Light Availability Research Articles

Machine learning to identify environmental drivers of phytoplankton blooms in the Southern Baltic Sea

Phytoplankton blooms exhibit varying patterns in timing and number of peaks within ecosystems. These differences in blooming patterns are partly explained by phytoplankton:nutrient interactions and external factors such as temperature, salinity and light availability. Understanding these interactions and drivers is essential for effective bloom management and modelling as driving factors potentially differ or are shared across ecosystems on regional scales. Here, we used a 22-year data set (19 years training and 3 years validation data) containing chlorophyll, nutrients (dissolved and total), and external drivers (temperature, salinity, light) of the southern Baltic Sea coast, a European brackish shelf sea, which constituted six different phytoplankton blooming patterns. We employed generalized additive mixed models to characterize similar blooming patterns and trained an artificial neural network within the Universal Differential Equation framework to learn a differential equation representation of these pattern. Applying Sparse Identification of Nonlinear Dynamics uncovered algebraic relationships in phytoplankton:nutrient:external driver interactions. Nutrients availability was driving factor for blooms in enclosed coastal waters; nutrients and temperature in more open regions. We found evidence of hydrodynamical export of phytoplankton, natural mortality or external grazing not explicitly measured in the data. This data-driven workflow allows new insight into driver-differences in region specific blooming dynamics.

Performance and feasibility analysis of an integrated airlift microalgae photobioreactor for cultivation and pre-harvesting.

Microalgae technology is highly attractive in the realm of wastewater treatment and CO2 removal. However, during the cultivation of microalgae, the phenomenon of light attenuation intensifies with the increasing cell concentration, resulting in a decrement in microalgal growth rate. To maintain high light transmittance and growth rate of microalgae, this study introduces a two-step pre-harvesting process involving flocculation and filtration within an airlift photobioreactor. In this way, the growth performance of microalgae was bolstered by an improvement in light availability, which was increased 1.59 times by harvesting 30% of the microalgae biomass. Additionally, the microalgae productivity was increased 12.3%. By diluting the cationic starch concentration to 3gL-1, the harvesting efficiency approached levels comparable to those achieved through magnetic stirring, while filtration resulted in a 1.9-fold increase in final biomass concentration. Moreover, a comparative life-cycle assessment of three harvesting methods revealed that the flocculation-filtration method exhibited the lowest global warming potential of -0.09 CO2 eq, positioning it as a viable and low-carbon alternative for microalgae harvesting.

Stand Diversity Does Not Mitigate Increased Herbivory on Climate-Matched Oaks in an Assisted Migration Experiment.

Assisted migration is a tree-planting method where tree species or populations are translocated with the aim of establishing more climate-resilient forests. However, this might potentially increase the susceptibility of translocated trees to herbivory. Stand diversification through planting trees in species or genotypic mixtures may reduce the amount of damage by insect pests, but its effectiveness in mitigation of excess herbivory on climate-matched trees has seldom been explored. Using the Climate Match Experiment which manipulates both tree climatic provenance and stand diversity, we compared growth, insect herbivory and leaf traits of pedunculate oaks (Quercus robur) of local and Italian provenances in monocultures, provenance mixtures or species mixtures. Additionally, we investigated whether tree apparency and light availability cause variation in leaf traits and herbivory and tested whether these factors were influenced by stand diversity. We found that Italian oaks were subject to greater herbivore damage than those of local English provenance regardless of stand diversity and that insect herbivory in Italian oaks was higher on more apparent trees. Italian oaks also had lower concentrations of hydrolysable tannins than English oaks, but tannin concentrations were poor predictors of herbivory. Additionally, we show that leaf trait variation is strongly associated with differences in light availability.

