An application of wavelet analysis to paleoproductivity records from the Southern Ocean

We have performed wavelet analysis of the paleoproductivity records from the southeastern Atlantic sector of the Southern Ocean. In particular, we have applied a continuous wavelet transform to the phosphorus-to-titanium (P/Ti) ratios obtained from the Ocean Drilling Program (ODP) Sites 1089 and 1094 over the past ∼600 kyr, and computed their wavelet power spectra in order to elucidate the spectral–temporal aspects of phosphorus deposition at these sites. Because data are unevenly sampled in time, they are first resampled using a uniform sampling interval prior to wavelet analysis. The wavelet power spectra of the P/Ti data are presented on a time-period plane from which the dominant periodicities of P export and their duration in time are discerned by visual inspection. Our results indicate that at the ODP Site 1089, the strongest P export occurs within a periodic band with the most dominant period of ∼100 kyr, which corresponds to the eccentricity period of Milankovitch cyclicity. On the other hand, at the ODP Site 1094, which is completely covered with ice during the glacial times, the strongest periodicity of P export is found to be around 82 kyr. This periodicity is twice the period of the 41-kyr Milankovitch obliquity cycle, implying that obliquity forcing drives the productivity at this site in a period doubling scenario. Given the strong influence of ice cover at this site, another implication is that sea ice extent itself is strongly influenced by the obliquity signal, and productivity simply responds to the availability of ice-free conditions. We have also performed wavelet analysis of the carbonate production data at the ODP Site 1089, and found a dominant periodicity of ∼100 kyr. In addition, a few weaker decadal-scale periodicities are observed in both P/Ti and carbonate data which can be linked to Milankovitch cycles.