical eels share a sympatric spawning area.

Analytical phytoplankton carbon measurements spanning diverse ecosystems

The measurement of phytoplankton carbon (Cphyto) in the field has been a long-sought but elusive goal in oceanography. Proxy measurements of Cphyto have been employed in the past, but are subject to many confounding influences that undermine their accuracy. Here we report the first directly measured Cphyto values from the open ocean. The Cphyto samples were collected from a diversity of environments, ranging from Pacific and Atlantic oligotrophic gyres to equatorial upwelling systems to temperate spring conditions. When compared to earlier proxies, direct measurements of Cphyto exhibit the strongest relationship with particulate backscattering coefficients (bbp) (R2=0.69). Chlorophyll concentration and total particulate organic carbon (POC) concentration accounted for ~20% less variability in Cphyto than bbp. Ratios of Cphyto to Chl a span an order of magnitude moving across and within distinct ecosystems. Similarly, Cphyto:POC ratios were variable with the lowest values coming from productive temperate waters and the highest from oligotrophic gyres. A strong relationship between Cphyto and bbp is particularly significant because bbp is a property retrievable from satellite ocean color measurements. Our results, therefore, are highly encouraging for the global monitoring of phytoplankton biomass from space. The continued application of our Cphyto measurement approach will enable validation of satellite retrievals and contribute to an improved understanding of environmental controls on phytoplankton biomass and physiology.

Temporal changes in total and size-fractioned chlorophyll-a in surface waters of three provinces in the Atlantic Ocean (September to November) between 2003 and 2010

Phytoplankton total chlorophyll concentration (TCHLa) and phytoplankton size structure are two important ecological indicators in biological oceanography. Using high performance liquid chromatography (HPLC) pigment data, collected from surface waters along the Atlantic Meridional Transect (AMT), we examine temporal changes in TCHLa and phytoplankton size class (PSC: micro-, nano- and pico-phytoplankton) between 2003 and 2010 (September to November cruises only), in three ecological provinces of the Atlantic Ocean. The HPLC data indicate no significant change in TCHLa in northern and equatorial provinces, and an increase in the southern province. These changes were not significantly different to changes in TCHLa derived using satellite ocean-colour data over the same study period. Despite no change in AMT TCHLa in northern and equatorial provinces, significant differences in PSC were observed, related to changes in key diagnostic pigments (fucoxanthin, peridinin, 19′-hexanoyloxyfucoxanthin and zeaxanthin), with an increase in small cells (nano- and pico-phytoplankton) and a decrease in larger cells (micro-phytoplankton). When fitting a three-component model of phytoplankton size structure — designed to quantify the relationship between PSC and TCHLa to each AMT cruise, model parameters varied over the study period. Changes in the relationship between PSC and TCHLa have wide implications in ecology and marine biogeochemistry, and provide key information for the development and use of empirical ocean-colour algorithms. Results illustrate the importance of maintaining a time-series of in-situ observations in remote regions of the ocean, such as that acquired in the AMT programme.