Photon budgets and the relative effects of CDOM and pigment absorptions on primary production along a coastal salinity gradient

The study highlights the critical role of CDOM in coastal light attenuation and its impact on primary production (PP). We investigated the spectral attenuation of light due to water, phytoplankton pigments, detritus and coloured dissolved organic matter (CDOM) along a salinity gradient in the outer Oslofjord, Norway. By examining the effects of these components across different seasons, we aimed to elucidate their relative contributions to light absorption and PP. The findings suggest that increased terrestrial CDOM inputs, driven by climate, changed atmospheric deposition and land-use changes, could significantly affect coastal ecosystems by altering light attenuation and consequently PP and potentially leading to other ecological pressures. CDOM consistently dominated light absorption across all stations and seasons, contributing 50%–80% of the total absorption of photosynthetically active radiation. The absorption by CDOM and detritus decreased with increasing salinity, while phytoplankton absorption followed a seasonal succession. PP estimates show high seasonal variability from maximums in June to minimums in November, mainly attributed to, changes in seasonal light availability and phytoplankton biomass, followed by light attenuation by CDOM and differences in quantum yields of photosystem II (PSII). Nutrient analysis showed a seasonal pattern, with the highest nitrogen concentrations in November and depletion during more productive seasons, as well as conservative mixing throughout the salinity gradient. CDOM absorption played substantial, albeit not leading, role in influencing PP estimates, derived from a bio-optical model. CDOM was the main determinant of light attenuation across most wavelegnths.

Nutritional consistency of macroalgae across a sea ice cover gradient along the Western Antarctic Peninsula.

Sea ice can profoundly influence photosynthetic organisms by altering subsurface irradiance, but it is susceptible to changes in the climate. The patterns and timing of sea ice cover can vary on a monthly to annual timescale in small sub-regions of the Western Antarctic Peninsula (WAP). During the latter part of the 20th century, sea ice coverage significantly decreased in the WAP, a trend that aligns with warming in this area. Macroalgal biochemical components are impacted by light availability, often showing a close relationship between photosynthesis and biochemical compositions. We used satellite imagery of annual sea ice duration and extent as well as water turbidity during ice-free periods to identify 14 study sites that differed dramatically in sea ice coverage but were similar in terms of turbidity along the central WAP between 68° S and 64° S. The common macroalgal species Desmarestia menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. were collected by scuba divers between 5 m and 35 m depth at each site where they occurred, for later biochemical analyses. Overall percentages of major biochemical components as well as carbon and nitrogen percentages and C:N were determined and correlated with four different sea ice indices. Surprisingly, most of the chemical components were not significantly correlated with sea ice cover. The few significant correlations varied between species and chemical components. This indicates that although patterns of sea ice coverage have major implications for macroalgal abundance, on a per-biomass basis, sea ice coverage does not impact the nutritional contributions of macroalgae to food webs.

Seasonal agricultural activities and monsoon shifts drive fluctuations in nitrogen levels in eutrophic coastal waters: A case study of Xiangshan Bay, China.

Xiangshan Bay, one of China's most eutrophic semi-enclosed bays, was studied to examine the seasonal distributions of salinity, temperature, nutrients, and nitrate isotopes (δ15N and δ18O) to elucidate seasonal variations in nitrate sources and the key factors driving nitrogen level fluctuations. Based on nitrate δ15N (6.1-8.9‰) and δ18O (0-5.7‰) values, the primary nitrogen sources in Xiangshan Bay were identified as domestic sewage and agricultural runoff, influenced by seasonal agricultural activities and monsoon-driven Changjiang Diluted Water (CDW) dynamics. Nitrate levels peaked in autumn (53.1±1.6μmol/L), due to intensive agricultural activity and strong CDW intrusion driven by the northeast monsoon. Conversely, the southwest monsoon in summer, coupled with higher nitrogen uptake due to warmer temperatures and increased light availability, resulted in the lowest nitrate levels (35.2±5.4μmol/L). In winter, reduced nitrate inputs were observed, reflecting minimal agricultural activity and weaker Changjiang discharge. Differences in nitrate levels between the upper and lower bay were attributed to weaker mixing and stronger local inputs in the upper bay.

Photobioreactor design utilizing procedural three-dimensional modelling and ray tracing.

