Summary
The carbon:chlorophyll a ratio (C:chl a or θ) is a sensitive indicator of physiological state in microalgae. The dependence of θ on photon flux density (PFD or I) and temperature in exponentially growing nutrient-sufficient microalgae can be described by an empirical equation with four coefficients. C:chl a increases linearly with increased light level at constant temperature and decreases exponentially with increased temperature at constant light level. Both the slope (ɛ) and intercept (θ0) of linear regressions of θ on photon flux density increase at low temperature. The intercept, θ0, increases from 6 to 40 g of carbon per gram of chlorophyll a (g C g chl a−1) between 30 and 0 °C and ɛ increases by over an order of magnitude from 004 to 1·9 g C g chl a−l m2 s μol photon−1 over the same temperature range.

Low-temperature chlorosis can be interpreted as an adaptive response in the allocation of cell resources between temperature-independent biophysical reactions involved in light-harvesting and temperature-dependent biochemical reactions. This response also reduces the potential for photoinhibitory damage at high light levels which can be exacerbated by low temperatures.

The range of values for θ in nature has not been adequately determined because of difficulty in separating phytoplankton from detritus, bacteria and microzooplankton. Based on the laboratory observations summarized in this paper, it would appear that use of a single value of θ for phytoplankton is inappropriate for ecological studies. For example, at a PFD of 50 μmol m−2 s−1, θ increases from 10 to 130 g C g chl a−1 between 30 and 0 °C under nutrient-sufficient conditions.

These conclusions are based on observations for eight diatoms, two green algae, one euglenoid and two cyanobacteria for which the appropriate data are available. In contrast to these groups, the dinofiagellates contain substantially less chlorophyll a The available data indicate that θ is about three times larger in dinoflagellates than in other algae under comparable PFDs at 20 °C. There are insufficient data available, however, to evaluate the light and temperature dependence of θ in dinoflagellates.

LIGHT AND TEMPERATURE DEPENDENCE OF THE CARBON TO CHLOROPHYLL a RATIO IN MICROALGAE AND CYANOBACTERIA: IMPLICATIONS FOR PHYSIOLOGY AND GROWTH OF PHYTOPLANKTON

Seasonal cycles of pelagic production and consumption

The marine diatom Thalassiosira jluvintilis was grown in a continuous culture system at 20°C on a 12:12 L:D cycle over a series of nutrient- and light-limited dilution rates. Bannister’s theoretical model describing nutrient-saturated growth gave an excellent fit to the light-limited data. A simple extension of the model allows description of nutrient-limited growth as well. Dark carbon loss rates were in the range lo-20% of daytime production rates at dilution rates >0.25*d-‘. The relationship hctwcen Chl n:C ratios and dilution rate was linear under nutrient limitation and independent of the type of limiting nutrient. Productivity indices under nutrient limitation were found to be a hyperbolic function of dilution rate. N:C ratios were linearly correlated with dihltion rate llnder both light and nutrient limitation, but with the regressions having opposite signs.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1980.25.3.0457

Nutrient‐ and light‐limited growth of Thalassiosira fluviatilis in continuous culture, with implications for phytoplankton growth in the ocean

Plankton primary production of the World Ocean.

Deep chlorophyll maxima (DCMs) are widespread in large parts of the world's oceans. These deep layers of high chlorophyll concentration reflect a compromise of phytoplankton growth exposed to two opposing resource gradients: light supplied from above and nutrients supplied from below. It is often argued that DCMs are stable features. Here we show, however, that reduced vertical mixing can generate oscillations and chaos in phytoplankton biomass and species composition of DCMs. These fluctuations are caused by a difference in the timescales of two processes: (1) rapid export of sinking plankton, withdrawing nutrients from the euphotic zone and (2) a slow upward flux of nutrients fuelling new phytoplankton production. Climate models predict that global warming will reduce vertical mixing in the oceans. Our model indicates that reduced mixing will generate more variability in DCMs, thereby enhancing variability in oceanic primary production and in carbon export into the ocean interior.

/pdf/reduced-mixing-generates-oscillations-and-chaos-in-the-14dlj4d4ca.pdf

Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum

Data collected on several expeditions through the temperate and tropical Pacific Ocean show that during most of the year the maximum concentrations of chlorophyll occur below the surface, typically in a narrow layer near or below the depth of penetration of 10/0 of the surface light. The layer appears to be continuous across most of the Pacific although the depth and chlorophyll concentration vary regionally. The depth of the layer is more closely related to the depth of the nitrite maximum and to the position of the nutricline than to either light or density regimes. Productivity within the layer is low but positive, and contributes substantially to the total production of the water column. The maximum layer may be a seasonal phenomenon developing in the summer after the stabilization of the water column and mixing to the surface during the winter. Year to year fluctuations of depth and concentration of chlorophyll within the maximum layer may be related to large-scale meteorological fluctuations. Doty and Capurro (1961) have tabulated the position, date, depth, and values of chlorophyll and productivity in the world's oceans. There are several thousands of these measurements in the Pacific. Most are in the Northern Hemi­ sphere, and most are near land masses or is­ lands (e.g., Hawaii, Luzon, Hokkaido, New Cal­ edonia, New Zealand), along the equator, or north of lat 40 0

J.A. McGowan

Papers

Deep maxima of photosynthetic chlorophyll in the Pacific Ocean