Ocean Productivity Research Articles

Near-surface particulate backscattering observations with bio-optical Lagrangian drifters

Abstract Particulate matter concentration is an essential ocean variable (EOV) useful for understanding biogeochemical processes, improving ocean productivity estimates, and constraining coupled physical and biogeochemical numerical models. While direct observations of this parameter are difficult to obtain, the optical backscattering coefficient of marine particles (bbp) can be used as a reliable proxy. However, most in-situ multi-spectral bbp measurements are ship-borne or obtained from moored systems, thus with a limited spatial and temporal coverage. Utilizing Surface Velocity Programme (SVP) drifting buoys with self-contained backscatter sensors designed for extended deployment periods offers a promising solution for collecting data in challenging marine environments. In this study, we presented for the first time the integration of a commercially available, high-frequency and multispectral optical backscatter sensor into an SVP drifter, the so-called BO-SVP drifter designed to collect bbp measurements near the ocean surface. bbp measurements obtained by the BO-SVP drifter were reliable over a wide range of environmental conditions, showing a good agreement with independent datasets (relative bias < 10%; relative standard deviation < 36%). The BO-SVP drifter captures the satellite sub- and pixel scale variability by combining the Lagrangian approach and a high frequency sampling. This configuration enables the acquisition of measurements across numerous pixels in a single day, enhancing validation activities for ongoing and future satellite products and the quantification of associated uncertainties. The measurements acquired by these platforms can offer valuable insights into particle distribution at fine spatial scales, daily variability, and its relationship with water masses type and ocean dynamics.

Large igneous provinces played a major role in oceanic oxygenation events during the mid-Proterozoic

AbstractLow atmospheric oxygen levels during the mid-Proterozoic were occasionally interrupted by transient high oxygen levels. The cause of mid-Proterozoic ocean redox variability remains unclear. Here we investigate mercury chemostratigraphy across the Jixian section of North China Craton through two oxygenation intervals. Abnormal spikes in mercury concentration and excursions of mercury isotopes are observed in the Dahongyu and Hongshuizhuang formations, which occur just below the two oxygenation intervals, respectively. These mercury anomalies suggest that the two oxygenation events were preceded by subaerial volcanism. Furthermore, the two oxygenation intervals show increased nutrient concentrations and negative shifts in mercury isotopes, indicating that enhanced weathering and terrestrial nutrient influx occurred during oxygenation intervals. We infer that in the breakup setting of the Columbia supercontinent, large igneous province volcanism and its efficient low-latitude weathering could rapidly increase terrestrial nutrient influx into the ocean, promoting oceanic productivity and a pulsed rise in oxygen levels.

Expanded subsurface ocean anoxia in the Atlantic during the Paleocene-Eocene Thermal Maximum

The ocean has experienced substantial oxygen loss over recent decades, affecting marine ecosystems and fisheries. Investigating ocean deoxygenation during hyperthermal events, such as the Paleocene-Eocene Thermal Maximum (PETM), offers insights into its future dynamics. Here, sediment cores from the South Atlantic reveal a pronounced decline in foraminifera-bound δ15N, concurrent with an increase in marine barite δ34S and enhanced ocean productivity during the PETM. These findings suggest an expansion of oxygen-deficient zones (ODZs) from suboxia to anoxia in the thermocline, with ammonium and sulfide accumulation. Model simulations indicate “ammonium-type” ODZs were driven by Southern Ocean warming and elevated productivity. Intense fixed nitrogen loss at the upper boundary of these ODZs, along with increased oceanic phosphorus inventory, likely spurred a compensatory rise in N2 fixation. While the Pacific might experience different oxygenation conditions during the PETM, parts of the Atlantic thermocline became anoxic, highlighting potential spatial variabilities of ocean deoxygenation under global warming.

Patterns of (micro)nutrient limitation across the South Pacific Ocean

Nutrient limitation regulates phytoplankton growth throughout much of the global ocean and its assessment is important for our understanding of future changes in ocean productivity. The South Pacific Ocean represents a vast region where limiting nutrients have so far been investigated with only a handful of experiments. Here we report the results of eleven nutrient addition bioassay experiments conducted across the South Pacific Ocean at ca. 30°S as part of the GEOTRACES GP21 expedition. Nitrogen addition alone stimulated chlorophyll-a accumulation at all sites, whilst increases were larger following supplementary addition of iron in the eastern and central basin, and phosphate in the western basin. Enhanced iron stress following nitrogen addition in the eastern and central basin further pointed towards ambient iron concentrations approaching co-limiting levels. The overall east-to-west shift in serial limiting nutrients from iron to phosphate was attributed to a broadscale east-west increase in iron availability relative to nitrogen.

