The distribution of iodine and effects of phosphatization on it in the ferromanganese crusts from the Mid-Pacific Ocean
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The distribution of iodine and effects of phosphatization on it in the ferromanganese crusts from the Mid-Pacific Ocean JI Lihong1, 2, LIU Guangshan1*, HUANG Yipu1, XING Na1, CHEN Zhigang1 1 College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China 2 College of Resources and Environment, Linyi University, Linyi 276000, China
Received 9 February 2014; accepted 4 June 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015
Abstract
In the present paper, iodine (I), iron (Fe), manganese (Mn), cobalt (Co), phosphorus (P) and calcium (Ca) contents in three ferromanganese crusts from the Pacific Ocean are measured by spectrophotometric method and inductively coupled plasma atomic emission spectrometers (ICP-AES) to investigate the contents and distribution of iodine in ferromanganese crusts. The results show that iodine contents in three crusts vary between 27.1 and 836 mg/kg, with an average of 172 mg/kg, and the profile of iodine in the three crusts all exhibits a two-stage distribution zone: a young non-phosphatized zone and an old phosphatized zone that is rich in I, P and Ca. The iodine content ratios of old to young zone in MP5D44, CXD62–1 and CXD08–1 are 2.3, 3.4 and 13.7, respectively. The boundary depths of two-stage zone in MP5D44, CXD62–1 and CXD08–1 locate at 4.0 cm, 2.5 cm and 3.75 cm, respectively, and the time of iodine mutation in three crusts ranges from 17–37 Ma derived from 129I dating and Co empirical formula, which is consistent with the times of Cenozoic phosphatization events. The present study shows that the intensity of phosphatization is the main responsible for the distribution pattern of iodine in the crusts on the basis of the correlation analysis. Consequently, iodine is a sensitive indicator for phosphatization. Key words: ferromanganese crust, iodine, phosphatization, Mid-Pacific Ocean, two-stage distribution Citation: Ji Lihong, Liu Guangshan, Huang Yipu, Xing Na, Chen Zhigang. 2015. The distribution of iodine and effects of phosphatization on it in the ferromanganese crusts from the Mid-Pacific Ocean. Acta Oceanologica Sinica, 34(8): 13–19, doi: 10.1007/s13131-015-0704-x
1 Introduction The geochemical behavior of iodine is great importance for two reasons. Firstly, iodine is an essential element for humans and other biological species, and the diseases in some regions of world caused by iodine deficiency are occurring. Secondly, radioactive iodine (129I), a cosmogenic radioisotope, can be a useful tool for age dating in geochemical studies (Fehn et al. 2000; Tomaru et al., 2009; Fehn, 2012). The half-life of 129I (15.7 Ma) is an order of magnitude longer than that of 10Be, which allows age determinations up to 80 Ma, i.e., the Tertiary dating. Iodine is mainly dominated by the marine system. Iodine in – seawater exists predominantly as iodate (IO ¡ 3 ), iodide (I ) and dissolved organic iodine. Although the concentration of total dissolved iodine is at around 0.45 μmol/L, those of I– and IO ¡ 3 are more spatially variable. The deep water
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