Pelagic nutrient and energy transfer during spring in the open and coastal Skagerrak

Abstract

In May 1987 multidisciplinary investigations focusing on die1 variations were performed at 4 horizontally stratified (pycnocline at 5 to 12 m) stations in the open Skagerrak (North Sea). Nutrients were lower above the pycnocline than below. Phytoplankton was numerically dominated by flagellates and monads indicating a regenerating plankton community, which was confirmed by the finding that about 80 % of the nitrogen uptake in surface waters was as NH4+ and urea, and about 20 O/O was N o 3 -Percentage of 'new' primary production (based on NOII-uptake) was similar to the percentage sedimentation rate (in C) of primary production (ca 20%). Growth of bacteria and grazing on bacteria were systematically dependent on time of day above, in and below the pycnocline. Abundance of bacteria and nanoflagellates was not regularly dependent on time of day, but systematically elevated in the pycnocline, as was chlorophyll a. Zooplankton grazing in the surface water was highest at night and early morning. Benthic investigations indicated heterogeneity in the area For comparison, samples of hydrography, nutrients, phytoplankton abundance and growth, and sedimentation were investigated at the same bme at a coastal station with horizontal stratification and slightly lower salinity. Here 'new' primary production was estimated to about 50 % of total production, based on percentage sedimentation. Nitrogen seemed in general to be in deficit for primary production relative to phosphorus in surface waters both in the open and coastal Skagerrak, but exceptions could occur That nutrients were in surplus just below the shallow pycnocline shows, however, that those primary producers and bacteria whi.ch could utilize this reservoir had access to unlimited nutrient resources at that time. It was estimated that bacteria and flagellates made up > 5 0 % of total pelagic respiration and consumed slightly more than the net primary production.

Cycling of marine dissolved organic matter. I. An experimental system

“…A regression analysis of the compiled mean values failed to demonstrate significant trends with time (p > 0.05) of the measured parameters in any of the 5 different culturevessels (except for nitrate in the B2 vessel, see 'Inorganic nutrients' below). In the B. vessel bacterial numbers reached 1.10 X 10q with minor variations around the mean (SD + 0.14 X 109, which is consistent with in situ numbers in surface water in the Skagerrak (Rosenberg et al 1990). Bacterial and flagellate numbers in the other vessels also displayed the same stable conditions (Table 1).…”

Partition of planktonic respiratory carbon requirements during a phytoplankton spring bloom

“…Our use of GF/C filters with a 1.2 µm pore size compared to the 0.7 µm pore size of GF/F filters would reduce the retention considerably, although we have no data support this assumption. Thus, a substantially lower retention of 51% would only marginally affect our results.The average respiratory CR of microzooplankton and nanoplankton in Mesocosms B and C exceeded 50% of PP, while bacterioplankton consumed less, with the highest overall consumption of 50% mainly occurring in Mesocosm F. This is similar to the open Skagerrak (North Sea), where bacteria and flagellates made up > 50% of total pelagic respiration and consumed slightly more than the net PP (Rosenberg et al 1990). Similarly, microzooplankton were estimated to consume 33 to 43% of the daily PP, in environments varying from estuarine to oceanic and from tropical to polar (Calbet & Landry 2004).…”

Annual study of bacterioplankton community dynamics

“…3). Also the data from diel and depth-profile studies performed in the Gulf of Bothnia, the Skagerrak, and the Mediterranean Sea (Wikner et al 1990;Rosenberg et al 1990;Hagstriim et al 1988) followed this relationship (Table 2, Fig. 3).…”