Surface Phytoplankton Biomass Research Articles

Vertical stratification of phytoplankton biomass in a deep estuary site: implications for satellite-based net primary productivity

The accuracy of satellite estimates for water column net primary productivity (NPP) are contingent upon the reliability of surface phytoplankton biomass, specifically chlorophyll a (Chl.a) and carbon (Cphyt), as indicators of euphotic biomass and photosynthetic rate. We assessed patterns in water column biomass at a deep estuary site (~40 m) in the Firth of Thames, Hauraki Gulf, New Zealand, using ten years (2005-2015) of in situ sampling (40 seasonal voyages and moored instrumentation). Seasonal biomass stratification coincided with physical and chemical stratification and exhibited a reasonable predictability based on surface Chl.a measures from mooring timeseries. High Chl.a (but not Cphyt) accumulated from late-spring (Nov.) in the lower portion of the water column, under nutrient deficient, clear surface water with deep euphotic zone conditions, peaking in mid-summer (Jan.) and ending by early autumn (Mar.). Satellite (MODIS-Aqua) NPP (2002-2018), was estimated with and without correction for deep biomass in two vertically generalized production models (Chl.a-VGPM and Cphyt-CbPM). Mean annual NPP (220-161 g C m-2 y-1, VGPM and CbPM respectively) increased 5-18% after accounting for euphotic zone deep biomass with a mid-summer maxim (Jan.: 30-33%). Interannual anomalies in biomass and NPP (about -10% to 10%) were an order of magnitude greater than small decreasing trends (<< 1% y-1). We discuss the impacts of observational factors on biomass and NPP estimation. We offer contextual insights into seasonal patterns by considering previous observations of biomass trends and nutrient enrichment in the Firth of Thames region. We propose future directions in accounting for deep biomass variations from shallow coastal areas to deeper continental shelf waters.

Impact of tropical Indian Ocean warming on the surface phytoplankton biomass at two significant coastal upwelling zones in the Arabian Sea

The Sea Surface Temperature (SST) of the Arabian Sea undergoes large seasonal variations owing to the monsoonal forcing and upwelling. Warming of the ocean adversely affects its biological productivity. The present study examined the role of the rapid warming of the tropical Indian Ocean and associated changes in physical forcing parameters on phytoplankton biomass in the Arabian Sea. SST during the summer monsoon period (June-September) of 1971–2020 showed an increasing trend of 0.6 °C in the southeastern Arabian Sea (SEAS) and 1.6 °C in the northwestern Arabian Sea. During the recent summer monsoon period of 1998–2020, surface chlorophyll-a (chl-a) concentration showed a decreasing trend of – 0.32 mg m−3 in the SEAS and an increasing trend of 0.56 mg m−3 in the northwestern Arabian Sea. High-resolution satellite and reanalysis data of physical forcing parameters such as surface winds, SST, Sea Level Anomaly (SLA) that influence the surface chl-a concentration at two distinct upwelling locations in the Arabian Sea, were analysed for the recent two decades (1998–2020). Multiple linear regression (MLR) analysis showed that SLA was the most important parameter that determines the surface chl-a variability in the SEAS, whereas alongshore wind stress was dominant in the northwestern Arabian Sea. An epochal analysis showed that in the most recent decade, SLA in the SEAS became less favourable for upwelling, whereas summer monsoon winds became increasingly favourable for upwelling in the northwestern Arabian Sea. These differences corroborate the contrasting trends in surface chl-a in the two locations in the Arabian Sea. The present study has shown that the inconsistent response of surface chl-a at distinct locations within the Arabian Sea depends on the relative strength of the influencing physical forcing mechanisms.

Assessing the Intensity of Marine Biogenic Influence on the Lower Atmosphere: An Insight into the Distribution of Marine Biogenic Aerosols over the Eastern China Seas.

