CaCO3 Accumulation Research Articles

Ethyl methanesulfonate (EMS) mediated dwarfing mutation provides a basis for CaCO3 accumulation by enhancing photosynthetic performance in Ceratostigma willmottianum Stapf.

Ceratostigma willmottianum Stapf is a unique chalk gland (salt-excreting) plant from China, with a salt gland structure that excretes white crystals of calcium carbonate (CaCO3), which has potential biomineralization and carbon sequestration functions. Due to the narrow distribution of wild germplasm resources, there is a lack of diversity of new varieties to satisfy commercial development and scientific exploration. Therefore, we used ethyl methanesulfonate (EMS) mutagenesis to obtain new dwarf mutant germplasm, and analysed it in terms of morphology, growth, photosynthesis, salt glands, and excretion traits. All four dwarfing mutant strains (DM1, DM2, DM3, and DM4) exhibited extreme dwarfing (62.28%, 62.28%, 74.55% and 61.68% reduction in plant height, respectively), faster growth, increased belowground root biomass, and earlier bud differentiation and flowering. Photosynthetic capacity was enhanced: chlorophyll content, maximum quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qP), electron transfer rate (ETR), net photosynthesis (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), and transpiration (Tr), were significantly higher in leaves of DM mutants. The density of salt glands per unit leaf area and average Ca2+ excretion rate of individual salt glands increased significantly (especially in DM2), and CaCO3 accumulation per unit leaf area was 28.57% higher than that of the wild type. Pearson correlation analysis showed that photosynthetic capacity was significantly and positively correlated with CaCO3 excretion. The above study not only provided enriched new germplasm of C. willmottianum, but also important research material for studying the mechanism of CaCO3 excretion by salt glands and carbon sequestration capacity of biomineralization.

Multilevel Micronanoscale Texture Effects on Fly Wing Membrane-Water Droplet Interaction.

The wettable surface or nonwettable surface that is derived from a multilevel micronanoscale structure is abundant in nature and biomimetic commodities. Those hoverflies with the seta-coated wing membrane detached from impacting free-falling raindrops were observed in static states. A hoverfly wing membrane with well-ordered setae was identified as a robust nonwettable surface, and the static water contact angle θ on the wing membrane at the microscopic scale is 136.84 ± 0.98°. Hoverfly wing membrane-water droplet interaction with the actual truth and the theoretical models was discussed and indicated that the theoretical calculation might not state the actual situation, arising from the membrane or seta-drop-bubble interaction and those multilevel micronanoscale structure characteristics on the wing membrane. Detailed investigation on nonwettable surface-wettable surface transformation with surface CaCO3 accumulation in a carbonization reaction and the characteristic transformation toward the hoverfly wing membrane with the multilevel micronanoscale structure was carried out. Then, the CaCO3 accumulation on PDMS texture films was carried out and the static water contact angle θ was tested. Those observations offer ideas to fabricate artificial films with a multilevel micronanoscale structure that could obtain some characteristics, i.e., nonwettable surface-wettable surface transformation.

Paleoclimatic reconstruction of the Karewa deposits of Kashmir Valley, northwest Himalaya: A review

Plio-Pleistocene sedimentary successions, comprised of fluvio-glacial-lacustrine sediments capped by loess, are widespread in the Kashmir Valley, NW Himalaya, India. These sediments act as a repository of climate records for the past 4.4 Ma suggesting the dominance of southwestern monsoon up to 1.95 Ma and thereafter the dominance of mid-latitude western disturbances in the region. However, the younger strata of the loess-paleosol sequences (LPSs), <200 ka old, and Holocene sediments have been studied for high-resolution climate records compared to older archives because of the contentious chronological issues of the older deposits. Earlier studies revealed moderate climatic conditions from ∼65.8 ± 7.2 ka to 44.3 ± 5.8 ka, followed by periods of extreme dry phases of enhanced wind velocity, coinciding with the last major magnetic inversion. The climatic conditions have produced strong pedogenic signatures on the LPSs during the MIS-3 (∼43–34.7 ± 2.3). The dry arid climate phases recorded during the MIS-2 stage up to ∼14.7 ± 5.4 ka revealed a weak pedogenic alteration and a high amount of CaCO3 accumulation in the loess. Subsequent sporadic alluvial deposition of sediments over the LPSs implies widespread precipitation and glacial melting linked to the onset of the Holocene warming punctuated by dry and cold climate phases corresponding to the Bond events of 0, 3, 4, 5, and 7, which indicated a westerly-dominated climate during the Holocene. This review therefore critically examines existing literature on Karewa deposits in the Kashmir Valley, identifies knowledge gaps, and offers recommendations for future research, emphasizing their paleoclimatic potential for the Quaternary Period.

