Annual Phytoplankton Cycle Research Articles

Annual cycle of phytoplankton in the Pacific ocean near Guatemala in relation to physicochemical parameters

Due to the lack of basic information on the behavior of the phytoplankton community of the Guatemalan Pacific, particularly of the factors that cause harmful algal blooms, monthly monitoring was performed during a year (January–December 2021), which included three hydrometeorological seasons at three sampling sites in Puerto Quetzal (Texaco Buoy, Recalada Buoy and Entre Morros Buoy) at two depths (1.5 m and 5.0 m). These sites are influenced by shipping and nearby human populations. The structure of the phytoplankton community (species composition, abundance, richness and diversity), with an emphasis on potentially toxic and non-toxic harmful species, were evaluated. A total of 53 diatom species from 26 genera and 13 orders and 42 dinoflagellate species from 14 genera and six orders were identified. No significant differences between the sampling depths and different quarters of the year were found. The comparison of the total cell abundance between the three sites showed no significant differences. The results obtained present novel information on the phytoplankton community of the Guatemalan Pacific, filling a gap in a region where algal blooms occur annually with consequent ecological impacts and human poisonings.

Phytoplankton size distributions in the western North Atlantic and their seasonal variability

AbstractPhytoplankton play a major role on Earth, impacting the global distribution and cycles of carbon, oxygen, nitrogen, sulfur, and other elements, and structuring marine food webs. One fundamental trait of phytoplankton with direct biogeochemical implications is their size, as it governs metabolic and sinking rates as well as prey–predator interactions. Phytoplankton size spans approximately 3.5 orders of magnitude (when expressed as an equivalent spherical diameter), and thus measuring the full range in size distribution of phytoplankton is challenging and rarely attempted. Here, we constructed phytoplankton size spectra by merging state‐of‐the‐art cytometry and imaging cytometry measurements that were collected in the western North Atlantic Ocean, along a latitudinal gradient (36°N to 55°N) and during different phases of the annual cycle of phytoplankton. The derived spectra show a seasonal pattern that parallels changes in phytoplankton biomass, and do not always follow a commonly assumed power‐law model. Shifts in size spectra were more pronounced in the sub‐Arctic and temperate subregions, compared to the subtropical region of the study area. We evaluated the relationships between different size groups and environmental parameters to derive ecologically meaningful size groups. Finally, to simulate Ocean Color remote‐sensing algorithms of phytoplankton size, we compared temporal variations in descriptors of the size spectra (median particle size, phytoplankton size distribution exponent) with optical size proxies derived from light absorption and attenuation; good agreement was observed in the northern sections of the study area where temporal changes in community size structure were more pronounced.

Annual cycle of phytoplankton, protozoa and diatom species from Scotia Bay (South Orkney Islands, Antarctica): Community structure prior to, during and after an anomalously low sea ice year

Deepening the knowledge on Antarctic coastal plankton and its links with environmental conditions is essential to understand the role of these organisms in the carbon and energy flow, and to detect and predict impacts of climate change. This study addresses for the first time the seasonal succession (February 2016 to April 2017) of the phytoplanktonic and protozoan communities of Scotia Bay (Laurie Island, South Orkney Islands) and covers the period of the largest negative anomaly in Antarctic sea ice coverage in the last 40 years and the lowest sea ice duration in the bay since 2012. The density and biomass of diatoms, dinoflagellates, silicoflagellates, pigmented and non-pigmented nanoflagellates, and ciliates were assessed in relation with physico-chemical and meteorological variables. Prevailing groups were diatoms in spring-summer, and nanoflagellates (pigmented and non-pigmented) and ciliates in autumn–winter. A marked contrast was found between February 2016 and February 2017 in coincidence with a time shift in the sea ice breakout (December 2015 vs. October 2016): February 2016 was dominated by diatoms (∼250 µgC l−1), whereas the bulk of biomass in February 2017 was represented by dinoflagellates (∼9 µgC l−1) and preceded in January by a massive bloom of the diatoms Odontella weissflogii, Eucampia antarctica, Thalassiosira tumida and Chaetoceros socialis (90% of total diatom biomass: ∼687 µgC l−1). The bloom occurred in association with an event of intense wind followed by days of relative calm. The strong 2015/2016 El Niño and a positive SAM coincided with a late 2015 sea ice breakout and a short productive period in Scotia Bay (January-March 2016), while the early breakout in 2016 occurred during a negative SAM and lead to a more extensive productive period (October 2016-January 2017). Future studies should cover interannual scales in order to understand feedbacks in the structure of microbial communities and environmental forces acting in normal and atypical conditions.

