Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...     

Partitioning of heavy metals into mineral and organic fractions in a sediment core sample from Osaka Bay

Partitioning of copper, zinc, iron and manganese into oxide, sulfide, organic and silicate fractions has been determined with a selective chemical leaching technique on sediment samples from a core collected in Osaka Bay. The samples have been dated by the²¹⁰Pb method. Most of the copper and zinc in the polluted surface sediment layer are contained in both oxide and sulfide fractions. This suggests that the transformation of oxides and hydroxides to sulfides under anoxic conditions within the sediment is significant for the fixation of copper and zinc discharged through human activities into the sediment. Manganese is apparently enriched in oxide and hydroxide fractions of the surface layer due to the post-depositional migration of manganese within the sediment. The copper, zinc and manganese contents of the 30 % H₂O₂ soluble fraction (mostly organic fraction) decrease with depth in the sediment core, and correlate significantly with the organic carbon content. The heavy metal (Cu, Zn, Fe and Mn) contents of the silicate fraction, without exchangeable sites, are almost constant with depth.     

Hydrogen isotope fractionation by Methanothermobacter thermoautotrophicus in coculture and pure culture conditions

We grew a hydrogen-utilizing methanogen, Methanothermobacter thermoautotrophicus strain ΔH, in coculture and pure culture conditions to evaluate the hydrogen isotope fractionation associated with carbonate reduction under low (< several tens of μM; coculture) and high (>6 mM; pure culture) concentrations of H₂ in the headspace. In the cocultures, which were grown at 55 °C with a thermophilic butyrate-oxidizing syntroph, the hydrogen isotopic relationship between methane and water was well represented by the following equation:

δD_CH4=0.725(±0.003)·δD_H2O-275(±3),     

Partial derivative of love numbers

We present a simple formula for the partial derivatives of Love numbers with respect to density, bulk modulus and rigidity without urging the Adams-Williamson condition in the liquid core. Partials of the second degree Love numbers are computed for model 1066 A. Love numbers prove to be either completely or virtually independent of the elastic profile within the whole core. Delta-function-like changes occur in Love numbers when we perturb the density of the top and bottom layers of the outer core.     

Carbon isotopic fractionation associated with lipid biosynthesis by a cyanobacterium: relevance for interpretation of biomarker records

For the cyanobacterium Synechocystis UTEX 2470, grown photoautotrophically to a logarithmic stage of growth, the total lipid extract is depleted in 13C by 4.8% relative to average biomass. Depletions observed for acetogenic (straight-chain) lipids range from 7.6 (hexadecanoic acid) to 9.9% (a C16 n-alkyl chain bound in a polar-lipid fraction), with a mass-weighted average of 9.1%. Polyisoprenoid lipids fall into two isotopic groups, with phytol, diplopterol, and diploptene depleted by 6.4-6.9% and bishomohopanol (produced from the extracts by the preparative degradation of bacteriohopanepolyol) depleted by 8.4%. Analysis of the pattern of depletions indicates that two carbon positions in each C5 biomonomer leading to polyisoprenoid products are probably depleted in 13C relative to average biomass. The depletion of bacteriohopanepolyol relative to other polyisoprenoids can be ascribed to changes that occur over the life of each cell: (1) the 13C content of carbon flowing to lipid biosynthesis decreases as the cell size increases and (2) a greater proportion of the bacteriohopanepolyol which, unlike other polyisoprenoids, is present mainly in the cytoplasm rather than in membranes and is synthesized when cells are larger. Chlorophyll a is depleted relative to average biomass by O.7%. Given the observed depletion of 13C in phytol, the heteroaromatic, chlorophyllide portion of chlorophyll must be enriched in 13C by 2.7%. This enrichment is large relative to that in chlorophyllides produced by eukaryotes and may be related to a parallel enrichment of 13C in cyanobacterial glutamic acid. As in many previous investigations of cyanobacterial lipids, long-chain n-alkanes (C22-C29) are found in the extracts. They are, however, enriched in 13C relative to biomass and have isotopic compositions suggesting that they are contaminants of petrochemical origin. Available results indicate that cyanobacterial lipids will be depleted relative to dissolved CO2 that has served as a carbon source by 22-30% and that a wider range of depletions will be characteristic of eukaryotic products. The absence of long-chain n-alkanes in cyanobacteria reduces the possibility that petroleum ever formed from pre-eukaryotic sedimentary debris.     

