Respiration, mineralization, and biochemical properties of the particulate matter in the southern Nansen Basin water column in April 1981

Determinations of the activity of the respiratory electron transport system (ETS), during the FRAM III expedition permit us to estimate oxygen utilization rates (RO2) from the surface to 2000 m under the polar pack ice in the Nansen Basin just north of Svalbard (83°N, 7°E) during April 1981. We found RO2 at in situ temperatures ranging from 20 pM O2 min−1 just below the ice to 0.2 pM O2 min−1 at 2000 m. These rates are low compared to most other ocean regions, but they could decrease particulate organic carbon and nitrogen by 76% and 74%, respectively, over a period of ∼6 months. The RO2 calculations based on measurements made at 0 °C yielded a power function of RO2 vs. depth (Z) of RO2=67Z−0.5534. When this RO2 profile was superimposed on a more recent oxygen utilization rate profile made using the 3He–3H–AOU method (OUR), in the same vicinity of the Nansen Basin during 1987 (OUR=52Z–0.4058, [Zheng, Y., Schlosser, P., Swift, J.W., Jones, E.P., 1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]), the agreement of the two profiles was close. On one hand, this was to be expected because RO2 is the biological basis of OUR, on the other hand, it was a surprise because the methodologies are so different. Nitrate mineralization obtained from ETS activities also compared favorably with calculations based on the data of Zheng et al. [1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]. Chlorophyll ranged from 6 ng L−1 at 5 m to 0.06 ng L−1 at 2000 m. Particulate organic carbon (POC) decreased from 0.93 μM C just below the ice to less than 0.4 μM C at 500 m. Particulate organic nitrogen (PON) was not detectable below 70 m, however in the upper 70 m it ranged from 0.16 to 0.04 μM N. The C/N mass ratio over these depths ranged from 5.8 to 11.3. Annual carbon productivity as calculated to balance the total water column respiration was 27 g C m−2 y−1. The integrated respiration rate between 50 and 4000 m suggests that exported production and carbon flux from the 50 m level was 24 g C m−2 y−1. These are minimal estimates for the southern Nansen Basin because they are based on measurements made at the end of the Arctic winter.