Calcite Saturation State Research Articles

Carbonate mineral saturation states along the U.S. East Coast

To assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern United States (South Atlantic Bight [SAB]), we measured carbonate mineral saturation states from January 2005 to May 2006. The findings reveal that aragonite (Ωarag: 2.6–4.0) and calcite (Ωcal: 4.1–6.0) saturation states were considerably higher than those recently reported along the West Coast of North America. Different water mass age between the Atlantic and Pacific Oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the SAB than along the West Coast. The contrasting water temperatures in the two coasts contribute to such differences. Both upwelling and freshwater discharge also play important roles in controlling saturation state. Carbonate mineral saturation in the surface water of the West Coast is strongly controlled by the upwelling of high‐salinity, low‐temperature, low‐oxygen, and low‐pH deep water. In comparison, saturation states in the surface water of the SAB coast are rarely affected by upwelling. Instead, they are strongly influenced by the input of low‐saturation‐state water from rivers. Continued increases of atmospheric CO2 under the Intergovernmental Panel on Climate Change B1 emission scenario will decrease the carbonate mineral saturation states by up to 40% by the end of this century, and aragonite will approach undersaturation near the coast.

Strain-Induced Segmentation of Magnesian Calcite Thin Films Growing on a Calcite Substrate

In crystal growth of mineral species or different compositional members of a solid solution on one another, the degree of lattice mismatch at their interface affects the growth pattern of the precipitating mineral phase. Fast layer-by-layer growth of magnesian calcite on pure calcite (1014) substrates has been observed at Mg 2+ /Ca 2+ ratios of 2-7 using in situ atomic force microscopy. Under solution conditions of calcite saturation states starting from Ω ≈ 33, depending on Mg 2+ /Ca 2+ ratios and carbonate content, bulging in the epitaxial magnesian calcite thin film led to the formation of networks of ridges along the [441], [481], and [421] directions. Eventually, spreading of monolayers stopped at the ridges and formed stationary multilayer steps, resulting in separate and individually growing crystal segments. Molecular dynamics computational modeling suggests that relaxation of strain energy, caused by the interfacial lattice mismatch between pure calcite and the isostructural magnesium-containing phase with smaller lattice constants, leads to a semicoherent interface and disordered linear zones cutting through the thin film. As a consequence, the surface bulges up in a way similar to our laboratory observations. This strain-induced segmentation produces aggregates of aligned microcrystals and increase knowledge of the behavior of strained thin films in general.

Environmental drivers of ophiuroid species richness on seamounts

AbstractBenthic communities on seamounts are frequently characterised as being species rich, yet there is considerable variation in observed species richness. Although large‐scale patterns of species richness have been described from many marine and terrestrial habitats, their environmental drivers often remain poorly understood. We compared species richness of ophiuroids (brittle‐stars) on 60 seamounts throughout the South West Pacific Ocean, and used an information‐theoretic approach and generalized linear models to determine the relative importance of predictor variables. Due to high correlation among many environmental variables, we used a reduced set of predictors in an a priori model framework. Temperature was the only environmental predictor of any importance in these models over the bathymetric range of the study. Post‐hoc analyses of other potential environmental predictor variables showed that depth, calcite saturation state, temperature range, modelled current velocity and latitude all had some predictive value, but were also highly correlated with temperature or other environmental variables included in the a priori model. Longitude, large‐area species richness, habitat suitability for stony corals, and modelled POC flux did not have high predictive value. We hypothesise that temperature affects richness by constraining species distributions; in particular fewer species can tolerate the conditions on relatively warm shallow seamount summits.