Investigation of zirconium (Zr) coated heat exchanger surface for the enhancement of heat transfer and retardation of mineral fouling

BackgroundFouling is a major problem in many industrial heat exchangers as in these devices water has been used for heat exchanging purposes. With the commencement of foulants deposition on heat exchanger surface the performance of heat exchangers is deteriorated due to lower thermal conductivity of the deposits formed on the heat exchanger surface. This study investigated the heat transfer and mitigation of CaCO3 fouling by applying zirconium coating layer on heat exchanger surface. MethodsZirconium was chosen as a coating material because of its surface adhesion and one of the best corrosion resistance materials. The Physical Vapor Deposition approach was implemented to develop a coating layer on heat exchanger surface. Heat transfer was investigated at numerous temperatures and flow rates to examine the impact of coating on heat transfer. Fouling experiments were conducted to examine the CaCO3 accumulation on the uncoated SS316L and Zirconium coated surfaces. After the fouling experiments, the coupon was disassembled from the test segment for the investigation of surface texture, after fouling effect and the morphology of deposits was assessed by using Field Emission Scanning Electron Microscopy (FESEM). Significant findingsResults reveal that the Zirconium coated surface declined the fouling deposition and improved the heat transfer.

Postglacial environmental change inferred from carbonate‐ and organic‐rich sediments of groundwater‐fed Kelly Lake, Kenai Peninsula, south‐central Alaska

ABSTRACTMajor shifts in hydroclimate have been documented during the last deglacial period and the Holocene in south‐central Alaska. Rare freshwater calcium carbonate (marl) deposits in lakes on the Kenai Peninsula can be used to reconstruct past changes in hydroclimate, including the influence of groundwater inflow to lakes. Here, the postglacial sediment sequence from groundwater‐fed Kelly Lake (60.514°N, 150.374°W) was analyzed for multiple proxies including isotopes of carbon and oxygen in marl calcite (δ13Cmarl and δ18Omarl), and isotopes of carbon (ẟ13COM) and abundances of C and N in organic matter. Bulk sediment analyses include organic matter and calcium carbonate (CaCO3) contents, visual stratigraphy and sediment flux. These analyses extend those of a previous paleoenvironmental reconstruction from Kelly Lake, which focused on sedimentary diatom oxygen isotopes and mass balance modeling over the past 10 000 years. Here, we show that Kelly Lake was deglaciated prior to 14.6 ka, and that by 14.0 ka marl dominated the sediments, with CaCO3 precipitation probably driven by groundwater input and mediated by shallow‐water charophytes. Marl accumulation decreased as organic and clastic inputs increased between ~12.2 and 11.5 ka. This shift, together with an increase in both δ13Cmarl and δ18Omarl values and a decrease in CaCO3 content, indicates an increase in the influence of meteoric water on the hydrologic budget under wet conditions, possibly driven by a strengthened Aleutian Low atmospheric pressure cell. A shift to lower δ13Cmarl and δ18Omarl values at ~11.5 ka is interpreted as an increase in the proportion of groundwater relative to meteoric water in the lake. Beginning around 9 ka, the proportion of meteoric water input continued to increase, the surrounding coniferous forest was established, and by 8 ka, CaCO3 accumulation ended. Our results elucidate the environmental conditions under which marl was deposited during the Lateglacial and early Holocene in this part of Alaska, and demonstrate how a variety of synoptic‐ and local‐scale climatic variables can converge to influence sedimentation in a groundwater‐fed lake.

