Integrated Primary Production Research Articles

Anomalous hydrographic and biological conditions in the northern South China Sea during the 1997–1998 El Niño and comparisons with the equatorial Pacific

It is demonstrated that weakened wind mixing and strengthened water column stratification resulted in the anomalously low sea surface chlorophyll in the northern South China Sea during the 1997–1998 El Niño event. Remotely sensed sea surface temperature, wind and chlorophyll, which were validated by shipboard observations at the SouthEast Asian Time-series Study (SEATS) station (18°N, 116°E) in the northern South China Sea (SCS) provided the basis for this study. During the 1997–1998 winter at the SEATS station, the sea surface temperature was elevated by about 2 °C above the climatological mean, while the wind speed of the northeast monsoon was reduced from a climatological mean of 9.4 to 6.8 m/s. The concentration of surface chlorophyll- a dropped from 0.2 to 0.1 mg/m 3. The monthly area-averaged integrated primary production estimated for the northern SCS area (112–119°E, 15–21°N) was reduced by about 40% of the normal winter value. Under the anomalously high sea surface temperature and weak monsoon, the mixed-layer depth would have been reduced from an average of 65 to 45 m and the nutrients in the mixed layer would have been reduced by half, according to observations at the SEATS station in more recent years. During the 1997–1998 El Niño event, the onset of warming in the northern SCS lagged behind that in the eastern equatorial Pacific by about 5 months and lingered for 11 months. This course of change resembled that of the western Pacific warm pool region. However, contrary to the northern SCS, the sea surface chlorophyll was enhanced in the warm pool region during the event, probably mainly because of the uplifted nutricline. Unlike the eastern equatorial Pacific, the dramatic recovery of biological production did not happen in the SCS in the summer of 1998. These distinctive biogeochemical responses reflect fundamental differences between the SCS and the equatorial Pacific in terms of upper water column dynamics.

The significance of phytoplankton photo-adaptation and benthic–pelagic coupling to primary production in the South China Sea: Observations and numerical investigations

The primary production in the South China Sea (SCS) has been assessed by a coupled physical–biogeochemical model with a simple NPZD ecosystem [Liu et al., 2002. Monsoon-forced chlorophyll distribution and primary production in the SCS: observations and a numerical study. Deep-Sea Research I 49(8), 1387–1412]. In recent years there have been an increasing number of observations in the SCS that may be used to check the validity of the previous approach. The coupled model of the SCS mentioned above employs a photo-adaptation scheme for the phytoplankton growth and uses the simplest bottom boundary condition of an inert benthic layer. These adopted schemes are checked against observations at the South-East Asian Time-series Study (SEATS) Station in the northern SCS and in the Gulf of Thailand. Numerical experiments with or without photo-adaptation or active benthic processes are carried out in this study. Additional experiments are performed with different parameters used for these processes. The observations at the SEATS Station provide direct evidence for the variable chlorophyll-to-nitrogen ratio in phytoplankton as required by photo-adaptation. It is concluded that a photo-adaptation scheme is critical to the phytoplankton growth, especially for the development of the subsurface chlorophyll maximum (SCM). Without photo-adaptation, the average value of the vertically integrated primary production (IPP) over the whole SCS domain would be 35% lower. It is noted that, the modeled SCM occurs at depths shallower than observations due to physical as well as biological processes employed by the model. Increasing the upper limit of the chlorophyll-to-nitrogen ratio, as suggested by observations, enhances chlorophyll level in the lower part of the euphotic zone and raises primary productivity in areas with rich nutrient supply. The observed values of the IPP in the Gulf of Thailand clearly demonstrate the importance of the benthic–pelagic coupling to the nutrient cycle. Without benthic nutrient regeneration the model grossly underestimates primary production due to failure to build up the nutrient reserve in the Gulf. On the other hand, a fully regenerated flux of particulate organic nitrogen at the sea floor without denitrification produces too strong a primary production. The improved model uses a higher upper limit for the chlorophyll-to-phytoplankton ratio of 3.5 g Chl/mol N and adopts benthic processes of a coupled nitrification–denitrification scheme with denitrification consuming 14% of the detritus flux at the bottom. The model predicts a mean annual IPP value of 406 mg C m −2 d −1 for the SCS, which is 44% higher than that predicted by the original model. The increase can be broken down to 39% attributed to the benthic nutrient regeneration and 5% to the enhanced photo-adaptation. The average IPP is 390 mg C m −2 d −1 for the basin region (>200 m) and 429 mg C m −2 d −1 for the shelf region (<200 m), both of which compare favorably with observed mean values. The model also predicts a mean nitrogen removal flux of 0.16 mmol N m −2 d −1 during denitrification for the shelf region.

