Document Type

Article

Publication Title

Limnology and Oceanography

Publication Date

1-1-2003

First Page

1521

Last Page

1534

Issue Number

4

Volume Number

48

Abstract/ Summary

In oligotrophic lakes and oceans, the deep chlorophyll maximum may form independently of a maximum of phytoplankton biomass, because the ratio of chlorophyll to phytoplankton biomass (in units of carbon) increases with acclimation to reduced light and increased nutrient supply at depth. Optical data (beam attenuation as proxy for phytoplankton biomass and chlorophyll fluorescence and absorption as proxies for chlorophyll concentration) and conventional measurements of biovolume, particulate organic carbon, and chlorophyll from two oligotrophic systems (Crater Lake, Oregon, and Sta. ALOHA in the subtropical North Pacific Ocean) are presented and show a vertical separation of the maxima of biomass and chlorophyll by 50-80 m during stratified conditions. We use a simple mathematical framework to describe the vertical structure of phytoplankton biomass, nutrients, and chlorophyll and to explore what processes contribute to the generation of vertical maxima. Consistent with the observations, the model suggests that biomass and chlorophyll maxima in stable environments are generated by fundamentally different mechanisms. Maxima in phytoplankton biomass occur where the growth rate is balanced by losses (respiration and grazing) and the divergence in sinking velocity, whereas the vertical distribution of chlorophyll is strongly determined by photoacclimation. A deep chlorophyll maximum is predicted well below the particle maximum by the model. As an interpretation of these results, we suggest a quantitative criterion for the observed coexistence of vertically distinct phytoplankton assemblages in oligotrophic systems: the vertical position at which a species occurs in highest abundance in the water column is determined by the "general compensation depth" - that is, the depth at which specific growth and all loss rates, including the divergence of sinking/swimming and vertical mixing, balance. This prediction can be tested in the environment when the divergence of sinking and swimming is negligible.

Citation/Publisher Attribution

This article was published in Limnology and Oceanography, Vol. 48, No. 4, 1521-1534, 2003

Publisher Statement

© 2003 American Society of Limnology and Oceanography, Inc.

DOI

10.4319/lo.2003.48.4.1521

Version

publisher's version of the published document

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