Phytoplankton and environmental drivers at a long-term offshore station in the northern Adriatic Sea (1988–2018)

A long term (1988–2018) data set of phytoplankton and physico-chemical parameters was analyzed for the first time in an offshore station of the LTER Senigallia-Susak transect (northern Adriatic Sea) not directly affected by the coastal nutrient input. The mean annual cycle of phytoplankton markedly differed from that observed in the coastal areas, showing the maximum in June and the minimum in November. The main component of phytoplankton community was represented by phytoflagellates, whose trend paralleled that of total phytoplankton. On average, diatoms peaked in July, dinoflagellates in June and coccolithophores in April. The phytoplankton maximum in summer is explained mainly by the allochthonous input of DIN and PO4 carried by the low salinity waters expanding eastward, during the stratification of water column. Resuspension processes seem to be less effective for PO4 than for DIN. The most representative phytoplankton taxa for each season as indicated by the IndVal analysis were identified and were only in part similar to those observed in the coastal area. The interannual anomaly trend showed a significant increase of temperature, DIN and phosphates. Although no significant changes were found for the total phytoplankton, a reduction of winter dinoflagellate and coccolithophore abundances was observed.

Variability of phytoplankton biomass and environmental drivers in a semi-enclosed coastal ecosystem (San Matías Gulf, Patagonian Continental Shelf, Argentina) using ocean color remote sensing (MODIS) and oceanographic field data: Implications for fishery resources

Annual cycles of phytoplankton biomass (using chlorophyll-a as a proxy) and seasonal patterns of environmental drivers were analyzed in a semi-enclosed coastal ecosystem (San Matías Gulf, SMG, Patagonian Continental Shelf, Argentina). Monthly climatologies (2003–2014) of satellite images of chlorophyll-a (Chla-sat), sea surface temperature (SST), photosynthetically available radiation (PAR), and euphotic depth (Z 1% ) were analyzed using Principal Component Analysis (PCA). Satellite environmental variables were evaluated together with oceanographic field data (temperature, nitrate, and chlorophyll-a). Thus, this study analyzes the Chla-sat data to describe the spatio-temporal distribution of the phytoplankton biomass in the SMG and investigates its relationship with the regional environmental drivers. Two contrasting phytoplankton annual cycles characteristic of these temperate waters were distinguished. PCA discriminated the inner and outer areas separated by a complex frontal system. The gulf's inner waters showed a bimodal phytoplankton cycle (maximums in autumn and spring) associated with the seasonal stratification of the water column in deeper areas and the consequent nitrate limitation in summer. The outer waters adjacent to the continental shelf showed unimodal cycles (maximum in autumn or spring) linked to the vertical mixing of the water column in shallow areas with moderate light intensity and nitrate availability. For both annual phytoplankton cycles, light is the main limiting factor in winter. Finally, the analyzed environmental patterns suggest that a tidal front favor feeding and spawning fishery resources in the north of the gulf. • Twelve years of chlorophyll-a MODIS data are analyzed in San Matías Gulf. • Environmental data from satellite and oceanographic cruises are investigated. • A frontal system separated two contrasting annual cycles of phytoplankton biomass. • Oceanographic features are favorable for feeding and spawning of fisheries resources.