Incorporation of Mg and Sr in calcite of cultured benthic foraminifera: impact of calcium concentration and associated calcite saturation state

Abstract. We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (Ω) on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing) and Ammonia tepida (low-Mg calcite, symbiont-barren) were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite)/(TE/Caseawater). The culturing study shows that DMg of A. tepida significantly decreases with increasing Ω at a gradient of −4.3×10−5 per Ω unit. The DSr value of A. tepida does not change with Ω, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing Ω, while DSr increases considerably with Ω at a gradient of 0.009 per Ω unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50–100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep-sea benthic foraminifera typically used for paleostudies, the higher Ca concentrations in the past may potentially bias temperature reconstructions to a considerable degree. For instance, 25 Myr ago Mg/Ca ratios in A. tepida would have been 0.2 mmol/mol lower than today, due to the 1.5 times higher [Ca2+] of seawater, which in turn would lead to a temperature underestimation of more than 2 °C.

Data‐based estimation of anthropogenic carbon and acidification in the Weddell Sea on a decadal timescale

The amount of anthropogenic CO2 (Cant) that entered the Weddell Sea between 1992 and 2008 (Cant1992–2008) was assessed using the extended multiple linear regression (eMLR) method. In the Warm Deep Water (WDW) and the Weddell Sea Bottom Water (WSBW), Cant1992–2008 values were insignificant, whereas values as high as 8 μmol kg−1 were observed over the shelf. Cant1992–2008 concentrations in the surface layer varied with latitude between 2 and 11 μmol kg−1. Weak intrusion of anthropogenic CO2 into Weddell Sea Deep Water (WSDW) was demonstrated (Cant1992–2008 yields 1.5–2 μmol kg−1). That more Cant1992–2008 was found in the WSDW than in the WSBW is surprising, but can be explained by intense ventilation of the WSDW originating from east of the Weddell Gyre. The invasion of Cant1992–2008 provokes a shift in the equilibria of the carbonate system, resulting in acidification and reduction of CO32− concentration. The mean decrease of pH in the upper 200 m layer was 0.016. The largest decrease of calcite and aragonite saturation states was observed at the surface. This implies that surface waters might become undersaturated with respect to aragonite in the future while the underlying WDW is still saturated. Results of this analysis suggest that complete undersaturation of surface waters in the Weddell Sea will be reached after the 21st century.

Mg/Ca variability of the planktonic foraminifera G. ruber s.s. and N. dutertrei from shallow and deep cores determined by electron microprobe image mapping

The Mg/Ca ratio of planktonic foraminifera is widely used for reconstructing sea surface and thermocline temperatures. Dissolution, driven by changes in the bottom water calcite saturation state (a function of water mass chemistry and depth/pressure), lowers the bulk Mg/Ca ratio which results in an implied cooler reconstructed temperature. Here we employ electron microprobe analysis (EMPA) to characterize how dissolution alters shell Mg/Ca variability. Using EMPA we have generated Mg/Ca image maps of two species widely used in paleoceanographic reconstructions: Globogerinoides ruber sensu stricto (G. ruber s.s.) and Neogloboquadrina dutertrei (N. dutertrei). We first characterize the Mg/Ca ratio in the better-preserved shells from a shallow core (2.8 km) and compare those characteristics to the samples from a deep core (4.0 km) obtained from the same locality (Ceara Rise, western equatorial Atlantic). Though preliminary, results suggest EMPA Mg/Ca ratio mapping can reveal characteristics of well preserved shells that can be used to assess changes in the Mg/Ca ratio that occur with dissolution.

Influences of alkalinity and pCO2 on CaCO3 nucleation from estimated Cretaceous composition seawater representative of “calcite seas”