A Global Reassessment of the Spatial and Temporal Expression of the Late Miocene Biogenic Bloom

AbstractThe Late Miocene Biogenic Bloom (LMBB) is a late Miocene to early Pliocene oceanographic event characterized by high accumulation rates of opal from diatoms and calcite from calcareous nannofossils and planktic foraminifera. This multi‐million year event has been recognized in sediment cores from the Pacific, Atlantic, and Indian Oceans. Based on existing studies, it is not clear whether the LMBB is a global omnipresent event, or whether it is restricted to certain regions or oceanographic environments. Moreover, the origin of this event is still widely discussed. In this study, we aim to provide a comprehensive overview of the geographical and temporal aspects of the LMBB by compiling published ocean drilling (DSDP, ODP, and IODP) records of sedimentation rates, and CaCO3, opal, and terrigenous accumulation rates that cover the late Miocene and early Pliocene interval. Our data compilation shows that manifestations of the LMBB are present in many different locations but in a very heterogeneous way. The compilation shows that the sites where the LMBB is expressed are mainly located in areas with a high productivity regime (i.e., upwelling systems). We suggest that one of the possible hypotheses to explain the onset of the LMBB could be a global increase in upwelling intensity due to an increase in wind strength or an increase in deep water formation, ramping up global thermohaline circulation.

Sedimentary CaCO3 Accumulation in the Deep West Pacific Ocean

Distribution of calcium carbonate (CaCO3) in marine sediment has been studied over the last century, and influence by multiple factors with regard to dissolution and dilution of sedimentary CaCO3 has long been established. There is still lack of quantification on the influence of those factors, so it remains elusive to determine which specific process is driving the down-core variation of CaCO3 content (wtCaCO3%) records. Here, based on a newly compiled CaCO3 data set and a carbonate model, depth-profiles of sedimentary wtCaCO3% from the West Pacific Ocean can be well illustrated, and influence from different factors on their distribution features can be quantified. The deep ocean circulation is found to largely shape the inter-basin disparity in sedimentary wtCaCO3% distribution between the equatorial regions (e.g., the Western Equatorial Pacific Ocean and the Central Pacific Ocean) and the north–west regions (the Philippine Sea and the Northwest Pacific Ocean) in our study region. Moreover, the slow carbonate dissolution rate in the deep Central Pacific Ocean guarantees better accumulation of CaCO3 at depth compared to that in other regions. However, enhanced dilution by non-carbonate materials of sedimentary CaCO3 on a topographic complex can potentially obstruct the dissolution profiles constituted by sedimentary wtCaCO3% in the pelagic ocean. The aforementioned assertion suggests that changes of wtCaCO3% accumulation in marine sediment in the West Pacific Ocean can be used to dictate past changes of the deep ocean circulation (2,500 to 3,000 m) in this area but constraint on the non-carbonate flux, especially on the topographic complex, should be necessary.

Indian Ocean sedimentary calcium carbonate distribution and its implications for the glacial deep ocean circulation

The ocean plays a critical role in the global climate by modulating atmospheric CO2 via carbon exchange between the atmosphere and the ocean, a process tightly linked to ocean circulation changes. Ocean circulation transports atmospheric CO2 to the deep ocean via deep water formation and then transfers it with respired CO2, which regulate CaCO3 accumulation in marine sediments on seafloor. Compared to studies on the Atlantic and Pacific, much less has been done on past circulation changes in the Indian Ocean. This is partly due to the lack of systematic investigation on sub-basinal scales calcium carbonate (CaCO3) distributions and limited understanding of their controlling mechanisms in the Indian Ocean. Based on an extensive data compilation and a simple carbonate accumulation model, here we show that CaCO3 distributions in various basins of the Indian Ocean are mainly controlled by ocean circulation changes with productivity only playing a secondary role. Comparison of CaCO3 distributions between the Last Glacial Maximum (LGM) and the late Holocene suggests little change in deep water acidity between these times. If the source-water acidity remains unchanged through time, this finding suggests a vigorous ventilation of the deep Indian Ocean during the LGM. Given that the glacial oceans were likely more alkaline, the stability of deep Indian acidity must suggest greater storage of carbon (mainly as bicarbonate ion) during the LGM. Additionally, we find a very corrosive LGM deep water in the Southwest Indian Basin which may be attributed to intrusion of the Pacific Deep Water.

Characterization of Scale Deposits in a Drinking Water Network in a Semi-Arid Region.