The design of photobioreactors for microalgae cultivation aims to achieve an architecture that allows the most efficient photosynthetic growth. The availability of light at wavelengths that are important for photosynthesis is therefore particularly crucial for reactor design. While testing different reactor types in practice is expensive, simulations could effectively limit the range of material and reactor design options. In this study, procedural three-dimensional modelling together with ray tracing was used to create virtual models of a conventional glass photobioreactor lit from the outside and a steel photobioreactor with embedded light sources. The measured transmittance and reflectance of Chlorella vulgaris culture were used as a basis for light interaction simulation, and spectral images of the same species were used to validate the simulation results. This type of simulation could have the potential for comparing different reactor architectures, geometries and light attenuation to facilitate the transition to large-scale cultivation. Our results show that the proposed simulator is usable in photobioreactor geometry design as well as in the estimation of available illumination on wavelengths where microalgae have strong absorption peaks, but the handling of light scattering still needs improvement. To the authors' best knowledge, this is the first attempt, not focused on a specific use case, to build a general photobioreactor design tool capable of estimating hyperspectral light attenuation in microalgae suspension. All software code and used datasets are made available for the reader as open source.

The influence of subtidal Laminaria canopies on local environmental conditions and the structure of understorey communities.

Understanding the role of species interactions (e.g. competition and facilitation) in structuring communities is a fundamental goal of ecology. It is well established that large canopy-forming seaweeds (e.g. kelps and fucoids) exert a strong influence on community structure, by offering biogenic habitat, altering environmental conditions and interacting with other species. While many studies have manipulated the density of seaweeds to causatively examine their effects on the local environment and associated communities, they are biased towards certain regions and canopy-forming species. We conducted a manipulative experiment at two subtidal sites characterised by mixed Laminaria canopies, in southwest England, UK. Three treatments were established in multiple replicate circular plots (area of 7.1m2): 0% kelp removal (i.e. unmanipulated control), 50% kelp removal (i.e. thinning), and 100% removal. Within each plot, temperature, light levels and sedimentation rates were monitored over 3 months, and after 5 months the density of juvenile kelp recruits, the biomass of understorey macroalgae and the abundance of recruiting fauna were quantified. We found kelp canopies had no impact on temperature or sedimentation rates but their removal led to marked increases in light availability, juvenile kelp recruitment and understorey macroalgal biomass. Overall, our study shows that physical disturbance to Laminaria canopies alters resource availability (i.e. light and space), leading to increased abundances of kelp recruits and understory algae. Significant reductions in kelp canopy density, driven by storm disturbance, harvesting or decreased water quality for example, would lead to shifts in community structure and ecological functioning.

Deer Browsing Increases Stem Slenderness and Crown Irregularity and Modifies the Effects of Light Gradients on Architecture of Forest Tree Saplings.

Browsing by ungulates is commonly assumed to target the upper parts of sapling crowns, leading to reduced vertical growth or even growth cessation. However, the extent to which browsing induces shifts in resource allocation toward lateral growth remains unclear. This study explores the impact of browsing intensity (BI) and light availability on the architectural traits of six temperate tree species, focusing on height-diameter ratio (H/D), crown slenderness (CL/CW), and crown irregularity (CI) across sapling height classes. Browsing pressure and architectural responses varied across height groups, reflecting diverse adaptive strategies. BI was weakly but negatively correlated with sapling height, indicating that even tall saplings (> 2 m) experience browsing, particularly in the lower crown. H/D consistently increased with BI across all height classes, with stronger effects in medium and tall saplings. Light influenced H/D differently between browsed and unbrowsed saplings: unbrowsed saplings showed reduced H/D only under high light conditions, while browsed saplings exhibited consistent reductions regardless of light levels. CL/CW was negatively but insignificantly affected by BI. Light increased CL/CW in unbrowsed saplings across all height classes but decreased it in browsed short and medium saplings, suggesting a 'pruning' effect of browsing that altered competition dynamics. Species-specific analysis of Fagus sylvatica revealed an increase in CL/CW with BI, reflecting unique adaptive responses. CI increased significantly with BI across all height classes, with the strongest effects in medium and tall saplings. Light reduced CI in browsed short saplings but had inconsistent effects on unbrowsed individuals. Variation partitioning showed that light explained most variation in H/D and CL/CW for shorter saplings, while BI predominantly influenced CI in taller ones. By integrating the effects of browsing and light, this study provides insights into juvenile tree adaptations and resilience under ecological stressors, advancing our understanding of tree growth strategies in challenging environments.