Marine biological activities make a non-negligible contribution to atmospheric aerosols, leading to potential impacts on the regional atmospheric environment and climate. The eastern China seas are highly productive with significant emissions of biogenic substances, but the spatiotemporal variations of marine biogenic aerosols are not well known. Air mass exposure to chlorophyll a (AEC) can be used to indicate the influence of biogenic sources on the atmosphere to a certain degree. In this study, the 12 year (2009-2020) daily AEC were calculated over the eastern China seas, showing the spatial and seasonal patterns of marine biogenic influence intensity which were co-controlled by surface phytoplankton biomass and boundary layer height. By combining the AEC values, relevant meteorological parameters, and extensive observations of a typical biogenic secondary aerosol component, methanesulfonate (MSA), a parameterization scheme for MSA simulation was successfully constructed. This AEC-based approach with observation constraints provides a new insight into the distribution of marine biogenic aerosols. Meanwhile, the wintertime air mass retention over land exhibited a significant decrease, showing a decadal weakening trend of terrestrial transport, which is probably related to the weakening of the East Asian winter monsoon. Thus, marine biogenic aerosols may play an increasingly important role in the studied region.

Simulation Experiment of Environmental Impact of Deep-Sea Mining: Response of Phytoplankton Community to Polymetallic Nodules and Sediment Enrichment in Surface Water.

In this paper, simulation experiments were conducted to study the response of phytoplankton biomass and community composition to the influence of polymetallic nodules and sediment at four stations in the western Pacific in 2021. Chlorophyll a, pico-phytoplankton cell abundance, and metal concentration were measured before and after 24 h of deck incubation. The results show that there were three different patterns of response, namely, restrained, stimulated, and unaffected patterns. The restrained pattern appeared in the filtered treatments at station Incub.01, and the stimulated pattern appeared in the unfiltered treatments at station Incub.02. The response of the phytoplankton was not detectable at stations Incub.03 and 04. Regardless, positive and negative responses were found in the dominant pico-phytoplankton group—Prochlorococcus—and with slight variation in Synechococcus. The concentration of manganese varied among the treatments compared to that of iron and other metals. The factors affecting the growth of the phytoplankton in this study were metal concentrations and turbidity. The phytoplankton biomass baseline may also have played an important role: the lower the biomass, the higher the growth rate. This study proved that deep-sea polymetallic nodule mining will have a specific impact on surface phytoplankton biomass, but turbidity and particle retention time could be important factors in mitigating the extent of the impact.

Seasonal cycles of phytoplankton and net primary production from Biogeochemical Argo float data in the south-west Pacific Ocean

We present annual cycles of chlorophyll a, phytoplankton carbon, nitrate and oxygen for Subtropical (STW), Subantarctic (SAW), and Subantarctic Mode (SAMW) waters near Aotearoa New Zealand from data collected by two Biogeochemical (BGC) Argo floats. We develop two simple models of depth-integrated net primary production (NPP), tuned against 14C-uptake measurements, to compare with Vertically-Generalised Production Model (VGPM) satellite-based estimates of NPP. One model is the simplest possible, and assumes production is proportional to light multiplied by chlorophyll a concentration. The second model modifies the light response profile to account for photoacclimation. In STW at 30–35°S, enhanced production is initiated in austral autumn when the mixed layer deepens to entrain nutrients into the photic zone. For about half the year, there is substantial production within a deep chlorophyll maximum that sits below the mixed layer. Consequently, depth-integrated NPP is only loosely related to surface biomass as imaged from satellite remote-sensing, and BGC Argo-based model estimates of depth-integrated NPP are about double VGPM estimates. In SAW at 45–55°S, production is initiated when vertical mixing decreases in austral spring. Production is largely within the mixed layer, and depth-integrated phytoplankton biomass and depth-integrated NPP follow surface phytoplankton biomass. Model estimates of depth-integrated NPP based on BGC Argo float profiles are comparable with VGPM estimates for the southern water masses.

Non‐Marine Sources Contribute to Aerosol Methanesulfonate Over Coastal Seas

AbstractMethanesulfonate (MSA) in the marine boundary layer is commonly considered to be solely contributed by the oxidation of ocean‐derived dimethyl sulfide (DMS) and often used as an indicator of marine biogenic sources. But whether this judgment is valid in coastal seas and how the validity is affected by air mass transport history have been less discussed. Based on multi‐year observations of aerosol MSA in the coastal East China Sea (ECS) and the Gulf of Aqaba (GA), as well as the analysis of air mass transport pattern and exposure to ocean surface phytoplankton biomass, we found that terrestrial sources made a non‐negligible contribution to MSA over the ECS but not over the GA. The abundant MSA in winter over the coastal ECS was likely associated with substantial emissions of volatile organic sulfur compounds from both anthropogenic and natural sources in eastern China and significant terrestrial transport influenced by the East Asian Monsoon. Good correlations between aerosol MSA and air mass exposure to surface phytoplankton biomass were established by removing the influence of terrestrial transport and confining the air transport height within boundary layer, which makes it possible to construct parameterizations for obtaining the spatiotemporal distributions of marine biogenic aerosol components using satellite ocean color datasets.

