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Inorganic minerals that form via regulated biological processes exhibit remarkable properties. This is due to the involvement of macromolecules that control biomineralization. Even though the interactions of these biopolymers with solid mineral phases are intensely studied, not much is known about their involvement in the preceding steps of intracellular transport of the mineral building blocks. In this work, the model system of coccolith calcite crystallization is utilized to address the role of mineral‐associated polysaccharides in the transport of calcium ions. State‐of‐the‐art cryo‐electron tomography is used to image in situ ion‐rich dense phases in the wild‐type and in two mutant strains, defected in coccolith production. The results show that the abundance and solubility of the calcium‐rich condensates need to be finely tuned for proper crystallization. When the native macromolecular assemblage is compromised, calcium is still present in the calcifying fluid as a solute, but this is not sufficient for coccolith development. These results suggest that biomineralizing systems achieve superior regulation of crystallization due to the use of dense macromolecule‐rich phases. [ABSTRACT FROM AUTHOR]

In mid-May 2020, a coccolithophore bloom of Gephyrocapsa oceanica Kamptner, 1943 was observed in Sagami Bay, Japan, possibly for the first time in 25 years. This species is a common yet elusive taxon in the waters around Japan, but there has only been one report of a bloom observation in Sagami Bay in 1995. The G. oceanica bloom in 2020 was observed by the combined approach of the JAXA ocean color remote sensing satellite "Shikisai" and field surveys. The true-color RGB images from the satellite showed the initial bloom in Tokyo Bay appears to have advected into Sagami Bay on May 5. On May 15, ad hoc field sampling was conducted based on visual confirmation from the shore. Nitrate, nitrite and phosphate concentrations at the sea surface were 3.28 µM, 0.11 µM and 0.29 µM, respectively, and higher than the median of May from 1997 to 2019. Chlorophyll a concentration was 2.23 µg L-1 at the sea surface, and cell density was 5.3 × 10³ cells mL-¹. The large bloom appears to have reached the western shorelines of the bay, and dispersed counterclockwise within the bay. The bloom reached an estimated 1119.02 km² surface expression on May 17, and completely disappeared by May 24. Further, the median value of 19'-hexanoyloxyfucoxanthin (a signature pigment of haptophytes, including coccolithophores) concentration has been increasing from 2017 to 2020, and the coastal area of Sagami Bay may have changed to a region favorable for haptophytes. [ABSTRACT FROM AUTHOR]

Coccolithophores are well-known haptophytes that produce small calcium carbonate coccoliths, which in turn contribute to carbon sequestration in the marine environment. Despite their important ecological role, only two of eleven haptophyte plastid genomes are from coccolithophores, and those two belong to the order Isochrysidales. Here, we report the plastid genomes of two strains of Ochrosphaera neapolitana (Coccolithales) from Spain (CCAC 3688 B) and the USA (A15,280). The newly constructed plastid genomes are the largest in size (116,906 bp and 113,686 bp, respectively) among all the available haptophyte plastid genomes, primarily due to the increased intergenic regions. These two plastid genomes possess a conventional quadripartite structure with a long single copy and short single copy separated by two inverted ribosomal repeats. These two plastid genomes share 110 core genes, six rRNAs, and 29 tRNAs, but CCAC 3688 B has an additional CDS (ycf55) and one tRNA (trnL-UAG). Two large insertions at the intergenic regions (2 kb insertion between ycf35 and ycf45; 0.5 kb insertion in the middle of trnM and trnY) were detected in the strain CCAC 3688 B. We found the genes of light-independent protochlorophyllide oxidoreductase (chlB, chlN, and chlL), which convert protochlorophyllide to chlorophyllide during chlorophyll biosynthesis, in the plastid genomes of O. neapolitana as well as in other benthic Isochrysidales and Coccolithales species, putatively suggesting an evolutionary adaptation to benthic habitats. [ABSTRACT FROM AUTHOR]