Analyses of sea surface chlorophyll a trends and variability from 1998 to 2020 in the German Bight (North Sea)

Abstract. Satellite remote sensing of ocean colour properties allows observation of the ocean with high temporal and spatial coverage, facilitating the better assessment of changes in marine primary production. Ocean productivity is often assessed using satellite-derived chlorophyll a concentrations, a commonly used proxy for phytoplankton concentration. We used the Copernicus GlobColour remote sensing chlorophyll a surface concentration to investigate seasonal and non-seasonal variability, temporal trends, and changes in spring bloom chlorophyll a magnitude. Complementary, we analysed the chlorophyll a relationship with sea surface temperature and mixed-layer depth in the German Bight from 1998 to 2020. Empirical orthogonal functions were employed in order to investigate dominant spatial and temporal patterns (modes) related to the main processes of chlorophyll a variability. Multi covariance analysis was used to extract the dominant structures that maximize the covariance between chlorophyll a and sea surface temperature mixed-layer depth fields. High levels of chlorophyll a were found near the coast, showing a decreasing gradient towards offshore waters. A significant chlorophyll a positive trend was observed close to the Elbe estuary and adjacent area, while 55 % of the German Bight was characterized by a significant chlorophyll a negative trend. The chlorophyll a non-seasonal variability showed that the first four modes explained around 45 %, with the first and second modes related to inter- and intra-annual variability, respectively, observed in the temporal principal components spectral analyses. Monthly chlorophyll a concentration anomalies co-varied by 45 % with sea surface temperature anomalies and 23 % with mixed-layer depth anomalies. The monthly averages of chlorophyll a anomaly fields were suitable to investigate long-term trends and variability. The rising water temperature, combined with its indirect effects on other variables, can partially explain the observed trends in chlorophyll a.

Glacial interglacial variations in the natural iron fertilization during the low sea ice periods along the eastern continental margin of Antarctica

The Southern Ocean sequesters atmospheric CO2 through biological pumps, though its driving factors are debated. Modern productivity is regulated by natural iron fertilization from micronutrient influx through dust, regeneration, and Antarctic glaciers and sea ice melting (ice melt). The productivity along the eastern Antarctic continental margin was low during the last glacial period and gradually increased through the deglacial to Late Holocene, marked by distinct productivity peaks. The micronutrients also varied similarly, with reduced glacial influx and an increase in the Holocene, which may cause productivity peaks. Therefore, the coherence of enhanced productivity and micronutrient influx is considered as enhanced iron fertilization period. The productivity peaks declined within ∼1.5 kyr, mostly due to the Ekman transport and sea ice formation. Along with ice melt, the independent weathering pattern that responds with glacial- interglacial ice volume changes suggest the source of micronutrients is not terrigenous. Shelf interaction of oceanic currents can influence the water column nutrient stock significantly, while its utilization occurs during reduced ice periods (low sea ice and high glacier melting) for productivity. Therefore, enhanced natural iron fertilization periods are considered as ice low periods that occurred in a periodicity of 2 kyrs, at ∼7.5 kyr BP, ∼5.5 kyr BP, ∼4 kyr BP, ∼ 2.5 kyr BP, and ∼0.5 kyr BP, likely due to the combined effects of atmospheric and oceanographic factors driven by the high amplitude regional temperature variability during the mid to late Holocene.

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition

Abstract Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dust aerosols are a key source of bio-essential nutrients, can be transported in the atmosphere over large distances, and ultimately deposited onto the ocean's surface, alleviating nutrient limitation and increasing oceanic primary productivity. Currently, the linkages between desertification, dust emissions and ocean fertilization remain poorly understood. Here, we show that dust emitted from Southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected. The conditions required for triggering blooms of this magnitude are anomalous, but current trends in air temperatures, aridity, and dust emissions in Southern Africa suggest that such events could become more probable in the future. Together with the recent findings on ocean fertilization by drought-induced megafires in Australia, our results point toward a potential link between global warming, drought, aerosol emissions, and ocean blooms.

