W. G. Harrison

Vertical flux of respiratory carbon by oceanic diel migrant biota

Interzonal diel migrant plankton and nekton obtain organic carbon by feeding at night above the main pycnoline of subtropical and tropical oceans, and respire part of it by day in the interior of the ocean below the pycnocline. Using data from seven oceanic stations, and conservative models to compute respiration at depth, we show that this flux of respiratory carbon ranged from 20 to 430 mg C m−2 d−1 or 13–58% of computed particulate sinking flux across the pycnocline. If this flux occurs consistently between 50°N and 50°S, it will add about 5–20% (depending on method of calculation) to current estimates of global sinking flux of organic carbon across the pycnocline.

Photosynthesis-irradiance relationships in polar and temperate phytoplankton populations

SummaryAnalyses of some 700 photosynthesis-irradiance (P-I) experiments made on natural marine phytoplankton assemblages in over six years of field work are summarized. Observed variations in P-I parameters are discussed in relation to geographical location, sample depth and temporal cycles (diel to interannual). Results suggest that P-I characteristics and therefore regional primary production are largely under physical control; temperature and light appear to be the most important environmental covariables.

Photosynthesis and photoadaptation of marine phytoplankton in the arctic

Abstract In Baffin Bay, phytoplankton populations from the 1% light level were susceptible to photoinhibition whereas populations from the 50% light level were not. Both the initial slope of the light saturation curve and the assimilation number were smaller for the deep samples than for the shallow ones. The optimal irradiance for photosynthesis by the near-surface populations was comparable to the maximum irradiance to which they might be exposed in situ , but that for the populations near the bottom of the photic zone was higher than the populations could experience in situ . The general magnitudes of the photosynthesis parameters for these late summer arctic populations fell towards the low end of the range observed in temperate waters.

Nutrient Regeneration and Primary Production in the Sea

Planktonic photoautotrophs account for virtually all of the primary organic production in the world’s oceans (1). Requirements for light restrict their growth to the upper 100 m or so, where essential micronutrient (N, P, Si, etc.) reserves are normally sufficient for sustaining growth for only short periods of time. As a consequence, continuous nutrient resupply from external and internal sources is required. Estimates of global nutrient fluxes (Table 1) have clearly shown that external nutrient inputs (riverflow, rainfall) can account for less than 1% of the annual nutrient requirements for oceanic primary production. Almost all required nutrients come from internal recycling. Internal sources can be further subdivided into in situ (principally, upper 100–200 m) regeneration and allochthonous inputs from deep ocean reserves by upwelling and eddy diffusion. Recent estimates (4) suggest that about 20% of the nutrient requirements come from the latter source, leaving 80% from regeneration in situ.

Biomass and production of bacteria and phytoplankton during the spring bloom in the western North Atlantic Ocean

During the 1989 spring bloom in the western North Atlantic, we estimated the biomass and productivity of bacteria and phytoplankton at two sites (40 and 45°N) representing different water masses. At 40°N, almost all of the phytoplankton carbon could be accounted for by photosynthetic nanoplankton and picoplankton; in contrast, at 45°N, only about half was thus accounted, implying a substantial contribution by photosynthetic microplankton. At both sites, bacterial abundance was quite high (up to 2 × 109 cells l−1), and the rates of bacterial production assessed by incorporation of [3H]thymidine (up to 8 pmol l−1 h−1) and [3H]leucine (up to 240 pmol l−1h−1) were significant. Specific growth rates of bacteria based on [3H]thymidine incorporation were 0.08–0.25 day−1. Taken together, our measurements and assumptions implied a demand for primary production in the order of 16–36% over the euphotic zone or 24–78% over the upper 100 m in the water column. We conclude that ultraphytoplankton and bacteria played significant roles in the flux of carbon during the 1989 North Atlantic spring bloom.

The distribution and metabolism of urea in the eastern Canadian Arctic

Urea concentrations, uptake, and excretion were measured at various locations in northern Baffin Bay and surrounding waters during the summer of 1980. Concentrations were variable ( 2.00 mg-at. N m−3) but followed patterns of decreasing concentration with depth in the euphotic zone and with distance from land. Urea accounted for > 50% of the total dissolved nitrogen in the upper mixed layer at most stations. Urea uptake rates showed generally the same distributional patterns as did concentrations and on the average accounted for 32% of the total nitrogen (NO3− + NH4+ + urea) productivity in the eupholic zone. Ammonium, and frequently NO3−, were utilized in preference to urea. Dual isotope (14C and 15N-urea) labelling experiments suggested that most urea-C was respired as CO2 while 50 to 80% of the urea-N was incorporated by the phytoplankton. Excretion measurements suggested that the four dominant macrozooplankton species (Calanus hyperboreus, C. finmarchicus, C. glacialis, and Metridia sp.) supplied only −3% of the urea-N but –40% of the NH4+-N requirements of the primary producers.

