Diel periodicity of nitrogen uptake by marine phytoplankton in nitrate-rich environments

Journal Article · Sun Dec 01 04:00:00 EST 1991 · Limnology and Oceanography; (United States)

DOI:https://doi.org/10.4319/lo.1991.36.8.1689· OSTI ID:6994347

Cochlan, W P ^[1]; Harrison, P J ^[2]; Denman, K L ^[3]

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1. Scripps Institution of Oceanography, La Jolla, CA (United States)
2. Univ. of British Columbia, Vancouver (Canada)
3. Dept. of Fisheries and Oceans, Sidney, British Columbia (Canada)

It has been suggested that daily measurements of NO{sub 3}{sup {minus}} uptake by phytoplankton are indicative of the magnitude of flux of organic matter from the surface layers to the deep ocean. The authors used the {sup 15}N tracer technique to examine the magnitude of diel periodicity in the uptake of nitrogenous nutrients by microplankton in nutrient-rich environments of the oceanic subarctic Pacific and an upwelled plume off the British Columbia coast. In the subarctic Pacific, specific NO{sub 3}{sup {minus}} uptake rates, calculated at 3-h intervals for 24 h, demonstrated a clear diel pattern; average nighttime rate was about half the average daylight rate. Off British Columbia, drogued drifter buoys were used to guide repeated sampling of the euphotic zone of an upwelled plume at 6-h intervals for >48 h. Specific rates of NO{sub 3}{sup {minus}} and NH{sub 4}{sup +} uptake by phytoplankton from the near-surface and the 30% I{sub 0} light depth showed pronounced diel periodicity, whereas uptake rates of N were more or less constant over the day-night cycle at the bottom of the euphotic zone (1%I{sub 0}). The average nighttime rates of the upper waters were 15-16 and 30-36% of the NO{sub 3}{sup {minus}} and NH{sub 4}{sup +} daylight rates. The results differ from several previous diel studies in that both NO{sub 3}{sup {minus}} and NH{sub 4}{sup +} uptake demonstrated definitive diel cycles with the magnitude of periodicity in NH{sub 4}{sup +} uptake being similar to that of NO{sub 3}{sup {minus}} uptake. The authors also found that NO{sub 3}{sup {minus}}, not NH{sub 4}{sup +}, seems to be the preferred source of N during daylight, while NH{sub 4}{sup +} is preferred at night. Estimates of daily NO{sub 3}{sup {minus}} uptake rates extrapolated from short-term incubations may considerably underestimate the magnitude of the biological pump, depending on the magnitude of diel periodicity in NO{sub 3}{sup {minus}} uptake.

• OSTI ID: 6994347
• Journal Information: Limnology and Oceanography; (United States), Journal Name: Limnology and Oceanography; (United States) Vol. 36:8; ISSN LIOCA; ISSN 0024-3590
• Country of Publication: United States
• Language: English

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