Figure 1.
Ammonium and nitrite gradients in the Eastern English Channel at 3 s intervals.
The steepest and largest gradients are at the shortest scales, those most relevant to individual phytoplankton cells.
Figure 2.
Two-dimensional (x,y) plots of nitrite (a), nitrate (b), phosphate (c) and silicate (d) concentrations estimated from an array of 10×10 syringes of 60 ml simultaneously sampled at a spatial resolution of 5 cm.
The strongest changes were 3, 7, 21 and 4-fold, respectively, for nitrite, nitrate, phosphate and silicate, and were observed over distances ranging from 5 cm for silicate (d) to 20 cm for phosphate (c).
Figure 3.
Three representative examples of 90 profiles of chlorophyll fluorescence taken over 3 months in the eastern English Channel.
They are from 23/3/04 (a), 26/5/04 (b) and 20/6/04 (c). Fluorescence measurements are in relative arbitrary units (a.u.). Expanded sections of b, showing the regularity of peak spacing (d) and the variety of peak width and height (e). The baseline is 25 times below the highest peak. Noise levels were under 200 a.u.
Figure 4.
The diatoms Coscinodiscus sp. (a–c) and T. eccentrica (d–f) with close ups of their outer surfaces (b and e) and cut away sections of the frustule showing trapping (c) and open (f) morphologies.
A schematic shows the effects of trapping (g) and open (h) morphologies, where the net nutrient flux (arrows) after a nutrient pulse passes is inwards (g) or outwards (h). The diatoms are 60 and 30 µm across. The large openings are approximately 1 µm and the small openings are 40 nm. The latter are expanded here for graphical clarity. Additional siliceous membranes with intermediate pore sizes may be present in some forms (c).
Figure 5.
Nutrient fluxes across the aerola and membrane.
In (a), the sieve plate is at the top of the aerolar opening as is seen in Coscindiscus sp. The different points show equivalent diameters for the open area of the sieve plate. The drop in flux indicates diffusion limitation. In (b), the fluxes are at the membrane surface of Coscinodiscus sp. Again, the steep drop approaching 1 s indicates diffusion limitation. In (c) the fluxes are for the open aerola of T. eccentrica at the areola and at the membrane. The absence of a drop approaching 1 s in (c) indicates no diffusion limitation. (d) is an expansion of the upper concentrations in (a). The diffusion limitation in (d) and (e) is evident with the drop in fluxes. However, comparison with (f) shows that temporarily the fluxes into the aerolar chamber are higher for the Coscindiscus sp. geometry than for the T. eccentrica geometry.