Cold Surface Waters of the Sub-Antarctic Pacific Ocean Support High Cyanophage Abundances and Infection Levels.

Cyanobacterial distributions are shaped by abiotic factors including temperature, light and nutrient availability as well as biotic factors such as grazing and viral infection. In this study, we investigated the abundances of T4-like and T7-like cyanophages and the extent of picocyanobacterial infection in the cold, high-nutrient-low-chlorophyll, sub-Antarctic waters of the southwest Pacific Ocean during austral spring. Synechococcus was the dominant picocyanobacterium, ranging from 4.7 × 103 to 1.2 × 105 cells∙mL-1, while Prochlorococcus abundances were relatively low overall, ranging from 1.0 × 103 to 3.9 × 104 cells∙mL-1. Using taxon-specific, single-virus and single-cell polony methods, we found that cyanophages were on average 15-fold, and up to 50-fold, more abundant than cyanobacteria in these waters. T4-like cyanophages (ranging from 1.7 × 105 to 6.5 × 105 phage·mL-1) were 2.7-fold more abundant than T7-like cyanophages (ranging from 3.1 × 104 to 2.8 × 105 phage·mL-1). Picocyanobacteria were primarily infected by T4-like cyanophages with more Synechococcus (4.8%-12.1%) infected than Prochlorococcus (2.5%-6.2%), whereas T7-like cyanophages infected less than 1% of both genera. These infection levels translated to daily mortality in the range of 5.7%-26.2% and 2.9%-14.3% of the standing stock of Synechococcus and Prochlorococcus, respectively. Our findings suggest that T4-like cyanophages are significant agents of cyanobacterial mortality in the cold, low-iron, sub-Antarctic waters of the South Pacific Ocean.

Predictable shifts from nutrient to energy limitation determine the responses of planktonic autotrophs, bacteria and mixoplankton to browning

Abstract Within aquatic ecosystems, heterotrophic, mixotrophic and autotrophic plankton are entangled in a complex network of competitive, predatory and mutualistic interactions. “Browning,” the increase of colored dissolved organic matter (CDOM) from terrestrial catchments, can affect this network of interactions by simultaneously decreasing light availability and increasing organic carbon and nutrients supplies. Here, we introduce a conceptual, process-based numerical model to investigate the effects of browning on a microbial food web consisting of heterotrophic bacterioplankton, bacterivorous phago-mixoplankton, autotrophic phytoplankton and the resources light, inorganic phosphorus and DOM. Additionally, we explore how the investment in autotrophic vs. phagotrophic resource acquisition influences mixoplankton performance. Several model predictions are in broad agreement with empirical observations under increasing CDOM supply, including increased bacterial biomass and inorganic phosphorous, decreased light penetration, the potential for a unimodal phytoplankton biomass response and a local minimum in mixoplankton biomass. Our results also suggest that mixoplankton with a high investment in phototrophy perform best in many conditions but that phosphorous acquisition via prey is crucial under high light-low nutrient conditions. Overall, our model analyses suggest that responses to altered CDOM supply are largely determined by systematic changes in the relative importance of nutrient vs. energy limitation of each plankton group.