The quantity and quality of the supply of fresh water to households, commercial areas, small industries, green spaces irrigation and public and private institutions in large cities face challenges from the supply sources availability and suitable distribution network performance to the full satisfaction of the established drinking water guidelines. In Mexico, the main source of water comes from groundwater. Most of the Mexican aquifers are located in arid and semi-arid weather conditions. The groundwater’s physical–chemical properties are closely related to geology. This study was carried out at the north-central part of the country in which igneous and sedimentary rocks predominate, with high calcium carbonate (CaCO3) concentrations. The accumulation of CaCO3 in the pipelines is also known as scale deposit that decreases the fluid flow, causing a deficiency in the water supply. The main objectives of this study were determining the physical–chemical groundwater parameters and saturation indexes injected into the drinking water networks and characterizing the scale deposits by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicate that the scale deposits are mainly calcium carbonate and silica oxide crystals, caused by the water aggressiveness according to the saturation indexes and the lack of control over the saturation pH.

A Review on the Performance Evaluation of Autonomous Self-Healing Bacterial Concrete: Mechanisms, Strength, Durability, and Microstructural Properties

The development of cracks, owing to a relatively lower tensile strength of concrete, diverse loading, and environmental factors driving the deterioration of structures, is an inescapable key concern for engineers. Reparation and maintenance operations are thus extremely important to prevent cracks from spreading and mitigating the lifetime of structures. However, ease of access to the cracked zone may be challenging, and it also needs funds and manual power. Hence, autonomous sealing of cracks employing microorganisms into the concrete sans manual intervention is a promising solution to the dilemma of the sustainable improvement of concrete. ‘Ureolytic bacteria’, key organism species in rumen-producing ‘urease’ enzymes such as Bacillus pasteurii or subtilis—when induced—are capable of producing calcium carbonate precipitations into the concrete. As their cell wall is anionic, CaCO3 accumulation on their surface is extensive, and the whole cell, therefore, becomes crystalline and ultimately plugs pores and cracks. This natural induction technique is an environmentally friendly method that researchers are studying intensively. This manuscript reviews the application process of bacterial healing to manufacture autonomous self-healing bacterial concrete. Additionally, it provides a brief review of diverse attributes of this novel concrete which demonstrate the variations with the auto-addition of different bacteria, along with an evaluation of crack healing as a result of the addition of these bacteria directly into concrete or after encapsulation in a protective shell. Comparative assessment techniques for autonomous, bio-based self-healing are also discussed, accompanied by progress, potential, modes of application of this technique, and its resultant benefits in the context of strength and durability. Imperatives for quantitative sustainability assessment and industrial adoption are identified, along with the sealing of artificially cracked cement mortar with sand as a filling material in given spaces, as well as urea and CaCl2 medium treatment with Bacillus pasteurii and Sporosarcina bacteria. The assessment of the impact on the compressive strength and rigidity of cement mortar cubes after the addition of bacteria into the mix is also considered. Scanning electron microscope (SEM) images on the function of bacteria in mineral precipitation that is microbiologically induced are also reviewed. Lastly, future research scope and present gaps are recognised and discussed.

Middle to Late Eocene Changes of the Ocean Carbonate Cycle

AbstractSedimentary records show that calcium carbonate (CaCO3) preservation fluctuated during the Eocene. These fluctuations are well documented for the equatorial Pacific. However, data from other basins are sparse. In this study, we report new middle and late Eocene bulk calcium carbonate percentages and accumulation rates from the northwestern Pacific (Ocean Drilling Program—ODP—Site 884) and the Atlantic (ODP Sites 1053, 1090, and 1263) Oceans; in addition, we calculate CaCO3 accumulation rates for sites with published percentage bulk CaCO3 to expand geographic and paleobathymetric coverage. Using these data, we investigate the response of the carbonate cycle to environmental changes (e.g., temperatures, primary productivity, weathering, and ocean circulation) at the beginning of the greenhouse‐icehouse transition (∼43–34 Ma). Our results show that in the middle to late Eocene CaCO3 accumulation rates were highly variable at different paleodepths and ocean basins suggesting that the evolution of carbonate accumulation rates over the Eocene was influenced by different processes in different locations. In particular, our data emphasize the role of surface CaCO3 production and ocean ventilation in driving changes in CaCO3 preservation and burial at the seafloor. Our study also highlights the need for a better understanding of the processes regulating CaCO3 surface production today in order to correctly interpret geological records.

