Premium
Low specific nitrate uptake rate: A common feature of high‐nutrient, low‐chlorophyll marine ecosystems
Author(s) -
Dugdale R. C.,
Wilkerson F. P.
Publication year - 1991
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1991.36.8.1678
Subject(s) - upwelling , oceanography , environmental science , nutrient , phytoplankton , ecosystem , nitrate , biomass (ecology) , chlorophyll a , marine ecosystem , geology , ecology , biology , botany
We have searched for common features of three high‐nutrient, low‐chlorophyll (HNLC) regions of interest—the Southern Ocean, the eastern equatorial Pacific, and Station P in the northeast Pacific. In each of these areas, the rates of specific NO 3 uptake, whether normalized to particulate organic nitrogen (PON) or chlorophyll, are low compared to coastal upwelling systems with comparable nutrient concentrations. When maximum values of NO 3 concentration and maximum values of PON‐specific 15 NO 3 uptake, V 15 NO 3 , are plotted together with values from coastal upwelling systems, the data diverge into a high V 15 NO 3 track for the coastal systems, and a low V 1 5 NO 3 track for the three HNLC regions which have V 15 NO 3 values consistent with oligotrophic regions and so are functionally oligotrophic. These values of V 15 NO 3 are too low to allow biomass accumulation and the formation of blooms of diatoms. One possible reason for the lack of high V 1 5 NO 3 values in the HNLC regions is that seeding of the large, fast‐growing, fast‐sinking diatoms is inadequate and primarily due to the lack of a bottom or other recirculation system to assure a supply of these diatoms to the surface regions. Grazing control limits biomass development and may function to hold V 1 5 NO 3 to low values resulting in conditions certain to appear as HNLC. Comparison with model results suggests that deep mixed layers in the Southern Ocean and at Station P may limit V 1 5 NO 3 and that in much of the eastern equatorial Pacific NO 3 concentrations are too low for V NO 3 to develop to coastal upwelling values. Strong dependence on temperature of N and C uptake in psychrophilic Antarctic phytoplankton and sea‐ice algae may be a dominant factor in constraining V 15 NO 3 to low values in the Southern Ocean. Inadequate levels of available Fe could be expected to lead to low specific 15 NO 3 uptake. However, experiments conducted to date in all three HNLC regions fail to show a response of V 15 NO 3 to Fe additions within the first few days of enclosure experiments. Si(OH) 4 concentrations are low with respect to half‐saturation values, K s for Si(OH) 4 ) in the eastern equatorial Pacific and in the Southern Ocean where surprisingly high K s values for Si(OH) 4 have been reported.