Research Article| February 01, 2010 Influences of alkalinity and pCO2 on CaCO3 nucleation from estimated Cretaceous composition seawater representative of “calcite seas” Janie Lee; Janie Lee * Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA *E-mail: jlee@ocean.tamu.edu. Search for other works by this author on: GSW Google Scholar John W. Morse John W. Morse Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Janie Lee * Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA John W. Morse Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA *E-mail: jlee@ocean.tamu.edu. Publisher: Geological Society of America Received: 17 Jul 2009 Revision Received: 20 Aug 2009 Accepted: 21 Aug 2009 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (2): 115–118. https://doi.org/10.1130/G30537.1 Article history Received: 17 Jul 2009 Revision Received: 20 Aug 2009 Accepted: 21 Aug 2009 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Janie Lee, John W. Morse; Influences of alkalinity and pCO2 on CaCO3 nucleation from estimated Cretaceous composition seawater representative of “calcite seas”. Geology 2010;; 38 (2): 115–118. doi: https://doi.org/10.1130/G30537.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Experiments were conducted on CaCO3 nucleation in seawater of estimated Cretaceous Period “calcite sea” (i.e., low-magnesium calcite being the primary inorganic marine calcium carbonate precipitate) composition to determine the influences of alkalinity and pCO2 on calcite versus aragonite formation. The pH was continually monitored throughout the experiments and it was used, in combination with the initial alkalinity, to calculate the pCO2 and saturation state of aragonite and calcite at the time of nucleation. The morphology and mineralogy of the precipitates were determined using scanning electron microscopy and X-ray diffraction analyses. It was observed that the initial alkalinity affected greatly the nucleation pCO2 and the CaCO3 polymorph that is precipitated. In seawater with Mg2+/Ca2+ = 1.2, ∼10 mM alkalinity, and a pCO2 <2500 μatm, calcite is the initial polymorph that nucleates. Aragonite nucleates when the pCO2 is >2500 μatm. Seawater with Mg2+/Ca2+ = 1.2 and a wide range of initial alkalinities (5–50 mM) produces variable results. Seawater with Mg2+/Ca2+ = 1.7 produces only aragonite at lower alkalinities (<∼11 mM), but calcite is formed when the alkalinity is >∼18 mM. These results demonstrate the need to also consider the effects of alkalinity and pCO2 in the critical Mg2+/Ca2+ ratio region of ∼1–2 for calcite seas versus “aragonite seas” (in which the primary inorganic carbonate precipitates are aragonite and high-magnesium calcite) at various times throughout the Phanerozoic Eon and to use reasonable estimated values of alkalinity and pCO2 in experimental studies. The results of this study indicate that it may have been possible for CaCO3 to commonly nucleate directly from Cretaceous seawater due to elevated calcium and alkalinity concentrations, even though atmospheric pCO2 was higher. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean

Calcium carbonate (CaCO3) mineral saturation states for aragonite (Ωaragonite) and calcite (Ωcalcite) are calculated for waters of the Chukchi Sea shelf and Canada Basin of the western Arctic Ocean during the Shelf‐Basin Interactions project from 2002 to 2004. On the Chukchi Sea shelf, a strong seasonality and vertical differentiation of aragonite and calcite saturation states was observed. During the summertime sea ice retreat period, high rates of phytoplankton primary production and net community production act to increase the Ωaragonite and Ωcalcite of surface waters, while subsurface waters become undersaturated with respect to aragonite due primarily to remineralization of organic matter to CO2. This seasonal “phytoplankton‐carbonate saturation state” interaction induces strong undersaturation of aragonite (Ωaragonite = &lt;0.7–1) at ∼40–150 m depth in the northern Chukchi Sea and in the Canada Basin within upper halocline waters at ∼100–200 m depth. Patches of aragonite undersaturated surface water were also found in the Canada Basin resulting from significant sea ice melt contributions (&gt;10%). The seasonal aragonite undersaturation of waters observed on the Chukchi Sea shelf is likely a recent phenomenon that results from the uptake of anthropogenic CO2 and subsequent ocean acidification, with seasonality of saturation states superimposed by biological processes. These undersaturated waters are potentially highly corrosive to calcifying benthic fauna (e.g., bivalves and echinoderms) found on the shelf, with implications for the food sources of large benthic feeding mammals (e.g., walrus, gray whales, and bearded seals). The benthic ecosystem of the Chukchi Sea (and other Arctic Ocean shelves) is thus potentially vulnerable to future ocean acidification and suppression of CaCO3 saturation states.

