Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere

A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO ₄ ^2– ) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH₃SCH₃) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH₃SO₃H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO ₄ ^2– toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO₂). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO₂ is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO₃) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO₂, MSA, and nss-SO ₄ ^2– are almost independent of NO _x concentration and radiation field. If dimethylsulfoxide (DMSO or CH₃S(O)CH₃) is produced by the addition reaction and further converted to sulfuric acid (H₂SO₄) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO ₄ ^2– at high latitudes.     

Simulations of seasonal variations of sulfur compounds in the remote marine atmosphere

A photochemical box model is used to simulate seasonal variations in concentrations of sulfur compounds at latitude 40° S. It is assumed that the hydroxyl radical (OH) addition reaction to sulfur in the dimethyl sulfide (DMS) molecule is the predominant pathway for methanesulfonic acid (MSA) production, and that the rate constant increases as the air temperature decreases. Concentration of the nitrate radical (NO₃) is a function of the DMS flux, because the reaction of DMS with NO₃ is the most important loss mechanism of NO₃. While the diurnally averaged concentration of OH in winter is a factor of about 8 smaller than in summer, due to the weak photolysis process, the diurnally averaged concentration of NO₃ in winter is a factor of about 4–5 larger than in summer, due to the decrease of DMS flux. Therefore, at middle and high latitudes in winter, atmospheric DMS is mainly oxidized by the reaction with NO₃. The calculated ratio of the MSA to SO₂ production rates is smaller in winter than in summer, and the MSA to non-sea-salt sulfate (nssSO₄ ^2-) molar ratio varies seasonally. This result agrees with data on the seasonal variation of the MSA/nssSO₄ ^2- molar ratio obtained at middle and high latitudes. The calculations indicate that during winter the reaction of DMS with NO₃ is likely to be a more important sink of NO_x (NO+NO₂) than the reaction of NO₂ with OH, and to serve as a significant pathway of the HNO₃ production. If dimethyl sulfoxide (DMSO) is produced through the OH addition reaction and is heterogeneously oxidized in aqueous solutions, half of the nssSO₄ ^2- produced in summer may be through the oxidation process of DMSO. It is necessary to further investigate the oxidation products by the reaction of DMS with OH, and the possibility of the reaction of DMS with NO₃ during winter.     

利用断层应力积累探讨大地震发生的地点——以日本2011年东北9级大地震为例

大地震在哪里发生是地震预报首先要解决的问题.利用反演GNSS观测数据得到的2011年日本东北9级大地震前7年(2004-2010年)断层上的应力变化,我们发现了这次地震断层的孕震区.为了进一步研究该孕震区的演化过程,本文继续反演这次大地震在1997-2003年间的断层应力变化过程.通过这两期的反演工作,我们看到,在这1...     

Governance of disaster emergency wells in three cities in Japan affected by earthquakes

Concern has grown regarding how public and private sectors should make effective use of local groundwater to alleviate negative impacts of water-supply cutoff following an earthquake event, which can be regarded as an emergency groundwater governance problem. Existing literature on groundwater governance, however, is based on the tacit assumption of groundwater utilization under normal social conditions, and scant consideration has been given to the role of groundwater following occurrence of a natural disaster. This study conducted questionnaire surveys to reveal how groundwater was used in three cities (Kumamoto, Sapporo, and Sendai) in Japan struck by large earthquakes between 2010 and 2020. Results revealed substantial differences between these cities in terms of groundwater utilization following earthquake occurrence. The time between the restoration of the electricity supply and restoration of the waterworks, and the social capital accumulated by local governments, are indicated as possible reasons for such differences. Analysis also identified policy challenges for improved groundwater governance in an emergency: (1) establishment of a strategy for emergency water supply through combined use of groundwater and other water sources, (2) enhancement of methods for timely inspection of groundwater quality following occurrence of a disaster, (3) maintenance of records of the number of registered disaster emergency wells (DEWs), (4) creation of methods for publicizing locational information on DEWs with adequate regard for the privacy of well owners, and (5) recognition of the importance of making DEWs part of overall disaster preparedness.

     

Midnight reversal of ionospheric plasma bubble eastward velocity to westward velocity during geomagnetically quiettime: Climatology and its model validation

In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles – WTB – occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station São João do Cariri (Geographic 7.45°S, 36.5°W, dip ～20°S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between ～20 and 40 ms^?1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July–September. No WTB have been observed from November until April in all years 2001–2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.     