Chlorophyll, bacteria and picophytoplankton in ecological provinces of the North Atlantic

A comparative ecology of chlorophyll, bacteria and picophytoplankton is presented for seven ecological provinces in the North Atlantic. Depth-integrated standing stocks of these biota were measured from boreal polar to subtropical gyral regions. Averaging over all sampling times and locations within each province, it appeared that the integrated biomass of bacteria did not exceed that of phytoplankton in any province. Although this biomass ratio often exceeded unity in surface waters of the subtropical gyral provinces, the ratio for the upper water column as a whole was lowered by the subsurface chlorophyll layer. Bacteria and picophytoplankton, as the potential food resource of micrograzers, appeared to complement each other such that their total biomass did not vary much more than 2-fold amongst the seven provinces. Characteristic parameters of the biotic depth profiles, namely surface concentrations, integrated stocks and depth of maximum, were used to cluster the provinces. The original classification of provinces based on surface chlorophyll fields and characteristic regional physics was reinforced by the inclusion of bacteria and picophytoplankton.

New production at the VERTEX time-series site

Particulat organic carbon and nitrogen fluxes measured with free-floating seediment traps deployed six times over an 18-month period were combined with 14C primary production and 15N uptake measurements in order to obtain annual estimates of new production (NP) and associted f-ratios at the VERTEX time-series site. The site, located in the northeast Pacific Ocean at 33°N, 139°W, was occuped at trimonthly intervals to conduct water column studies and to recover/redeploy the sediment traps. The upper 250m of the VERTEX site exhibited considerable variability in some biological properties over seasonal time scales. While integrated photoautotrophic biomass remained relatively constant (0.57 ± 0.1 g C m−2) during the 18-month period, both integrated primary production and particulate ATP varied approximately 2.5-fold, ranging from 220 to 550 mg C m−2d−1 and 0.6–1.5 g C m−2, respectively. There was also considerable variation in both NP and f-ratios over the 18-month sampling period, although most of the NP variability was associated with short-term (i.e <72 h) estimates. Despite the relatively large range in NP values derived from 72 h sediment trap deployments and the 15N tracer work (18–179 mg C m−2d−1), no clear relationship between NP and primary productivity was found. However, the f-ratio appeared to be inversely related to primary production, with lowest estimates obtained during the period of highest productivity. Values of annual NP derived from various estimates were remarkably similar ranging from 13–17 g C m−2y−1. The average annual f-ratio ranged from 0.11 to 0.14.

The western North Atlantic bloom experiment

An investigation of the spring bloom was carried out in the western North Atlantic (40–50°W) as one component of the multi-nation Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment (NABE). The cruise track included an extended hydrographic section from 32 to 47°N and process studies at two week-long time-series stations at 40 and 45°N. Biological and chemical data collected along the transect indicated that the time-series stations were located in regions where the spring bloom was well developed; algal biomass was high and surface nutrient concentrations were reduced from maximum wintertime levels. Despite similarities in the vertical structure and magnitude of phytoplankton biomass and productivity, the two stations clearly differed in physical, chemical and other biological characteristics. Detailed depth profiles of the major autotrophic and heterotrophic microplankton groups (bacteria, phytoplankton, microzooplankton) revealed a strong vertical coherence in distribution at both sites, with maximum concentrations in the upper 50 m being typical of the spring bloom. Ultraplankton (< 10 μm) were an important component of the primary producers at 40°N, whereas larger netplankton (diatoms, dinoflagellates) were more important at 45°N. Silicate depletion was clearly evident in surface waters at 45°N, where diatoms were most abundant. Despite the relative importance of diatoms at 45°N, dinoflagellates dominated the biomass of the netplankton at both sites; however, much of this community may have been heterotrophic. Bacterial biomass and production were high at both stations relative to phytoplankton levels, particularly at 45°N, and may have contributed to the unexpectedly high residual ammonium concentrations observed below the chlorophyll maximum layer at both stations. Microzooplankton grazing dominated phytoplankton losses at both stations, with consumption as high as 88% of the daily primary production. Grazing losses to the mesozooplankton, on the other hand, were small (<10%), but mesozooplankton contribution to the vertical flux of organic matter (fecal pellets) was important at 45°N. F-ratios estimated by 15N tracer methods and sediment trap fluxes were similar and suggeste that ∼30% of the daily primary production was lost by direct sedimentation during the observation period. Numerous similarities in bloom characteristics were noted between the western and eastern Atlantic study sites.

A comparison of nitrogen assimilation rates based on 15N uptake and autotrophic protein synthesis

Abstract A comparison of nitrogen assimilation rates based on uptake of 15 NH 4 + and incorporation of 14 CO 2 into protein at three stations near the Hawaiian Islands indicates that heterotrophic processes accounted for at least 50 to 75% of the NH 4 + uptake. These results suggest that bacteria may compete effectively with phytoplankton for inorganic nutrients in the sea.