The impact of salinity on the Mg/Ca and Sr/Ca ratio in the benthic foraminifera Ammonia tepida: Results from culture experiments

Over the last decade, sea surface temperature (SST) reconstructed from the Mg/Ca ratio of foraminiferal calcite has increasingly been used, in combination with the δ 18O signal measured on the same material, to calculate the δ 18O w, a proxy for sea surface salinity (SSS). A number of studies, however, have shown that the Mg/Ca ratio is also sensitive to other parameters, such as pH or [ CO 3 2 - ] , and salinity. To increase the reliability of foraminiferal Mg/Ca ratios as temperature proxies, these effects should be quantified in isolation. Individuals of the benthic foraminifera Ammonia tepida were cultured at three different salinities (20, 33 and 40 psu) and two temperatures (10–15 °C). The Mg/Ca and Sr/Ca ratios of newly formed calcite were analyzed by Laser Ablation ICP-MS and demonstrate that the Mg concentration in A. tepida is overall relatively low (mean value per experimental condition between 0.5 and 1.3 mmol/mol) when compared to other foraminiferal species, Sr being similar to other foraminiferal species. The Mg and Sr incorporation are both enhanced with increasing temperatures. However, the temperature dependency for Sr disappears when the distribution factor D Sr is plotted as a function of calcite saturation state ( Ω). This suggests that a kinetic process related to Ω is responsible for the observed dependency of Sr incorporation on sea water temperature. The inferred relative increase in D Mg per unit salinity is 2.8% at 10 °C and 3.3% at 15 °C, for the salinity interval 20–40 psu. This implies that a salinity increase of 2 psu results in enhanced Mg incorporation equivalent to 1 °C temperature increase. The D Sr increase per unit salinity is 0.8% at 10 °C and 1.3% at 15 °C, for the salinity interval 20–40 psu.

Effect of salinity and seawater calcite saturation state on Mg and Sr incorporation in cultured planktonic foraminifera

Trace elements incorporated in planktonic foraminiferal test carbonate are commonly used as paleoproxies. For instance, Mg/Ca ratios are frequently used for reconstructing sea surface temperature and, together with the foraminiferal stable oxygen isotope ratios, are also used as paleosalinity proxy. Foraminiferal Sr/Ca ratios constitute another example of the application of trace elements in paleostudies since they may reflect the Sr/Ca values of seawater. However, over the past few decades it has been proven that the incorporation of trace elements in foraminiferal calcite is controlled by more than one environmental parameter. To quantify the effect of salinity on Mg and Sr incorporation planktonic foraminifera Globigerinoides sacculifer (sensu stricto) were grown in the laboratory under different environmental conditions. Laboratory experiments allowed us to separate a direct salinity effect from a possible independent impact through differences in the calcite saturation state of the seawater ( Ω). Although the temperature effect is more important than the salinity effect, a change of 4 salinity units is equivalent to a 1 °C bias on Mg/Ca-based temperatures. This effect of salinity on Mg incorporation is minor. However, when using Mg/Ca-based temperatures in combination with foraminiferal δ 18O to calculate salinity, it cannot be neglected. The present study shows salinity as the overriding control on Mg incorporation within the range of Ω studied ( Ω between 5.25 and 6.50; [CO 3 2−] between 218 and 270 μmol/kg) at a constant temperature of 26 °C. In contrast, Ω appears to be the main control on foraminiferal Sr incorporation (0.10 mmol/mol per 100 µmol/kg rise in [CO 3 2−]), whereas salinity has a non significant influence on Sr/Ca.