Different characteristics and source contributions to aerosol aminiums over a coastal city and adjacent marginal seas

Environmental context Amines in the atmosphere play important roles in atmospheric chemistry and have potential climate effects. We characterise the concentrations, size distributions and chemical pathways of aerosol aminiums over a coastal city and marginal seas, and estimated the contribution of marine biogenic sources. This study can facilitate our understanding about the interactions between human activities, biogenic emissions and the atmospheric environment. Abstract Atmospheric amines are gaining more and more attention in the field of atmospheric chemistry owing to their important roles in new particle formation and growth. In this study, aerosol aminiums over a coastal city (Shanghai) and the Yellow and East China seas (YECS) were characterised. The concentrations of NH4+, dimethylaminium (DMAH+) and trimethylaminium + diethylaminium (TMDEAH+) over Shanghai were all found to be higher in the winter of 2018 than in the summer of 2019, suggesting their non-negligible terrestrial contributions. DMAH+ and TMDEAH+ concentrations over the YECS in summer were closely correlated and linked to surface phytoplankton biomass, implying that marine biogenic sources might be a predominant contributor to aminiums at this time. Aminiums over Shanghai generally showed a bimodal distribution with a main peak in droplet mode and a secondary peak in condensation mode, suggesting the notable contribution of aqueous-phase or heterogeneous reaction to the formation of aminiums. In contrast, aminiums over the YECS often showed a unimodal distribution, which may be caused by the competition between amines and NH3 for reaction with acidic compounds. We estimated the contributions of marine biogenic sources, ~73.6 % to DMAH+ and 80.1 % to TMDEAH+ over the YECS, using methanesulfonate/non-sea-salt SO42– as an indicator. Our results suggest that marine biogenic emission of amines from China’s marginal seas may have a potential impact on coastal cities, and this source should be considered in modelling new particle formation and air quality in coastal areas.

New index of organic mass enrichment in sea spray aerosols linked with senescent status in marine phytoplankton

Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OMSSA). Here we show a new index to present OMSSA using concentrations of Chl a and chlorophyllide (Chllide) a, which is a breakdown product of Chl a and has been used as a biomarker of senescent algal cells. The index was compared with submicrometer OMSSA, based on surface seawater and aerosol samples obtained during the pre-bloom in the western subarctic Pacific. Our results showed that the OMSSA was highly correlated with this unique index, suggesting that the OMSSA was closely linked with senescent algal cells and/or cell lysis. Furthermore, the hygroscopicity parameters κ derived from water-extracted SSA samples implied a reduction in the SSA hygroscopicity with increasing senescent status of phytoplankton. The index can represent OMSSA on a timescale of a day during the pre-bloom period, which should be further examined over different oceanic regions.

Biogeography of marine giant viruses reveals their interplay with eukaryotes and ecological functions.

Nucleocytoplasmic large DNA viruses (NCLDVs) are ubiquitous in marine environments and infect diverse eukaryotes. However, little is known about their biogeography and ecology in the ocean. By leveraging the Tara Oceans pole-to-pole metagenomic data set, we investigated the distribution of NCLDVs across size fractions, depths and biomes, as well as their associations with eukaryotic communities. Our analyses reveal a heterogeneous distribution of NCLDVs across oceans, and a higher proportion of unique NCLDVs in the polar biomes. The community structures of NCLDV families correlate with specific eukaryotic lineages, including many photosynthetic groups. NCLDV communities are generally distinct between surface and mesopelagic zones, but at some locations they exhibit a high similarity between the two depths. This vertical similarity correlates to surface phytoplankton biomass but not to physical mixing processes, which suggests a potential role of vertical transport in structuring mesopelagic NCLDV communities. These results underscore the importance of the interactions between NCLDVs and eukaryotes in biogeochemical processes in the ocean.

