THE UNKNOWN GREEN FROM THE DEEP
To determine the origin of a shallow subsurface chlorophyll maximum at ca. 50 m depth
encountered at some stations along the cruise track in the northern/central part of the
survey area, two samples were provided: a net sample from the Mocness of stn. 104
(5/6/2002) from the depth horizon 25-50 m; and a water bottle sample from stn. 95 (5/5/2002)
from 58 m depth (chlorophyll maximum). For the location of these stations, refer to the
cruise protocols. It was my understanding that both stations were outside the center of
the immense shallow subsurface maximum. Both samples were preserved by Lugol's Iodine and
studied by light microscopy. All photographs taken at 400x magnification on a Zeiss
Axioskop equipped with a Nikon CoolPix 990 digital camera.
The Mocness sample contained numerous clumps of spherical cells, which appeared to be in
the process of degradation, in part highly covered by bacteria, and of dinoflagellate
origin (Figs. 1, 2). The cell clumps were entangled in a transparent organic matrix and
zooplankton, predominantly chaetognaths. Despite their unhealthy look, cells still contained
chlorophyll that may have produced the subsurface chlorophyll maximum signal of the in-situ
CTD probe. The water bottle sample (phytoplankton was enriched in Utermöhl sedimentation
chambers for inspection) contained the same spherical cells. In addition, Gymnodinium-like
dinoflagellates were quite abundant (Fig. 3A-C), as were oligotrich ciliates (Fig. 4).
Amphidinium (Fig. 3D), coccolithophorids (Fig. 3E), and the diatoms Skeletonema
sp. (Fig. 5A) and Chaetoceros sp. (Fig. 5B) were found in small numbers. Small forms
of the diatom Rhizosolenia, which were discussed in relation to the Florida black
waters, occurred only sporadicly.
Figs. 1, 2: Clumps of degrading cells from the Mocness sample. Cells appear to be of
Fig. 3 (left): Dinoflagellates at 58 m depth at stn 95. Fig. 4 (right): Ciliates at 58 m
depth at stn 95 (note that the lower left organism is a dinoflagellate; they just happened
to arrange themselves in line for the photograph). All organisms documented at same
Fig. 5: Diatoms at 58 m depth at stn 95; A = Skeletonema sp., B = Chaetoceros sp.