In 2015 ,a hydrothermal field named Daxi was discovered during the Chinese DY 33 cruise at 6°48′N , Carlsberg Ridge ,Northwest Indian Ocean .The chemistry of water samples and particles of a CTD station near Daxi Hydrothermal Field was studied .In the water depth of 3150～3400 m ,the water chemistry shows slight depletion of Cl ,Br ,Mg and intense enrichment of DFe and DMn .The concentrations of Cl ,Br ,Mg deplete 2 .87％ ～5 .27％ ,3 .21％ ～4 .53％ and 2 .52％ ～3 .82％ ,respectively ,when comparing to background seawater .It is suggested that the hydrothermal fluid has been subjected to phase separation ,resulting in the depletion of Cl and Br .The depletion of Mg suggests that the hydrothermal plume has been well mixed with the ambient seawater and the contribution of hydrothermal fluid is account for about 3 .90％ . The concentrations of DFe and DM n reach to 127 nmol/L and 29 .0 nmol/L ,respectively ,for the sample collected at 3150 m water depth .The particles have been investigated under scanning electron microscope and analyzed by energy dispersive X-Ray spectrometer .The results show that among the particles in the water depth of 2900～3400 m ,there are more iron oxides or hydroxides (49 .1％ ～95 .2％ FeO) present ,and this discovery is consistent with the enrichment of DFe and DMn in the water samples .According to the current speed and the diffuse radius of Fe(Ⅱ) ,the calculated value of Fe (Ⅱ ) oxidation half-live in Daxi hydrothermal field is 0.56～2.22h.%2015年中国大洋33航次在西北印度洋卡尔斯伯格脊6°48′N附近进行了热液异常探测,成功发现了大糦热液区.本文对该热液区附近采集的CTD水样开展了水化学与颗粒物分析.结果表明,在3150～3400 m水深范围内水体存在Cl、Br、M g负异常以及DFe和DM n正异常.其中Cl、Br、M g的浓度较研究区海水背景值分别亏损2.87％ ～5.27％ 、3.21％ ～4.53％ 和2.52％ ～3.82％,C l和B r的亏损指示海底释放的热液流体曾经发生了相分离.根据Mg的亏损情况,可以估算热液羽状流中热液流体的贡献约3.90％.DFe和DM n的浓度峰值分别为127 nmol/L和29.0 nmol/L,均出现在水深3150 m层位.颗粒物的电镜观察和能谱分析结果显示,在2900～3400 m深度范围内存在热液成因的富铁氧化物(FeO占49.1％ ～95.2％),与海水样品中发现的高浓度DFe和DM n相印证.根据实测底层流流速与Fe(Ⅱ)扩散半径对研究区的Fe(Ⅱ)氧化半衰期进行了估算,得到大糦热液区Fe(Ⅱ)氧化半衰期为0.56～2.22 h.
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