Optimal primary production model and parameterization in the eastern East China Sea

Integrated primary production (IPP) datasets from the eastern East China Sea (ECS) were used to validate the depth dependent and time integrated model (TIM), the empirical model (EM), and the vertically generalized production model (VGPM). Employing constant maximum chlorophyll-a (Chl-a) specific carbon fixation rate (P opt B ), the original TIM could not explain measured IPP variance, while the low P opt B estimated using P opt B models originally embedded in the EM were responsible for original EM low estimations. The disparity between P opt B expressions originally embedded in the VGPM and that observed in this study was responsible for the low accuracy of the original VGPM. After locally tuning on the P opt B model, TIM and VGPM could predict well, whereas EM still gave low estimates. This was probably due to the fact that, unlike TIM and VGPM, EM employs a constant factor instead of a light dependent function in describing the depth of light-saturation primary production. The high accuracy of TIM was limited by the complexity of estimating many variable inputs. EM, as a simplest model, should be used with caution in the eastern ECS. Global VGPM with locally adjusted P opt B seemed to be an effective model for estimating IPP in the eastern ECS.

Phytoplankton production, biomass and community structure following a summer nutrient pulse in Chesapeake Bay

Unusually high concentrations of NH4+ (up to 10 μM) were observed in the surface waters of polyhaline Chesapeake Bay during July 2000, supporting elevated rates of simulated in situ integrated primary production (4.6 g C m−2 day−1) and chlorophyll-a (chl-a) specific integrated primary production (56 mg C mg chl-a−1 day−1). These rates were the highest measured in the polyhaline Bay during a 5-year sampling program. Chl-a and the percent contribution of phytoplankton >20 μm to the total phytoplankton increased after the ammonium pulse. We hypothesize that increased wind-driven mixing and a tilting of the pycnocline caused by northeast winds combined to increase the transport of NH4+ from below the pycnocline to the surface water. Summer wind and chl-a data collected in the southern Bay between 1984 and 2000 revealed that chl-a was significantly higher 2 weeks after northeast winds than in years when no northeast wind occurred. Episodic peaks in NH4+ and primary productivity resulting from wind events lasting only a few days are poorly captured by traditional shipboard surveys, but may be detected if sampling is focused on periods when wind forcing favors enhanced NH4+ transport to the surface waters. This process of introduction of NH4+ to the surface water from sediments followed by enhanced primary productivity may help explain some of the phytoplankton blooms that are observed in the polyhaline Bay and other estuaries during summer months.

Estimating Chlorophyll-a Vertical Profiles from Satellite Data and the Implication for Primary Production in the Kuroshio Front of the East China Sea

An algorithm was evaluated for estimating primary production in the Kuroshio front of the East China Sea. The algorithm involves three principal inputs: chlorophyll-a (Chl-a) vertical profile, water column photosynthetic parameter and underwater irradiance parameter. We construct empirical models for estimating those three inputs from sea surface variables accessible by means of satellite remote sensing. Types of Chl-a vertical profile were closely associated with water mass features, and sea surface temperature seemed to be a potential variable to distinguish profile types. The consequence of the deep Chl-a maximum (DCM) presence was investigated by comparing the vertically non-uniform Chl-a profile against the uniform Chl-a profile in terms of the integrated biomass and primary production estimates. Since the DCM in the frontal region occurred in a relatively shallow layer with relatively high light level, allowing intensive photosynthetic processes to take place in the DCM layer. In contrast, as the DCM in the Kuroshio region occurred in the low-light, deep layer, it contributed less to the integrated primary production. We inferred that the DCM formation is more important in the frontal region than in the Kuroshio region, as they potentially contributed within 30.9% (±9.1%) and 20.9% (±5.4%) to the integrated primary production in the frontal and the Kuroshio regions, respectively. Such different degrees in the DCM contribution was then revealed by the higher integrated primary production in the frontal region than in the Kuroshio region.

