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Spectral Analysis in Marine Science
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Spectral analysis has been an important tool in the investigation of marine patchiness since the 1970's. The basic idea is that the total variance of a signal is partitioned as a function of frequency or sampling scale. In the figure below, high frequencies (smallest spatial sampling scales) are to the right.
The temperature spectra above shows good scaling (a straight line on a log-log graph) as expected of a passive tracer in a turbulent velocity field. Our research has found that the plankton spectra deviate from this passive turbulent regime at certain scales up to 300 m. At these scales, the spectra are much "whiter" (i.e. flatter, the slope=0) than turbulence, therefore the distributions have much greater variance at the high frequencies (small spatial scales). This deviation from turbulence is only seen in the "biological" measures (fluorescence for phytoplankton, and zooplankton biomass from an optical plankton counter and acoustics), but not in any of the "physical" measurements (temperature, salinity, turbidity etc.). Therefore the origin of the patchiness is likely biological.
Currie WJS and JC Roff. Scaling properties of coastal plankton distributions in relation to turbulence.
Relevant Publications:
- Abbott MR, Powell TM, Richerson PJ (1982) The relationship of environmental variability to the spatial patterns of phytoplankton biomass in Lake Tahoe. J Plankton Res 4: 927-941
- Cliff AD, Ord JK (1981) Spatial Processes; models and applications. Pion Ltd., London
- Denman KL, Platt T (1976) The variance spectrum of phytoplankton in a turbulent ocean. J Mar Res 34: 593-601
- Fasham, MJR (1978) The statistical and mathematical analysis of plankton patchiness. Oceanogr. Mar. Biol. Ann. Rev. 16: 43-79
- Kolmogorov AN (1941) The local structure of turbulence in incompressible viscous fluid for very large Reynolds numbers. Dokl Akad Nauk SSSR 30: 301-305
- Kolmogorov AN (1962) A refinement of previous hypotheses concerning the local structure of turbulence in viscous incompressible fluid at high Reynolds number. J Fluid Mech 13: 82
- Lekan JF, Wilson RE (1978) Surface variability of phytoplankton biomass in the surface waters of Long Island. Estuar coast mar sci 6: 239-251
- Mackas DL, Boyd CM (1979) Spectral analysis of zooplankton spatial heterogeneity. Science 204: 62-64
- Obukhov AM (1962) Some specific features of atmospheric turbulence. J Fluid Mech 13: 77
- Percival DB, Walden AT (1993) Spectral analysis for physical applications. Cambridge University Press, New York
- Platt T (1972) Local phytoplankton abundance and turbulence. Deep-Sea Res 19: 183-187
- Powell TM, Okubo A (1994) Turbulence, diffusion and patchiness in the sea. Phil Trans R Soc Lond B 343: 11-18
- Tsuda A, Sigisaki H, Ishimaru T, Saino T, Sato T (1993) White-noise-like distributions of the oceanic copepod Neocalanus cristatus in the subarctic North Pacific. Mar Ecol Prog Ser 97: 39-46