Baseline geochemical characteristics of groundwater in the mountainous area of Jeju Island, South Korea: Implications for degree of mineralization and nitrate contamination

Hydrogeochemical characteristics of groundwater were investigated to elucidate baseline quality for basaltic aquifers of a mountainous area dominated by natural land cover in the volcanic island of Jeju, South Korea. Principal component analysis (PCA) resulted in four principal components (PC) of which PC1, PC3 and PC4 represented natural mineralization by water–rock interaction, while PC2 corresponded to anthropogenic contamination from nitrate sources. Hierarchical cluster analysis (HCA) was performed to assess the effect of the geochemical and hydrologic processes on each sample. Six sample groups, distinguished by total dissolved solids (TDS), nitrate concentration, and water type, resulted from the HCA: high-altitude springs, low-mineral water, nitrate-contaminated water, intermediate-mineral water, and two groups of high-mineral water. Water types were transformed from Na(Mg, Ca)–HCO 3 for low-mineral water to Na–HCO 3 for high-mineral water. Nitrate-contaminated water occurred near the boundary of natural and agricultural land uses of the western area. High-mineral water had higher calcite saturation states than other groups. The high-mineral water also had tritium ( 3 H) values lower than 1.5 TU, indicating a significant contribution of old groundwater. In contrast, low-mineral water had tritium values of about 3 TU, which is close to those of rainwater. Geographically, the high-mineral water was concentrated in the southwestern area, where intermediate-mineral water was also found. This distribution was likely related to the presence of extensive trachytic rocks, which could have formed locally isolated aquifers, enabling prolonged water–rock interactions; the higher location of low-permeability hydrovolcanic tuffs in the subsurface of the southern area would also increase chances of tapping aquifers below the hydrovolcanic tuffs. The cumulative probability of TDS showed two breakpoints of 50 and 150 mg/L that distinguished high-altitude springs, low-mineral water, and high-mineral water. The cumulative probability of nitrate provided possible threshold values for anthropogenic contamination of 2.5 and 5.5 mg/L. That 32% of samples had nitrate concentrations higher than 2.5 mg/L indicated high vulnerability to surface contamination sources in this mountainous area. HCA seems to be more effective for interpreting the baseline chemistry of groundwater than other threshold-calculating statistics in that HCA revealed geochemical processes including natural mineralization and anthropogenic contamination. Our study suggests that the cumulative probability and HCA are useful as complementary methods for determining threshold values.

Shallow water dissolution of settling calcite at station ALOHA

The dissolution of settling calcite at the Hawaii Ocean Time‐Series Sta. ALOHA in the North Pacific is examined using a calculation of the calcite saturation state based on 5 yr of alkalinity measurements and contemporary understanding of calcite dissolution kinetics. The results are consistent with previously reported field observations of calcite dissolution in the upper 1000 m at Sta. ALOHA. At low settling velocities, uncertainties in the parameterization of the dissolution equation can result in between 20% and 100% dissolution of sinking calcite in the upper 1000 m. The results introduce some doubt with regard to previous claims that field results at ALOHA provide evidence of biologically mediated calcite dissolution.

Carbon and nutrient mixed layer dynamics in the Norwegian Sea

Abstract. A coupled carbon-ecosystem model is compared to recent data from Ocean Weather Station M (66° N, 02° E) and used as a tool to investigate nutrient and carbon processes within the Norwegian Sea. Nitrate is consumed by phytoplankton in the surface layers over the summer; however the data show that silicate does not become rapidly limiting for diatoms, in contrast to the model prediction and in contrast to data from other temperate locations. The model estimates atmosphere-ocean CO2 flux to be 37 g C m−2 yr−1. The seasonal cycle of the carbonate system at OWS M resembles the cycles suggested by data from other high-latitude ocean locations. The seasonal cycles of calcite saturation state and [CO32-] are similar in the model and in data at OWS M: values range from ~3 and ~120 μmol kg−1 respectively in winter, to ~4 and ~170 μmol kg−1 respectively in summer. The model and data provide further evidence (supporting previous modelling work) that the summer is a time of high saturation state within the annual cycle at high-latitude locations. This is also the time of year that coccolithophore blooms occur at high latitudes.

