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hundred or a thousand metres on a daily basis. The diel movements and
feeding of these fish were probably one of the key links between the
mesopelagic layer and the epipelagic zone.
Meso- and bathypelagic ecosystems
The meso- and bathypelagic systems were based predominantly on
detritus in different forms, particulate or in aggregates such as marine
snow. The detritus was colonised by bacteria, which were being grazed by
microzooplankton that in turn served as the food of macrozooplankton.
While no one understood what the impact of discharge would be, one
possible impact might be dilution: though it was not clear to what extent
macrozooplankton were filtering out particulates as they moved through the
water, if there was a lot of discharge material it could dilute what was
already a very dilute food source. Another possibility was that, as the
sediment sank rapidly through the water column, it might strip the water of
organics.
Biogeography of the CCFZ
Describing some features of the Clarion-Clipperton Fracture Zone
(CCFZ), Koslow said it seemed to straddle two biogeographic provinces and
had the characteristics of both. According to work by John McGowan 24 , who
had looked at the dominant copepod communities of the Pacific Ocean, the
two provinces corresponded to the dominant water masses and current
systems of the central tropical gyre region and the tropical equatorial Pacific
region.
Alan Longhurst 25 , looking at seasonal cycles of productivity in the
region, had seen only slight seasonality in the mixed-layer depth of the
central gyre, although there seemed to be some increase in the summer.
As Craig Smith had pointed out (chapter 3 above), this was a low
productivity system, producing about 5 grams of carbon per m² each month,
which translated to about 60 g per year. A productive zone such as the
upwelling regions of the California or Peru currents produced hundreds or
even 1000 g per year, greater by a factor of 10 or more. In the North
Pacific Equatorial Countercurrent area, the mixed-layer depth again showed
little seasonality, though with some indication of both a spring and an
autumn bloom. Thus, that the seasonality in these two regions was quite
different -- potentially a spring and autumn bloom on one side and
potentially a summer bloom on the other.
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