Seasonality of zooplankton active flux in subtropical waters

AbstractThe biological carbon pump (BCP) is the mechanism by which the ocean transports organic matter below the mixed layer, exporting or sequestering it for years to millennia. Physical transport of dissolved and particulate organic carbon, the sinking of particles, and the carbon transported by diel and seasonal vertical migrants are the three main mechanisms of the BCP. In the study of active flux, seasonality is almost unknown and changes in ocean productivity during the annual cycle could promote differences in this transport. Here, we show the results of a cruise performed during spring in the Canary Current System, where we studied zooplankton active flux in two transects from the coastal zone off Northwest Africa toward the ocean. We measured biomass and the enzymatic activity of the electron transfer system (ETS) as a proxy for respiration in the water column down to a depth of 900 m. Compared with a previous survey during fall, we found higher values of specific ETS activity in the mesopelagic zone, promoting a higher active flux. Our results showed that the seasonality of active flux is driven not only by differences in biomass but also by differences in respiration rates in the mesopelagic zone, mainly due to differences in zooplankton body size. A review of the zooplankton active flux values around the Canary Islands showed a fourfold increase during spring compared with other seasons. This small window of higher flux should be considered in models of active carbon export in the ocean.

Cross-frontal variability of phytoplankton productivity in the Indian sector of the Southern Ocean during austral summer of 2010–2018

Oceanic phytoplankton productivity, which regulates atmospheric CO2, is crucial for unraveling the complexities of the global carbon cycle. Despite its substantial contribution to the global carbon budget and its critical role in anthropogenic carbon sink, the Southern Ocean (SO) remains under-sampled due to logistical challenges. The present study attempts to elucidate the variability of water column primary production (PP) in the Indian Sector of the Southern Ocean (ISSO) by examining associated physicochemical parameters and physiological conditions of phytoplankton that drive this variability. The study revealed the nutrient limitation in the region north of the Subantarctic Front (SAF) and light limitation coupled with intense zooplankton grazing in the region south of the SAF. Coastal waters exhibit higher PP, characterized by the prevalence of large phytoplankton. The SAF displayed maximum productivity among the fronts, while the Polar Front 2 (PF-2) recorded the lowest. The water column PP varies from 27.01 to 960.69 mg C m−2 d−1 in the frontal region, while the coastal waters recorded productivity up to 1083.56 mg C m−2 d−1. Phytoplankton in the frontal regions indicated a stable surface abundance, except north of the Subtropical Front (STF), where the oligotrophic condition fosters the growth of picoplankton, subjected to high grazing by microzooplankton. Conversely, in the colder coastal waters, the phytoplankton experienced physiological acclimation. Model-based estimates of PP highlighted the efficacy of the Carbon-based Production Model (CbPM) in estimating net PP (NPP) in these polar waters, surpassing the Vertically Generalized Production Model (VGPM) and Eppley-VGPM. Notably, all model-based PP estimates significantly improved with in situ chlorophyll as input instead of satellite-retrieved chlorophyll. While the models performed well in the coastal water, their performance was suboptimal in the frontal region. This study advances our understanding of the intricate dynamics of phytoplankton productivity in the SO, offering valuable insights for future research endeavors.

Multiple controls on the preservation of organic matter in the lower Mississippian Luzhai Formation black shale in southern China

The early Carboniferous experienced profound climate cooling that drove the Earth's climate from a mid-Paleozoic greenhouse into the Late Paleozoic Ice Age. Several climate cooling events have been reported, including the Tournaisian and Visean (early to mid-Early Carboniferous). In this study, we perform multi-proxy analyses (organic carbon isotopes, nitrogen isotopes, major and trace elements and organic petrology/geochemistry) of samples from an early Carboniferous section in Nandan region (Guangxi, China). Our goal is to investigate the global carbon‑nitrogen cycle, and associated oceanic productivity and redox perturbations, during a key climatic transition interval, as well as the controls on organic matter enrichment in the sediments. The carbon and nitrogen isotope profiles of the Nandan section record major perturbations during the mid-Tournaisian and early Visean. The mid-Tournaisian carbon isotope excursion (TICE) is marked by a positive δ13Corg shift of 1.8 ‰ (from −27.7 ‰ to −25.9 ‰), correlating with a positive δ15N shift. The early Visean carbon isotope excursion (VICE) is characterized by a positive shift in δ13Corg (from −28.2 to −25.5 ‰, with an excursion magnitude of 2.7 ‰), but associated with a negative shift in δ15N (from +5 ‰ to +4 ‰). The positive δ13Corg excursions during these events most likely reflect enhanced organic matter burial with expansion of anoxic seafloor in the global ocean. The drop in nitrogen isotope values in the early Visean is interpreted to be linked with less denitrification under more oxic conditions. The decrease of organic matter contents up section is consistent with the shift to more oxic conditions and increased sedimentary dilution caused by sea-level fall, which is ultimately controlled by orogenic events and climate cooling.

