The Geochemistry Of Iodine In Ocean Water And The Jiulong River Estuarine Sediment

Iodine/starch-multiplier spectrophotometry was used to measure iodine content in ocean surface water and molten alkali extraction-centrifugal separation iodine/starch-multiplier spectrophotometry was adopted to decide iodine content in sediment from the Jiulong River Estuary, also preparation method of129I in seawater for accelerator mass spectrometry was discussed. Main findings are:1. Mean concentration of iodine in global ocean surface water was50.19μg/L iodine content showed average values with49.79μg/L,52.16μg/L,48.85μg/L,49.36μg/L and52.32μg/L, in the Pacific, central Pacific, west Pacific, Indian Ocean and the Southern Ocean, respectively, indicating that iodine concentration in these sea areas were:the Southern Ocean>the central Pacific>the Indian ocean>the Pacific>the west Pacific. Iodine concentration in the Southern Ocean varied a little while in the Pacific and the Indian ocean, it had a much wider range. The highest iodine concentration emerged near the equator, the maximum value is76.12μg/L; along the equator iodine concentration decreased with increasing latitude until30°N and30°S; between30°S and60°S, iodine concentration increased with increasing latitude, with high content near the Antarctic.2. Average total dissolved phosphorus (TDP) content in surface water was0.70μmol/L. Mean TDP concentration in the Pacific, central Pacific, west Pacific, Indian ocean and the Southern Ocean surface water were0.29μmol/L,0.38μmol/L,0.25μmol/L,1.07μmol/L and1.52μmol/L, respectively, with relations of the Southern Ocean>the Indian ocean>the central Pacific>the Pacific> the West Pacific.3. Similar trends of iodine and TDP concentration in ocean water were found. There was a significant positive relation (R2=0.5834) between iodine and TDP contents in the southeast India ocean. Distribution of iodine and TDP concentration was controlled by primary productivity:higher the primary productivity, lower the iodine and TDP content and viceversa, suggesting that iodine is biological preferred as nutrients, which can be absorbed when phytoplankton is taking biogenic elements and released in the process of mineralization. No relationship between iodine and δ18O, suggesting different mechanism forthose two parameters.4. Deposition year, iodine content, phosphorus content, I/Corg (10-4), I/P (10-2) and Corg/P of XG1sediment core were2003-2012,14.5-26.1mg/kg,630.5-821.6mg/kg,3.9-7.7,1.9-3.6and41.2-53.6, respectively. Average value of iodine was17.2mg/kg, with a maximum in8-10cm layer, showing an exponential decay in the vertical direction. No relationship between organic carbon and phosphorus was discovered. Relatively stable iodine/phosphorus was found in layers below10cm, ranging from2.1to3.0.5. Deposition year, iodine content, phosphorus content, I/Corg (10-4), I/P (10-2) and Corg/P of XG1sediment core were1984-2012,16.0-24.3mg/kg,385.7-693.1mg/kg、5.1-8.2、2.6-5.4and41.1-76.5, respectively. Mean iodine concentration was19.3mg/kg, reduced between0to6cm, with maximum in8cm, showing an turning point between12-14cm. Vertically, iodine concentration decayed exponentially. Deposition rates of sediment cores from7to30cm and30to54cm were1.94cm/a and1.69cm/a, respectively. Poor correlation existed between iodine content and organic carbon and phosphorus concentration, but the overall trend is similar, that is, iodine/phosphorus was stable in layer below10cm, ranging from2.6to4.8.6. Deposition year, iodine content, phosphorus content, I/Corg (10-4), I/P (10-2) and Corg/P of H3sediment core were1987-2012、15.4-23.5mg/kg、625.0-860.9mg/kg、4.3-8.2、2.0-3.0and29.6-49.9, respectively. Mean iodine concentration was17.8mg/kg, high values rose in2-4cm layer and8-10cm layer, and then decreased sharply.7. Deposition year, iodine content, phosphorus content, I/Corg (10-4), I/P (10-2) and Corg/P of JY4sediment core were1996-2012、13.8-25.7mg/kg、256.7-488.2mg/kg、4.1-11.7、3.1-8.5and66.7-127.0, respectively. Average iodine concentration was16.9mg/kg, maximum value with25.7mg/kg appeared in8cm. Negative relationship (R2=0.475) between iodine and organic carbon was found, while poor relationship between iodine and phosphorus. 8. Iodine content in surface sediments, phosphorus content, I/Corg (10-4), I/P (10-2)and Corg/P in the Jiulong River Estuary were19.3-35.7mg/kg,302.1-674.8mg/kg,6.0-40.3,3.0-7.3and15.8-60.5, respectively. Average value of iodine content was24.2mg/kg. Iodine concentration fluctuated smaller with increasing salinity, remained stable after entering the sea.9. In reducing environment, processes like decomposition of organic matter, reduction of oxide and desorption of absorbed materials would lead to recapture of iodine in oxidation environment, which can be reached after being emitted into water and diffused upward. Iodine enriched in the surface of all sediment cores, which further confirmed the former conclusion about the recapture of iodine.10. The decomposition rate constants of iodine in marine sediments was greater than that in intertidal sediments, as a result of increasing mineralization rate caused by intense interchange between overlying water and sediments, which was affected by high pressure and intense reciprocating flow.11. The results of Corg/P could be used for qualitative analysis of sediment sources. Results show showed that JY4sediment core was greatly affected by marine biogenic process, while the other three sediment cores suffered from terrigenous detritus more obviously. Iodine content in JY4surface sediment is higher than XG1, which was in consistent with the conclusion that iodine content in marine phytoplankton was higher than that in terrestrial plants.