Nutrient anomalies in Fragilariopsis kerguelensis blooms, iron deficiency and the nitrate/phosphate ratio (A. C. Redfield) of the Antarctic Ocean
DeBaar, HJW × VanLeeuwe, MA Scharek, R Goeyens, Leo Bakker, KMJ Fritsche, P #
Pergamon-elsevier science ltd
Deep-sea research part ii-topical studies in oceanography vol:44 issue:1-2 pages:229-&
During seasonal development of blooms in the Polar Frontal region, concentrations of nitrate and phosphate decreased in surface waters. In blooms of Fragilariopsis kerguelensis at the southern rim (49-50 degrees S) of the Polar Frontal region the dissolved ratio NO3/PO4 increased from the winter value of similar to 14 to 15.8 (18 October 1992) to as high as 25 (23 November 1992). Ambient dissolved Fe in these blooms was subnanomolar compared to similar to 1.1-1.9 nM in the overall Polar Frontal region. Blooms more northerly in the Polar Frontal region were dominated by other diatoms and higher dissolved Fe (>1 nM), and showed only very modest NO3/PO4 anomalies. From nutrient inventories the biogenic pools (PON and DON) and export of settling biogenic debris would have N/P ratios as low as 4.4-6.1 compared to similar to 14 in deep Antarctic waters. Such shifts are consistent with decreasing availability of Fe for nitrate reduction, but also may be due to intrinsically low N/P in Fragilariopsis kerguelensis cells. Moreover, a low ratio DON/DOP in dissolved organic matter and enhanced recycling of N versus P cannot be excluded either.