Geochemical investigation of gametogenic calcite addition in the planktonic foraminifera Orbulina universa

Several species of planktonic foraminifera precipitate a final layer of calcite onto the shell surface immediately prior to gamete release at the end of the foraminifera life cycle. Here, we present the results of carbon-13, oxygen-18 and thermal labeling experiments conducted under high (HL) and low light (LL) regimes that vary symbiont photosynthetic activity. Mean experimental group data show that gametogenic (gam) calcite contributes between 4–17% and 14–20% to final shell mass for high and low light experiments respectively. These data indicate that past studies of gam calcite addition have overestimated the amount of gam calcite on foraminifera shells by ~ 30–55%. Calculations indicate that the mass of gam calcite added to the O. universa shell, 4.2 ± 2.0 μg and 4.0 ± 2.4 μg, is constant in the HL and LL groups respectively. We propose that the production of gam calcite may be the result of the discharge of a relatively constant-volume cytoplasmic pool of either Ca 2+ or alkalinity (carbon pool) that increases the calcite saturation state in the microenvironment adjacent to the foraminifera shell just prior to gamete formation and release. Results from these experiments indicate that the geochemistry of thin-walled O. universa from deep sea sediments is composed of > 80% ontogenetic calcite that was precipitated in the primary, near surface habitat of this species.

Mechanism for calcite dissolution and its contribution to development of reservoir porosity and permeability in the Kela 2 gas field, Tarim Basin, China

This study is undertaken to understand how calcite precipitation and dissolution contributes to depth-related changes in porosity and permeability of gas-bearing sandstone reservoirs in the Kela 2 gas field of the Tarim Basin, Northwestern China. Sandstone samples and pore water samples are collected from well KL201 in the Tarim Basin. Vertical profiles of porosity, permeability, pore water chemistry, and the relative volume abundance of calcite/dolomite are constructed from 3600 to 4000 m below the ground surface within major oil and gas reservoir rocks. Porosity and permeability values are inversely correlated with the calcite abundance, indicating that calcite dissolution and precipitation may be controlling porosity and permeability of the reservoir rocks. Pore water chemistry exhibits a systematic variation from the Na2SO4 type at the shallow depth (3600–3630 m), to the NaHCO3 type at the intermediate depth (3630–3695 m), and to the CaCl2 type at the greater depth (3728–3938 m). The geochemical factors that control the calcite solubility include pH, temperature, pressure, Ca2+ concentration, the total inorganic carbon concentration (ΣCO2), and the type of pore water. Thermodynamic phase equilibrium and mass conservation laws are applied to calculate the calcite saturation state as a function of a few key parameters. The model calculation illustrates that the calcite solubility is strongly dependent on the chemical composition of pore water, mainly the concentration difference between the total dissolved inorganic carbon and dissolved calcium concentration (i.e., [ΣCO2]−[Ca2+]). In the Na2SO4 water at the shallow depth, this index is close to 0, pore water is near the calcite solubility. Calcite does not dissolve or precipitate in significant quantities. In the NaHCO3 water at the intermediate depth, this index is greater than 0, and pore water is supersaturated with respect to calcite. Massive calcite precipitation was observed at this depth interval and this intensive cementation is responsible for decreased porosity and permeability. In the CaCl2 water at the greater depth, pore water is under-saturated with respect to calcite, resulting in dissolution of calcite cements, as consistent with microscopic dissolution features of the samples from this depth interval. Calcite dissolution results in formation of high secondary porosity and permeability, and is responsible for the superior quality of the reservoir rocks at this depth interval. These results illustrate the importance of pore water chemistry in controlling carbonate precipitation/dissolution, which in turn controls porosity and permeability of oil and gas reservoir rocks in major sedimentary basins.