Ecology and seasonality of Pseudo-nitzschia species (Bacillariophyceae) in the northwestern Adriatic Sea over a 30-years period (1988–2020)

The ecology and seasonality of Pseudo-nitzschia species and their contribution to phytoplankton community were analysed for the first time at the coastal station of the LTER-Senigallia-Susak transect (north-western Adriatic Sea) from 1988 to 2020. Species composition was addressed using DNA sequence data obtained from 106 monoclonal strains isolated from January 2018 to January 2020. The mean annual cycle of total phytoplankton in the study period (Feb 1988–Jan 2020) showed maximum abundances in winter followed by other peaks in spring and autumn. Diatoms were the main contributors in terms of abundance during the winter and the spring blooms. The autumn peak was due to phytoflagellates and diatoms. In summer phytoflagellates dominated the community, followed by diatoms and dinoflagellates, which in this season reached their annual maximum. Pseudo-nitzschia spp. represented on average 0.4–17.6% of diatom community, but during their blooms they could reach up to up to 90% of the total diatom abundances with 106 cells l-1. By LM, six different taxa were recognized: Pseudo-nitzschia cf. delicatissima and P. cf. pseudodelicatissima were the most abundant, followed by P. cf. fraudulenta, P. pungens, P. multistriata and P. cf. galaxiae. P. cf. fraudulenta and P. pungens were indicator taxa of winter. P. cf. delicatissima and P. cf. pseudodelicatissima were spring and summer taxa, respectively. P. galaxiae showed maximum abundances in autumn. DNA sequences revealed the presence of two species belonging to the ’P. seriata group’ (i.e. P. fraudulenta and P. pungens) and four species belonging to the ‘P. delicatissima group’ (P. calliantha and P. mannii within the P. pseudodelicatissima species complex, and P. delicatissima and P. cf. arenysensis within the P. delicatissima species complex). The presence of several cryptic and pseudo-cryptic species highlights the need to combine LM observations with DNA sequence data when the ecology of Pseudo-nitzschia is investigated.

Annual phytoplankton cycle in a meromictic anoxic basin of a Rhode Island (USA) estuarine river

Estuarine Pettaquamscutt River is a unique habitat 10 km in length with physical and biogeochemical characteristics analogous to a miniature fjord. Its meromictic upper basins are characterized by a permanent oxic–anoxic vertical gradient in which a well-oxygenated upper layer overlies a deeper, anoxic reservoir, with persistent blooms of phototrophic anoxygenic bacteria (Chromatium, Chlorobium) at the oxic–anoxic transition layer. A diverse assemblage of nanoplanktonic, centric diatoms (Cyclotella caspia, Thalassiosira pseudonana, cf. Cyclotella cryptica) dominated the seasonal phytoplankton cycle in the aerobic layer, similar to comparable meromictic habitats elsewhere. This assemblage of nano-centric diatoms appears to be trait-separated from other species clusters and is potentially useful as a functional group flora with ecophysiology diagnostic of marine estuarine rivers and meromictic habitat niche structure. The most conspicuous phytoplankton feature, however, was the year-round occurrence of the photoautotrophic euglenid Euglenaformis (Euglena) proxima, restricted in its upper water column distribution to the O2–H2S boundary layer where it formed a consortium with the photosynthetic green and purple sulfur bacteria community. The association of E. proxima with meromixis, H2S, and phototrophic anoxygenic bacteria is similar to that reported previously in a brackish Norwegian oyster poll and a brackish loch in Scotland.

Reply to “Comment on ‘Spring blooms and annual cycles of phytoplankton: a unified perspective’, by Chiswellet al.”

Reply to “Comment on ‘Spring blooms and annual cycles of phytoplankton: a unified perspective’, by Chiswell<i>et al</i>.”

Comment on “Spring blooms and annual cycles of phytoplankton: a unified perspective,” by Chiswellet al.

Comment on “Spring blooms and annual cycles of phytoplankton: a unified perspective,” by Chiswell<i>et al</i>.