Stream bryophytes promote “cryptic” productivity in highly oligotrophic headwaters

AbstractRecent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this “greening up” of HBEF streams may be due to climate change, with rising temperatures, altering terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream “greening” could be from the slow recovery of stream chemistry after decades of acid rain, which has led to rising pH, declining concentrations of toxic Al3+, and low solute concentrations. Four years of weekly algal measurements on artificial moss and ceramic tiles, along with six nutrient enrichment experiments, revealed new insights about the interactions between these two autotrophs. We found that in protected weir ponds and in stream channels, algal biomass was higher on artificial moss substrates than on tiles—with this effect amplified in the stream channels. These results suggest that bryophytes can provide physical protection from flood scour or may trap nutrients to support algal growth. In stream channels, algal biomass was higher in well‐lit habitats and time periods indicating strong light limitation. We only measured nitrogen and phosphorus limitation of algal biomass in nutrient enrichment experiments conducted within weir ponds, with higher light availability and lower flow. By comparison, results from the remaining four instream experiments provided little evidence for nutrient limitation, with only one trial showing increased algal growth in response to nutrient addition. The most striking implication of our study is the role of bryophytes in providing refugia, and potentially nutrients, to algae in shaded and oligotrophic headwater streams.

Lowering the target daily light integrals following days with excessive lighting can reduce lettuce production costs

Given the fluctuating availability of natural lighting throughout the year, supplemental light is frequently employed to maintain the optimal daily light integral (DLI) levels necessary for adequate plant growth. However, the use of supplemental light translates into higher operational costs. Recent reports suggest that plants can tolerate a day with low DLI following exposure to a day with high DLI from natural light. This was referred to as the ‘carryover’ effect. In such cases, supplemental lighting may not be necessary, resulting in energy savings. In this study, we determined if plants can withstand such DLI fluctuations over multiple days without compromising plant growth. Additionally, we calculated the energy requirements for trese treatments to evaluate the potential energy savings of the carryover effect. To test this, we cultivated lettuce plants (Lactuca sativa cv. ‘Waldmand’s Dark Green’ and ‘Rouxai’) in a walk-in grow chamber, subjecting them to six different lighting treatments. Each treatment consisted of a day with a high DLI of 22.5 mol·m-2·d-1 followed by a varying number of consecutive days with low DLI, ranging from 1 to 5 days, with DLIs of 7.5, 11.25, 12.5, 13.13, and 13.5 mol·m-2·d-1 respectively. The combined DLI for each treatment, calculated as the average DLI across high and low DLI days, was maintained at 15 mol·m-2·d-1. Additionally, we included a control treatment where plants were exposed to a constant DLI of 15 mol·m-2·d-1. We measured plant growth rate, final fresh and dry weights, leaf number, leaf area, specific leaf area, light use efficiency, and relative pigment content to assess differences in plant growth under the different lighting regimes. We observed a decrease in biomass accumulation, as indicated by a 13% reduction in final dry weight only for the treatment involving one day of high DLI followed by one day of low DLI, compared to our control. We discovered that plants can tolerate multiple days of low DLI following a day with high DLI, in contrast to the optimal values reported in the literature. This finding can lead to reduced energy consumption for supplemental lighting and consequent operational cost savings.

The effects of biomass depth distribution on phytoplankton spring bloom dynamics and composition in an Arctic fjord

Fjord systems are among the most productive and best described of Arctic marine habitats. Contributing substantially to that overall productivity, spring phytoplankton blooms are one of the most important features of fjord systems and of mid- and high-latitude oceans in general. Understanding specific mechanisms that control the timing, magnitude, and composition of these blooms is among the most central, and yet unresolved, questions within biological oceanography. To elucidate how the distribution of phytoplankton with depth affects bloom dynamics, we analyzed a comprehensive dataset on spring blooms in an Arctic fjord from three consecutive years, covering environmental drivers as well as ecological and biogeochemical dynamics. Our data show that the build-up of biomass correlated positively with the chlorophyll layer depth (CLD, defined as the depth at the bottom of the layer containing a threshold concentration of chlorophyll a), with highest rates of biomass accumulation occurring in more depth-extended distributions despite lower light availability at greater depths. Based on our results, we hypothesize that this relationship is caused by reduced grazing pressure under conditions of deepening mixing layers. Further, we postulate that changes in the depth to which phytoplankton biomass is distributed have the potential to control the species composition of the Arctic phytoplankton spring bloom, with diatoms dominating in situations with shallow CLDs and Phaeocystis pouchetii with deepening CLDs, which may impact the biogeochemistry of the studied fjord system differently.