Spatial and seasonal variations of nitrate-based new production and primary production in the South China Sea

The results from eight cruises that were conducted between 2000 and 2003 are used to elucidate the spatial and temporal dynamics of both nitrate-based new production (NP) and primary production (PP) in the northern South China Sea (SCS). The spatial variation study, which was based on the results of three cruises, compares the differences among the shelf, slope and basin of the SCS in the spring and fall. Temporal (seasonal) variation was studied during eight cruises at a basin site and two shelf sites in the SCS. Nutrient enrichment experiments were conducted concurrently with field biochemical surveys to evaluate the role of nitrogen, phosphorus and iron in limiting phytoplankton growth. The results clearly show that winter was the most productive season of the year in the basin and possibly on the shelf as well. Integrated primary production (IPP) and nitrate-based new production (INP) of the basin were 0.55 and 0.26 g C m −2 d −1, respectively, in winter; 0.26 and 0.07 g C m −2 d −1, respectively, in spring; 0.19 and 0.03 g C m −2 d −1, respectively, in summer; and 0.28 and 0.05 g C m −2 d −1, respectively, in fall. The f-ratio (INP/IPP) was as high as 0.47 in winter, decreasing to 0.29–0.36 in early mid-March and 0.14–0.20 from late March to October, and fluctuated coincidentally with abundance of nitrate. The presence of nutrients in the surface layer, supporting the winter productivity, could be attributed to the shallow nitracline, which made nutrient mixing possible when a cold and strong northwest monsoon prevailed, reflecting the vital role of nitrate availability in modulating new production in the SCS. Spatial variation of INP or IPP among the basin, slope and shelf are not as obvious as the seasonal variations because of great local variability. In general, however, the shelf was more productive than the slope and the basin. In the spring, mean IPP and INP in the shelf, slope and basin were 0.72 and 0.16, 0.34 and 0.10, 0.49 and 0.15 g C m −2 d −1, respectively. In the fall, IPP and INP in the shelf and basin were 0.45 and 0.14 g C m −2 d −1, and 0.34 and 0.09 g C m −2 d −1, respectively. There exists a positive correlation between INP and IPP for the spatial data set in either the spring or the fall. f-Ratios are not statistically different between spring (0.28) and fall (0.29). While both nitrate availability and irradiance significantly modulated the spatial variations of production, effects of nitrate availability were more prevalent than light intensity. Diatoms and coccolithophores prospered in winter in the basin or on the shelf in both winter and summer, when surface water was rich in nitrate, and were more abundant than in summer in the basin when nitrate was scarce. The results of the nutrient enrichment experiments also supported the role of nitrogen availability in productivity of the SCS water. In these experiments, chlorophyll a concentration and primary productivity responded to nitrate supplementation, while iron and phosphorus supplementation did not stimulate phytoplankton growth. The predicted ratio of nitrate-based NP to N 2-fixation-based NP from Trichodesmium is greater than 50:1, indicating that nitrate derived from the subsurface water was the main source of new nitrogen, which supported phytoplankton growth in the SCS.

Small-scale study of primary productivity during spring in a Mediterranean coastal area (Gulf of Lions)

Euphotic zone concentrations of chlorophyll, NO 3 −, NH 4 + and fluxes of nitrogen ( 15 NO − 3 and 15 NH + 4 ) and carbon (H 14 CO − 3 ) were measured in the northwestern part of the Mediterranean Sea during the High-Frequency Flux (HFF) experiment. The study site (700 km 2) was investigated with a set of five daily cruises during March–May, 1997 to study the importance of short-term changes in water masses on productivity. Hydrographic data showed a transition between typical winter conditions (cold, mixed water column) and early summer (thermal stratification of surface layer) MAW (Modified Atlantic Water) predominance dominated with low NO 3 − (<0.50 μM) and chl (<1 mg m −3), low integrated primary production (IPP <400 mg C m −1 d −1) and a regeneration regime ( f-ratios∼0.30, NH 4 + uptake prevailing). This regime changed within a few weeks as a result of the intrusion of NO 3 − rich Coastal Water (CW) and offshore Levantine Intermediate Waters (LIW) onto the continental shelf. Transient CW, moved into the area and caused an increase in chl (1.5 mg m −3) and IPP (400–600 mg C m −1 d −1) in the western part of the study site. Intrusion of LIW into the euphotic layer resulted in a large increase in production (1154 mg C m −1 d −1) and f-ratios (>0.45) suggesting that production was supported by NO 3 −. Throughout the study, vertical profiles of carbon assimilation were typical for early spring with highest rates in the surface layer (45 mg C m −3 d −1 at 20 m) decreasing to <2 mg C m −3 d −1 at 60 m. Nitrogen uptake profiles exhibited similar profiles with uptake rates ranging from 10 to 75 and 45 to 220 nM d −1 for NO 3 − and NH 4 +, respectively. No increase in NO 3 − uptake was observed near the nitracline indicating NO 3 − uptake was light limited during spring. Over the course of the study, new production was estimated of 4.9 g C m −2, an exceptional low rate for a spring period.