An analytical system enabling consistent and long-term measurement of atmospheric dimethyl sulfide

We describe here an analytical system capable of continuous measurement of atmospheric dimethylsulfide (DMS) at pptv levels. The system uses customized devices for detector calibration and for DMS trapping and desorption that are controlled using a data acquisition system (based on Visual Basic 6.0/C 6.0) designed to maximize the efficiency of DMS analysis in a highly sensitive pulsed flame photometric detector housed in a gas chromatograph. The fully integrated system, which can sample approximately 6 L of air during a 1-hr sampling, was used to measure the atmospheric DMS mixing ratio over the Atlantic sector of the Arctic Ocean over 3 full annual growth cycles of phytoplankton in 2010, 2014, and 2015, with minimal routine maintenance and interruptions. During the field campaigns, the measured atmospheric DMS mixing ratio varied over a considerable range, from <1.5 pptv to maximum levels of 298 pptv in 2010, 82 pptv in 2014, and 429 pptv in 2015. The operational period covering the 3 full annual growth cycles of phytoplankton showed that the system is suitable for uninterrupted measurement of atmospheric DMS mixing ratios in extreme environments. Moreover, the findings obtained using the system showed it to be useful in identifying ocean DMS source regions and changes in source strength.

Annual cycle of phytoplankton with emphasis on potentially harmful species in oyster beds of Términos Lagoon, southeastern Gulf of Mexico

espanolPara definir la composicion de la comunidad fitoplanctonica con enfasis en las especies nocivas en los bancos ostricolas de la laguna de Terminos, SE del Golfo de Mexico, 6 sitios de muestreo fueron monitoreados mensualmente desde agosto 2012 a septiembre 2013. Se midio la temperatura del agua, salinidad, potencial de hidrogeno, saturacion de oxigeno, nutrientes inorganicos y la abundancia de fitoplancton. La temperatura y la salinidad se caracterizaron por diferencias estacionales marcadas. Los valores de pH y saturacion de oxigeno sugirieron un predominio de la actividad fotosintetica. La comunidad fitoplanctonica se caracterizo por el predominio de nanoflagelados y diatomeas. La abundancia de fitoplancton y su variacion estacional presentaron los valores minimos (10³ celulas L-1) durante la epoca de secas (febrero-mayo) y valores altos (10(6) celulas L-1) durante la temporada de lluvias (junio-septiembre). Otra caracteristica importante de la comunidad fitoplanctonica fue la presencia de especies de dinoflagelados nocivos: Akashiwo sanguinea, Karenia cf. mikimotoi, Pyrodinium bahamense var. bahamense, Prorocentrum mexicanum y P. minimum. Las cianobacterias Anabaena y Cylindrospermopsis cuspis alcanzaron abundancias de 1.9x10(6) y 1.3x10(6) celulas L-1, respectivamente. Los generos Alexandrium y Pseudo-nitzschia estuvieron presentes, pero los taxones no fueron identificados a nivel de especie. En conclusion, la comunidad fitoplanctonica se somete a cambios en la composicion de especies y en la estructura de la comunidad durante cada temporada climatica, en respuesta a la variacion ambiental, que permite el desarrollo de la comunidad fitoplanctonica de acuerdo a las condiciones imperantes. EnglishTo define the composition of the phytoplankton community, with an emphasis on harmful species, 6 stations were monitored monthly in the oyster beds of Terminos Lagoon, SE Gulf of Mexico, from August 2012 to September 2013. Water temperature, salinity, hydrogen potential, oxygen saturation, inorganic nutrients and abundance of phytoplankton were determined. Temperature and salinity were characterized by marked seasonal differences. The pH values and the oxygen saturation suggest a predominance of photosynthetic activity. The phytoplankton community was characterized by the dominance of nanoflagellates and diatoms. The abundance and seasonal variation of phytoplankton showed minimum values (10³ cells L-1) during the dry season (February-May) and high values (10(6) cells L-1) during the rainy season (June-September). Another significant feature of the phytoplankton community was the presence of the harmful dinoflagellate species Akashiwo sanguinea, Karenia cf. mikimotoi, Pyrodinium bahamense var. bahamense, Prorocentrum mexicanum and P. minimum. The cyanobacteria Anabaena and Cylindrospermopsis cuspis reached abundance of 1.9x10(6) and 1.3x10(6) cells L-1, respectively. The genera Alexandrium and Pseudo-nitzschia were present, but the taxa were not identified to the species level. In conclusion, the phytoplankton community undergoes changes in both species composition and structure of the community during each climatic season, in response to environmental variation, which allows the development of the phytoplankton community according to the conditions.