The marine biological calcification and photosynthesis, which can produce particulate inorganic and organic carbon (PIC and POC), have the opposite effects on seawater pCO2. Coccolithophores are a kind of marine unicellular algae with both of the two biological processes, and PIC and POC productions of them can shape the water column rain ratio as a dominant driver for Earth's carbon cycle. Thus, the changes in ancient coccolithophore PIC:POC can be important for the paleoceanographic and paleoclimatic studies of carbon cycle modeling. However, ancient coccolithophore PIC:POC is poorly constrained because of the occasional occurrences of intact coccospheres in deep ocean sediments, as detached coccoliths are commonly the remnants of fossilized coccolithophores. Here, we carry out the biometric analysis of coccosphere and coccolith from the living cells of Emiliania huxleyi and Gephyrocapsa oceanica in the South China Sea, and confirm a significant correlationship between their PIC:POC and lateral coccolith aspect ratio (ARL). ARL here is defined by the ratio of mean coccolith thickness with respect to coccolith length. A linear regression is given, PIC:POC=15.023∗ARL−0.083 $\mathrm{P}\mathrm{I}\mathrm{C}:\mathrm{P}\mathrm{O}\mathrm{C}=15.023\ast A{R}_{L}-0.083$ (R2 = 0.59, n = 121), for the reconstruction of ancient Noelaerhabdaceae coccolithophore PIC:POC based on individual coccoliths in marine sediments. Based on this equation, we reconstruct ancient Noelaerhabdaceae coccolithophore PIC:POC since 14 million years ago (Ma) using published coccolith data, which reveal a long‐term decrease in PIC:POC from 7 to 4 Ma. We suggest that such a change in coccolithophore physiology may be induced by a simultaneous long‐term decline in seawater calcium concentration. Plain Language Summary: Coccolithophores are a kind of marine algae which produce calcium carbonate through calcification. Photosynthesis of coccolithophores uses seawater CO2, on the contrary, calcification releases CO2. Therefore, the relative strength of calcification and photosynthesis, that is termed PIC:POC, can determine whether coccolithophore growth is a net CO2 sink or source. The knowledge of ancient coccolithophore PIC:POC is important to understand the mechanisms of Earth carbon cycle and climate changes in the geological history, as coccolithophores are one of the major components of marine carbon cycle. However, it remains unclear the characters of ancient coccolithophore PIC:POC, because detached or loosened coccoliths, which are the exoskeleton of a coccolithophore cell, are more commonly found in marine sediments, rather than intact coccospheres. Here, based on the biometric analysis of coccosphere and coccolith morphology, we refine a method to estimate ancient coccolithophore PIC:POC based on detached coccolith geometry. Key Points: Coccosphere PIC content is estimated based on coccosphere geometryPIC:POC of Emiliania huxleyi and Gephyrocapsa oceanica is estimated in the modern South China SeaAncient coccolithophore PIC:POC can be estimated by coccolith geometry in sediments [ABSTRACT FROM AUTHOR]

The calcite platelets of coccolithophores (Haptophyta), the coccoliths, are among the most elaborate biomineral structures. How these unicellular algae accomplish the complex morphogenesis of coccoliths is still largely unknown. It has long been proposed that the cytoskeleton plays a central role in shaping the growing coccoliths. Previous studies have indicated that disruption of the microtubule network led to defects in coccolith morphogenesis in Emiliania huxleyi and Coccolithus braarudii. Disruption of the actin network also led to defects in coccolith morphology in E. huxleyi, but its impact on coccolith morphology in C. braarudii was unclear, as coccolith secretion was largely inhibited under the conditions used. A more detailed examination of the role of actin and microtubule networks is therefore required to address the wider role of the cytoskeleton in coccolith morphogenesis. In this study, we have examined coccolith morphology in C. braarudii and Scyphosphaera apsteinii following treatment with the microtubule inhibitors vinblastine and colchicine (S. apsteinii only) and the actin inhibitor cytochalasin B. We found that all cytoskeleton inhibitors induced coccolith malformations, strongly suggesting that both microtubules and actin filaments are instrumental in morphogenesis. By demonstrating the requirement for the microtubule and actin networks in coccolith morphogenesis in diverse species, our results suggest that both of these cytoskeletal elements are likely to play conserved roles in defining coccolith morphology. [ABSTRACT FROM AUTHOR]