Monitoring and modeling primary production in coastal waters:studies in Massachusetts Bay 1992-1994

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 148:155-168 (1997) - doi:10.3354/meps148155 Monitoring and modeling primary production in coastal waters: studies in Massachusetts Bay 1992-1994 Kelly JR, Doering PH During 1992-1994, we made shipboard incubations suitable for determining rates of primary production in water from Boston Harbor, Massachusetts Bay, and Cape Cod Bay (Massachusetts, USA). These measurements were part of an extensive baseline monitoring program to characterize water quality prior to diversion of effluent from Boston Harbor directly into Massachusetts Bay via a submarine outfall diffuser. Production (P) was measured using whole-water samples exposed to irradiance (I) levels from ~5 to 2000 µE m-2 s-1. P-I incubations were performed on 6 surveys a year, spaced to capture principal features of the annual production cycle. The number of stations and depths examined varied between years. There were 10 stations and 2 depths sampled in 1992-1993. In 1994, we performed in-depth studies at 2 stations (Boston Harbor's edge and western Massachusetts Bay) by sampling 4 depths. Using depth-intensive 1994 data a simple empirical regression model, using information on chlorophyll biomass, incident daily light, and the depth of the photic zone, predicted integrated primary production rates derived from P-I incubations. The regression model was virtually the same as described for other coastal waters, giving confidence in general use of the model as an extrapolation tool. Using the 1994-based empirical model, we obtained favorable comparisons with production rates modeled from 1992-1993 P-I incubations. Combining the regression model with data on chlorophyll, light, and the photic zone collected on frequent hydrographic surveys (up to 16 yr-1), annual primary production was estimated for 1992-1994. Primary production in an intensively studied region of western Massachusetts Bay (21 hydrographic profile stations in an area ~100 km2) ranged from 386 to 468 g C m-2 yr-1. For a station at the edge of Boston Harbor near Deer Island extrapolations suggested production rates of 263 to 546 g C m-2 yr-1. Based on 2 stations in central Cape Cod Bay (1992-1993 only), model extrapolations suggested an annual production of 527 to 613 g C m-2 yr-1. Analyses using incubation and modeling results suggested that production variability was strongly related to fluctuations in incident irradiance, especially at daily to seasonal time scales. Chlorophyll variability secondarily influenced production, especially at seasonal to annual time scales. Finally, we provide a case where equivalent production was achieved in environments with contrasting water quality (nutrient and chlorophyll concentrations) because of variations in the depth of the photic zone (controlled by both chlorophyll and non-chlorophyll turbidity). Comparative analyses showed that our study estimates of primary production were consistent with the literature on nutrient-rich shelf environments. In conclusion, our study validated an empirical modeling approach to determining primary production in coastal marine waters. Primary production · Monitoring · Modeling · Massachusetts Bay · Boston Harbor Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 148. Publication date: February 27, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Remote sensing of primary production—I. A comparison of empirical and semi-analytical algorithms

We have evaluated several algorithms for their ability to predict integrated primary production using remotely sensed data. Published empirical algorithms and a previously unpublished algorithm were compared using data from the Southern California Bight Study and the California Cooperative Fisheries Investigation. The algorithms also were checked using satellite-derived chlorophyll measurements, and the predicted production then was compared to the shipboard-derived production estimate. A semi-analytical algorithm was derived that predicts production based on temperature and chlorophyll. Typically, the empirical algorithms accounted for about 25–38% of the variance in integral primary production. The performance of the empirical algorithms improved when satellite pigment data were used as input. The semi-analytical algorithm explained about 69% of the variance in surface production and 38% of the variance in integral production when shipboard data were used. The algorithm only explained 6–24% of the variance when satellite data were used. The explained variance in integral production could be increased to 44% by in situ “calibration” of the algorith m.