Dynamics of subsurface chlorophyll maxima in the northern Indian Ocean

Subsurface chlorophyll maxima (SCM) significantly contributes to oceanic primary productivity, emphasizing the need to study its dynamics and governing mechanisms. We used datasets from various platforms to investigate relationships between the SCM characteristics (SCM depth (ZSCM), SCM magnitude (Chlmax), SCM thickness (TSCM)) and environmental variables modulated by various physical processes in the Northern Indian Ocean (NIO). In the Arabian Sea (western NIO), seasonal processes like convective mixing and upwelling, primarily regulated the SCM characteristics. In the Bay of Bengal (eastern NIO), SCM characteristics were jointly influenced by fresh water influx, barrier layer formation, presence of eddies, and the propagation of Kelvin and Rossby waves. Any changes in these oceanic processes, potentially driven by climate change, could therefore impact oceanic primary production. Additionally, a positive association obtained between Chlmax and downward CO2 flux, while a shallower ZSCM, associated with higher concentrations of DMS, indicated SCM's role in regulating atmospheric gases.

Unraveling the declining Indian ocean primary productivity and key drivers

Climate change severely affects the third-largest maritime regions, disrupting physical and biogeochemical processes and Ocean Net Primary Productivity (NPP), which affects the marine food web, fisheries, and livelihoods of surrounding regions. This study examined changes in NPP in the Indian Ocean and its drivers. The Ocean warming, equatorial and Pacific warm pools, stratification fluctuations, circulation changes, nutrient transport, monsoons, and different seasonal processes significantly influenced these microbial mats. The Copernicus Marine Environment Monitoring Service (CMEMS) reanalysis data shows a high declining NPP trend in the Indian Ocean (-0.85 mgC/m3/day/yr). The high warming rate (0.01–0.02 °C/yr) primarily drives regional NPP alterations. The causal discovery analysis shows that sea surface temperature (SST) provides high negative feedback to NPP during all-time delays. Nitrate and phosphate show a positive association, reinforcing positive feedback, and Redfield stoichiometry holds paramount significance in fostering the NPP. Negative feedback is observed from the Western Pacific Index (WP), Oceanic Niño Index (ONI), Multivariate ENSO Index (MEI), and Pacific Decadal Oscillation (PDO). This climate pattern can modify mesoscale atmospheric circulation, influence currents, and change temperature and nutrient availability. The positive connection between the Southern Oscillation Index (SOI) and NPP underscores the complex interplay between climate patterns in the region. The Indian Ocean Dipole (IOD) negatively feedbacks the NPP. Various other climate patterns and events indirectly affect IO biogeochemical processes.

New insights on Late Pliensbachian-Early Toarcian seawater chemistry based on belemnite rostra element content

Belemnites were a type of cephalopod abundant in the Jurassic and Cretaceous, whose fossils have been extensively used for paleo-oceanographic studies. For this study, we analyzed 69 elements by Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS) in 15 belemnite rostra from the West Rodiles section in the Asturian Basin, Northern Spain. We aim to determine if belemnite rostra carbonate chemistry reflects changes in seawater chemistry during the Late Pliensbachian–Early Toarcian time interval and examine how belemnites can be used to trace known drivers of the Early Toarcian Oceanic Anoxic Event (T-OAE) and associated oceanographic processes.Discarding drastic intra-species effects and assuming a similar influence of growth rates, diet, and other physiological processes for all analyzed belemnite specimens and taking into consideration the sizeable analytical uncertainty, we assess if determined belemnite rostra element chemistry reflects broad and relative changes in paleo-seawater chemistry. Many determined elements are present in only ppb amounts, and their interpretation is uncertain. We found that Mg, Mn, and P increase in the interval chronocorrelative to the T-OAE. This is interpreted to have resulted from an increase in these elements' inventory in seawater due to an increase in continental weathering and fluvial runoff associated with this global event. Iron, K, and Na contents decrease upwards in the section, potentially indicating that these elements became limited and likely hampered oceanic productivity. Our study also found a correspondence between a change in the behaviour of several elements, warming, the T-OAE negative CIE, and a reduction in the diversity and size of both calcareous nannofossils and belemnites in the study area.