Growth and biomass-allocation responses of arabica coffee young plants subjected to the interactive effects of root deformation and light availability

Growth and biomass-allocation responses of arabica coffee young plants subjected to the interactive effects of root deformation and light availability

Evaluation of twelve algorithms to estimate suspended particulate matter from OLCI over contrasted coastal waters

Remote sensing of suspended particulate matter (SPM) is crucial for water-quality monitoring, as it influences turbidity, light availability, or nutrient transport. This study aims to provide a comprehensive evaluation of twelve common and well-used SPM models for the Ocean and Land Color Instrument (OLCI) on-board Sentinel-3 satellite, based on different methods and assumptions, including estimation from water-leaving reflectance or proxies, a combination of semi-analytical equations, and machine learning algorithms. The models are tested in three stages: 1) performance assessment on in-situ measurements, 2) matchup exercise with OLCI and 3) visual assessment of satellite SPM products. The models are first tested on the GLORIA dataset (n = 767, 0.21 g.m−3 <SPM <2,626.82 g.m−3). The matchup analysis is then conducted in French coastal waters using the SOMLIT dataset (n = 71, 0.2 g.m−3 <SPM <722 g.m−3), based on the standard OLCI L2 remote sensing reflectance product. Finally, the visual assessment of the SPM maps provided by the twelve models is conducted for two French coastal sites. Results show that the algorithms proposed by Jiang et al. [ Remote. Sens. Environ. 258, 112386 (2021)10.1016/j.rse.2021.112386 ] and Novoa et al. [ Remote. Sens. 9, 61 (2017)10.3390/rs9010061 ] exhibit the highest score and the most accurate retrievals when compared to in-situ measurements. However, the matchup exercise shows that the method from Jiang et al. demonstrates more overall accurate SPM retrievals (Error = 49.85%, Bias = 0.55%, RMSLE = 0.35, Slope = 1.06). The visual assessment of SPM maps reveals that this model displays a larger dynamic range, making it suitable for applications in regions with a wide range of SPM concentrations. The sensitivity of these models to the atmospheric correction procedure is further explored. When all OLCI spectra are taken into account for the matchup exercise, the performance of the algorithms from Han et al. [ Remote. Sens. 8, 211 (2016)10.3390/rs8030211 ] improve, relative to the other one. Finally, the standard OLCI SPM product is evaluated, and the advantages of using the OLCI standard product over the MODIS one for studying coastal waters are discussed.

Temporal dynamics in a red alga dominated geothermal feature in Yellowstone National Park.

Alga-dominated geothermal spring communities in Yellowstone National Park (YNP), USA, have been the focus of many studies, however, relatively little is known about the composition and community interactions which underpin these ecosystems. Our goal was to determine, in three neighboring yet distinct environments in Lemonade Creek, YNP, how cells cope with abiotic stressors over the diurnal cycle. All three environments are colonized by two photosynthetic lineages, Cyanidioschyzon and Galdieria, both of which are extremophilic Cyanidiophyceae red algae. Cyanidioschyzon, a highly specialized obligate photoautotroph, dominated cell counts at all three Lemonade Creek environments. The cell cycle of Cyanidioschyzon in YNP matched that observed in synchronized cultures, suggesting that light availability plays a strong role in constraining growth of this alga in its natural habitat. Surprisingly, the mixotrophic and physiologically more flexible Galdieria, was a minor component of these algal populations. Arsenic detoxification at Lemonade Creek occurred via complementary gene expression by different eukaryotic and prokaryotic lineages, consistent with this function being shared by the microbial community, rather than individual lineages completing the entire pathway. These results demonstrate the highly structured nature of these extreme habitats, particularly regarding arsenic detoxification.

