@ 1980, by the American Society of Limnology and Oceanography, Inc. Nitrate and ammonium uptake in Antarctic waters1

• Main Author: Robert J. Olson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Holm-Hansen; Pacific; Ross Sea; Scotia Sea; The Antarctic; Antarc*; Antarctica
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.501.8943; http://www.aslo.org/lo/toc/vol_25/issue_6/1064.pdf

Nitrate and ammonium uptake rates were measured by the 15N tracer technique in Antarctic waters. The ratio f= NOs- uptake NOs- uptake + NH4+ uptake averaged 0.54 in the Scotia Sea in early spring and 0.40 in the Ross Sea in summer, indicating that NO,- and NH4+ contribute about equally to primary production in these regions and that a large proportion of the primary production is exported from the surface layers. Uptake rates in laboratory experiments increased with increasing temperature and the relative uptake of NH,+ was positively correlated with increasing mean ambient NH,+ concentration and depth in the water column. A common image of the Antarctic ma-rine ecosystem is one of large herbivore and carnivore stocks supported by vast pastures of phytoplankton, these in turn made possible by the massive upwelling of nutrient-rich waters around the edges of the continent of Antarctica. Early workers emphasized the richness of the phytoplankton crop (Hart 1934), but more recent work with 14C uptake measure-ments has shown that the rate of primary production is quite low, being compara-ble to oligotrophic areas such as the cen-tral North Pacific gyre on an annual basis (El-Sayed 1967; Holm-Hansen et al. 1977b). The idea of a short and direct food chain (e.g. diatoms-krill-whales) was proposed to account for the prodigious production of higher trophic levels in the Antarctic (Murphy 1962). The clarification and interpretation of these observations is complicated by a lack of knowledge of the fate of primary production. Turnover rates for the higher trophic levels are unknown, and hence their impact on and utilization of the pri-mary production is also unknown. The trophic levels may be coupled tightly so that primary production is recycled quickly; alternatively, losses by sinking