Coccolithophore Bloom Research Articles

Impact of airborne algicidal bacteria on marine phytoplankton blooms.

Ocean microbes are involved in global processes such as nutrient and carbon cycling. Recent studies indicated diverse modes of algal-bacterial interactions, including mutualism and pathogenicity, which have a substantial impact on ecology and oceanic carbon sequestration, and hence, on climate. However, the airborne dispersal and pathogenicity of bacteria in the marine ecosystem remained elusive. Here, we isolated an airborne algicidal bacterium, Roseovarius nubinhibens, emitted to the atmosphere as primary marine aerosol (referred also as sea spray aerosols) and collected above a coccolithophore bloom in the North Atlantic Ocean. The aerosolized bacteria retained infective properties and induced lysis of Gephyrocapsa huxleyi cultures.This suggests that the transport of marine bacteria through the atmosphere can effectively spread infection agents over vast oceanic regions, highlighting its significance in regulating the cell fate in algal blooms.

Coccolithophore Distribution in the Western Black Sea in the Summer of 2016

Coccolithophores are an important component of phytoplankton abundance and biomass in the brackish environments of the Black Sea. Here, the abundance, composition, and distribution of coccolithophores were investigated in water samples taken from the first 50 m at 18 stations in the western Black Sea during a coccolithophore bloom, in June 2016. The total cell abundances ranged from 2 to 763 × 104 coccospheres L−1; Emiliania huxleyi was the most dominant species, but also Syracosphaera spp. (S. dilatata and S. molischii), Acanthoica (A. acanthifera and A. quattrospina), and Algirosphaera robusta displayed remarkably high concentrations. The formation of the seasonal thermocline significantly affects the vertical distribution of coccolithophores. Emiliania huxleyi, Syracosphaera spp., and Acanthoica spp. were restricted to the upper part of the water column, whereas high abundances of Algirosphaera robusta occurred below the thermocline. Overall, our results show significant differences in the vertical (ANOSIM R = 0.50, p = 0.0001) and spatial (ANOSIM R = 0.18, p = 0.0006) distribution of coccolithophores. Higher abundances of E. huxleyi and Syracosphaera spp. were recorded in the northwestern inner shelf region when compared to the open-sea samples. The observed coccolithophore spatial distribution is suggested to be mostly associated with the influx of less saline river water with high nutrient concentrations.

Biological sources and sinks of dimethylsulfide disentangled by an induced bloom experiment and a numerical model

AbstractDimethylsulfide (DMS) is a climatically active trace gas promoting cloud formation. The biochemical precursor of DMS, dimethylsulfoniopropionate (DMSP), is a phytoplankton metabolite and a source of reduced sulfur for many microbial species. Because of the complex interactions between their many producers and consumers, the dynamics of DMSP and DMS in the ocean are still poorly constrained. In this study we measure particulate DMSP, dissolved DMSP (), and DMS concentrations in seven mesocosms where two consecutive phytoplankton blooms (first, pico‐ and nano‐algae; second, Emiliania huxleyi) were induced by nutrient addition, and we build a mechanistic numerical model to identify the sources and sinks that best account for the observations. The mesocosms were designed as replicates but differ from each other by their E. huxleyi virus abundance due to stochastic differences in initial conditions. The model shows that heterotrophic bacteria cannot be the only consumers of . A fraction of dissolved must be consumed by phytoplankton to avoid excessive accumulation during the first bloom. The induced blooms increase DMS concentration by 220% on average, until an increase in the abundance of DMS‐consuming bacteria brings DMS concentration back to its pre‐bloom value, after 3 weeks of experiment. Therefore phytoplankton blooms can increase DMS emission to the atmosphere, but only during a transient regime of a few weeks. The model also shows that the DMS yield, production and emission are increased when the coccolithophore bloom is terminated by a viral infection, but decreased if the infection occurs several days before the bloom can reach its maximum.

