Water Column Primary Production Research Articles

Recent diatom record of McMurdo Sound, Antarctica: Implications for history of sea ice extent

Analyses of diatom assemblages within surface sediments from McMurdo Sound, Antarctica, document the regional circulation patterns in this large embayment in the southwestern Ross Sea. Thalassiosira spp., indicative of water column primary productivity, is most common in eastern and portions of northwestern McMurdo Sound as a result of its advection into these regions from areas of open water primary productivity. Surface sediments from southwestern McMurdo Sound are composed mainly of Nitzschia curta, a small pennate form commonly found both as a member of the sea ice microbial community as well as a dominant component in ice edge blooms in the Ross Sea. The northward advection of oligotrophic water into the western Sound from beneath the McMurdo Ice Shelf results in the dominance of an autochthonous flora in the southwestern Sound. Sediments deposited during the past 500 years also have been dominated by Thalassiosira spp. and Nitzschia curta. Thalassiosira spp. concentrations reached a maximum between 1600 and 1875 A.D., corresponding to the time of the “Little Ice Age.” More persistent winds may have been responsible for more prevalent polynyas at that time, resulting in greater amounts of open water primary productivity and subsequent higher percentages of Thalassiosira spp. Increased areal extent and/or duration of coastal polynyas during the “Little Ice Age” suggests that within the southwestern Ross Sea, the production of High Salinity Shelf Water, and hence Antarctic Bottom Water, may have been greater at that time.

Ocean primary production and available light: further algorithms for remote sensing

In the context of remote sensing of the ocean, the general problem of estimating water column production from surface irradiance and column chlorophyll concentration is examined, and some refinements are made to the linear theory presented by Platt (1986, Deep-Sea Research, 33, 149–163). Further empirical evidence is presented to show the stability of the relationship between surface light and biomass-normalized primary production of the ocean water column. A theoretical explanation is given for the non-zero intercept often obtained when these two variables are regressed. The systematic errors in the estimation of primary production by remote sensing, due to non-uniformity in the biomass profile, are examined through sensitivity analyses on a generalized biomass profile. The errors are shown to be functions of the parameters of the biomass profile, of the photosynthetic parameters and of the optical properties of the water. The probable random errors in the estimation of water column primary production using remotely sensed data are evaluated. Some general issues related to the collection and assimilation of data on ocean primary production are addressed.

WATER COLUMN PRODUCTIVITY ATTRIBUTABLE TO DISPLACED BENTHIC DIATOMS IN WELL‐MIXED SHALLOW ESTUARIES1

ABSTRACTWe attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow‐water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A perliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary, Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K‐systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity. Benthic pennate diatoms, represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well‐mixed shallow estuarine waters is often greatly aumented by displaced benthic algae.

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic bio-mass

The shelf waters of the northern Bering and Chukchi Seas are ice-covered for 7 mo of the year, but despite thls harsh environment, they are characterized by high benthic biomass. Coupling between water column primary production and the benthos was investigated in summers 1984 to 1986 by measurements of sediment characteristics in relation to those of the water column. Low surface sediment C/N ratios (5.8 to 7.6) suggested a higher quality, nitrogen-rich marine carbon supply to the benthos in the highly productive (ca 250 to 300 g C m-' yr-') Bering Shelf-Anadyr Water (BSAW) compared to lower quality, higher C/N ratios (7 7 to 14 0) in sediment under the less productive (ca 50 g C m-' yr-l) Alaska Coastal Water (ACW). Stable carbon isotope ratios suggested a manne origin for organic matter in BSAW compared to a mixture of manne and terrestrial input in ACW. Mean benthic biomass was significantly different between water locations, with mean benthic biomass decreasing from 20.2 g C m-* under BSAW to 6.3 g C m-2 under ACW Summer benthic biomass remained seasonally constant for the 3 yr. Benthic communities underlying BSAW received a high quality marine food supply on a regular basis interannually, while those in ACW received an interannually variable amount of temgenous organic matter in addition to marine organic matter. We conclude that the quality and quantity of organic carbon deposited to the benthos directly influence benthic biomass.

Phytoplankton dynamics in the central Great Barrier Reef—II. Primary production

Water column primary production was measured 43 times over a 3-year period (1983–1985) on the outer shelf of the central Great Barrier Reef province and in the adjacent East Australian Current. No seasonal production cycle could be established. Estimated daily production rates in shelf and offshore waters ranged between 0.1 and 1.5 g C m −2, with most between 0.2 and 0.7 g C m −2. Annual primary production during 1983 in mid-shelf, shelf break and offshore zones was estimated to be 183, 167 and 211 g C m −2, respectively. Annual production by the<10μm size fraction at the same sites was 114, 94 and 127 g C m −2, 62, 56 and 60% of total production, respectively. Corresponding proportions of chlorophyll standing crop in the<10μm fraction were 65, 85 and 79%. In a subset of the above experiments, picoplankton (<2μm size fraction) accounted for 37–99% of total water column production and 32–85% of the chlorophyll standing crop. At first order, annual phytoplankton plus coral reef primary production on the outer shelf in the central GBR is estimated to be 404 g C m −2, with phytoplankton contributing 37%.

