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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., Marine Geology, 457, ISSN:0025-3227

The Southern Ocean is warming faster than the average global ocean and is particularly vulnerable to ocean acidification due to its low temperatures and moderate alkalinity. Coccolithophores are the most productive calcifying phytoplankton and an important component of Southern Ocean ecosystems. Laboratory observations on the most abundant coccolithophore, Emiliania huxleyi, suggest that this species is susceptible to variations in seawater carbonate chemistry, with consequent impacts in the carbon cycle. Whether anthropogenic environmental change during the industrial era has modified coccolithophore populations in the Southern Ocean, however, remains uncertain. This study analysed the coccolithophore assemblage composition and morphometric parameters of E. huxleyi coccoliths of a suite of Holocene-aged sediment samples from south of Tasmania. The analysis suggests that dissolution diminished the mass and length of E. huxleyi coccoliths in the sediments, but the thickness of the coccoliths was decoupled from dissolution allowing direct comparison of samples with different degree of preservation. The latitudinal distribution pattern of coccolith thickness mirrors the latitudinal environmental gradient in the surface layer, highlighting the importance of the geographic distribution of E. huxleyi morphotypes on the control of coccolith morphometrics. Additionally, comparison of the E. huxleyi coccolith assemblages in the sediments with those of annual subantarctic sediment trap records found that modern E. huxleyi coccoliths are 2% thinner than those from the pre-industrial era. The subtle variation in coccolith thickness contrasts sharply with earlier work that documented a pronounced reduction in shell calcification and consequent shell-weight decrease of 30-35% on the planktonic foraminifera Globigerina bulloides induced by ocean acidification. Results of this study underscore the varying sensitivity of different marine calcifying plankton groups to ongoing environmental change. FCT: UIDB/04326/2020; info:eu-repo/semantics/publishedVersion

The potential use of two raw clays (Clay A: kaolin; Clay B: calcareous montmorillonite) as supplementary cementitious material (SCM) in blended cements was investigated. Cement replacement in mortars by 20% calcined Clay A and Clay B resulted in a considerable 28 day compressive strength improvement. The pozzolanic reactivity of Clay A and B is explained by characterisation of the structural changes upon calcination with XRD, ICP-MS, FT-IR, 27Al NMR, Mossbauer spectroscopy and SEM. At the temperature giving highest pozzolanic reactivity, kaolinite and montmorillonite were completely dehydroxylated, while calcite from Clay B was not completely decomposed. FT-IR, 27Al NMR and Mossbauer spectroscopy revealed considerable structural deformations of kaolinite in Clay A and montmorillonite in Clay B resulting in an amorphous, reactive state. Oxidation of iron in Clay B during calcination contributed to strong distortions of the octahedral sheet in the montmorillonite structure. Additionally, the formation of a glass phase due to reaction of coccoliths (CaCO3) and montmorillonite was observed.

Coccolithophore fluxes were determined in the Sea of Okhotsk using samples from a 1 year experiment (12 August 1990 to 12 August 1991) with sediment traps at 258 and 1061 m depth. A special study was made on Coccolithus pelagicus , using fragmentation and the degree of etching, as indicators of transport mechanisms. A Corrosion Index for C. pelagicus is developed. The coccolithophore flux pattern at 258 m depth was characterised by a strong seasonality, with flux peaks during autumn 1990 (late November to early December) and spring 1991 (March). The assemblage consisted almost entirely of the two species C. pelagicus and Emiliania huxleyi . During autumn, coccolithophore transportation to 258 m depth mainly occurred within cylindrical fecal pellets and marine snow aggregates of silicoflagellates, and through agglutination on tintinnids. Grazing caused severe fragmentation of coccoliths and disintegration of coccospheres. Marine snow aggregates contained many intact coccospheres of C. pelagicus . During spring, coccolithophores were probably removed from the euphotic zone by the ballast effect of sinking diatoms. The coccolithophore flux peak in spring occurred immediately after the ice had retreated from the trap station, and the trapped assemblage included coccoliths of subtropical species. These features indicate drifting from an ice-free location to the south or east. The coccolith and coccosphere flux at 1061 m was respectively 7 and 12 times lower than at 258 m depth, and maximum fluxes were recorded 2 months later. Increasing carbonate dissolution from 258 to 1061 m depth is expressed in the coccolithophore–CaCO 3 flux reduction of 82%, and in the increasing percentage of etched coccoliths of Coccolithus pelagicus from 32 to >90%.