Pelagic calcifying protists such as coccolithophores and foraminifera represent an important microbial component of the marine carbon cycle. Although their calcitic shells are preserved in oceanic sediments over millennia, their resilience in the future decades is uncertain. We review current literature describing the response of calcifying protists to ocean acidification and temperature warming. We examine these key ecological and biogeochemical processes through the cellular perspective, exploring the physiological, metabolic, and molecular responses of calcifying protists. Ocean acidification is a chemical process that takes place in the seawater outside the cell, whereas protists calcify inside a modified cellular microenvironment. The function of these calcification compartments depends on cellular response to ocean acidification, such as maintaining pH homeostasis. The response of calcifying protists to ocean acidification and temperature warming is species-specific, with no unifying trends but rather a range of sensitivity levels. Coccolithophores and foraminifera display physiological sensitivity that may hamper their ecological success in comparison to non-calcifying species. Yet, certain species may be more adaptable, especially when comparing to highly vulnerable calcifying molluscs as pteropods. As the molecular machinery mediating cellular calcification is not fully resolved, as well as the functional role of the calcitic shell, our ability to predict the fate of calcifying microorganisms in a warmer, more acidic ocean is limited. We propose the urgent need to expand the study of these model systems by advancing cell biology approaches, to better understand the impact of climate change on microbial food webs in the ocean., (© The Author(s) 2025. Published by Oxford University Press on behalf of the International Society for Microbial Ecology.)

We present a new high-resolution reconstruction of annual sea-surface temperatures (SSTa) and net primary productivity (NPP) using novel coccolithophore-based models developed for the Eastern Equatorial Pacific (EEP). We combined published coccolithophore census counts from core-tops in the Eastern Pacific with 32 new samples from the Equatorial region, to derive a new statistical model to reconstruct SSTa. Results show that the addition of the new EEP samples improves existing coccolithophore-based SST-calibrations, and allow reconstructing SSTa in the EEP with higher confidence. We also merged the relative abundance of deep-photic species Florisphaera profunda in the same surface sediment samples with existing calibration datasets for tropical regions, to reconstruct annual NPP. Both temperature and productivity calibrations were successfully applied to fossil coccolith data from Ocean Drilling Project Site 1240, in the EEP. The coccolith-based SSTa estimates show a cooling during the Last Glacial Maximum (LGM) and the Younger Dryas, and warming at the start of the Holocene. This pattern differs in the timing and magnitude of the temperature changes from other available SST-reconstructions based on biogeochemical and faunal proxies. We discuss these discrepancies to be the result of different proxy sensitivities to insolation forcing, seasonal bias, and/or preservation artifacts. Reconstructed annual NPP shows a general decreasing trend from the late last glacial period to recent times, which we relate to the weakening of wind-driven equatorial upwelling towards the Holocene. We also calculated carbon export using our SSTa and NPP reconstructions, and compared to other geochemical-based reconstructions for the same location. Our coupled SSTa-NPP reconstruction provides key data to more fully assess the evolution of primary and export productivity as well as organic carbon burial in the EEP, with implications for its role in global biogeochemical cycles across glacial terminations.

The crystallographic orientation and its relationship to the morphology of coccoliths were investigated for the Neogene-Quaternary calcareous nannoplankton Umbilicosphaera lineage using scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The c -axis of the calcite forming the distal shield elements was inclined upward at 66–68° (U. sibogae), 65–68° (U. foliosa), 57–58° (U. rotula), and 55–57° (U. patera) from the coccolith plane. Accordingly, the outward dip angle of one of the { 10 1 ¯ 4 } faces forming the surface of the distal shield of U. patera coccolith was shallower than those of U. sibogae and U. foliosa , explaining the nearly flat distal shield and the steep inner slope, formed by another equivalent { 10 1 ¯ 4 } face, around the central opening of U. patera. Our results showed that the evolution from U. rotula to U. patera during the Late Miocene was not accompanied by a change in crystallographic orientation. In contrast, the evolution from U. patera to U. sibogae and U. foliosa during the Pliocene was accompanied by a rotation of the orientation. The crystallographic orientation of calcite nuclei on the baseplate with a combination of other factors would have resulted in species-specific differences in shield shape and suture lines within the same phylogeny, consequently producing morphological diversity in the coccolith throughout geological time. • The crystallographic orientation and its relationship to the morphology of coccoliths were investigated for Umbilicosphaera lineage using SEM-EBSD. • The c-axis of the calcite forming the distal shield elements was inclined upward at 55°–68° from the coccolith plane. • The evolution from U. patera to U. sibogae and U. foliosa was accompanied by a rotation in the crystallographic orientation. • The orientation of the crystals that are first precipitated on the baseplate play an important role in species-specific differences of the coccoliths within the same phylogeny. [ABSTRACT FROM AUTHOR]

