Dm. Wolgast et al., NITRATE RESPIRATION ASSOCIATED WITH DETRITAL AGGREGATES IN AEROBIC BOTTOM WATERS OF THE ABYSSAL NE PACIFIC, Deep-sea research. Part 2. Topical studies in oceanography, 45(4-5), 1998, pp. 881-892
Rates of nitrate utilization in tube core respirometers (TCR) placed o
ver aggregates on the seafloor at an abyssal site (Station M) in the e
astern North Pacific Ocean increased at times of high particle flux. I
n the presence of aggregates, both oxygen and nitrate were used in res
piration. The ratio of O-2:NO3 concentrations in ambient waters was 3.
9, while O-2:NO3 utilization rates in TCR overlying and TCR aggregate
pore waters were 2.6 and 0.6, respectively. We postulated that denitri
fication was occurring in microzones of the particle-rich oxygenated (
135 mu M) waters. To test this, nitrate respiration was measured aboar
d a ship in oxygen-minimum( similar to 26 mu M) water supplemented wit
h particulate matter collected by a surface net tow. Disserved oxygen
consumption occurred immediately, followed by nitrate utilization whil
e oxygen was still present. Calculations from cell densities indicated
0.6 mu M of the original 42 mu M of nitrate was assimilated into bact
erial biomass during 36 h of incubation, suggesting the major portion
of the utilized nitrate was used in respiration. Nitrate utilization r
ates in the in situ incubation study and those of the shipboard experi
ment were 3.1 and 2.7 mu M d(-1), respectively. The results of the pre
sent studies suggest nitrate respiration occurs in microzones of aggre
gates in oxygenated bottom waters at times of high particle flux and c
auses some loss of fixed nitrogen. (C) 1998 Elsevier Science Ltd. All
rights reserved.