In the open ocean pelagic sedimentation occurs at various scales. As a background signal, the everyday process is a rather slow and continuous rain of biogenic debris produced mainly by the planktic flora and fauna in the upper part of the water column. In addition to this, distinct regions of the oceans reveal pronounced, short-term, often seasonal sedimentation pulses following biogenic bloom events, such as the yearly coccolith blooms starting at low latitudes in late spring to early summer and spreading out into higher latitudes during summer and early autumn. A significant portion of this material, consisting of calcareous and siliceous skeletal remains as well as soft organic tissue, reaches the sea floor under the influence of gravity as marine snow and fecal pellets. This chapter presents an overview of the principal factors that control this pelagic flux through the water column and determine the character and distribution of the resulting deep-sea sediments. All modern biological groups that contribute to the pelagic sedimentation will be discussed from coccolithophorids, planktic foraminifers and pteropods (calcareous oozes) to diatoms, radiolarians and dinoflagellates (opal oozes). It outlines, in addition, the history of ancient pelagic sediment factories since the evolutionary invention of planktic life on Earth and discusses how the biosphere influenced the whole earth system through changes in ocean chemistry and how these changes, in turn, controlled the evolution of marine life.

The response of coccolithophore export production to non-El Nino and El Nino conditions was monitored during a two year period (26 March 1996–3 April 1998) in the centre of the Santa Barbara Basin (34°14′ N; 120°02′ W), California borderland. During the 1997–1998 El Nino the seasonal cycle of the surface water conditions was altered by the presence of a relatively warm, low-nutrient and low-salinity water mass. Throughout the studied period, the total mass flux is dominated by lithogenic components with terrigenous input being highest during El Nino period. Although the annual biogenic sediment fluxes were largely dominated by silica, with diatoms as the major contributor to the opal flux, the coccolith flux was high during the entire studied period. During winter 1998 carbonate fluxes were unusually high for this time of the year. Moreover, a strong positive correlation between organic carbon and opal flux indicates that siliceous phytoplankton production is the most important factor controlling organic carbon flux in the Santa Barbara Basin. A positive correlation between carbonate and organic carbon fluxes existed indeed during the final phase of El Nino, when the correlation between organic carbon and opal fluxes is poor. The sinking coccolithophore assemblage was dominated by Emiliania huxleyi, followed by Florisphaera profunda, Umbilicosphaera sibogae, Gephyrocapsa oceanica, Helicosphaera carteri, Gephyrocapsa muellerae and Calcidiscus leptoporus. The intensification of El Nino 1997–1998 conditions altered the typical hydrographic structure of the Santa Barbara Basin weakening the spring upwelling as reflected by reduced diatom fluxes. In contrast, the coccolith flux was relatively high during El Nino, particularly for the tropical species G. oceanica, that showed a pronounced increase in its flux when the spring upwelling was reduced under El Nino conditions. In addition, we have found that this species has a strong correlation with nitrite, phosphate and iron availability in surface water.

Recently, many kinds of CO2 fixation method have been proposed. In the present work, a biosolar reactor system has been used for CO2 removal, biomass production and calcification by microalgae which include calcareous algae. Solar light was collected by Fresnel lenses, transmitted to the photobioreactor which contained a bundle of light diffusing optical fibers (LDOFs) and then distributed through the algal culture. The biosolar reactor system was applied for the cultivation of Emiliania huxleyi, a unicellular calcareous alga. E. huxleyi was cultured for eight days using natural sunlight and 43 mg/l of CaCC3 particle (coccolith) was obtained.