Environmental Drivers of Coccolithophore Growth in the Pacific Sector of the Southern Ocean

AbstractThe Great Calcite Belt (GCB) is a band of high concentrations of suspended particulate inorganic carbon (PIC) spanning the subantarctic Southern Ocean and plays an important role in the global carbon cycle. The key limiting factors controlling coccolithophore growth supporting this high PIC have not yet been well‐characterized in the remote Pacific sector, the lowest PIC but largest area of the GCB. Here, we present in situ physical and biogeochemical measurements along 150°W from January to February 2021, where a coccolithophore bloom occurred. In both months, PIC was elevated in the Subantarctic Zone (SAZ), where nitrate was >1 μM and temperatures were ∼13°C in January and ∼14°C in February, consistent with conditions previously associated with optimal coccolithophore growth potential. The highest PIC was associated with a relatively narrow temperature range that increased about 1°C between occupations. A fresher water mass had been transported to the 150°W meridian between occupations, and altimetry‐informed Lagrangian backtracking estimates show that most of this water was likely transported from the southeast within the SAZ. Applying the observations in a coccolithophore growth model for both January and February, we show that the ∼1.7°C increase in temperature can explain the rise in PIC between occupations.

Daily turnover of active giant virus infection during algal blooms revealed by single-cell transcriptomics.

Giant viruses infect many unicellular eukaryotes, including algae that form massive oceanic blooms. Despite the major impact of viruses on the marine ecosystem, the ability to quantify and assess active viral infection in nature remains a major challenge. We applied single-cell RNA sequencing, to profile virus and host transcriptomes of 12,000 single algal cells from a coccolithophore bloom. Viral infection was detected already at early exponential bloom phase, negatively correlating with the bloom intensity. A consistent percent of infected coccolithophores displayed the early phase of viral replication for several consecutive days, indicating a daily turnover and continuous virocell-associated metabolite production, potentially affecting the surrounding microbiome. Linking single-cell infection state to host physiology revealed that infected cells remained calcified even in the late infection stage. These findings stress the importance of studying host-virus dynamics in natural populations, at single-cell resolution, to better understand virus life cycle and its impact on microbial food webs.

Viral infection switches the balance between bacterial and eukaryotic recyclers of organic matter during coccolithophore blooms

Algal blooms are hotspots of marine primary production and play central roles in microbial ecology and global elemental cycling. Upon demise of the bloom, organic carbon is partly respired and partly transferred to either higher trophic levels, bacterial biomass production or sinking. Viral infection can lead to bloom termination, but its impact on the fate of carbon remains largely unquantified. Here, we characterize the interplay between viral infection and the composition of a bloom-associated microbiome and consequently the evolving biogeochemical landscape, by conducting a large-scale mesocosm experiment where we monitor seven induced coccolithophore blooms. The blooms show different degrees of viral infection and reveal that only high levels of viral infection are followed by significant shifts in the composition of free-living bacterial and eukaryotic assemblages. Intriguingly, upon viral infection the biomass of eukaryotic heterotrophs (thraustochytrids) rivals that of bacteria as potential recyclers of organic matter. By combining modeling and quantification of active viral infection at a single-cell resolution, we estimate that viral infection causes a 2–4 fold increase in per-cell rates of extracellular carbon release in the form of acidic polysaccharides and particulate inorganic carbon, two major contributors to carbon sinking into the deep ocean. These results reveal the impact of viral infection on the fate of carbon through microbial recyclers of organic matter in large-scale coccolithophore blooms.

Reduced salinity exacerbates the viral infection on the coccolithophorid Emiliania huxleyi at elevated pCO2

The blooms of coccolithophores are usually terminated by their viruses. However, little has been documented on the interplay between the host with virus under different environmental conditions. We investigated the relationship of Emiliania huxleyi (BOF92) and its virus (EhV99B1) after the coccolithophorid had acclimated to different levels of salinity (S35: 35‰; S25: 25‰) and CO2 (AC: 400 μatm; HC: 1000 μatm) for about 15 generations. Our results showed that the virus infection decreased the growth of E. huxleyi along with decreased photochemical efficiency and photosynthetic carbon fixation under all the combinations of the treatments. Lowered salinity exacerbated the impacts of the viral infection on the growth and photosynthetic performance of E. huxley. The elevated pCO2 appeared to have alleviated the impacts of the viral infection on its photosynthetic performance with enhanced levels of Fv/Fm, by about 49% under S35 and by about 16% under S25, respectively. Nevertheless, the elevated pCO2 enhanced the virus burst size by about 18% under the high and by about 46% under the low levels of salinity, respectively. It is concluded that reduced salinity under the elevated pCO2 exacerbates the impact of the virus on E. huxleyi, leading to the highest burst sizes and the lowest photosynthetic carbon fixation, and the enhanced photochemical efficiency and increased levels of Chl a under the elevated pCO2 could have facilitated the energy supply for the virus multiplication in the infected cells of E. huxleyi.