Spring blooms and annual cycles of phytoplankton: a unified perspective

Several hypotheses exist that describe phytoplankton spring blooms in temperate and subpolar oceans: the critical depth, shoaling mixed layer (ML), critical turbulence, onset of stratification and disturbance-recovery hypotheses. These theories appear to be mutually exclusive and none of them describe the annual cycle of phytoplankton biomass. Here, we present a model of the annual cycle in phytoplankton that recognizes that phytoplankton are not always mixed throughout the so-called ML, and that it is important to distinguish between the surface biomass and depth-integrated phytoplankton. Once these important distinctions are made, the annual cycles and blooms in surface and depth-integrated phytoplankton can be described straightforwardly in terms of the physical drivers and biotic responses.

Phytoplankton phenology in the coastal upwelling region off central‐southern Chile (35°S–38°S): Time‐space variability, coupling to environmental factors, and sources of uncertainty in the estimates

AbstractThe annual cycle and phenology of phytoplankton (satellite‐derived chlorophyll‐a, Chl‐a) in the coastal upwelling region off central‐southern Chile, their time‐space variation, the extent of their coupling with those of wind‐driven upwelling (as Zonal Ekman Transport, ZET), Sea Surface Temperature (SST), and Photosynthetically Active Radiation (PAR) were analyzed using a ∼10 year satellite time series (2002–2012). Wavelet analysis (WA) was applied to extract the dominant frequencies of variability and their recurrence, to derive the phenological indexes, and to assess the extent of the coupling between Chl‐a and environmental forcing in the annual frequency. Index estimates were obtained from minimum and maximum accumulated values in two different frequency bands, annual (WA‐ANF) and all except the synoptic (WA‐ALF). The annual frequency was dominant in all the variables; however, the annual cycle and phenology of Chl‐a displayed higher submeso and mesoscale variability. The mean onset date of Chl‐a was similar to those of PAR and ZET with WA‐ALF and cross WA indicated that, for the most part, their annual cycles were coupled or coherent. Few interannual changes in Chl‐a phenology were detected, including a ∼1 month longer duration (WA‐ALF) during La Niña 2010–2011. The mean anomalies in the magnitudes of Chl‐a and ZET during the upwelling season showed a slight but significant trend, negative for Chl‐a and positive for ZET, while SST remained relatively constant. This pattern was unexpected since three La Niña‐related conditions were identified during the 2007–2012 period.

Establishing a global climatology of marine phytoplankton phenological characteristics

The timing or phenology of the annual cycle of phytoplankton biomass can be monitored to better understand the underpinnings of the marine ecosystem and assess its response to environmental change. Ten‐year, global maps of the mean date of bloom onset, peak concentration and termination of bloom duration were constructed by extracting these phenological metrics from Generalized Linear Models (GLM) fit to time series of 1° × 1° daily estimates of SeaWiFS chlorophyll concentrations dating from September 1997 to December 2007 as well as to MODIS chlorophyll concentrations from July 2002 to July 2010. The fitted models quantitatively define the annual cycle of phytoplankton throughout the global ocean and from which a baseline of phenological characteristics was extracted. The analysis revealed regionally consistent patterns in the shape and timing of the annual cycle of chlorophyll concentration that are broadly consistent with other published studies. The results showed that a single bloom predominates over the global ocean with secondary, autumn blooms being limited in both location and spatial extent. Bloom duration tended to be zonally consistent, but meridionally complex and did not become progressively shorter with increasing latitude as is sometimes depicted. Both the shape of the annual cycle and the phenological climatologies can be used in future studies to detect significant departures over time.

