Coccolithophore Assemblage Response to Indian Monsoon-ENSO Teleconnections During the Last Century

We present a new, annually resolved coccolithophore relative abundance record (1889-1993 CE) from a laminated marine sediment core obtained from the northeastern Arabian Sea to document assemblage variations during the last century. Our analysis revealed that similar to 80% of the assemblage is composed of the coccolithophore species Gephyrocapsa oceanica, Emiliania huxleyi, and Florisphaera profunda. Hierarchical clustering of the coccolithophore data delineates time intervals (1889-1909 CE, 1910-1959 CE, 1960-1993 CE) comparable to previously reported interdecadal changes of the El Ni & ntilde;o-Southern Oscillation (ENSO)-Indian monsoon variance. We find that F. profunda (Fp%) is positively correlated with central Pacific ENSO (Ni & ntilde;o 4 and Ni & ntilde;o 3.4). Frequency analyses of Fp% match ENSO quasiperiodicity reported from instrumental data and proxy records and support the existence of previously described ENSO-Indian monsoon teleconnections. Furthermore, the increased variance of Fp% and associated decrease in marine primary productivity starting similar to 1960 CE appears to be driven by decreased upward nutrient transport linked to increased surface water stratification due to surface ocean warming. With the predicted increases in frequency and strength of central Pacific El Ni & ntilde;o as well as surface ocean warming and upper ocean stratification in the Indian Ocean over the coming century, our results imply further impacts on coccolithophores in the northeastern Arabian Sea that may have cascading effects on the marine food web and global biogeochemical cycles.