Influence of the Accuracy of Chlorophyll-Retrieval Algorithms on the Estimation of Solar Radiation Absorbed in the Barents Sea

The aim of this work is to study the influence of errors on the accuracy of estimation of absorbed solar energy in the visible spectral range in the water column of the Barents Sea occurring due to the use of various satellite ocean color chlorophyll-retrieval algorithms. The estimates of absorbed energy are based on data obtained during field experiments conducted in various parts of the Barents Sea in June-August 2021, as well as on modeling results. A new regional algorithm for evaluation of chlorophyll concentration in the Barents Sea (B22) is presented as a data source. This algorithm provides more accurate estimates compared to the standard MODIS algorithm under conditions of coccolithophore bloom. Comparing of the results of hydro-optical modeling to the data of shipboard hydro-optical measurements made it possible to validate the obtained data and confirmed the correctness of the selected models. Furthermore, we calculate the parameters of underwater light fields and the absorbed thermal energy in the visible spectral range in the seawater column, showing that differences in the chlorophyll concentration due to the accuracy of satellite bio-optical algorithms (30–50%) have little effect on the vertical distribution of solar energy absorbed in the seawater column.

The influence of particle concentration and bulk characteristics on polarized oceanographic lidar measurements.

Oceanographic lidar measurements of the linear depolarization ratio, δ, contain information on the bulk characteristics of marine particles that could improve our ability to study ocean biogeochemistry. However, a scarcity of information on the polarized light‐scattering properties of marine particles and the lack of a framework for separating single and multiple scattering effects on δ have hindered the development of polarization‐based retrievals of bulk particle properties. To address these knowledge gaps, we made single scattering measurements of δ for several compositionally and morphologically distinct marine particle assemblages. We then used a bio‐optical model to explore the influence of multiple scattering and particle characteristics on lidar measurements of δ made during an expedition to sample a mesoscale coccolithophore bloom. Laboratory measurements of linear depolarization revealed a complex dependency on particle shape, size, and composition that were consistent with scattering simulations for idealized nonspherical particles. Model results suggested that the variability in δ measured during the field expedition was driven predominantly by shifts in particle concentration rather than their bulk characteristics. However, model estimates of δ improved when calcite particles were represented by a distinct particle class, highlighting the influence of bulk particle properties on δ. To advance polarized lidar retrievals of bulk particle properties and to constrain the uncertainty in satellite lidar retrievals of particulate backscattering, these results point to the need for future efforts to characterize the variability of particulate depolarization in the ocean and to quantify the sensitivity of operational ocean lidar systems to multiple scattering.

Sinking velocity of small particles in the Black Sea: Vertical distribution and seasonal variability from continuous Bio-Argo measurements of backscattering

High-resolution Bio-Argo measurements of backscattering ( bbp ) were used to study the vertical distribution and time variability of the sinking of small, highly reflective particles in the Black Sea in the 0–200 m layer. The evolution of particles is divided into three stages: formation, sinking, and removal. The formation of small, highly reflective particles is mainly related to early summer and early winter coccolithophore blooms and the formation of suspended oxidized manganese in the suboxic zone. The removal rate of the particles was estimated from the vertical distribution of bbp in relation to its values at the layers of particle formation. Further, contour analysis of the time-depth diagram of bbp anomalies was used to automatically estimate the vertical distribution and seasonal and interannual variability of sinking velocity ( w ). The average value of w is ~0.8 m/day, which agrees with laboratory estimates of coccolith sinking ( Fritz and Balch, 1996 ). Physical processes significantly affect w : mixed layer deepening in late autumn-early winter increase w up to 1–1.5 m/day; warming and a decrease in density of upper layers promote coccolithophores deepening in summer ( w = 0.9–1.1 m/day). Minimum sinking velocity is observed in the warm period of a year in the strongly stratified layers of the main pycnocline at 40–80 m. On interannual time scales, we observed an increase in w during the strongest coccolithophore blooms, which is probably related to the enhanced particle aggregation. Sinking particles after winter coccolithophore blooms are traced up to the suboxic zone, where it probably affects the settling of manganese-containing particles and related biochemical processes. • Temporal and vertical variability of sinking velocity (w) is estimated using Bio-Argo bbp data. • Mixed layer deepening, stratification, and warming affect variations in w. • The estimated average sinking velocity of coccoliths is ~0.8 m/day. • Winter particles formed in the upper layers affect particles dynamics in the suboxic zone. • On interannual time scales w increases during strongest coccolithophore blooms.