Anthropogenic CO2 of High Emission Scenario Compensated After 3500 Years of Ocean Alkalinization With an Annually Constant Dissolution of 5 Pg of Olivine

The CO2 removal model inter-comparison (CDRMIP) has been established to approximate the usefulness of climate mitigation by some well-defined negative emission technologies. I here analyze ocean alkalinization in a high CO2 world (emission scenario SSP5-85-EXT++ and CDR-ocean-alk within CDRMIP) for the next millennia using a revised version of the carbon cycle model BICYCLE, whose long-term feedbacks are calculated for the next 1 million years. The applied model version not only captures atmosphere, ocean, and a constant marine and terrestrial biosphere, but also represents solid Earth processes, such as deep ocean CaCO3 accumulation and dissolution, volcanic CO2 outgassing, and continental weathering. In the applied negative emission experiment, 0.14 Pmol/yr of alkalinity—comparable to the dissolution of 5 Pg of olivine per year—is entering the surface ocean starting in year 2020 for either 50 or 5000 years. I find that the cumulative emissions of 6,740 PgC emitted until year 2350 lead to a peak atmospheric CO2 concentration of nearly 2,400 ppm in year 2326, which is reduced by only 200 ppm by the alkalinization experiment. Atmospheric CO2 is brought down to 400 or 300 ppm after 2730 or 3480 years of alkalinization, respectively. Such low CO2 concentrations are reached without ocean alkalinization only after several hundreds of thousands of years, when the feedbacks from weathering and sediments bring the part of the anthropogenic emissions that stays in the atmosphere (the so-called airborne fraction) below 4%. The efficiency of carbon sequestration by this alkalinization approach peaks at 9.7 PgC per Pmol of alkalinity added during times of maximum anthropogenic CO2 emissions and slowly declines to half this value 2000 years later due to the non-linear marine chemistry response and ocean-sediment processes. In other words, ocean alkalinization sequesters carbon only as long as the added alkalinity stays in the ocean. To understand the basic model behavior, I analytically explain why in the simulation results a linear relationship in the transient climate response (TCR) to cumulative emissions is found for low emissions (similarly as for more complex climate models), which evolves for high emissions to a non-linear relation.

Soil classification in Romanian catenas via advanced proximal sensors

The Transylvanian Plain (TP), Romania is widely used for agronomic production. The Chernisol soil class covers a vast majority of the TP as defined by the Sistemul Roman De Taxonomie A Solurilor (SRTS). Chernisols are fertile, dark soils similar to Mollisols in the United States. Chernisols have four key soil types, two of them occur in the TP: chernozems and phaeozems. While these two classifications appear similar to those found in the World Reference Base (WRB) for Soil Resources, only the Romanian system (SRTS) is applied in this paper. Chernozems require a chroma of ≤2 in the Am horizon when moist and a calcic horizon or secondary CaCO3 within 125 cm. Phaeozems require chroma of ≤3.5 when wet and a calcic horizon or secondary CaCO3 deeper than 125 cm. Traditionally, morphological assessment in combination with laboratory data has been used to assess the depth of secondary CaCO3, thus establishing the taxonomic classification. Herein, the efficacy of portable X-ray fluorescence (PXRF) and visible near infrared spectroscopy (VisNIR) were evaluated to make such determinations in lieu of laboratory data on 25 soil cores collected across five toposequences. Cores were scanned on-site with both sensors at 10 cm increments to determine depth to CaCO3 accumulation. Comparing Ca percentages from only PXRF with traditional laboratory pressure calcimetry via simple linear regression (SLR), the following model validation data (based on whole core splitting, Coreval) were obtained: R2 = 0.92; root mean squared error (RMSE) = 0.81%; residual prediction deviation (RPD) = 3.27: ratio of performance to interquartile range (RPIQ): 5.34. Thus, most of the Ca in soils of the TP is associated with secondary CaCO3. Using the three most prominent latent variables, VisNIR spectra (smoothed to 10 nm bands) were combined with PXRF data via partial least squares regression (PLSR) to determine if any improvements could be achieved by the combined approach. Combined Coreval models produced the following: R2 = 0.89; RMSE = 0.98%; RPD = 2.73; RPIQ = 4.46. Boosted regression tree Coreval modeling produced similar results (R2 = 0.90; RMSE = 0.89%; RPD = 2.99; RPIQ = 4.87). With deference to the law of parsimony, use of PXRF data without VisNIR for calcic horizon identification and quantification in conjunction with morphological assessment and interpretation appears preferable for most Pedological applications given its robust, strong performance. Minimal differences were observed using two different sample splitting schemes (whole core vs. full sample set) relative to PXRF data predictive models for CaCO3 prediction, especially for PXRF with no VisNIR contribution. Of the sites investigated, PXRF identified six phaeozems (P) and nineteen chernozems (C). Specifically, the following were identified on different slope profiles: summits (1P/4C), shoulders (1P/2C), backslopes (3P/7C), footslopes (0P/4C), and toeslopes (1P/2C). Localized landslides and erosion precluded the identification of a common landscape model differentiating P/C on landscapes. Nonetheless, proximal sensors were adept at informing soil properties needed for taxonomic classification on-site, with minimal need for traditional pressure calcimetry.