Phytoplankton dynamics within Gulf Stream intrusions on the southeastern United States continental shelf during summer 1981

During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 10 1 km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area. Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m − d −1 and 75 mg m −, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO 3-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a −1 h −1), high mean α (14 mg C mg Chl a −1 Ein −1 m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters. The results imply a seasonal (June to August) middle shelf production of 150 g C m −1, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area.

Light‐Productivity Model for Onondaga Lake, N.Y.

Two models were calibrated to the 1978 primary productivity conditions of nutrient‐rich hypereutrophic Onondaga Lake, N.Y.; one was based on the approach of Bannister, the other on a more conventional format. The data base, necessary for model development, included continuously monitored incident photosynthetically active radiation (PAR), and 115 parallel measurements of water column temperature, PAR attenuation, chlorophyll a, primary productivity, and key nutrients. Values of key parameters for the Bannister model, obtained by evaluation of the data set, differed from those recommended in the literature. Both models effectively predicted seasonal and shortterm trends in primary productivity for most of the study, though the Bannister model was slightly better. The Bannister model predictions were particularly sensitive to estimates of the maximum quantum yield of photosynthesis. The Bannister model is preferred on theoretical grounds, since it incorporates more fundamental and more constant parameters, ...

Phytoplankton standing crop, primary productivity, and near-surface nitrogenous nutrient fields in the Ross Sea, Antarctica

In austral summer 1978 a study was made of the phytoplankton standing crop, primary productivity, and nutrient chemistry of the waters along a north-south transect between New Zealand and the Ross Ice Shelf and along two east-west transects in the Ross Sea. The area was characterized by a high degree of spatial biological variability, with pronounced differences in phytoplankton biomass, primary productivity, and near-surface nitrate and ammonium fields between the northern, central, and southern regions of the Ross Sea. An extensive bloom of the colonial flagelate Phaeocystis pouchetiii (Prymnesiophyceae) was encountered along the barrier edge of the Ross Ice Shelf and extended to depths of 100 to 150 m at some stations. Chlorophyll a throughout the euphotic zone along the ice shelf barrier edge averaged > 1 mg m −3, and primary productivity locally reached nearly 1 g C m −2 day −1 there. In contrast, both chlorophyll a concentration and rates of 14C uptake averaged two- to four-fold less some 200 km offshore of the Ross Ice Shelf, where P. pouchetii generally was rare. Where P. pouchetii was abundant, more than 25% of the water column primary production occurred at depths below the 1% light penetration level. Near-surface nitrate concentrations were about a third lower at the stations where P. pouchetii was abundant than at those with few or no P. pouchetii. Regionally there was a strong negative correlation between NH 4 + and chlorophyll a, suggesting that the biogenic uptake of NH 4 + by the phytoplankton controlled the distribution of NH 4 + within the euphotic zone.

Phytoplankton production and water motion in surface mixed layers

An analog, incubator technique is described to simulate the effect of vertical motions, either organized or turbulent, on the photosynthesis of phytoplankton. Experiments using this method on natural assemblages of phytoplankton in the eastern Canadian Arctic support the view that, for these stations, vertical mixing has little quantitative effect on water column primary production.

A simulation model of the effects of vertical mixing on primary productivity

A random walk stimulation model was developed to explore the effects of variations in light regimes due to vertical mixing on primary productivity. Cells were allowed to light-shade adapt on some time scale by altering chl:carbon ratios in response to variations in light regimes. Photosynthetic response was adjusted according to variations in chl: carbon ratios by either varying the initial slopes of photosynthesis-irradiance curves, or varying photosynthetic capacities. The model suggests that despite physiological adaptation to light, vertical mixing may have little effect on the integrated water column primary productivity. It is suggested that if photoinhibition does not have a pronounced effect, the average distribution of primary production in a water column is not related to variations in light regimes arising from turbulent diffusion processes.

Aspects of water column primary productivity in the Chukchi Sea during summer

Measurements of primary productivity, chlorophyll a, incident solar radiation, phosphate-P, silicate-Si, nitrate-N, nitrite-N, ammonium-N, temperature and salinity were made in the Marginal Ice Zone of the Chukchi Sea in summer 1974. Low to moderate levels of primary productivity (0.07 to 0.97 g C m-2 half-day-1) were observed; primary productivity exceeded 3 g C m-2 half-day-1 at two stations. Surface primary productivity was nitrogen-limited at most stations. Mean chlorophyll a concentration in the photic zone varied from 0.4 to 17.8 mg m-3. Higher concentrations and significant subsurface accumulation of chlorophyll a, reaching 40 mg m-3, were observed in July at stations near the ice-edge than those in open water. No chlorophyll maximum was noted in September, when values ranged from 0.4 to 2.2 mg m-3. It is postulated that the contribution of sea-ice algae to the total chlorophyll content can be substantial, but that the stay of these cells in the water column may not be long. Non-linear regression estimates from solar radiation and chlorophyll-specific primary productivity data showed a maximal photosynthetic rate of 18 mg C mg chlorophyll a -1 half-day-1, an optimal light intensity of 54 langleys half-day-1, and markedly reduced primary productivity at moderately higher light intensities. These features indicate that phytoplankton was shade-adapted.