Short‐term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic CO2: A model study

This study addresses the potential for and the quantification of dissolution of marine calcium carbonate (CaCO3) sediments occurring on century timescales in response to the invasion of anthropogenic CO2. It presents results obtained with the global biogeochemical model PISCES interactively coupled to a global sediment model. The latter represents the principal reactions involved in early diagenesis of biogenic opal, CaCO3, and organic matter. The model reproduces observed distributions of core top CaCO3 content and bottom water carbonate chemistry (e.g., [CO32−]). Starting from the climatological state, a model experiment is carried out according to the standard CMIP scenario of atmospheric pCO2 increasing at a rate of 1% per year from 286 to 1144 ppm over a 140 year time period. The invasion of anthropogenic CO2 results in a strong decrease in bottom water [CO32−] reaching −100 μM in areas of deep water formation in the North Atlantic and mode and intermediate water formation in the Southern Hemisphere. The concomitant decrease in calcite saturation state of bottom waters drives the dissolution of CaCO3. The absolute CaCO3 content averaged over the top first centimeter decreases by up to 6%, while the change in advection calculated at the base of the bioturbated layer (10 cm) is indicative of net erosion. The predicted changes in bottom water chemistry are discussed in terms of their potential impact on benthic communities.

Calcification morphotypes of the coccolithophorid Emiliania huxleyi in the Southern Ocean: changes in 2001 to 2006 compared to historical data

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 348:47-54 (2007) - DOI: https://doi.org/10.3354/meps07058 Calcification morphotypes of the coccolithophorid Emiliania huxleyi in the Southern Ocean: changes in 2001 to 2006 compared to historical data J. C. Cubillos1, S. W. Wright2,3, G. Nash2, M. F. de Salas1, B. Griffiths3,4, B. Tilbrook3,4, A. Poisson5, G. M. Hallegraeff1,* 1School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia 2Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050, Australia 3Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart, Tasmania 7001, Australia 4Wealth from Oceans Flagship, CSIRO, GPO Box 1538, Hobart, Tasmania 7001, Australia 5Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques, Université Pierre et Marie Curie, 75252 Paris, France *Corresponding author. Email: hallegraeff@utas.edu.au ABSTRACT: We conducted a scanning electron microscopic survey of morphological variations in the calcareous nanoplankton species Emiliania huxleyi in Southern Ocean surface water samples collected along a transect from 43 to 64°S and 141 to 145°E during November 2001, October to February 2002/2003, 2003/2004, 2004/2005 and 2005/2006. The results were compared with historical data from a similar transect occupied in December to January 1983/1984 and January to February 1994 and 1995. While E. huxleyi was absent or extremely sparse (0.1 to 1 cells ml–1) south of 60°S in 1983/1984 and 1994/1995, this species was consistently present at about 100 cells ml–1 between 60 and 65°S during 2002 to 2006. The extended geographic range and/or increased southward abundance of this keystone species suggests a significant shift in Southern Ocean ecology over the past 2 decades, analogous to an observed recent range extension into the Bering Sea. Morphotype A ‘overcalcified’ mainly occurred north of the Subantarctic Front and was replaced by the weakly calcified Morphotype B/C between the Subantarctic Front and Southern Antarctic Circumpolar Current Front. This north–south shift in E. huxleyi calcification morphotypes closely tracked the north–south decline in the calcite saturation state as calculated from carbonate system measurements. Based on current evidence, no significant changes are apparent in the calcification status of E. huxleyi in the Southern Ocean during the past 12 yr. All cultured isolates from north of the Polar Front belonged to Morphotype A, while all strains isolated south of the Polar Front belonged to Morphotype B/C and their morphologies appeared conservative in culture. The north–south trend of decreased calcification of E. huxleyi in the Southern Ocean thus reflects the shift in dominance of one ecotype to another, rather than the environmental effect of decreased carbonatre ion concentrations and calcite saturation state on a single, ‘apparently cosmopolitan’, population. KEY WORDS: Southern Ocean · Emiliania huxleyi · Calcite saturation state · Ocean acidification Full text in pdf format PreviousNextCite this article as: Cubillos JC, Wright SW, Nash G, de Salas MF and others (2007) Calcification morphotypes of the coccolithophorid Emiliania huxleyi in the Southern Ocean: changes in 2001 to 2006 compared to historical data. Mar Ecol Prog Ser 348:47-54. https://doi.org/10.3354/meps07058 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 348. Online publication date: October 25, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Occurrence of calcareous foraminifera and calcite-carbonate equilibrium conditions – a case study in Minho/Coura estuary (Northern Portugal)

