|Seasonal variation of nutrients and suspended biomass on a transect across Nordvestbanken, north Norwegian shelf,in 1994|
Wassmann, P.; Andreassen, I.; Rey, F. (1999). Seasonal variation of nutrients and suspended biomass on a transect across Nordvestbanken, north Norwegian shelf,in 1994. Sarsia 84: 199-212
In: Sarsia. University of Bergen. Universitetsforlaget: Bergen. ISSN 0036-4827, more
|Authors|| || Top |
- Wassmann, P.
- Andreassen, I.
- Rey, F.
Nutrient consumption in the uppermost, well-mixed 100 m of Nordvestbanken in 1994 started in March across the entire shelf. Significant nitrate reduction in the euphotic zone was reached in June at the inner and middle shelf, but not until September at the shelf edge. The variations of nutrient concentrations were generally similar for nitrate, silicate and phosphate. Increased stratification, giving rise to a pronounced nutricline around 40 m depth, was observed from August to October at the shelf edge, but not on the middle and inner shelf. The maximum carbon equivalent of cumulative nitrate consumption in the upper 100 m at the inner, middle and outer shelf was about 72,52,and 55 g C m - 2 and occurred in June,August, and July, respectively. The suspended chlorophyll a concentrations were generally low throughout the transect and never higher than 2.4 mg m -3 . Maxima were observed in June and July. Suspended phaeopigment concentrations were generally lower than 1 mg m -3 .The concentration of suspended organic carbon was moderately high, varying between about 100 to 450 mg m -3. Maxima were found in the upper 40 m from May/June to October and in the entire water column in October. New production, as reflected by the decrease of nutrients, not exactly quantifiable in the present context. Thus the carbon equivalent of cumulative NO 3 disappearance, was interpreted as a minimum approximation of the new production rate. Estimates of new production were far greater on the inner shelf than generally assumed for adjacent north Norwegian coastal waters and are probably >75 g C m - 2 y -1. However, a concomitant accumulation of large quantities of phytoplankton in the water column did not take place, probably due to grazing, as reflected by low chlorophyll a, relative high phaeopigment and high POC concentrations as well as high POC/PON ratios (about 6-16). Increased POC/PON ratios throughout the water column in March and during July and August at depths up to 40 m indicate supply of degraded organic matter from the sides or below, probably due to resuspension from the slope and the shelf bottom.