Morpho-Physiological Adjustment of Swietenia humilis Zucc. Plants to Varied Nutrient and Light Conditions and Their Performance in Nurseries and Fields Under Soils with Different Preparations

To enhance the plantation performance of Swietenia humilis Zucc., a threatened precious woody species from the dry tropics of Latin America, this study examined its morpho-physiological responses to variations in nutrient and light availability. We established a nursery trial with factorial treatments: three levels of fertilization (4, 6, and 8 g L−1 of substrate using a controlled-release fertilizer, CRF, 18-6-12) and two shade intensities (60% and 40%), alongside a full sun treatment. The field performance of nursery-raised plants was evaluated under two site conditions (with and without mechanical soil preparation) over 48 months. In the nursery, S. humilis exhibited diverse morpho-physiological characteristics influenced by the studied factors, with optimal growth observed at 6 g of the CRF and 40% shade. Mechanical soil preparation significantly improved plant survival, reducing mortality risk by 99.16% and increasing survival probability to nearly 75%. Height growth was also enhanced, being 2.5 times greater in the prepared site compared to that in the unprepared one. S. humilis showed acclimatization in the field, producing new foliage with high chlorophyll content. In conclusion, nursery management and soil site preparation influence the field performance of S. humilis. These findings have practical implications for improving the management of S. humilis in plantations across the dry tropics.

Diurnal Changes in Cloud Cover in Eastern Gabon and Their Impacts on Energy Balance, Light Availability, and Water Demand: A Case Study of the 2022 Dry Season

Abstract Western central Africa is atypical of the equatorial domain as the main dry season is cloudier than the rainy seasons. To understand this cloud cover’s diurnal evolution, we set up an infrared camera and acquired measurements of the total cloud cover fraction (TCF) and cloud optical depth at Bambidie, Gabon (0°44′30.5″S, 12°58′12.4″E), from May to October 2022. Diurnal variations in TCF can be summarized into four types, mostly discretized through the timing and duration of clouds clearing in the afternoon [early afternoon clearing (EaC), late afternoon clearing (LaC), and clear night (CNi)], while one type [no clearing (NoC)] shows overcast conditions all day long. Meteorological measurements show that NoC days record 50 W m−2 less shortwave incoming surface radiation, resulting in daytime temperatures 1°C lower than the seasonal norm, but 20% more diffuse light and 0.5 mm day−1 less ETo. Conversely, EaC days record 50 W m−2 more shortwave incoming surface radiation, leading to temperatures 1.5°C higher than the seasonal norm, but 40% more direct light. The larger water demand (0.5 mm day−1 more ETo) is partly compensated by more frequent rainfall at nighttime. The satellite estimates of Satellite Application Facilities for supporting Nowcasting and very short-range Forecasting (SAFNWC) capture the TCF variations for most of the four types well. They confirm that TCF is dominated by very low and low clouds whose dissipation in the afternoon and evolution into fractional and cumuliform convective clouds explains the clearings on EaC and LaC days. Satellite estimates also show that the four types of days extracted at Bambidie are representative of a larger-scale cloud cover evolution in western central Africa, with a west–east gradient in the timing of afternoon cloud dissipation.

The Impact of Consecutive Tropical Cyclones on Changes in Environmental Factors and Phytoplankton Distributions in Overlapping Areas

Tropical cyclones are known to have significant ecological impacts, particularly on marine productivity. This study investigates the effects of two tropical cyclones (TC “MARIA” and TC “AMPIL”) on changes in environmental factors and phytoplankton in overlapping marine areas during August 2024. Our findings indicated that TC “MARIA”, despite its lower wind speeds, resulted in significant increases in surface chlorophyll-a (Chl-a) due to its prolonged duration, while depth-integrated Chl-a showed a declining trend, suggesting limitations on phytoplankton growth due to water column instability and reduced light availability. In contrast, TC “AMPIL”, with its higher wind speeds and faster translation speed, caused more immediate disturbances, leading to increases in surface Chl-a. However, the depth-integrated Chl-a did not significantly increase, as phytoplankton growth was hindered by the succession of the two typhoons. Additionally, we observed a pronounced cooling in sea surface temperature after both typhoons, likely linked to ongoing mixing processes and atmospheric influences. This study can provide us with more insights into the interaction between tropical cyclone dynamics and marine ecology.