Seasonal and Long-Term Variability of Coccolithophores in the Black Sea According to Remote Sensing Data and the Results of Field Investigations

Based on satellite data from the SeaWiFS, MODIS-Aqua, and MODIS-Terra scanners, the long-term dynamics of coccolithophores in the Black Sea and their large-scale heterogeneity have been studied. During the twenty years in May and June, mass development of coccolithophores population of different intensities was recorded annually. Summer blooms of coccolithophores reached peak levels in 2006, 2012, and 2017, after abnormally cold winters. It was noted that in conditions of low summer temperatures, the blooming of coccolithophores could be significantly reduced or acquire a local character (2004). In the anomalous cold summer of 2001, coccolithophore blooms was replaced by the mass growth of diatoms. Over twenty years, numerous signs of coccolithophores mass development in the cold season have been revealed. Winter blooms develop mainly in warm winters with periods of low wind activity. The formation of a thermocline and the surface layer’s stability are essential factors for initiating winter blooms of coccolithophores. It was noted that after the winter blooms of coccolithophores, their summer growth was poorly expressed. It is shown that during periods of rapid growth, the bulk of coccolithophores is concentrated in the upper mixed layer and thermocline. During the blooming period, the share of coccolithophores in phytoplankton biomass constituted 70–85%. The intensity of coccolithophore’s blooms is associated with the previous diatoms’ growth level. The effect of eddies circulation on the distribution and growth of coccolithophores is considered.

Empirical algorithm for detecting coccolithophore blooms through satellite observation in the Barents Sea

Coccolithophores are a key phytoplankton group with a major influence on the carbon cycle in global oceans. Understanding its phenological responses to climate change is vital, particularly in Arctic regions that are experiencing warming faster than the global average. Ocean color remote sensing is a powerful tool that provides the global distribution and spatial extent of coccolithophore blooms. However, remotely observing coccolithophore blooms in Arctic regions is challenged by severe conditions, such as heavy cloud cover. In this work, an ocean color index (CI)-based approach is developed to detect coccolithophore blooms in the Arctic Sea by using Moderate Resolution Imaging Spectroradiometer (MODIS) images. The optical properties of clouds and coccolithophore blooms are characterized by employing the band difference of Rayleigh-corrected reflectance (ρR) at 412 and 469 nm (CI412–469) and 555 and 645 nm (CI555–645), respectively. A hybrid threshold is further determined to classify coccolithophore bloom and nonbloom waters. Results show that the algorithm can reduce the negative effects of heavy clouds and persistent fog on detecting coccolithophore blooms and increase the coverage of satellite observation. Compared with the traditional particulate inorganic carbon concentration-based approach, the algorithm yields more coverage and frequency of coccolithophore blooms. Global evaluation reveals that the CI-based algorithm has great potential applications in global oceans and different ocean color sensors.

Alaskan Seabird Die-Offs

Prior to 2015, seabird die-offs in Alaskan waters (Northern Gulf of Alaska, eastern Bering Sea, eastern Chukchi Sea) were rare, typically occurred in mid-winter, and were linked to epizootic disease events (Bodenstein et al., 2015) or above-average ocean temperatures associated with strong El Nino-Southern Oscillation events. An exception was late summer of 1997, a year with unusually warm waters in the southeastern Bering Sea, when possibly as many as 10% of the several million short-tailed shearwaters (Ardenna tenuitortris) present in the area died of starvation because their principal prey, euphausiids, were scarce or hard to find in a widespread coccolithophore bloom (Baduini et al., 2001). Since 2015, such mass mortality events have been annual occurrences. In 2015, between 470,000 and 1.03 million common murres (Uria aalge) were estimated to have died in the Gulf of Alaska due to anomalous ocean conditions and the impacts on forage fish associated with the 2014–2016 Pacific marine heatwave (Piatt et al., 2020; Arimitsu et al., 2021). Another large die-off event occurred during late summer of 2019 (Figure 1), when over 10,000 carcasses of short-tailed shearwaters washed onto beaches of Bristol Bay and the Alaska Peninsula in the southeastern Bering Sea. Total mortality during that summer was likely much greater than reported given the region’s expansive coastline and sparse human population.