The Minho/Coura estuary, northern Portugal, has been studied for the influence of hydrochemical and geochemical parameters on living (Rose Bengal stained) foraminiferal assemblages. Our previous works showed a prevalence of agglutinated species in the inner estuary and tidal marsh and significant abundance of calcareous species only in the estuary mouth. The new results clarify syndepositional aspects of the calcareous species related to calcite dissolution, such as thin tests that frequently lack the carbonate layer and show typical destruction features. Sites from the estuary mouth, tidal marsh and river were sampled, under Spring and Autumn conditions, in order to describe physical-chemical features and to allow the geochemical modelling of the solution in which calcification occurs. In particular, the chemical equilibrium regarding calcite was evaluated from the saturation index (SI). Such modelling suggests strongly undersaturated conditions at the majority of the sampling sites, in both sampling periods. The water quality data revealed strong spatial and temporal variability, mainly in the tidal marsh environment, and also the existence of a stressed medium regarding calcite saturation state. The observed geochemical trends provide a plausible explanation for (1) the scarcity and distribution of living calcareous foraminifera in the Minho/Coura estuary and (2) the destruction features observed in the carbonate tests.

Calcium isotope fractionation in coccoliths of cultured Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa

Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO 3 2−], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO 3, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO 3 export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δ sed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δ sed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages.

Environmental setting, (micro)morphologies and stable C–O isotope composition of cold climate carbonate precipitates—a review and evaluation of their potential as paleoclimatic proxies

Given the growing interest in carbonate deposits from polar regions as paleoclimatic proxies, this review paper first provides a classification of the various types of cold-climate carbonate precipitates followed by a summary of the 13C and 18O composition of the carbonate deposits and parent water from which the carbonates precipitated. The cold-climate carbonate precipitates were classified into three broad categories: powders, crusts and speleothem. The carbonate powders include those that precipitated in relation to aufeis aggradation (cryogenic aufeis calcite) and in relation to the growth of various annual/perennial ice formations in freezing caves (cryptocrystalline calcite and calcite pearls). The carbonate crusts can be further subdivided based on their lithic environment; those that precipitated on the upper surface of bedrock/clasts (i.e. subglacially precipitated calcite and evaporative calcite crusts); those that are located on the underside of clasts (i.e. pedogenic carbonates); and those that precipitated in rock outcrop fissures (i.e. endostromatolites). The cold-climate carbonate precipitates have a highly variable isotopic composition with δ 18O values ranging between −6.5‰ and 28‰ VSMOW and δ 13C values in the −10–20‰ VPDB range. However, each type of carbonate precipitates has a specific δ 13C and δ 18O range, suggesting that their environmental setting and the mechanism by which they formed controls their 13C and 18O signature. It was found that carbonate deposits that precipitated under equilibrium physico-chemical conditions had a δ 13C value that is in equilibrium with that of the parent water, while its δ 18O composition was more variable, as it is in part controlled by the temperature of reaction and by the δ 18O and calcite saturation state of the parent water. By contrast, the δ 18O composition of biologically precipitated carbonate deposits (endostromatolites) reflect that of the parent water, while its δ 13C composition was enriched over that of the parent water due to bacterial methanogenesis. In the case of kinetically precipitated carbonate deposits, the δ 18O and δ 13C values are out-of-equilibrium relative to that of the parent water due to the faster rate of reaction.