This summit has an extensive platform to the east, whose depths reach the
euphotic layer (not shown).
During the period when resting cells were found in the Piraque Channel, the water temperature was 28.4 [degrees]C from the surface to bottom, and the data for the Secchi disk and
euphotic zone indicated availability of light at the bottom of the channel.
The R1 surface expression at 50 m deep suggests that the interaction between the eddy and topography may favor the ascent of the nutricline within the
euphotic layer and may also inject the nutrients needed to promote an increase in phytoplankton population.
The extension of the
euphotic zone achieved almost the whole water column during most part of the season, as depicted from values of [Z.sub.eu]:[Z.sub.max] (Table 1).
Based on these [K.sub.PAR] values, the depth of the
euphotic zone (i.e., 1% of surface PAR) varied between 0.35 and 2.3 m during the year (data not shown).
Because of the presence of drowned original vegetation ("paliteiros") at the sampling stations, hauls were made in the
euphotic zone as determined by Secchi disk.
The
euphotic zone is dominated by oligotrophic warm tropical waters having low productivity and primary productivity that is not uniform either spatially or temporally.
Samples were obtained by vertical integrated hauls through the
euphotic zone using nets with a mesh of 25 pm.
The
euphotic depth of the reservoirs was reduced during the entire sampling period, resulting in the nonexistence of seasonal variation in water transparency (P > 0.05).
The extension of the
euphotic zone was variable, light penetrating to the bottom in most dates in A and B, but only in August and October in C.
The extent of the
euphotic zone was calculated by multiplying the Secchi disk readings by 3.0 (Esteves, 1998).
Annual flux of dissolved organic carbon from the
euphotic zone in the northwestern Sargasso Sea.