Nutrient supply and biological response to wind-induced mixing, inertial motion, internal waves, and currents in the northern Chukchi Sea

A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6-hourly) and microstructure turbulence measurements (two to three times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (>10 m s-1) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin

「みらい」北極航海 (MR13-06)におけるチャクチ海定点観測 : 大気イベントに対する海洋環境の変化

近年の北極海の急激な変化を考える上で、北極圏の大気循環、とりわけ高・低気圧の役割に着目する必要がある。温度勾配が強い氷縁域で発生する低気圧については、その形成・発達メカニズムが「みらい」の直接観測により明らかになるとともに、海洋との熱の交換過程が北極の急激な温暖化に寄与することが示唆された (Inoue and Hori, 2011)。またボーフォート高気圧の変動は、北極海の海氷分布や海洋物理場 (海洋循環・渦)の変動を通じて、海洋中の熱・淡水・栄養塩の分布を変化させ、生態系にも影響を及ぼすことが「みらい」等の観測で明らかになってきた。例えば、Nishino et al. (2009)は、シベリア沖北極海での夏季の海氷消失は水中の光環境を改善し、生物活動 (植物プランクトン量や生物ポンプの能力など)を増加させることを示唆した。ところが、Nishino et al. (2011a)では、アラスカ沖北極海での海氷消失は逆に生物活動を低下させることを明らかにした。生物活動の低下は、海氷消失によりアラスカ沖北極海 (カナダ海盆)でボーフォート高気圧が駆動する海洋循環が強まり、その循環内に淡水が蓄積され、表層の栄養塩濃度が低下することに起因する。このような表層栄養塩濃度が低下した海域においては、渦による栄養塩の供給が以前にも増して生物活動に重要になってきていることも示された (Nishino et al., 2011b)。しかし、これまでの観測はスナップショットであり、大気のイベントに対して海洋がどう応答し、さらに生物活動がどう変化するかといった時系列での観測は行われておらず、高時間分解能の観測が求められる。近年、北極海では低気圧活動が活発化しており、それにより海洋の鉛直混合が促進され、栄養塩が表層に供給されれば、生物活動が増加する可能性もある。MR13-06航海では定点観測点で高時間分解能の大気観測を行うと同時に海洋観測も行い、大気イベントに対する海洋の応答を調査するとともに、生物活動の変化を捉える観測を行った。また、定点観測に加え、広域観測を行うことにより、生物活動の時空間変動と海洋循環との関係を調査した。BE14-18講演要旨 / ブルーアース2014（2014年2月19日～20日, 東京海洋大学品川キャンパス

定点観測で捉えたチャクチ海での気象擾乱に伴う海洋環境の変化

近年の北極海の急激な変化を考える上で、北極圏の大気循環、とりわけ高・低気圧の役割に着目する必要がある。温度勾配が強い氷縁域で発生する低気圧については、その形成・発達メカニズムが「みらい」の直接観測により明らかになるとともに、海洋との熱の交換過程が北極の急激な温暖化に寄与することが示唆された (Inoue and Hori, 2011)。またボーフォート高気圧の変動は、北極海の海氷分布や海洋物理場 (海洋循環・渦)の変動を通じて、海洋中の熱・淡水・栄養塩の分布を変化させ、生態系にも影響を及ぼすことが「みらい」等の観測で明らかになってきた (e.g., Nishino et al., 2011a, b)。しかし、これまでの観測はスナップショットであり、大気のイベントに対して海洋がどう応答し、さらに生物活動がどう変化するかといった時系列での観測は行われておらず、高時間分解能の観測が求められる。近年、北極海では低気圧活動が活発化しており、それにより海洋の鉛直混合が促進され、栄養塩が表層に供給されれば、生物活動が増加する可能性もある。2013年「みらい」北極航海では定点観測点で高時間分解能の大気観測を行うと同時に海洋観測も行い、大気イベントに対する海洋の応答を調査するとともに、生物活動の変化を捉える観測を行った。また、定点観測に加え、広域観測を行うことにより、生物活動の時空間変動と海洋循環との関係を調査した。要旨 ; 2014年度日本海洋学会春季大会（2014年3月26日～3月30日, 東京海洋大学

Effective balloon-occluded retrograde transvenous obliteration of the superior mesenteric vein?inferior vena cava shunt in a patient with hepatic encephalopathy after living donor liver transplantation

Balloon-occluded retrograde transvenous obliteration (BRTO) has become a common and effective procedure for treating hepatic encephalopathy due to a portosystemic shunt related to cirrhosis of the liver. However, this method of treatment has rarely been reported in patients after liver transplantation. Here, we report the case of a 52-year-old patient who underwent living donor liver transplantation (LDLT) due to hepatitis C virus-infected hepatocellular carcinoma that was complicated with portal vein thrombosis and a large portosystemic shunt between the superior mesenteric vein (SMV) and inferior vena cava (IVC). The SMV-IVC shunt was not obliterated during LDLT because there was sufficient portal flow into the graft after reperfusion. However, the patient was postoperatively complicated with encephalopathy due to the portosystemic shunt. BRTO was performed and was demonstrated to have effectively managed the encephalopathy due to the SMV-IVC shunt, while preserving the hepatic function after LDLT

Identification of a novel fluorophore, xanthurenic acid 8- O -β- D -glucoside in human brunescent cataract

We have identified the chemical structure of a novel protein-unbound fluorescent glucoside (Fl-Glc), found to be far more abundant in the human brunescent cataractous lens nuclei than in non-brunescent ones. Our earlier experiments showed that long-term incubation of the protein-free filtrate of non-brunescent cataractous nuclei generated increasing amounts of a particular yet to be characterized fluorophore (Fl-X). High performance liquid chromatography (HPLC) analyses revealed Fl-X and Fl-Glc to be identical. HPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MS) disclosed the molecular weights (MW) of Fl-X and its β-glucosidase-digest (Fl-X-aglycon) to be 367 and 205, respectively. Fl-X-aglycon and authentic xanthurenic acid (MW = 205) not only eluted at exactly the same retention time on HPLC but also revealed their protonated ions at the same m / z of 206.1 by positive ion analysis on HPLC-ESI-MS. These results suggest that Fl-X ( = Fl-Glc) is a β-glucoside of xanthurenic acid. Fl-Glc was finally identified as xanthurenic acid 8- O -β- D -glucoside because the retention times of both completely agreed with three kinds of HPLC conditions

Role of xanthurenic acid 8-O-β-D-glucoside, a novel fluorophore that accumulates in the brunescent human eye lens

We have been able to identify a blue fluorophore from the low-molecular weight soluble fraction of human adult nondiabetic brunescent cataract lenses as xanthurenic acid 8-O-β-D-glucoside (XA8OG) (excitation = 338 nm and emission = 440 nm). To determine the role of this fluorophore in the lens, we have examined its photophysical and photodynamic properties. We found XA8OG to have a fluorescence quantum yield (Φ) of 0.22 and a major emission lifetime of 12 ns. We found it to be a UVA-region sensitizer, capable of efficiently generating singlet oxygen species but little of superoxide. We also demonstrated that XA8OG oxidizes proteins when irradiated with UVA light, causing photodynamic covalent chemical damage to proteins. Its accumulation in the aging human lens (and the attendant decrease of its precursor O-β-D-glucoside of 3-hydroxykynurenine) can, thus, add to the oxidative burden on the system. XA8OG, thus, appears to be an endogenous chromophore in the lens, which can act as a cataractogenic agent