Spectral variations of the remote sensing reflectance during coccolithophore blooms in the Western Black Sea

Among the many calcifying marine organisms, coccolithophores are the major producer of particulate inorganic carbon (PIC). Calcium carbonate plates covering coccolithophores, called coccoliths and released during blooms, are responsible for a large increase of the water reflectance. Aiming at investigating the spectral features of the remote sensing reflectance RRS(λ) of marine waters during coccolithophore blooms, this study exploits the radiometric data of Ocean Color sites of the Aerosol Robotic Network (AERONET-OC) in the Western Black Sea (Galata and Gloria/Section-7) by focusing on bloom events that occurred in 2017 and 2020. The analysis, besides showing elevated RRS(λ) in the blue-green spectral region in the presence of coccoliths, confirms a shift toward the blue of the RRS(λ) spectra as the bloom declines and coccoliths accumulate at the surface. Results also document a decreased capability of determining the bloom state in the presence of optically complex waters such as those associated with river runoff. Finally, the comparison of satellite versus AERONET-OC radiometric data for the extreme conditions created by the presence of coccolithophores, indicates agreements between RRS(λ) not significantly different from those previously determined for various satellite data products in the absence of appreciable concentrations of coccoliths.

Linking ocean colour features in the Western Iberian margin to wave-induced sediment resuspension and coccolithophore patches

Two ocean colour features in the western Iberian margin (western Europe) were described in present work. They were identified in 10 years (2002–2012) of MODIS-AQUA normalized water-leaving radiance (nLw) at 555 nm and their causes were investigated using complementary satellite, in-situ and model data. One feature was a band of high nLw555 (>0.8 mW cm−2 μm−1 sr−1) with exceptionally large widths (>20 km) along the coast. Over the 10-year period, this wide coastal band of high nLw555 only occurred during winter, following better the increases in wave height, than the increases in precipitation and river discharge. The band seemed particularly associated with episodes of large wave heights (>6 m), under weak thermal stratification and northerly winds. Findings suggest that the band is the signature of exceptional offshore extensions of the more reflective turbid coastal waters, as a result of wave-induced sediment resuspension along the coast. The other feature consisted in areas of equally high nLw555, but separated from the coast by more than 40 km. These offshore areas of high nLw555 shared spectral signatures of phytoplankton, namely coccolithophores, typically formed during spring following water column re-stratification and reached larger areas after winters with deeper oceanic mixed layers. Less commonly, they also occurred from summer to autumn. Results indicate they are mainly the signature of enhanced coccolithophore abundances that also create turbid reflective waters due to their calcite plates. The used methodology separated the two features in time and therefore seems to allow for satellite monitoring of sediment resuspension and coccolithophore blooms off west Iberia and similar coastal environments, which is particularly relevant for detecting events of sediment transport, potentially linked to water quality problems, and long-term changes in phytoplankton composition.

Quasi-tropical cyclone caused anomalous autumn coccolithophore bloom in the Black Sea

Abstract. A quasi-tropical cyclone (QTC) observed over the Black Sea on 25–29 September 2005 caused an exceptionally strong anomalous autumn coccolithophore bloom that lasted for more than 1.5 months. The QTC induced intense upwelling, causing a decrease in sea surface temperature of 15 ∘C and an acceleration of the cyclonic Rim Current up to extreme values of 0.75 m s−1. The Rim Current transported nutrient-rich Danube plume waters from the northwestern shelf to the zone of the cyclone action. Baroclinic instabilities of the plume boundary caused intense submesoscale processes, accompanied by mixing of the shelf and upwelling of the waters. These processes triggered the initial growth of remote sensing reflectance (Rrs) on the offshore front of the plume, indicating the beginning of the coccolithophore bloom. Furthermore, the bloom shifted to the zone of the strongest upwelling in the western cyclonic gyre. Intense vertical entrainment of nutrients in this area caused the increase in chlorophyll a concentration (Chl), which was then followed by a strong bloom of coccolithophores. Advection by the Rim Current spread the bloom over the entire southern part of the Black Sea, more than 1000 km from its initial source. A month after the QTC action, Rrs in these areas reached a value of 0.018 sr−1, corresponding to an estimate of a coccolithophore concentration of 107 cells per liter.