Propagating Neotethys slab break-off beneath Iran following Arabia-Eurasia collision

The closure of the Paleo- and Neotethys resulted in a long history of subduction of oceanic crust and production of a large variety of Phanerozoic magmatic rocks in the region occupied by present day Iran. Adakitic rocks of varying ages are common in this area and have distinctive geochemical signatures that have been variably linked to slab break-off or melting of the lower continental crust. The geographic distribution and age of the adakitic rocks indicates a potential younging trend from northwest to southeast Iran, but this trend was interrupted by an older outlier in the area of Tafresh, in the central part of the Neotethys arc. We obtained new geochemical and U-Pb geochronological data for Eocene volcanic and Miocene intrusive rocks from this anomalous locality. Our results show that adakitic signatures are only present in younger Miocene intrusive porphyritic bodies and not in the main calc-alkaline Eocene volcanic succession as previously thought. The Tafresh adakitic porphyritic bodies have an age of 15.7 ± 0.1 Ma (n = 183, 2σ SE), which fits well with a regional younging of the adakites towards the southeast of Iran. The Tafresh adakitic rocks are classified as the high-silica variety, and show trace element signatures and isotopic values that are consistent with melting of the lower continental crust. We hypothesise that progressive slab break-off provided a mechanism for the formation of high-silica adakitic rocks along the former Neotethys arc.

Future changes in coastal upwelling and biological production in eastern boundary upwelling systems

Upwelling along oceanic eastern boundaries has attracted significant attention due to its profound effects on ocean productivity and associated biological and socioeconomic implications. However, uncertainty persists regarding the evolution of coastal upwelling with climate change, particularly its impact on future biological production. Here, using a series of state-of-the-art climate models, we identify a significant seasonal advancement and prolonged duration of upwelling in major upwelling systems. Nevertheless, the upwelling intensity (total volume of upwelled water) exhibits complex changes in the future. In the North Pacific, the upwelling is expected to attenuate, albeit with a minor magnitude. Conversely, in other basins, coastal upwelling diminishes significantly in equatorward regions but displays a slight decline or even an enhancement at higher latitudes. The climate simulations also reveal a robust connection between changes in upwelling intensity and net primary production, highlighting the crucial impact of future coastal upwelling alterations on marine ecosystems.

Hemispherical scale mechanisms of nitrate formation in global marine aerosols

Nitrogen oxides (NOx) in the atmosphere directly affect air quality; however, their oxidation products (e.g., nitrate) are essential nutrients in terrestrial and marine ecosystems. To date, the mechanism and rate of nitrate formation in the global-scale marine boundary layer remains uncertain. Herein, aerosol nitrate isotopes covering the global ocean were analysed and observations indicated that nitrate formation was dominated by the proportion between the hydroxyl radical (daytime) and ozone (nighttime) pathways in the Northern Hemisphere (NH), whereas it changed to the BrO (Antarctic iceberg emission) pathway in the Southern Hemisphere (SH). These differences in the pathways suggested that the NOx removal (nitrate formation) efficiency was higher in the NH, which could be responsible for the much higher nitrate concentrations in the NH than in the SH (over twice). This study can assist in formulating effective policies to mitigate global NOx pollution and improve our understanding of the impact of increasing NOx concentrations on global ocean productivity.

