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On the paradox of high mesozooplankton biomass, throughout the year in the western Arabian Sea: Re-analysis of IIOE data and comparison with newer data

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Title On the paradox of high mesozooplankton biomass, throughout the year in the western Arabian Sea: Re-analysis of IIOE data and comparison with newer data
 
Creator Baars, Martien A
 
Description 125-137
The mesozooplankton
data from the northwestern Indian Ocean collected during 1962-1965 by the
International Indian Ocean Expedition (IIOE; displacement volumes from vertical
net catches, 330 μm mesh, upper 200 m) showed highest biomass in the summer
upwelling areas off Oman and Somalia but also suggested that zooplankton stocks
were relatively large outside the SW monsoon. Catches by 200 μm nets off Oman (1963/64), Yemen
(1984/85) and Somalia
(1992/93) confirmed that mean biomass during winter is considerably above the
level that is found in waters
with the typical tropical structure. In the Gulf
of Aden the NE monsoon is even the richest zooplankton season.
This is due to winter cooling, with entrainment of nutrients into the upper
layer, producing phytoplankton blooms. The relatively high zooplankton biomass

outside the
upwelling season seems less paradoxical since seasonal differences in
phytoplankton production and stock are less extreme than previously thought. On
the one hand the early 14C data underestimated primary production
outside the SW monsoon, and on the other hand the CZCS images exaggerated the
chlorophyll concentration during the SW monsoon. The productivity in the strong
Somali Current upwelling is below potential due to large advection and mixing,
and zooplankton stocks in July are probably much smaller than off Oman. Results
from an Arabian Sea model [McCreary et al.,
Prog,Oceanog. 37 (1996) 193], including zooplankton biomass and grazing,
support the observation that zooplankton development differs between subregions
and that entrainment blooms produce zooplankton peaks during the NE monsoon

as well. The IIOE data set
seems still useful for comparison with existing and recently collected data
from smaller-meshed nets, and for validation of JGOFS Arabian Sea modeling.
Displacements from 330 and 230 μm catches were strikingly similar (RV
Discovery 1963/64). In catches from hauls with a 50 μm net, the
50-300 μm fraction only added about 25% to the biomass> 300 μm (samples
without contamination by phytoplankton, RV Baldrige 1995).
 
Date 2014-01-15T08:52:51Z
2014-01-15T08:52:51Z
1999-06
 
Type Article
 
Identifier 0975-1033 (Online); 0379-5136 (Print)
http://hdl.handle.net/123456789/25688
 
Language en_US
 
Rights CC Attribution-Noncommercial-No Derivative Works 2.5 India
 
Publisher NISCAIR-CSIR, India
 
Source IJMS Vol.28(2) [June 1999]