Inger J. Andreassen

Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea

Large phytoplankton biomass accumulates during ice-edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophyte Phaeocystis pouchetii usually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance by P. pouchetii as opposed to periods when diatoms dominated. This alternation of P. pouchetii and diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. Although P. pouchetii contributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice-edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north-south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom- and P. pouchetii-rich phytoplankton was observed in these stations. In contrast, the station located in ice-free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom- and P. pouchetii-dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice-edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOC, than previously thought.

Distribution and sedimentation of faecal on the Nordvestbanken shelf, northern Norway, in 1994

Abstract A close seasonal coherence between mesozooplankton and abundance of faecal pellets was encountered at Nordvestbanken, northern Norwegian shelf, in 1994. Mesozooplankton at Nordvestbanken influenced the vertical flux of organic matter by production, consumption, modification, and destruction of faecal pellets. On average, 11-37% of particulate organic, vertical carbon flux was comprised by faecal pellets. The pelagic degradation of organic matter at Nordvestbanken appears to be reduced due to the low pelagic residence time in the upper 100 m of the water column of faecal pellets ( 1.3-8.3 d). The specific seasonal sinking rates of faecal pellets (12-77 m d-1)fell well into the range of in situ and in vitro sinking rates reported in the literature for the dominating classes of faecal pellets al Nordvestbanken, i.e. from calanoid copepods and pteropods. The shape, colour, density, and degree of fragmentation of faecal pellets appears to reflect variations and changir1g preferences in the diet of mes...

Contribution by mezooplankton focal pellets to the carbon flux on Nordvestkbanken, north Norwegian shelf in 1994

Abstract Fecal pellet production rates for mesozooplankton (> 500 µm) were measured monthly at a shelf edge and inshore station in northern Nonvegian coastal waters during Nlarch-September as part of the Ocean Margin Exchange (OMEX) stLrdy. The total potential fecal pellet carbon flux was higher at the inshore station except in May when Calanus finmarchicus (Gunnerus) was more abundant at the shelf edge. Mesozooplankton fecal pellets had the potential to contribute 2.5 % (April & September) to> 100% (May-August) of the POC flux found in sediment traps. This compared with only 5-35 %, when fecal pellet carbon flux was measured from trap pellets suggests that a significant amount of fecal pellet remineralization or coprophagy was occurring in the surface waters. Calanus finmarchicus apparently plays a pivotal role in moderating pellet carbon flux on Nordvestbanken both through its potential fecal pellet production and possibly through coprophagy. Carbon ingestion by the lccrge mesozooplankton at the shelf e...

Spatial variability of phytoplankton, nutrients and new production estimates in the waters around Svalbard

Phytoplankton dynamics and carbon input into Arctic and sub-Arctic ecosystems were investigated around Svalbard, in summer 1991. Phytoplankton biomass, species composition and dissolved nutrient concentrations were analysed from water samples collected along seven transects. Phytoplankton biomass was low especially to the north (Chlorophyll-a mean 0.3 μg 1-1), where flagellates dominated the communities and only ice-diatoms were present. To the west, the phytoplankton composition was representative of a summer Atlantic community, in a post-bloom state. Zooplankton grazing, mainly by copepods, appeared to be the main control on biomass to the west and north of Svalbard. In the Barents Sea (east of Svalbard), an ice edge bloom was observed (Chlorophyll-a max. 6.8 μg1 -1) and the ice edge receded at a rate of approximately 11 km day-1. The phytoplankton community was represented by marginal ice species, especially Phaeocystis poucherii and Chaeroceros socialis. South of the ice edge, Deep Chlorophyll Maxima (DCM) were observed, as surface waters became progressively nutrient-depleted. In these surface waters, the phytoplankton were predominantly auto- and heterotrophic flagellates. Carbon production measurements revealed high net production (new and regenerated) to the north of the Barents Sea Polar Front (BSFW); it was especially high at the receding ice edge (reaching 1.44g C m-1 day-1). To the south, a low level of production was maintained, mainly through regenerative processes.