Extremely strong coccolithophore blooms in the Black Sea: The decisive role of winter vertical entrainment of deep water

The Black Sea is characterized by powerful summer coccolithophore blooms with strong interannual variability. In this paper, we used satellite and Bio-Argo measurements to show that the emergence of extremely strong blooms in several years was caused by intense vertical entrainment of nutrients from deep isopycnal layers during winter convection. In the highly stratified Black Sea, the depths of maximum nutrient concentrations are tightly associated with certain isopycnals. Due to this, the density of the winter upper mixed layer can be used as an indicator of the amount of newly entrained nutrients penetrating into the euphotic layer. In years with the weak bloom of coccolithophores, the average density in the mixed layer during February–March was less than 1013.9–1014.2 kg m−3. In years with moderately strong blooms (2006, 2008, and 2019) the density reached 1014.25–1014.3 kg m−3, while with the strongest blooms (2012 and 2017) it was 1014.35–1014.45 kg m−3. Such differences in density corresponded to a twofold and threefold difference in the newly entrained amount of phosphate, which is known to be the main nutrient that stimulates the growth of coccolithophores in the Black Sea. Despite the long-term rise of average winter temperature in the Black Sea, an increase in density has been observed in the upper layer in the recent period caused by the rise of its salinity, the sharpest since 2014. The increase in salinity of upper layers weakens the vertical haline stratification and intensifies vertical mixing and related nutrient fluxes, which can explain the extremely strong coccolithophore blooms observed in the recent period, particularly in a moderately cold 2017.

Anomalous Phenomena in the Development of Phytoplankton in the Black Sea on the Basis of Remote Sensing Data

Anomalous phenomena in the development of phytoplankton in the Black Sea for the period of 2000–2020 have been recorded on the basis of satellite data. Anomalous summer blooms of diatoms were detected in the field of chlorophyll a for the blooming periods of 2001, 2010, and 2015. These blooms were unusual for the summer periods and developed under conditions of a negative anomaly in the surface layer temperature caused by active wind mixing. The highest level of development of summer blooms of coccolithophore was recorded in 2006, 2012, and 2017. These phenomena have been observed after abnormally cold winters. It has been shown that in some years, under conditions of low summer temperatures and active wind mixing, the summer vegetation of coccolithophores is poorly manifested and can be replaced by the development of diatoms. Satellite data over a twenty-year period demonstrated numerous signs of mass development of coccolithophores during the cold season. Winter blooms of coccolithophorids occur in warm winters with low wind activity. It has been noted that after the winter blooms of coccolithophores, their summer vegetation is largely smoothed. The influence of hydrometeorological factors on the seasonal and interannual variability of phytoplankton is discussed.

Salvando el planeta con biotecnología apropiada: 4. Cultivo de cocolitóforos e implementación

Cultivating coccolithophore algae for carbon sequestration is discussed. Coccolithophores have been major calcium carbonate producers in the world’s oceans for about 250 million years. Today, they account for about a third of the total marine CaCO3 production by coating their single cells externally with plates of microcrystalline CaCO3. The possibility that these algae could be used to trap atmospheric CO2 with existing technology has not been widely considered. There is scope for both high technology cultivation in bioreactors and low technology cultivation in terraced raceway ponds or lagoons on tropical coastal sites. The latter could produce a sludge of pure CaCO3 as a feedstock for cement production in place of the fossilised limestone currently used (cement production accounts for around 8% of industrial fossil CO2 emissions). On the high seas coccolithophores naturally produce extensive blooms, which emit the volatile gas dimethyl sulfide to the atmosphere, where it promotes formation of clouds that block solar radiation. The vision is for aquaculture nurseries onboard factory ships, cultivating both coccolithophores and bivalve molluscs, creating and maintaining blooms of coccolithophores in the oceanic high seas to sequester carbon from the atmosphere and generate cloud cover to cool the immediate environment.

Detection of Coccolithophore Blooms With BioGeoChemical-Argo Floats.

Coccolithophores (calcifying phytoplankton) form extensive blooms in temperate and subpolar oceans as evidenced from ocean‐color satellites. This study examines the potential to detect coccolithophore blooms with BioGeoChemical‐Argo (BGC‐Argo) floats, autonomous ocean profilers equipped with bio‐optical and physicochemical sensors. We first matched float data to ocean‐color satellite data of calcite concentration to select floats that sampled coccolithophore blooms. We identified two floats in the Southern Ocean, which measured the particulate beam attenuation coefficient (c p) in addition to two core BGC‐Argo variables, Chlorophyll‐a concentration ([Chl‐a]) and the particle backscattering coefficient (b bp). We show that coccolithophore blooms can be identified from floats by distinctively high values of (1) the b bp/c p ratio, a proxy for the refractive index of suspended particles, and (2) the b bp/[Chl‐a] ratio, measurable by any BGC‐Argo float. The latter thus paves the way to global investigations of environmental control of coccolithophore blooms and their role in carbon export.