MEPS 201:73-89 (2000)  -  doi:10.3354/meps201073

Comparison of the springtime vertical export of biogenic matter in three northern Norwegian fjords

Marit Reigstad1,*, Paul Wassmann1, Tatjana Ratkova2, Elena Arashkevich2, Anna Pasternak2, Sigrid Øygarden1

1Norwegian College of Fishery Science, University of Tromsø, 9037 Tromsø, Norway
2P. P. Shirshov Institute of Oceanology, Academy of Sciences of Russia, Nakhimovsky Avenue 36, 117581 Moscow, Russia

ABSTRACT: A comparison of vertical flux of biogenic matter, phytoplankton and faecal pellets was carried out in April 1997 in 3 fjords, Ullsfjord, Balsfjord and Malangen, which exhibit different hydrographic conditions in the inner northern Norwegian coastal zone. Vertical export of biogenic matter was high (200 to 850 mg particulate organoc carbon [POC] m-2 d-1) compared to previous years, particularly that of chlorophyll a (0.9 to 22 mg m-2 d-1). Some differences in the timing and composition between the fjords were detected, but on average, vertical export in the upper 100 m was similar in all three. Average phytoplankton carbon (PPC) sedimentation was 136 mg C m-2 d-1, and it contributed 35 ± 12% to the vertical export of POC. The diatoms Thalassiosira angulata, T. nordenskioeldii, Chaetoceros socialis and C. furcellatus were by far the most important taxa, contributing on average 68% to the PPC export. Another dominant spring bloom species in northern Norwegian fjords, the colony-forming prymnesiophyte Phaeocystis pouchetii, contributed on average only 12% to the vertical PPC flux, and it was of minor importance in Balsfjord. In contradiction to previous findings in the area, vertical POC export was not dominated by faecal pellet carbon (FPC) (125 mg C m-2 d-1). While a significant export of FPC and retention of PPC was observed during the vernal blooms in 1982, 1992 and 1996 (PPC/FPC = 0.23 ± 0.02), a mismatch scenario was encountered in 1997 (PPC/FPC = 1.32 ± 0.31), resulting in large-scale vertical export of diatoms. The differences in vertical export of biogenic matter between fjords were much smaller than interannual differences. It is suggested that interannual differences in oceanic-coastal coupling, crucial for the advection of meso- and macrozooplankton from the shelf adjacent to the fjords and for grazing, are the cause for the recurrent match and infrequent mismatch scenarios.

KEY WORDS: Vertical flux · Phytoplankton · Faecal pellets · Interannual variations · Northern Norwegian fjords

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