Palustrine wetland formation during the MIS 3 interstadial: Implications for preserved alluvial records in the South African Karoo

Dryland alluvial successions across interior South Africa are a focus of pedosedimentary research because they provide insights into past hydrogeomorphic changes and improve our understanding of allogenic and autogenic controls on fluvial system behaviour. This paper focuses on an alluvial succession preserved within the Wilgerbosch River, on the Great Escarpment, South Africa. The pedosedimentary architecture of a calcretized palaeosol formed within an abandoned MIS 3 (51–39 ka) floodplain was investigated using grain size, micromorphological, XRD and mineral magnetic analyses. The primary controls on pedogenesis are inferred and the impacts of their products on subsequent landscape development outlined. The biologically-dominated calcrete micromorphology is consistent with the rhizogenic calcrete variety, which together with XRD, grain size and soil magnetic data provides evidence for a palustrine palaeowetland system. Palustrine wetland systems have been documented across interior South Africa, but the formation of rhizogenic calcretes in association with these systems has, to our knowledge, not been reported previously. We interpret these palaeowetlands to have resulted from basin-wide hydrogeomorphic adjustments, rather than localised discontinuous channel and floodout processes. Magnetic enhancement of the soil column overlying the calcrete compared to the overlying floodplain deposits is indicative of moister climate conditions at ~51 ka relative to ~39 ka. We hypothesise that the longevity of geomorphic quiescence, coupled with relatively moist climate conditions in early MIS 3 resulted in enhanced soil CaCO3 accumulation. The resultant cementation of this abandoned floodplain deposit accounts for an alluvial record that is dominated by older rather than younger (e.g. Holocene) deposits, despite the narrow valley context (<150 m). These findings illustrate the interplay of factors that may generate sedimentary records in this and other confined catchment systems. Such insights may aid interpretation of palustrine wetlands formed in tectonically-stable dryland inland valleys preserved within the geological record.

Environmental and coastline changes controlling Holocene carbon accumulation rates in fjords of the western Strait of Magellan region

Organic-rich sediments of the southernmost Chilean Pacific coast and its fjord system constitute an important component of the global marine carbon budget. Sediment records from Trampa and Caribe bays and Churruca fjord in the western Magellan fjord system have been analyzed with the goal of understanding the factors controlling carbon accumulation and its regional fluctuation throughout the Holocene. The individual response in paleoproductivity at the different sites and related variations in accumulation rates document a very complex interplay among local and regional-scale environmental changes, and coastline elevation across the Holocene. Shallow sill basins close to the Pacific coast, as the ones studied here, are particularly sensitive to these processes, having responded with strong productivity changes throughout the Holocene.A Bayesian mixed model approach, using sediment archived provenance proxies, indicates that components of terrestrial plants and soils washed-out into these basins contribute with a variable proportion (20–80 wt%) of the total accumulated organic carbon. Accumulation rates of terrestrial carbon increase with the amount of precipitation in the hyper-humid mountain area, but also reflect distinct Holocene plant successions as well as long-term development of soil and vegetation cover that strongly overprint the direct precipitation impact. Over the Holocene accumulation rates of biogenic carbonate and aquatic-marine organic carbon range between 5 and 118 kg m−2 kyr−1 and 0.3–20 kg m−2 kyr−1, respectively. This variability depends on water column structure and conditions, which are regulated by the degree of marine transgression as a function of post glacial sea level rise and isostatic uplift as well as precipitation-related surface water freshening. In the Bahia Trampa record, a significant change in accumulation rates indicates a marine transgression at ca. 12.2 kyr BP, when the global sea level was 60–70 m lower than today and eustatic rise overcame isostatic rebound rates. In Caribe and Trampa records, CaCO3 accumulation rates were higher at ca. 7 kyr BP. The Churruca record shows organic carbon accumulation rates up to 36.2 kg m−2 kyr−1 during the early Holocene.