On the Life History ofTigriopus japonicus Mori (Copepoda)

This species is the neritic animal in warm waters, especially a large number of the species appear in the tide pool in spring to summer season. The species has the adaptability to the environment, namely, the species is eurythermal and euryhaline organism. Each nauplius stage ofT. japonicus changed into the next stage in 18 to 20 hours. After hatching the nauplius developed into the copepodite stage in 3 to 5 days. The nauplius is disk-shaped in outline. A small antennule is 3-segmented. The antenna and mandible are the assistant oral organs for foods rather than swimming ones. On the antenna the coxa has the process with the strong cutting edge, the basipodite is extremely small, the long endopodite has a hook and a seta ventrally, and a hook, a seta and a spine terminally, and the long exopodite has the setae of which the number was changed according to the stage. On the mandible the coxa with a seta is a bulge. The endopodite is a small mound, on this mound there are a strong hook and a few setae which were changed according to the stage. The exopodite has a ventral seta and a small and a long thick terminal setae. The caudal appendages are rudimentary. The maxillule first appears as a seta on the 2nd stage. On the copedite stage ofT. japonicus the segment of body is short. The cephalothoracic segments are indistinguishable from the abdominal segments. It is the character of Harpacticoida that the antennules are small. On this copedodite there are 6 stages as in the nauplius, but the last stage is the adult stage. The 1st and the 2nd stages changed into the next stage in 18 to 20 hours as in the nauplius. The 3rd to the 5th stages changed into the next stage within 1 day. After hatching the nauplius developed into the adult by 10 days. The period of each stage fluctuates according to the amount of foods which were supplied to the animal. On the starved condition the development of this animal does not occur by any means. The most of male have mated with the adult female, but some of them mated with the earlier stage, especially the 2nd copepodite stage female. The female which developed into the adult produced the first brood in a few minutes to 3 days. A period of the adult stage is assumed 1 to 2 months. A female produced 5～10 broods. After hatching of the brood the next brood was bred in a few minutes to 1 day. The female which was 0.9 mm in the mean length produced 30 eggs per a brood.     

DMSP and DMS in coastal fast ice and under-ice water of Lützow-Holm Bay, eastern Antarctica

The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lützow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r²=0.68, P<0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans.     

Ordering in double carbonates and implications for processes at subduction zones

We have studied cation ordering in dolomite in situ as a function of pressure, temperature, and experimental time using the multi-anvil apparatus and synchrotron radiation. Starting with ordered dolomite, we observe the onset of disordering taking place at 950°C, while complete disordering is achieved at 1,070 (±20)°C, for pressures ranging between 3.37 and 4.05 GPa. Pressure does not appear to have significant effect on the order/disorder transition over the investigated range. We find that dolomite can reach its equilibrium ordering state above 900°C within duration of laboratory experiment (few hours), both from disordered state and from ordered state. In addition, we have reversed the dolomite breakdown reaction [magnesite + aragonite = dolomite] between 4.5 and 5.5 GPa, by monitoring diffraction peak intensity. We also have determined that dolomite is stable up to 7.4 GPa at 1,100°C. We confirm some earlier studies where a change in slope (dP/dT) has been observed, but we find a non-zero slope in the low pressure range. Combining the values of entropy obtained from dolomite degree of ordering with enthalpy values deduced from our bracketing of [magnesite + aragonite = dolomite] equilibrium, we model the location of dolomite breakdown in the P–T space as a function of cation ordering. By comparing previous conflicting studies, we show that, although kinetics of order/disorder is fast, disequilibrium dolomite breakdown is possible. Our modeling shows that subducted disordered dolomite present in carbonated sediments could be decomposed to [magnesite + aragonite] at lower pressure (3.5 GPa) than usually considered (>5 GPa). This 2-GPa (60 km) difference is valid on a fast subduction path and is possible if disorder inherited from sedimentation is preserved. On a slow subduction path, however, dolomite breakdown is encountered at about 250 km depth, which is 100 km deeper than currently considered.     

Flux of low salinity water from Aniva Bay (Sakhalin Island) to the southern Okhotsk Sea

In this study, we examined the relationship between the low salinity water in the shelf region of the southern Okhotsk Sea which was seasonally sampled (0–200 m), and fluxes of low salinity water from Aniva Bay. To express the source of freshwater mixing in the surface layer, we applied normalized total alkalinity (NTA) and stable isotopes of seawater as chemical tracers. NTA-S diagrams indicate that NTA of low salinity water in the upper 30 m layer just off the Soya Warm Current is clearly higher than in the far offshore region in summer and autumn. Using NTA-S regression lines, we could deduce that the low salinity and high NTA water in the upper layer originates from Aniva Bay. For convenience, we defined this water as the Aniva Surface Water (ASW) with values S < 32, NTA > 2450 μmol kg⁻¹. Formation and transport processes of ASW are discussed using historical data. The interaction between the maximum core of high NTA water on the bottom slope of eastern Aniva Bay and an anticyclonic eddy at the mouth of Aniva Bay are concluded to control ASW formation. Upwelling of the Cold Water Belt water at the tip of Cape Krillion is considered to cause ASW outflow from Aniva Bay.