Evidence of Eddy‐Enhanced Winter Chlorophyll‐a Blooms in Northern Arabian Sea: 2017 Cruise Expedition

AbstractThe temperature, salinity, and chlorophyll‐a (Chl‐a) profiles of the upper ocean (0–200 m) were measured during the China‐Pakistan Joint Expedition, 2017. The cruise track passed through an identified cyclonic eddy, and the multi‐disciplinary records thus verify the eddy contributions to winter blooms in the northern Arabian Sea (AS). The records show that the strength of upper blooms within the mixed layer is mainly dominated by surface phytoplankton biomass (the Chl‐a concentration), which increases simultaneously with the shallow mixed layer and uplifted thermocline. A composite analysis of eddy‐tracked sea level anomalies (SLA) and Chl‐a reveals the pumping and stirring effects that cyclonic eddies make to the ocean surface nutrient supply. Based on the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) outputs, a mixed layer nitrogen budget calculation was subsequently conducted to quantify the contributions of mesoscale eddies to 10‐year climatological winter blooms. The results indicate that eddy flows are primary contributors to the increased nutrients in the coastal north AS during the mature period (usually in January and February) of the winter blooms, with a concentration histogram double that of convective mixing. The concentration decreases from the north to south, agreeing well with the seasonal northward nutrition gradient. This confirms that (i) the growth of nutrients over the northern AS, which is known to be triggered by convective mixing, would be further maintained by eddy‐induced advection; and (ii) higher concentration of nutrients would facilitate an easier response of Chl‐a to eddy dynamics.

Drivers to spatial and temporal dynamics of column integrated phytoplankton biomass in the shallow lake of Chaohu, China

Abstract Eutrophication of inland freshwater bodies is a major threat to the ecosystem services. Many studies have focused on using surface or near surface phytoplankton biomass to determine trophic status or bloom conditions. However, surface phytoplankton biomass can change quickly due to the vertical migration of phytoplankton. A more appropriate indicator is column integrated biomass which considers the vertical distribution of the phytoplankton. In this study, we estimated the spatial and temporal dynamics of column integrated biomass in a shallow eutrophic lake, Lake Chaohu in China, using a biomass estimation algorithm and fourteen years of satellite data. The built algorithm was validated by in situ datasets with a significant correlation with the coefficient of determination (R2) of 0.89, mean absolute relative difference, MARD = 25.97%, the root-mean-square error, RMSE = 20.17 mg·m−2. We decomposed the temporal dynamics of the satellite-based time series into inter-annual trends, seasonal and irregular behaviors of biomass in different lake sections. We compared these individual dynamics to nutrients, meteorological and climate variables, in particular with respect to ongoing effort to manage nutrients in this complex lake and catchment. Nutrient concentrations were shown to be determinant in the inter-annual trends. Irregular variation of biomass was found to be sensitive to global climate change events (ENSO) which influence regional conditions of precipitation and temperature. By taking the vertical profile of phytoplankton into consideration, the derived temporal and spatial distribution of phytoplankton biomass, rather than surface biomass, provided new sights into lake conditions and were seen to be a good support for lake management efforts.

Influence of sea ice concentration on phytoplankton community structure in the Chukchi and East Siberian Seas, Pacific Arctic Ocean

To clarify the influence of sea ice concentration on phytoplankton community distribution in the rapidly warming Arctic Ocean, we conducted field surveys in August 2012 and August 2015 in the Chukchi and East Siberian Seas. The phytoplankton community structures (derived from pigment analysis) were compared according to environmental variables between the two periods. August 2012 had the lowest average sea ice concentration since sea ice observations began in 1979, along with higher sea surface temperatures. A deeper mixed layer depth and higher surface nitrate concentrations were observed in 2012, caused by exposure of the sea surface to wind. The euphotic depth and subsurface chlorophyll maximum layer were deeper in 2015 than in 2012, and whereas the low surface phytoplankton biomass in both years indicated post-bloom periods. Similar phytoplankton biomass and different phytoplankton community structure were found between ice and melt years. Small phytoflagellates (e.g., prymnesiophytes, prasinophytes, dinoflagellates, and cryptophytes) dominated the phytoplankton biomass with different community structures in the eastern and western areas in 2012, while diatoms dominated over the whole study area in 2015. Several environmental factors affect the variation in phytoplankton community structure in the Chukchi and East Siberian Seas; however, the phytoplankton, especially diatoms, appeared to be controlled mainly by seeding from sea ice in the surface layer. Furthermore, euphotic depth and water mass structure are likely the main factors influencing the spatial distribution of phytoplankton in the subsurface layer of this area, indicating that the phytoplankton community structure might be influenced by the water mass distribution under future ice-free conditions.