Gravity change observed in a local gravity network and its implication to seasonal precipitation in Dali county,Yunnan province,China

This study investigates data-processing methods and examines the precipitation effect on gravity measurements at the Dali gravity network, established in 2005. High-quality gravity data were collected during four measurement campaigns. To use the gravity data validly, some geophysical corrections must be considered carefully. We first discuss data-processing methods using weighted least-squares adjustment with the constraint of the absolute gravity datum. Results indicate that the gravity precision can be improved if all absolute gravity data are used as constraints and if calibration functions of relative gravimeters are modeled within the observation function. Using this data-processing scheme, the mean point gravity precision is better than 12 μgal. After determining the best data-processing scheme, we then process the gravity data obtained in the four measurement campaigns, and obtain gravity changes in three time periods. Results show that the gravity has a remarkable change of more than 50 μgal in the first time period from Apr–May of 2005 to Aug–Sept of 2007. To interpret the large gravity change, a mean water mass change (0.6 m in height) is assumed in the ETOPO1 topographic model. Calculations of the precipitation effect on gravity show that it can reach the same order of the observed gravity change. It is regarded as a main source of the remarkable gravity change in the Dali gravity network, suggesting that the precipitation effect on gravity measurements must be considered carefully.     

http://dx.doi.org/10.1016/j.gsf.2016.10.001

The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N'goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N'goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ~(207)Pb/~(206)Pb ratio is 0.13707 ± 0.0010.corresponding to a ~(207)Pb/~(206)Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.     

Origin of the Tonaru body in the Sanbagawa metamorphic belt,SW Japan

Zircon U–Pb dating of the Tonaru metagabbro body in the Sanbagawa metamorphic belt, southwest Japan, suggests that igneous events at ca 200–180 Ma were involved in the protolith formation. The trace element compositions of the Tonaru zircons are enriched in U (a fluid‐mobile element) and Sc (an amphibole‐buffered element), and depleted in Nb (a fluid‐immobile element), suggesting that the parental magmas related to the Tonaru metagabbros formed in an arc setting. Integration of our results with previous studies of the metasedimentary rocks in the Tonaru body clearly indicates that the protoliths of the Tonaru body were produced by oceanic‐arc magmatism. With the previous geochronological and geological studies, the tectono‐magmatic–metamorphic history of the Tonaru and other mafic bodies in the Sanbagawa metamorphic belt may be summarized as follows: (i) the protolith formation by the oceanic‐arc magmatic event had occurred at 200–180 Ma; (ii) the protoliths were accreted in the trench at ca 130–120 Ma; and (iii) they were completely subducted into the depth of the eclogite‐facies condition after 120 Ma.     

Development of a numerical model for nitrates in groundwater in the reservoir area of the Komesu subsurface dam, Okinawa, Japan

A numerical model consisting of simplified equations was developed to simulate nitrate concentrations in groundwater in a reservoir area of a subsurface dam in a Quaternary limestone region. The model was composed of a water balance sub-model and a nitrogen balance sub-model; the water balance sub-model was built from tank models which can express the quick dilution near caves and the effect of dam construction; and the nitrogen balance sub-model was made to represent changes in nitrogen forms and movement of nitrogen in the soil and aquifer zones. The model was calibrated and verified by observed data before and after the dam construction and then applied to a predictive simulation under a simple assumption that rainfall descends gradually. The model seemed applicable to long-term prediction of changes in NO₃-N in the reservoir area.