With an annual average chlorophyll a in the mixed layer of 2.2 mg m " 3 and low nutrient levels in the euphotic zone, the lake is clearly oligotrophic.
22.
The outer margins of the wide continental shelves of Yucat�n and Florida receive cooler, nutrient-enriched waters from the deep by a process known as upwelling, which stimulates plankton growth in the euphotic zone.
23.
Since oxygen is not being produced as a byproduct of photosynthesis below the euphotic zone, these microbes use up what oxygen is in the water as they break down the falling organic matter thus creating the lower oxygen conditions.
24.
A DCM can also exist below the euphotic zone, where less than 1 % of the surface light remains and little photosynthetic growth is possible; these layers are formed by subduction of surface waters, or sinking of cells.
25.
It can provide a rough indication of the depth of the euphotic zone with a 3-fold division of the " Secchi depth ", however this cannot be used in shallow waters where the disk can still be seen on the bottom.
26.
"' Sediment traps "'are instruments used in oceanography to measure the quantity of sinking particulate ecological processes typically within the surface euphotic zone, and is of interest to scientists studying the role of the biological pump in the carbon cycle.
27.
The uppermost portion of the photic zone, where there is adequate light to support photosynthesis by phytoplankton and plants, is referred to as the euphotic zone ( also referred to as the " dysphotic zone ( dysphotic means " poorly lit " in Greek ).
28.
Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative nutrient cycle or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor.
29.
The euphotic zone is somewhat arbitrarily defined as extending from the surface to the depth where the light intensity is approximately 0.1 1 % of surface sunlight solid particles absorb and scatter light, and in coastal regions the high concentration of these substances causes light to be attenuated rapidly with depth.
30.
In 1999, using a numerical model, Huisman et al . formulated a " critical turbulence " hypothesis, based on the idea that spring blooms can occur even in deep mixed layers as long as turbulence stays below a critical value so that phytoplankton have enough time in the euphotic zone to absorb light.
