Using non-linear analysis to compare the spatial structure of chlorophyll with passive tracers

A form of non-linear analysis, termed the near-neighbour algorithm, was applied to transects of chlorophyll and salinity collected off eastern Antarctica in the Austral summer of 1995/96. The near-neighhour algorithm was initially developed to detect chaos in time series, but was applied here to compare the spatial structure of chlorophyll, a non-conservative tracer, with that of a conservative tracer, salinity. The validity of such an application is discussed in the context of the literature and as a complementary approach to traditional methods such as autocorrelation and spectral analysis. The results indicate that the spatial structure of salinity could be classified as non-linear in nature. The structure of chlorophyll at corresponding spatial scales contains a stochastic component, and it is postulated that this is caused by biological factors, specifically net phytoplankton growth. The potential for expanded, more detailed analyses is discussed, and parallels are drawn between the current state of non-linear analysis in biological oceanography and the development of spectral analysis over the last three decades.