The annual cycles of phytoplankton biomass

Terrestrial plants are powerful climate sentinels because their annual cycles of growth, reproduction and senescence are finely tuned to the annual climate cycle having a period of one year. Consistency in the seasonal phasing of terrestrial plant activity provides a relatively low-noise background from which phenological shifts can be detected and attributed to climate change. Here, we ask whether phytoplankton biomass also fluctuates over a consistent annual cycle in lake, estuarine-coastal and ocean ecosystems and whether there is a characteristic phenology of phytoplankton as a consistent phase and amplitude of variability. We compiled 125 time series of phytoplankton biomass (chlorophyll a concentration) from temperate and subtropical zones and used wavelet analysis to extract their dominant periods of variability and the recurrence strength at those periods. Fewer than half (48%) of the series had a dominant 12-month period of variability, commonly expressed as the canonical spring-bloom pattern. About 20 per cent had a dominant six-month period of variability, commonly expressed as the spring and autumn or winter and summer blooms of temperate lakes and oceans. These annual patterns varied in recurrence strength across sites, and did not persist over the full series duration at some sites. About a third of the series had no component of variability at either the six- or 12-month period, reflecting a series of irregular pulses of biomass. These findings show that there is high variability of annual phytoplankton cycles across ecosystems, and that climate-driven annual cycles can be obscured by other drivers of population variability, including human disturbance, aperiodic weather events and strong trophic coupling between phytoplankton and their consumers. Regulation of phytoplankton biomass by multiple processes operating at multiple time scales adds complexity to the challenge of detecting climate-driven trends in aquatic ecosystems where the noise to signal ratio is high.

Long‐term phytoplankton community changes in a deep subalpine lake: responses to nutrient availability and climatic fluctuations

Summary1. In natural lakes, modifications in the species composition and abundance of phytoplankton communities may ultimately be responses to changes in nutrient availability and climatic fluctuations. Phytoplankton and associated environmental factors were collected at monthly intervals from the beginning of the 1990s to 2007 in the large subalpine Lake Garda (zmax = 350 m, V = 49 × 109 m3). In this study period, the lake showed a slight and continuous increase of total phosphorus (TP) in the water column, up to concentrations of 18–20 μg P L−1. This increase represented the last stage of a long‐term process of enrichment documented since the 1970s, when concentrations of TP were below or around 10 μg P L−1.2. At the community level, annual phytoplankton cycles underwent a unidirectional and slow shift mainly due to changes in the species more affected by the nutrient enrichment of the lake. After a first and long period of dominance by conjugatophytes (Mougeotia) and diatoms (Fragilaria), phytoplankton biomass in recent years was sustained by cyanobacteria (Planktothrix). Other important modifications in the development of phytoplankton were superimposed on this pattern due to the effects of annual climate fluctuations principally mediated by the deep mixing events at spring overturn and, secondarily, by temperature and thermal stability of the water column during the growing season.3. Interannual variations in the stability and temperature of the water column appeared to influence the development of a few subdominant flagellates (dinophytes and cryptophytes). Nevertheless, the major impact of climate on phytoplankton was indirect, and mediated through the effects of winter climatic conditions on deep mixing dynamics. Winter climatic fluctuations proved to be a key element in a linked chain of causal factors including cooling of hypolimnetic waters, deep vertical mixing and epilimnetic nutrient replenishment. The process of fertilisation was measurable both for TP and dissolved inorganic nitrogen, although only the first had a large effect, reinforcing the seasonal growth of a few dominant groups. The degree of nutrient replenishment further increased the spring development of large diatoms and the increase of Planktothrix in summer and autumn.4. Currently, changes in nutrient concentrations have the greatest effect on the phytoplankton community, while direct effects due to the interannual variations in the thermal regime are of secondary importance compared with the indirect effects mediated through deep water mixing and spring fertilisation. Overall, the results demonstrate that the consequences of climatic fluctuations and climate warming on phytoplankton communities need to be studied at different levels of complexity and integration, from the direct effects of temperature and thermal regime, to the indirect effects mediated by the physiographic characteristics of water bodies.