Relationships between landscape features, soil properties, and vegetation determine ecological sites in a semiarid savanna of central Argentina

Semiarid grasslands are still managed without considering site-specific differences in productivity. A better understanding of spatial heterogeneity would improve land management and might avoid desertification in semiarid systems. We studied a toposequence in the semiarid savanna of central Argentina. By using Shuttle Radar Topography Mission (SRTM) for toposequence characterization, and radar images to identify a site with small area, we differentiated four ecological sites (ESs): valley floor, slope, plateau and deflation pits. Plateau presented the shallowest soil because of caliche layer present, while valley floor and deflation pit had the deepest CaCO3 accumulation. Moreover, valley floor had the thinnest A horizon (6.7 cm) while deflation pit had the thickest one (26.3 cm). Slope and deflation pit showed the highest organic matter (OM) contents (about 32 g kg−1). Total woody plant density was greater in slope and lower in valley floor. Plateau had higher shrubby Prosopis spp. density, and deflation pits higher tree Prosopis spp. density. Besides, we found a positive linear regression between OM content and woody plant cover, and an exponential relation between CaCO3 depth and shrub density. Chosen indicators explained ES variation, and the methodology allows to create ES maps and prescribe management strategies according to site limitations.

Hot Spots of Carbon and Alkalinity Cycling in the Coastal Oceans

Ocean calcium carbonate (CaCO3) production and preservation play a key role in the global carbon cycle. Coastal and continental shelf (neritic) environments account for more than half of global CaCO3 accumulation. Previous neritic CaCO3 budgets have been limited in both spatial resolution and ability to project responses to environmental change. Here, a 1° spatially explicit budget for neritic CaCO3 accumulation is developed. Globally gridded satellite and benthic community area data are used to estimate community CaCO3 production. Accumulation rates (PgC yr−1) of four neritic environments are calculated: coral reefs/banks (0.084), seagrass-dominated embayments (0.043), and carbonate rich (0.037) and poor (0.0002) shelves. This analysis refines previous neritic CaCO3 accumulation estimates (~0.16) and shows almost all coastal carbonate accumulation occurs in the tropics, >50% of coral reef accumulation occurs in the Western Pacific Ocean, and 80% of coral reef, 63% of carbonate shelf, and 58% of bay accumulation occur within three global carbonate hot spots: the Western Pacific Ocean, Eastern Indian Ocean, and Caribbean Sea. These algorithms are amenable for incorporation into Earth System Models that represent open ocean pelagic CaCO3 production and deep-sea preservation and assess impacts and feedbacks of environmental change.

Effect of KNO3 on Lipid Synthesis and CaCO3 Accumulation in Pleurochrysis dentata Coccoliths with a Special Focus on Morphological Characters of Coccolithophores.

Pleurochrysis genus algae are widely distributed in ocean waters. Pleurochrysis sp. algae are popularly known for its coccolithophores. Calcium carbonate (CaCO3) shells are major components of the coccolithophore, and they are key absorbers of carbondioxide. In this study, we have reported the effects of potassium nitrate (KNO3) concentration on calcium accumulation and total lipid, carbohydrate and protein contents of Pleurochrysis dentata. Results obtained from complexometric titration and scanning electron microscopy analysis showed higher rates of CaCO3 accumulation on Pleurochrysis dentata cell surface. We have also observed that overall cell size of Pleurochrysis dentata reached maximum when it was cultured at 0.75 mmol L-1 of KNO3. During 10 days of Pleurochrysis dentata culture total lipids and carbohydrate contents decreased, with slightly increased protein content. Results obtained from Fourier-Transform Infrared Spectroscopy (FTIR) also reported an increase in protein and decrease in lipids and carbohydrate contents, respectively. Similarly, Pleurochrysis dentata cultured at 1 mmol L-1 concentration of KNO3 exhibited the lowest carbohydrate (21.08%) and highest protein (32.87%) contents. Interestingly, Pleurochrysis dentata cultured without KNO3 exhibited 33.61% of total lipid content which reduced to a total lipid content of 13.67% when cultured at 1 mmol L-1 concentration of KNO3. Thus, culture medium containing higher than 1 mmol L-1 of KNO3 could inhibit the cell size of Pleurochrysis dentata and CaCO3 accumulation in shells but it could promote its cell growth. For the first time we have reported a relatively complete coccolith structure devoid of its protoplast. In this study, we have also described about the special planar structure of Pleurochrysis dentata CaCO3 shells present on its inner tube of the R unit and parallel to the outer tube of the V unit which we named it as “doornail structure”. We believe that this doornail structure provides structural stability and support to the developing coccoliths in Pleurochrysis dentata. Also, we have discussed about the “double-disc” structure of coccoliths which are closely arranged and interlocked with each other. The double-disc structure ensures fixation of each coccolith and objecting its free horizontal movement and helps in attaining a complementary coccolith structure.

