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Calcium carbonate formation is the primary pathway by which carbon is returned from the ocean-atmosphere system to the solid Earth . The removal of dissolved inorganic carbon from seawater by precipitation of carbonate minerals-the marine carbonate factory-plays a critical role in shaping marine biogeochemical cycling . A paucity of empirical constraints has led to widely divergent views on how the marine carbonate factory has changed over time . Here we use geochemical insights from stable strontium isotopes to provide a new perspective on the evolution of the marine carbonate factory and carbonate mineral saturation states. Although the production of carbonates in the surface ocean and in shallow seafloor settings have been widely considered the predominant carbonate sinks for most of the history of the Earth , we propose that alternative processes-such as porewater production of authigenic carbonates-may have represented a major carbonate sink throughout the Precambrian. Our results also suggest that the rise of the skeletal carbonate factory decreased seawater carbonate saturation states.

Cyanobacteria have affected major geochemical cycles (carbon, nitrogen, and oxygen) on Earth for billions of years. In particular, they have played a major role in the formation of calcium carbonates (i.e., calcification), which has been considered to be an extracellular process. We identified a cyanobacterium in modern microbialites in Lake Alchichica (Mexico) that forms intracellular amorphous calcium-magnesium-strontium-barium carbonate inclusions about 270 nanometers in average diameter, revealing an unexplored pathway for calcification. Phylogenetic analyses place this cyanobacterium within the deeply divergent order Gloeobacterales. The chemical composition and structure of the intracellular precipitates suggest some level of cellular control on the biomineralization process. This discovery expands the diversity of organisms capable of forming amorphous calcium carbonates.

Southern Ocean acidification via anthropogenic CO 2 uptake is expected to be detrimental to multiple calcifying plankton species by lowering the concentration of carbonate ion (CO 3 2− ) to levels where calcium carbonate (both aragonite and calcite) shells begin to dissolve. Natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of this undersaturation of calcium carbonate. We present a large-scale Southern Ocean observational analysis that examines the seasonal magnitude and variability of CO 3 2− and pH. Our analysis shows an intense wintertime minimum in CO 3 2− south of the Antarctic Polar Front and when combined with anthropogenic CO 2 uptake is likely to induce aragonite undersaturation when atmospheric CO 2 levels reach ≈450 ppm. Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038. Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina , have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem. Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification. carbon cycle climate change

The present research is to study hydrochemistry and water quality of Rewalsar Lake during pre-monsoon, monsoon, and post-monsoon seasons. The Ca 2+ and Na + are observed as the dominant cations from pre- to post-monsoon season. On the other hand, HCO 3 − and Cl − are observed dominant anions during pre-monsoon and monsoon seasons, whereas HCO 3 − and SO 4 2− during post-monsoon season. The comparison of alkaline earth metals with alkali metals and total cations (Tz + ) has specified that the carbonate weathering is the dominant source of major ions in the water of lake.  The HCO 3 − is noticed to be mainly originated from carbonate/calcareous minerals during monsoon and post-monsoon, but through silicate minerals during pre-monsoon.  The SO 4 2− in Rewalsar Lake is produced by the dissolution of calcite and dolomite etc. The alkali metals and Cl − in the lake can be attributed to the silicate weathering as well as halite dissolution and anthropogenic activities. Certain other parameters like NO 3 − , NH 4 + , F − , and Br − are mainly a result of anthropogenic activities. The alkaline earth metals are found to surpass over alkali metals, whereas weak acid (HCO 3 − ) exceed to strong acid (SO 4 2− ). The Piper diagram has shown Ca 2+ –HCO 3 − type of water during all the seasons. The water quality index has indicated that the water quality of the lake is unsuitable for drinking from pre- to post-monsoon. Several parameters like salinity index, sodium adsorption ratio, sodium percent, residual sodium carbonate, magnesium hazard etc. have revealed the water of Rewalsar Lake as suitable for irrigation.

This paper attempts to evaluate the mineralogical and chemical composition of sedimentary limestone mine waste alongside its mineral carbonation potential. The limestone mine wastes were recovered as the waste materials after mining and crushing processes and were analyzed for mineral, major and trace metal elements. The major mineral composition discovered was calcite (CaCO 3 ) and dolomite [CaMg(CO 3 ) 2 ], alongside other minerals such as bustamite [(Ca,Mn)SiO 3 ] and akermanite (Ca 2 MgSi 2 O 7 ). Calcium oxide constituted the greatest composition of major oxide components of between 72 and 82%. The presence of CaO facilitated the transformation of carbon dioxide into carbonate form, suggesting potential mineral carbonation of the mine waste material. Geochemical assessment indicated that mean metal(loid) concentrations were found in the order of Al > Fe > Sr > Pb > Mn > Zn > As > Cd > Cu > Ni > Cr > Co in which Cd, Pb and As exceeded some regulatory guideline values. Ecological risk assessment demonstrated that the mine wastes were majorly influenced by Cd as being classified having moderate risk. Geochemical indices depicted that Cd was moderately accumulated and highly enriched in some of the mine waste deposited areas. In conclusion, the limestone mine waste material has the potential for sequestering CO 2 ; however, the presence of some trace metals could be another important aspect that needs to be considered. Therefore, it has been shown that limestone mine waste can be regarded as a valuable feedstock for mineral carbonation process. Despite this, the presence of metal(loid) elements should be of another concern to minimize potential ecological implication due to recovery of this waste material.