Microbial respiration in contrasting ocean provinces via high-frequency optode assays

Microbial respiration is a critical component of the marine carbon cycle, determining the proportion of fixed carbon that is subject to remineralization as opposed to being available for export to the ocean depths. Despite its importance, methodological constraints have led to an inadequate understanding of this process, especially in low-activity oligotrophic and mesopelagic regions. Here, we quantify respiration rates as low as 0.2 µmol O2 L-1 d-1 in contrasting ocean productivity provinces using oxygen optode sensors to identify size-fractionated respiration trends. In the low productivity region of the North Pacific Ocean at Station Papa, surface whole water microbial respiration was relatively stable at 1.2 µmol O2 L-1 d-1. Below the surface, there was a decoupling between respiration and bacterial production that coincided with increased phytodetritus and small phytoplankton. Size-fractionated analysis revealed that cells <5 µm were responsible for the majority of the respiration in the Pacific, both at the surface and below the mixed layer. At the North Atlantic Porcupine Abyssal Plain, surface whole water microbial respiration was higher (1.7 µmol O2 L-1 d-1) than in the Pacific and decreased by 3-fold below the euphotic zone. The Atlantic size-fraction contributions to total respiration shifted on the order of days during the evolution of a phytoplankton bloom with regular storm disturbances. The high-resolution optode method used in the Atlantic captured these significant shifts and is consistent with coinciding stain-based respiration methods and historical site estimates. This study highlights the dynamic nature of respiration across vertical, temporal, and size-fractionated factors, emphasizing the need for sensitive, high-throughput techniques to better understand ocean ecosystem metabolism.

Convergent reductive evolution of cyanobacteria in symbiosis with Dinophysiales dinoflagellates

The diversity of marine cyanobacteria has been extensively studied due to their vital roles in ocean primary production. However, little is understood about the diversity of cyanobacterial species involved in symbiotic relationships. In this study, we successfully sequenced the complete genome of a cyanobacterium in symbiosis with Citharistes regius, a dinoflagellate species thriving in the open ocean. A phylogenomic analysis revealed that the cyanobacterium (CregCyn) belongs to the marine picocyanobacterial lineage, akin to another cyanobacterial symbiont (OmCyn) of a different dinoflagellate closely related to Citharistes. Nevertheless, these two symbionts are representing distinct lineages, suggesting independent origins of their symbiotic lifestyles. Despite the distinct origins, the genome analyses of CregCyn revealed shared characteristics with OmCyn, including an obligate symbiotic relationship with the host dinoflagellates and a degree of genome reduction. In contrast, a detailed analysis of genome subregions unveiled that the CregCyn genome carries genomic islands that are not found in the OmCyn genome. The presence of the genomic islands implies that exogenous genes have been integrated into the CregCyn genome at some point in its evolution. This study contributes to our understanding of the complex history of the symbiosis between dinoflagellates and cyanobacteria, as well as the genomic diversity of marine picocyanobacteria.

Mesoscale eddy variability over the Bay of Bengal in response to the contrasting phases of extreme Indian Ocean Dipole events

The present study is aimed to investigate the mesoscale eddy variability in response to the two contrasting phases of extreme Indian Ocean Dipole (IOD) events, the 2016 (negative mode) and 2019 (positive mode). A quantification of the eddy characteristics was done by estimating the number of eddies, eddy radius, eddy amplitude, and eddy rotation speed for each of the contrasting events. It is found from the analysis, that the phase of IOD has a significant impact on the spatiotemporal characteristics of eddies over the bay. The number of eddies increased and a gradual shift from anti-cyclonic to cyclonic eddies was observed during the positive IOD year. Eddies formed during 2016 had an average amplitude of 0.085 m, rotation speed was around 0.345 cm/s and eddy radius, on average was found to be 81.25 km. The presence of a unique eddy feature on the east coast of Sri Lanka was observed which remained as a cyclonic eddy during the negative IOD and as an anti-cyclonic eddy during the positive IOD. The sea surface height anomaly showed a dip of −0.1 m at the core of the cyclonic eddy and a +0.4 m bulge was observed at the core of the anti-cyclonic eddy. A high negative SST anomaly of −0.5 °C was observed at the core of the cyclonic eddy. A drastic increase in the mixed layer depth was seen with the presence of the anti-cyclonic eddy. Analysis of the temperature and salinity vertical profiles showed that the anti-cyclonic eddy had a greater influence on the vertical profile than the cyclonic eddy. Both the eddies contributed significantly to upper ocean primary productivity by different mechanisms. Eddy-induced upwelling was predominant in the cyclonic eddy whereas eddy stirring was predominant in the anti-cyclonic eddy.

A Comprehensive Study of Light Quality Acclimation in Synechocystis Sp. PCC 6803.

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality remains underexplored. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes that fine-tune light capture, such as state transitions, or the efficiency of energy transfer from phycobilisomes to photosystems (PS). We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the plastoquinone (PQ) pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.