Quantum yields of phytoplankton photosynthesis in the Gulf of Aqaba (Elat), Northern Red Sea

The Gulf of Aqaba (Elat) is characterized by oligotrophic waters and low productivity conditions in summer, when the euphotic zone of the stratified water column is severely nutrient-depleted. Winter is moderately productive, when mixing injects nutrients into the lit upper waters. The annual phytoplankton cycle and the bathymetric distribution of biomass and photosynthetic activity in the Gulf are analyzed in conjunction with the harvesting and utilization of light by cells. The harvesting of light energy at any depth is shown as an interaction between the optical properties of cells, a*, and the intensity and spectral distribution of the underwater light field. The efficiency by which phytoplankton cells utilize the absorbed light energy is the quantum yield of the photosynthetic process, Φ. The efficiency of light utilization by phytoplankton depends on the nutrient status of cells, their photoacclimation to ambient light, and the irradiance to which they are exposed. We show that the seasonal and spatial changes in the quantum yield of photosynthesis control the wax and wane of the different phytoplankton assemblages in the Gulf, thereby ultimately determining the flux of energy fueling all of the Gulf's planktonic and benthic biota.

Data assimilation in a coupled physical-biological model for the Bohai Sea and the Northern Yellow Sea

One difficulty with coupled physical-biological ocean models is determining optimal values of poorly known model parameters. The variational adjoint assimilation method is a powerful tool for the automatic estimation of parameters. We used this method to incorporate remote-sensed chlorophyll-a data into a coupled physical-biological model developed for the Bohai Sea and the Northern Yellow Sea. A 3-D NPZD model of nutrients (N), phytoplankton (P), zooplankton (Z) and detritus (D) was coupled with a physical model, the Princeton Ocean Model. Sensitivity analysis was carried out to choose suitable control variables from the model parameters. Numerical twin experiments were then conducted to demonstrate whether the spatio-temporal resolutions of the observations were adequate for estimating values of the control variables. Finally, based on the success of the twin experiments, we included remote-sensed chlorophyll-a data in the NPZD model. With the adjoint assimilation of these chlorophyll-a data, the coupled model better describes spring and autumn phytoplankton blooms and the annual cycle of phytoplankton at the surface layer for the study area. The annual cycle of simulated surface nutrient concentrations also agreed well with field observations. The adjoint method greatly improves the modelling capability of coupled ocean models, helping us to better understand and model marine ecosystems.

On non-linear sensitivity of marine biological models to parameter variations

Marine biological models are usually complex with many free parameters. Parameter prioritization (based on contribution to model output) is important for system management but difficult. A variance-based sensitivity analysis is developed in this paper using the Sobol’–Saltelli sensitivity indices, which measure the relative importance of each parameter (or group of parameters) and range these parameters along their contribution to output variability. To reduce the number of degrees of freedom, the model output is decomposed using the warping functions or irreversible predictability time. A simple three-component [nutrients, phytoplankton and zooplankton (NPZ)] model with 23 parameters for reproducing annual phytoplankton cycle of the Black Sea is taken as the example to show the usefulness and procedure of the sensitivity analysis. Single and total sensitivity indices showed strong sensitivity of the biological model to the light limitation of the phytoplankton growth. This agrees well with physical intuition. However, ranging model parameters along their contributions to model output variability does not follow exactly the physical intuition when model-related errors from large perturbations of the parameters are not small. For example, the model output becomes very sensitive to the nutrient stock parameterization for certain combinations of the light-related factors.

A Global Eddy-Resolving Coupled Physical-Biological Model: Physical Influences on a Marine Ecosystem in the North Pacific

Physical influences on a marine ecosystem in the open ocean are investigated using a simplified four-component ecosystem model embedded in an eddy-resolving ocean general-circulation model (OGCM). The annual cycle of temperature, nitrate, and phytoplankton in the upper ocean is well reproduced with the climatological monthly mean forcing.A comparison with satellite ocean color data shows that the model is capable of a realistic description of the annual mean and regional patterns of surface chlorophyll.Simulated chlorophyll distribution at the surface shows a pattern influenced by the western boundary current (Kuroshio) and meso-scale eddies.Nitrate distribution in the upper ocean in the northwestern Pacific is mainly controlled by physical processes, especially meso-scale variability, including many anticyclonic and cyclonic eddies, fine-scale fronts, and filaments.The warm-core eddy entrains high-nitrate water from the surrounding filaments, creating conditions for the high production in spring.