Long-term changes of 14 water constituents measured in continuously and water discharge proportionally collected samples of four Swiss rivers over a period of 39 years are analyzed using several statistical techniques. Possible drivers and causes for the identified trends and shifts are explained by consideration of catchment characteristics and anthropogenic activities. Water temperatures increased by 0.8–1.3 °C, whereas water discharges remained largely unchanged. Concentrations of alkalinity, total hardness, Ca, and Mg regulated by dominant carbonate lithologies in catchments increased by up to 10%. We attribute this change to an increase in the partial pressure of CO 2 in the subsurface, provoked by increasing temperatures. Re-oligotrophication processes in lakes also influence the behavior of alkalinity and silicic acid. In contrast to concentrations, most loads did not change significantly, due to their large variances. Therefore, no changes in overall weathering rates of carbonate rocks can be detected. The outgassing of CO 2 in rivers from the place of carbonate dissolution to measurement stations amounts up to 6% (mean) of CO 2 sequestered (mean 1.1 mol m −2  a −1 ) by the weathering of rock minerals. Changes in alkalinity/Ca/Mg ratios indicate an increase in calcite precipitation over time. Total nitrogen concentrations and loads peaked at the end of the 1980s and then decreased up to 50%, while NO 3 concentrations showed almost no changes. This dynamic matches the changes in the agricultural N balance. Concentrations and loads of Na and Cl increased up to 60% due to an increase in the various uses of rock salt.

The present work aims to observe the spatial distribution of metals associated with carbon forms (fraction < 2 mm) in surface sediments of two macrotidal estuaries, São Marcos Bay and Anil River Estuary, which are located within the transition region between the Amazonian and the semi-arid northeast regions. Grain size, metal content (Al, Fe, Mn, Cu, Pb, Cr, Zn, and Ni), organic matter, and calcium carbonate content were determined. Grain size analyses showed the predominance of the sand-sized fraction < 2 mm due to the local hydrodynamic conditions. Anil River Estuary sediments exhibited high organic matter content due to both the mangrove outwelling and domestic sewage discharge. They also presented high calcium carbonate content as a result of abundant remnants of gastropod shells. Organic matter acted as the primary geochemical carrier for most metals in both estuaries, while calcium carbonate acted as the secondary carrier. Enrichment factors indicated Mn sediment contamination in São Marcos Bay and Fe, Pb, and Zn contamination in the Anil River Estuary. These results also suggest that São Marcos Bay is influenced by harbor activities, mostly ore shipment, whereas Anil River Estuary sediments are enriched in these metals as a result of domestic and hospital effluents reaching the urbanized drainage basin.

Many aspects of the carbon cycle can be assessed from temporal changes in the 13C/12C ratio of oceanic bicarbonate. 13C/12C can temporarily rise when large amounts of 13C-depleted photosynthetic organic matter are buried at enhanced rates, and can decrease if phytomass is rapidly oxidized or if low 13C is rapidly released from methane clathrates. Assuming that variations of the marine 13C/12C ratio are directly recorded in carbonate rocks, thousands of carbon isotope analyses of late Precambrian examples have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life. Low 13C/12C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian. These include complete oxidation of all organic matter in the ocean and complete productivity collapse such that low-13C/12C hydrothermal CO2 becomes the main input of carbon. Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates, and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone. We show that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids, receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in 13C/12C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic examples. This influx of terrestrial carbon is not apparent in carbonates older than ∼850 Myr, so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces. As a result, biotically enhanced weathering generated carbon-bearing soils on a large scale and their detrital sedimentation sequestered carbon. This facilitated a rise in O2 necessary for the expansion of multicellular life.

Little is known about how stony corals build their calcareous skeletons. There are two prevailing hypotheses: that it is a physicochemically dominated process and that it is a biologically mediated one. Using a combination of ultrahigh-resolution three-dimensional imaging and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, we show that mineral deposition is biologically driven. Randomly arranged, amorphous nanoparticles are initially deposited in microenvironments enriched in organic material; they then aggregate and form ordered aragonitic structures through crystal growth by particle attachment. Our NMR results are consistent with heterogeneous nucleation of the solid mineral phase driven by coral acid-rich proteins. Such a mechanism suggests that stony corals may be able to sustain calcification even under lower pH conditions that do not favor the inorganic precipitation of aragonite.