title: Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean.
abstract: 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°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ(18)O and δ(13)C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75-200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ(18)O and δ(13)C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a 'vital effect' or a higher calcification rate. An interesting pattern of increase in the δ(13)C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ(13)C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude.
authors.affiliation: Centre for Earth Sciences (CEaS), Indian Institute of Science, Bangalore-560012, India.
authors.forename: K
authors.initials: K
authors.lastname: Prasanna
authors.affiliation: Centre for Earth Sciences (CEaS), Indian Institute of Science, Bangalore-560012, India.|Divecha Centre for Climate Change, Indian Institute of Science, Bangalore-560012, India.
authors.forename: Prosenjit
authors.initials: P
authors.lastname: Ghosh
authors.affiliation: Centre for Earth Sciences (CEaS), Indian Institute of Science, Bangalore-560012, India.
authors.forename: S K
authors.initials: SK
authors.lastname: Bhattacharya
authors.affiliation: Geology and Geotechnical Engineering Division, School of Mechanical and Building Sciences, VIT University (Chennai Campus), Chennai-600127, India.
authors.forename: K
authors.initials: K
authors.lastname: Mohan
authors.affiliation: National Centre for Antarctic and Ocean Research, Vasco da Gama, Goa-403 804, India.
authors.forename: N
authors.initials: N
authors.lastname: Anilkumar
mesh_terms: D018533:Biomass; D002119:Calcium Carbonate / Q000032:analysis; D002247:Carbon Isotopes / Q000032:analysis; D002734:Chlorophyll / Q000502:physiology*; D056908:Foraminifera / Q000502:physiology*; D019156:Indian Ocean; D010103:Oxygen Isotopes / Q000032:analysis; D010788:Photosynthesis / Q000502:physiology*; D010933:Plankton / Q000502:physiology*; D054712:Salinity; D012623:Seawater; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002734:Chlorophyll; D002119:Calcium Carbonate