Near shore distributions of phytoplankton and bacteria in relation to submarine groundwater discharge-fed fishponds, Kona coast, Hawai‘i, USA

Phytoplankton are important components of coastal marine ecosystems that are strongly influenced by freshwater inputs from land, including submarine groundwater discharge (SGD). Although SGD generates sharp onshore – offshore gradients in physical and chemical conditions at several locations around Hawaii Island little is known about the biotic responses of water column microbes to these conditions. We studied the distributions of phytoplankton and bacteria at two contrasting sites with SGD-fed fishponds, Kiholo and Kaloko Bay, including the full range of salinity extending from the fishponds to the coastal ocean. We addressed the hypotheses that (1) SGD-fed fishponds support a higher biomass and different composition of phytoplankton than the adjacent ocean, and (2) phytoplankton biomass and composition are related to SGD-driven salinity gradients in the coastal ocean. Phytoplankton biomass in fishponds was elevated (10–100-fold) and accompanied by higher average cell size pico- and nano-phytoplankton (2–6 μm) relative to sites outside the fishpond. General additive models (GAMs) showed elevated biomass and average cell size at mid-range salinities and declining biomass at salinity < 20 outside the fishponds. Multivariate RDA showed significant, site-specific relationships between surface phytoplankton biomass (Chl a), cell counts, and environmental parameters. Analysis of surface vs. deep samples from outside the fishponds showed elevated phytoplankton biomass at the surface, except in Kiholo lagoon where phytoplankton was elevated beneath the SGD-driven pycnocline. This study shows structuring of coastal phytoplankton through SGD inputs and suggest that changes in SGD due to coastal development or climate change can impact coastal marine ecosystems through effects on phytoplankton communities.

Observing and modelling phytoplankton community structure in the North Sea

Abstract. Phytoplankton form the base of the marine food chain, and knowledge of phytoplankton community structure is fundamental when assessing marine biodiversity. Policy makers and other users require information on marine biodiversity and other aspects of the marine environment for the North Sea, a highly productive European shelf sea. This information must come from a combination of observations and models, but currently the coastal ocean is greatly under-sampled for phytoplankton data, and outputs of phytoplankton community structure from models are therefore not yet frequently validated. This study presents a novel set of in situ observations of phytoplankton community structure for the North Sea using accessory pigment analysis. The observations allow a good understanding of the patterns of surface phytoplankton biomass and community structure in the North Sea for the observed months of August 2010 and 2011. Two physical–biogeochemical ocean models, the biogeochemical components of which are different variants of the widely used European Regional Seas Ecosystem Model (ERSEM), were then validated against these and other observations. Both models were a good match for sea surface temperature observations, and a reasonable match for remotely sensed ocean colour observations. However, the two models displayed very different phytoplankton community structures, with one better matching the in situ observations than the other. Nonetheless, both models shared some similarities with the observations in terms of spatial features and inter-annual variability. An initial comparison of the formulations and parameterizations of the two models suggests that diversity between the parameter settings of model phytoplankton functional types, along with formulations which promote a greater sensitivity to changes in light and nutrients, is key to capturing the observed phytoplankton community structure. These findings will help inform future model development, which should be coupled with detailed validation studies, in order to help facilitate the wider application of marine biogeochemical modelling to user and policy needs.

Are boundary conditions in surface productivity at the Southern Polar Front reflected in benthic activity?

In austral summer 2012, during the expedition ANT-XXVIII/3 on board RV Polarstern, two sites were sampled 1600km apart in the South Polar Front area (52°S) at the boundary of different productivity regimes for meio- and macrobenthos using a multiple-corer and an epibenthic sledge, respectively. Patterns in density and abundance data were compared between different size classes of the benthos and interpreted in relation to surface primary productivity data and sediment oxygen consumption. We tested the hypothesis that long-term satellite-derived surface phytoplankton biomass, in situ real time biomass, and productivity measurements at the surface and throughout the euphotic zone are reflected in abyssal benthos densities, abundances and activity. Specifically, we investigated the effect of boundary conditions for lower and higher surface productivity. Surface and integrated to 100m depth biomass and primary productivity measurements vary stations, with the lowest values at station 85 (0.083mgChl-am−3 at surface, 9mgChl-am−2 and 161mgCm−2 d−1− integrated over the first 100m depth), and the highest values at station 86 (2.231mgChl-am−3 at surface, 180mgChl-am−2 and 2587mgCm−2d−1 integrated over first 100m depth). Total meiofaunal densities varied between 102 and 335individuals/10cm². Densities were the highest at station 86-30 (335 individuals) and lowest at station 81-13 (102 individuals). Total macrofaunal densities (individuals/1000m²) varied between 26 individuals at station 81-17 and 194 individuals at station 86-24. However, three EBS hauls were taken at station 86 with a minimum of 80 and a maximum of 194 individuals. Sediment oxygen consumption did not vary significantly between stations from east to west. Bentho-pelagic coupling of meio- and macrobenthic communities could not be observed in the South Polar Front at the boundary conditions from low to high surface productivity between stations 81 and 86.

The unique environment of the most acidified permanently meromictic lake in the Czech Republic

Changes in the water properties and biological characteristics of the highly acidic Hromnice Lake (Western Bohemia) were investigated. This 110-year-old lake, formed as a consequence of the mining of pyritic shales, is permanently meromictic. Two chemoclines separate an extremely acidic (pH ∼ 2.6) mixolimnion from a metal-rich anoxic monimolimnion. The absence of spring mixolimnetic turnover due to ice melting and very slow heat propagation through the chemocline with a 6-month delay were observed. Extreme mixolimnetic oxygen maxima (up to 31 mg l −1 ) in phosphorus-rich lake (PO 4 3− up to 1.6 mg l −1 ) well correlated with outbursts of phytoplankton. Phytoplankton consist of several acido-tolerant species of the genera Coccomyxa , Lepocinclis , Chlamydomonas and Chromulina . Surface phytoplankton biomass expressed as chlorophyll- a varies from 2 to 140 μg l −1 . Multicellular zooplankton are almost absent with the exception of Cephalodella acidophila , a small rotifer occurring in low numbers. Large red larvae of the midge Chironomus gr. plumosus were found at the bottom close to the shore, with larvulae in the open water. Developmental stages (protonemata) of a moss, resembling filamentous algae, dwell in the otherwise plant-free littoral zone.

Variations in silicate concentration affecting photosynthetic carbon fixation by spring phytoplankton assemblages in surface water of the Strait of Malacca

The Strait of Malacca (SoM), the world’s busiest sea-route, is increasingly polluted as the rapid development of world trades, affecting phytoplankton primary productivity therein. The variations of surface phytoplankton biomass, size-structure and carbon fixation were investigated across the SoM during the spring period (May 4 to 9, 2011). Chlorophyll a concentration increased from 0.12 µg/L at the northwest entrance of the SoM to a maximal 0.63 µg/L at narrowest section, and decreased to 0.10 µg/L at the southeast entrance. Photosynthetic carbon fixation by phytoplankton coincided well with Chl a biomass, and increased from 10.8 to 22.3 µg C/(L·d), then decreased to 9.21 µg C/(L·d); while the carbon fixation rate showed an inverse pattern to the changes of Chl a, and decreased from 87.1 to 35.5 µgC/(µgChla·d) and increased thereafter to 95.3 µg C/(µg Chl a·d). Picophytoplankton cells (<3 µm) contributed to more than 60% and 50% of the total Chl a and carbon fixation at both the entry waters; while the contributions of pico-cells decreased sharply to the minimum of 18.3% and 27.5% at the narrowest part of the SoM. In particular, our results showed that the silicate concentration positively regulated Chl a biomass and carbon fixation, reflecting that the higher silicate favoured the growth of phytoplankton and thus led to higher primary production in this strait.