Carbonate dissolution and deposition in the deep ocean is a critical component of carbon cycle, but detailed pictures of carbonate dynamics below the Carbonate Compensation Depth (CCD) remains poorly understood. In this study, we present a ∼ 420 thousand years record of carbonate content below CCD in IODP Site U1433 at 4.4 km water depth in the South China Sea (SCS). Instead of carbonate-free sediment, we observed that the carbonate content in this deep site could reach as high as 40%. The dissolution-resistant biogenic carbonate, coccoliths, and stable isotope ratio of bulk carbonate were analyzed to trace the carbonate sources. The coccolith assemblage in IODP Site U1433 shows an unrealistic feature of high productivity, which indicates a lateral transport of coccoliths from the northern SCS to the central basin. Coccoliths' contribution to total carbonate was on average 30% and could be as high as ∼80%. Their contribution to carbonate increased at the expense of the dissolution of other biogenic carbonate, such as foraminifera, and decreased with the dilution of other terrestrial carbonate particles. According to the thickness of coccoliths, significant dissolution of coccoliths only happened when the carbonate content dropped below 3%. Marbles from Taiwan, with negative oxygen isotope ratios, and early diagenetic carbonates from carbonate platform nearby, with both negative carbon and oxygen isotope ratios, could be the other important sources besides the marine biogenic carbonate. With help of numerical simulations, we estimated that the lateral transport by turbidity currents could contribute up to 70–90% of the deep-sea sediment in the central basin of SCS. These new findings enrich our knowledge of the carbon fluxes from continental margins to the deep ocean as a key part of the carbon cycle. • Coccoliths in the SCS central basin contribute ∼30% to total carbonates. • Stable isotope ratios of carbonates indicate two mixing lines clearly. • Lateral transport dominates in the SCS deep-sea sediment. [ABSTRACT FROM AUTHOR]

The eastern Mediterranean Sea lies under the influence of high- and low-latitude climatic systems. The northern part of the basin is affected by Atlantic depressions and continental and polar air masses that promote intermediate and deep-water formation. The southern part is influenced by subtropical conditions and monsoon activity. Monsoon intensification results in enhanced freshwater discharge from the Nile River and other (now dry) systems along the North African margin. This freshwater influx into the Mediterranean Sea reduces surface water buoyancy loss. Disentangling the influences of these diverse climatic forcings is hindered by inherent proxy data limitations and by interactions between the climatic forcings. Here we use a wealth of published and new paleoclimate records across Termination II to understand the impacts of the higher latitude and subtropical/monsoon climate influences on coccolithophore ecology and holococcolith preservation in Aegean Sea sediment core LC21. We then use these findings to interpret coccolith assemblage variations at Ocean Drilling Program Site 967 (located nearby LC21, at the Eratosthenes Seamount) during multiple glacial-interglacial cycles across the Middle Pleistocene (marine isotopic stages 14–9). The LC21 analysis suggests that holococcolith preservation was enhanced during Heinrich Stadial 11 (∼133 ka) and cold spell C26 (∼119 ka). These two events have been previously linked to cold conditions in the North Atlantic and Atlantic Meridional Overturning Circulation weakening. We propose that associated atmospheric perturbations over the Mediterranean Sea promoted deep-water formation, and thus holococcolith preservation. Similarly, in the Middle Pleistocene (MIS 14-9) of Site 967, we observe temporal coincidence between ten episodes of enhanced holococcolith preservation and episodes of Atlantic Meridional Overturning Circulation slowdown. In Site 967, we also identified repeated fluctuations in placoliths and in Florisphaera profunda , which indicate nutricline depth variations. The development of a deep chlorophyll maximum is associated with the North Africa and wet phases, as recently observed using elemental proxy records at Site 967, during the deposition of sapropel layers. A further deep chlorophyll maximum development is identified during MISs 12 and 10, as a result of pycnocline and nutricline shoaling within the lower part of the photic zone due to glacial sea-level lowering and water mass transport reduction at both the Gibraltar and Sicily Straits. Finally, enhanced holococcolith preservation during cold/dry events is clearly correlated to weakened monsoon activity in both Africa and Asia. • F. profunda in sapropel S5 is in line with maximum rates of δ18O Asian speleothems and with the CH 4 overshoot in EDC; • F. profunda DCM development in glacials, due to sea-level lowering that reduced water-mass transport through straits; • Holococcolith enhanced preservation during cold spells, in response to AMOC slowdown and weakened monsoon activity; [ABSTRACT FROM AUTHOR]