Seasonal patterns in composition and biomass of autotrophic and heterotrophic nano- and microplankton communities on the north Norwegian shelf

Abstract From monthly transects on the shelf off northern Norway, data describe the size, abundance, and biomass of photosynthetic nano- and picoplankton, heterotrophic (aplastidic) nanoplankton, and ciliates. Samples were analyzed using a state-of-the-art color imaging system. The numerically dominant phytoplankton were pica- and nanoplankton. Highest biomasses occurred in summer, and increased earlier in the year and attained higher values in inshore stations compared to offshore stations. Mean cell sizes were small, 2-5μ.m diameter nanoplankton and 1μm eucaryotic picoplankton; cyanobacteria were comparatively unimportant contributors to biomass. The dominant herbivores appeared to be heterotrophic flagellates, which were generally similar in size, concentration, and biomass to the phototrophic forms. Their temporal and spatial distribution mimicked their putative prey, except that they often occurred in abundance deeper than the photosynthetic nanoplankton. Oligotrich ciliates were also abundant. The r...

Abundance and biomass of pico-, namo-, and microplankton on a transact across Nordvestbanken, north Norwegian shelf, in 1994

Abstract The seasonal variation of suspended microplankton on a transect across Nordvestbanken in 1994 revealed that pico- and nanoplankton flagellates and monads (< 2 fμm and 2-20 mμ, respectively) entirely determined total phytoplankton numbers and biomass. From March to May and from August to October nanoflagellates and monads comprised on average 90 % and up to 98 % of total phytoplankton biovolLrme. Only during the maximum diatom and dinoflagellate abundance in June and July, and during the appearance of Halosphaera viridis at selected stations on the mid shelf, did flagellates comprise less than 60-90% oftotal biovolume. In general, the abundances ofpicoplankton, coccolithophorids and Phaeocystis pouchetii were low, never comprising more than a few percent of total biovolume. The estimated total biomass of pico-, nano- and microplankton (from biovolume), phytoplankton (from chlorophyll and epifluorcscence estimates) and larger protozooplankton (from biovolmne) in the upper layers were on average 3-1...

Seasonal variaion of nutrients and suspended biomass on a transact across Nordvestbasken, north Norwegian shelf, in 1994

Abstract Nutrient consumption in the uppermost, well-mixed 100m 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 I 00 mat 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 observed in June and July. Suspended phacopigment concentrations were generally lower than 1 mg m-2 The concentration of suspended organic carbon was moderately high...

Seasonal variation of verticla flux of phytyoplankton and biogenic matter at Nordvestbasken, north Norwegian shelf in 1994

Abstract The seasonal magnitude and biochemical composition of vertical flux of biogenic matter and phytoplankton at the north Norwegian shelf break was investigated at 14 depths between 20 and 200 m depth. Data of vertical flux were collected for 24 hours at monthly intervals using free- drifting sediment traps. Samples were analysed for particulate organic carbon and nitrogen (POC and PON), chlorophyll a (Chl a), phaeopigments (Phaeo) and phytoplankton composition. Two main periods of POC and PON vertical flux were observed in May and July with sedimentation rates ∼300 mg POC m-2 d-1 at 200 m depth. During the other periods vertical flux was ∼100 rng POC m-2 d-1 at 200 m depth. Vertical flux of Phaeo and POC had maxima in concert and Phaeo was always larger than Chl a vertical flux. Chl a vertical flux was low. The largest vertical flux was recorded in the upper water column in May and June (0.4-0.7 mg Chl a m-2 d-1 at 20m) and decreased rapidly with depth. The highest Chl a flux at depth was recorded d...

Small time and spatial scale varaiability of phytoplankton biomass on the north Norwegian shelf in 1995

Abstract The temporal and spatial short-term variability of phytoplankton biomass was investigated in spring, summer and autumn in a polygon crossing the north Norwegian shelf between the two coastal banks Sveinsgnmnen and Malangsgrunnen. In addition to traditional sampling (CTD, nutrients and chlorophyll a), a remote sensing lidar technique was used to continuously investigate the phytoplankton biomass. The number of sensing spots on each of the 6 tracks through the polygon (lasting for about 18 hours) corresponded to about 100 000 sampling procedures. The penetration depth of the lidar ranged from 15 to 30m. High spatial and temporal short-term dynamics ( 1.5-2.5 nautical miles, 2 days) were recorded, apparently due to patches of phytoplankton (up to 4 times above background concentrations) observed in the study area. No strong relationship between variable water masses (as defined by temperature and salinity) and phytoplankton biomass could be established in the polygon. Care must be t8ken to interpret...