Summertime primary production in northwest South China Sea: Interaction of coastal eddy, upwelling and biological processes

The Northwest South China Sea (NWSCS) ecosystem is controlled by multiple physical processes in summer including the monsoon wind induced coastal upwelling, the cyclonic eddy off the eastern Leizhou Peninsular (ELP), and the Yuexi Coastal Current (YCC). Based on the high-resolution in situ and remote sensing data, this study examined in details the spatial patterns of phytoplankton biomass and primary production in the coast of NWSCS in summer and discussed the underline physical processes involved. The results suggested that the southwesterly monsoon wind induced coastal upwelling is the major mechanism for the relatively high phytoplankton biomass and primary production found in the coastal area. However, the waters off the ELP have relatively higher phytoplankton biomass than that off the eastern Hainan Island (EHI). This is probably due to the topography- and eddy-driven enhancement of nutrient supply and light availability along the ELP. A small but distinguishably high biomass/productivity area was found at the east side of the Qiongzhou Strait. This eddy-shaped feature appears to be separated from the larger high productivity area near the Qiongzhou Strait, and is likely caused by the interaction of multiple dynamical processes including coastal upwelling, topographically-induced double eddy circulation, the YCC and associated large-scale cold eddy, and possibly the tidal mixing in this area. The YCC tends to inhibit phytoplankton growth and thus depresses the surface phytoplankton biomass in the near-shore waters of the ELP, mainly through the stratification-induced nutrient limitation (primarily phosphorous limitation). Overall, the interaction of physical processes between wind-induced upwelling, coastal current and tidal-shoaling mixing as well as eddy upwelling are key drivers regulating the horizontal and vertical distribution of phytoplankton biomass and productivity in the NWSCS.

Longitudinal patterns of spring-intermonsoon phytoplankton biomass, species compositions and size structure in the Bay of Bengal

Vertical distributions of phytoplankton biomass, compositions and size structure were investigated during the spring-intermonsoon (April 22 to 30) of 2010 along transact 10°N of the Bay of Bengal, northern Indian Ocean. Surface phytoplankton biomass (Chl a) was (0.065±0.009) µg/L, being greater than 80% of which was contributed by pico-phytoplankton ( 20 µm) accounting for 58% and nano- (3–20 µm) or pico-cells for 15% and 27%, respectively. In particular, the cells concentration coupling well with phosphate level was observed at middle layer (75–100 m) of 87° to 89°E, dominated by micro-cells diatoms (e.g., Chaetoceros atlanticus v. neapolitana, Chaetoceros femur and Pseudonitzschia sp.) and cyanobacteria (i.e., Trichodesmium hildebrandtii), with the cells concentration reached as high as 4.0×104 and 4.3×104 cells/L. At the rest of the transact however, dinoflagellates (e.g., Amphisdinium carterae and Prorocentrum sp.) were the dominant species, with the cells concentration varying from 0.3×103 to 6.8×103 cells/L. Our results also indicate that the regulation of large cells (micro-, nano-) on phytoplankton biomass merely occurred at DCM layer of the Bay.

Remotely Sensed Chlorophyll: A Putative Trophic Link for Explaining Variability in Indian Oil Sardine Stocks

The landing of Indian oil sardines, Sardinella longiceps Valenciennes, 1847, along the southwest coast of India is highly variable. A few physical parameters and processes correlated with sardine landing could not establish a flawless connection and explain the phenomena of interannual variability. Earlier research has indicated that the probable appearance and disappearance of sardines is an active movement in search of food and favourable conditions. But no specific study has been carried out to explain the variability of sardine catch based on chlorophyll availability on a synoptic scale. An attempt is made in this study to correlate variability in chlorophyll a with sardine landings along the waters of the southwest coast of India. We have estimated monthly averaged surface phytoplankton biomass along the waters of the southwest coast of India from the shoreline up to the 200-m isobath for 10 years from SeaWiFS ocean-colour data. This estimation is compared with the biological calendar of Indian oil sardines. The average chlorophyll a for the bloom initiation month (1998–2006) matches very well with oil sardine landings. The results imply that the concentration of chlorophyll during the bloom initiation month can be used to assess the quantity of fish that recruit into the population. Finer scale spatial variations in the chlorophyll along the coastal waters help in deciphering the migratory pattern of sardines during their active breeding phase. This study shows that 39% of interannual variability in fish landings is related to availability of chlorophyll a during the bloom initiation month.