RE E geochemistry of seawater from Afanasy-Nikitin Seamount in North Central Indian Ocean by high resolution inductively coupled plasma mass spectrometry

REE (Rare Earth Elements) and yttrium in sea water samples, from the Afanasy-Nikitin Seamount (ANS) located around 3 South latitude and 83 East longitude in the north central Indian Ocean were precisely determined by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) method. A modified procedure has been designed for determination of REE and yttrium wherein the water samples were subjected to a pre-concentration step using bis-2-ethylhexyl phosphoric acid (HDEHP) complexing agent. Sea water reference materials such as NASS-5 and SLEW-3 were used for calibration as well as to check the accuracy of the procedure adopted. Samples were analyzed for REE and yttrium by HR-ICP-MS. Precisions achieved for various rare earths and yttrium is better than 8% RSD with comparable accuracies. Limit of detection (3σ) were generally in the range of 0.02-1.2 pg/ml range for all these elements. This method facilitates rapid and interference-free determination of REE and yttrium from relatively small volume of sea water (10 ml). Recoveries for different REE and Y were better than 5%, and accuracy and precision of the determinations are within 8% RSD. The Ce-negative anomalies with smooth normalized-REE patterns obtained for both certified reference materials and samples further substantiate that the procedure adopted and the data generated are extremely accurate. A slight enrichment of heavy REE were observed in the central Indian Ocean waters which might be attributed to the river flows containing more dissolved trace elements including REE. A sharp negative Ce-anomaly in the normalized REE distribution patterns indicates that the source of REE in particular Ce in marine sediments is seawater. Results of the variation in REE concentrations with depth indicated that the physico-chemical conditions of bottom ocean water follow a very complex mechanism.