The range and the average concentration of Fe, Mn, Ni, Co and Cr in different fractions in cores MD and SH are given in the Table 2. In core MD, Fe, Mn, Ni, Co and Cr were highest in the residual fraction. Metals viz. Fe, Ni, Co and Cr were present in more than 65 % in the residual fraction, while Mn was around 40 %. Next to the residual fraction, Mn, Ni and Co were present in the Fe-Mn oxide fraction, while Fe and Cr in the organic bound fraction. Metals viz. Fe, Ni, Co and Cr were available in least concentration in the carbonate fraction. Manganese was least in the organic bound fraction, whereas Zn in the exchangeable fraction. The concentration of Fe was the lowest in …show more content…
2b). Manganese was with high concentration in the exchangeable fraction, except between 18 and 14 cm where it showed less concentration. Manganese in carbonate and organic bound fractions was almost constant with depth, except higher value at 30 and 18 cm, respectively. Manganese in the Fe-Mn oxide phase showed slight increase from the bottom to 30 cm which was followed by a sharp decrease at 18 cm. Further, it maintained low concentration up to 10 cm and showed slightly higher values from 8 cm to surface. Sum of the bio-available phases was higher in the lower part of the core from bottom to 30 cm. From 14 cm to surface, bio-available Mn increased towards the surface. Nickel exhibited an increase in the bio-available fractions from the bottom to 18 cm. It was highest and constant between 18 and 14 cm, and then gradually decreased towards the surface. Cobalt in the exchangeable fraction increased from the bottom to 18 cm and then showed overall decrease towards the surface. Its concentration in both exchangeable and carbonate fractions was much higher between 18 and 14 cm. In the Fe-Mn oxide fraction, it decreased from the bottom to 8 cm followed by an increase towards the surface. Cobalt exhibited very high concentration at 8 cm in the organic phase. Chromium showed overall an increase from the bottom to 14 cm in exchangeable, carbonate and organic phases and then exhibited overall decrease towards the surface. The organic and Fe-Mn oxide phases showed slightly higher values between 18 and 14