Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

• Published in: Scientific Reports
• Main Authors: Prasanna, K, Ghosh, Prosenjit, Bhattacharya, SK, Mohan, K, Anilkumar, N
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: NATURE PUBLISHING GROUP 2016
• Subjects: Centre for Earth Sciences; Indian; Southern Ocean; Planktonic foraminifera
• Online Access: http://eprints.iisc.ernet.in/53462/; http://eprints.iisc.ernet.in/53462/1/Sci_Rep_6_21533_2016.pdf; https://doi.org/10.1038/srep21533

Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45 degrees E and 80 degrees E and 10 degrees N to 53 degrees S) were analysed and compared with the equilibrium delta O-18 and delta C-13 values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within similar to 0.25% for the region between 10 degrees N and 40 degrees S and 75-200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40 degrees S to 55 degrees S), however, the measured delta O-18 and delta C-13 values are higher than the expected values by similar to 2% and similar to 1% respectively. These enrichments can be attributed to either a `vital effect' or a higher calcification rate. An interesting pattern of increase in the delta C-13(DIC) value of the surface water with latitude is observed between 35 degrees S and similar to 60 degrees S, with a peak at similar to 42 degrees S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the delta C-13(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude.