We report measurements of iron, nutrients, dissolved oxygen, humic-type fluorescence intensity and chlorophyll a concentrations in the coastal waters at the inflow (western) and outflow (eastern) ends of Tsugaru Strait (Japan) in June
2003 and 2004. Two different water masses (intensive eastward flow “subtropical Tsugaru Warm Current Water (TWCw)” and weak
westward flow “subarctic Oyashio Water (OW)”) were observed at the eastern end of the strait. TWCw at the southern part of
the eastern strait was vertically homogeneous with a uniform concentrations of iron (0.7–1.1 nM for labile dissolved Fe and
14–20 nM for total dissolvable Fe in 2003) as well as other chemical, biological and physical components throughout the water
column of 200 m due to strong vertical mixing in the strait. The degree of mixing in the Tsugaru Warm Current (TWC) is predominantly
affected by diurnal tidal current, which is strong during the period of tropical tides and weak during the period of equinoctial
ones. The especially strong vertical water mixing in 2003 is caused by large dissipation energy input due to the bottom friction
of passage-flow through the strait and tidal current. At the northern part of the eastern strait, the fresh surface layer
overlying the OW and the deep-bottom waters in 2003 contained large concentrations of dissolved iron, resulting from iron
supplied from river runoff and shelf sediments, respectively. These results suggest that the most important mechanism for
transporting iron in the strait is the strong vertical water mixing due to the tidal current, and that the iron sources in
the coastal waters are the organic-associated, iron-rich freshwater input into the surface water. 相似文献
The Sutter's Mill (SM) CM chondrite fell in California in 2012. The CM chondrite group is one of the most primitive, consisting of unequilibrated minerals, but some of them have experienced complex processes occurring on their parent body, such as aqueous alteration, thermal metamorphism, brecciation, and solar wind implantation. We have determined noble gas concentrations and isotopic compositions for SM samples using a stepped heating gas extraction method, in addition to mineralogical observation of the specimens. The primordial noble gas abundances, especially the P3 component trapped in presolar diamonds, confirm the classification of SM as a CM chondrite. The mineralogical features of SM indicate that it experienced mild thermal alteration after aqueous alteration. The heating temperature is estimated to be <350 °C based on the release profile of primordial 36Ar. The presence of a Ni‐rich Fe‐Ni metal suggests that a minor part of SM has experienced heating at >500 °C. The variation in the heating temperature of thermal alteration is consistent with the texture as a breccia. The heterogeneous distribution of solar wind noble gases is also consistent with it. The cosmic‐ray exposure (CRE) age for SM is calculated to be 0.059 ± 0.023 Myr based on cosmogenic 21Ne by considering trapped noble gases as solar wind, the terrestrial atmosphere, P1 (or Q), P3, A2, and G components. The CRE age lies at the shorter end of the CRE age distribution of the CM chondrite group. 相似文献
We present petrographic and geochemical data on representative samples of the Devonian adakite, boninite, low-TiO2 and high-TiO2 basalts and associated rocks in the southern Altay areas, Xinjiang, NW China. These volcanic rocks mostly occur as tectonic blocks within suture zones between the Siberian and Junggar plates. Adakite occurs in the Suoerkuduke area ca. 40 km south of Fuyun, and actually represents a poorly-sorted massive volcaniclastic deposit, mostly consisting of a suite of hornblende andesite to pyroxene andesite. The geochemical features of the adakite suggest its generation by melting of subducted oceanic crust. Boninite occurs in the Saerbulake area ca. 20 km southwest of Fuyun, as pillowed lava or pillowed breccia. It is associated with high-TiO2 basalt/gabbro and low-TiO2 basalt. The boninites are metamorphosed, but contain relict clinopyroxene with Mg# (=100*Mg/(Mg+Fe)) of 90–92, and Cr2O3 contents of 0.5–0.7 wt% and chromian spinel with Cr/(Cr+Al) ratio of 0.84. The bulk rock compositions of the boninites are characterized by low and U-shaped REE with variable La/Yb ratios. They are classified as high-Ca boninite. The Cr-rich cpx phenocryst and Chromian spinel suggests that the boninites were formed by melting of mildly refractory mantle peridotite fluxed by a slab-derived fluid component under normal mantle potential temperature conditions. Basaltic rocks occur as massive flows, pillowed lavas, tuff breccia, lapilli tuff and blocks in tectonic mélanges. Together with gabbros, the basaltic rocks are classified into high-TiO2 (>1.7 wt%) and low-TiO2 (<1.5 wt%) types. They show variable trace element compositions, from MORB-type through transitional back-arc basin basalt to arc tholeiite, or within plate alkalic basalt. A notable feature of the Devonian formations in the southern Altay is the juxtaposition of volcanic rocks of various origins even within a limited area; i.e. the adakite and the boninites are associated with high-TiO2 and low-TiO2 basalts and/or gabbros, respectively. This is most likely produced by complex accretion and tectonic processes during the convergence in the Devonian–Carboniferous paleo-Asian Ocean between the Siberian and Junggar plates. 相似文献
To help the decision making regarding where to locate new observation instruments on the seafloor, we examined the detectability of interplate earthquakes and slow slips in the Nankai subduction thrust in Japan using seafloor observation instruments. Here, the detectability is defined as the smallest magnitude of the interplate fault slip detected by the assumed observation points based on crustal deformation simulation. In the detectability analyses, we considered the effect of sensor drifts that are particularly associated with seafloor observations. In addition, we introduced high-resolution three-dimensional (3D) finite element modeling of crustal deformation to consider the effect of the topography and 3D heterogeneous crustal structure around the Nankai Trough. The results of the detectability analyses show that introducing new seafloor stations for tilt observation in the Nankai region should increase the detectability of small- or medium-sized interplate earthquakes and slow slips significantly. Based on the obtained results, we also discuss the advantage of both the existing and the new observation instruments in detecting interplate fault slips.
Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using
a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity
in the 26.7–27.3σθ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade−1 at 26.8–26.9σθ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen
utilization in the most prominent core (26.9–27.0σθ) exceeded 0.05 ml l−1 decade−1. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly
toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in
the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at
26.7–27.0σθ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about
40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic
responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies. 相似文献
We investigated changes in the global distribution of surface-layer salinity by comparing 2003–2007 Argo-float data with annual
mean climatological surface-layer salinity data for 1960–1989 from the World Ocean Database 2005. The two datasets showed
similar patterns, with low values in subpolar and tropical regions and higher values in the subtropics. The recent Argo data
indicate that the contrast between low and high salinity has intensified in all areas except the subpolar North Atlantic.
The intensified contrast of the surface layer salinity was maintaining for 2003–2007. Using a simple method, we attempted
to estimate evaporation and precipitation changes on the basis of surface-layer salinity changes. The results show a high
probability that the global hydrological cycle has increased in the past 30 years. 相似文献
The variation of dissolved organic matter (DOM) and fluorescence characteristics during the phytoplankton bloom were investigated
in Yashima Bay, at the eastern part of the Seto Inland Sea, Japan. We found significant accumulations of dissolved organic
carbon (DOC), dissolved organic nitrogen (DON), chromophoric dissolved organic matter (CDOM) fluorescence, and UV260 during the phytoplankton bloom period in 2005, although lower accumulations of DOC and DON and only increases of CDOM fluorescence
were observed during the bloom period in 2006. Little or no correlation between DOM and phytoplankton abundance might be due
to the composition of DOM, which is a complex mixture of organic materials. The 3D-EEM results revealed that the DOM produced
around the phytoplankton bloom period contained tyrosine, tryptophan, and humic-like substances. Our results showed that the
occurrence of phytoplankton bloom contributed to the production of DOM in coastal water but the DOM accumulation depended
on the type of phytoplankton bloom, the phytoplankton species in particular. From our results, we concluded that phytoplankton
have a great role in the dynamics of DOM as a producer in a coastal environment. 相似文献
Over-exploited groundwater is expected to remain the predominant source of domestic water in suburban areas of Hanoi, Vietnam. In order to evaluate the effect on groundwater recharge, of decreasing surface-water bodies and land-use change caused by urbanization, the relevant groundwater systems and recharge pathways must be characterized in detail. To this end, water levels and water quality were monitored for 3 years regarding groundwater and adjacent surface-water bodies, at two typical suburban sites in Hanoi. Stable isotope (δ18O, δD of water) analysis and hydrochemical analysis showed that the water from both aquifers and aquitards, including the groundwater obtained from both the monitoring wells and the neighboring household tubewells, was largely derived from evaporation-affected surface-water bodies (e.g., ponds, irrigated farmlands) rather than from rivers. The water-level monitoring results suggested distinct local-scale flow systems for both a Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). That is, in the case of the HUA, lateral recharge through the aquifer from neighboring ponds and/or irrigated farmlands appeared to be dominant, rather than recharge by vertical rainwater infiltration. In the case of the PCA, recharge by the above-lying HUA, through areas where the aquitard separating the two aquifers was relatively thin or nonexistent, was suggested. As the decrease in the local surface-water bodies will likely reduce the groundwater recharge, maintaining and enhancing this recharge (through preservation of the surface-water bodies) is considered as essential for the sustainable use of groundwater in the area.