Landscape patterning created by the southern harvester termite, Microhodotermes viator: Spatial dispersion of colonies and alteration of soils

The southern harvester termite (Microhodotermes viator) is often associated with large, regularly spaced earthen mounds called heuweltjies in western South Africa. However, there is considerable debate regarding whether or not the termites play any role in either the creation of these mounds or the enrichment of mound soils with calcium carbonate (CaCO3) and plant nutrients. Colonies of M. viator are not always associated with heuweltjies. In some environments, the colonies construct small, cemented conical mounds; in others, colonies do not produce any emergent structure above the surrounding soil surface. Examining the spacing and soil conditions associated with these kinds of colonies provided a means of determining the inherent capacity of M. viator colonies to generate a highly regular spatial patterning of CaCO3- and nutrient-enriched patches. Those colonies were highly overdispersed and soils in altered zones around colonies were enriched with CaCO3, nitrogen, and phosphorus. These are the same characteristics exhibited by heuweltjies; consequently, we conclude that the sustained influence of colonies of M. viator contributes directly to both the uniform spacing of heuweltjies and the accumulation of CaCO3 and plant nutrients within heuweltjies.

Calcium carbonate productivity by Halimeda macroloba in the tropical intertidal ecosystem: The significant contributor to global carbonate budgets

SUMMARYHalimeda is a potential carbon sink species and an important player in the global carbonate budget. The objectives of this study were to: (i) examine the CaCO3 and sediment productions of H. macroloba by measuring the density, growth rate, and recruitment; (ii) quantify the numbers of aragonite crystals; (iii) document reproductive events; and (iv) determine the life‐span. This study was carried out at Lidee Lek Island, Satun, Thailand during July 2015 to April 2016. The density was measured using quadrats (0.25 m2) and three 50 m line transects. Alizarin Red‐S marking technique was used for the growth rate and CaCO3 accumulation rate assessments. The recruitment, reproduction and life‐span were measured by tagging 500 individuals. Tagged individuals and new plants were counted. In this study, mean and the highest density of Halimeda were 44.42 ± 13.95 and 138.22 ± 11.68 thalli m−2, respectively, and Halimeda produced 1–2 new segments.thallus−1 day−1 or 0.021 ± 0.001 g dry weight.thallus−1.day−1. The annual biomass production was 1910–5950 g m−2 year.−1. There was a low rate of occurrence of sexual reproduction, observed in late July to September, ranging from 0.17% to 1.92%. For the mortality and recruitment rates, approximately 70–80% of individuals were lost during July to September 2015, probably from sexual reproduction and the recruitment rate varied from 5.36 ± 0.79% to 21.03 ± 2.33%. The highest density of new recruits was found in September 2015 right after the sexual reproductive event occurred. New recruits have been found up to April 2016 without any reproductive events, suggesting that both sexual and asexual reproduction helped maintain the population. The life span of Halimeda was 8–12 months. In addition, Halimeda accumulated CaCO3 at approximately 0.018 g CaCO3 thallus−1 day−1 and produced CaCO3 at approximately 291.94–908.11 g m−2 year−1, indicating that Halimeda contributes to CaCO3 and helps to sink carbon through calcification. The results in terms of the density, growth rate, and CaCO3 accumulation rate can be used to calculate the mass of carbonate sediment contributed by Halimeda.