Seawater carbonate chemistry and processes during an experiment with coral reef, 2000

The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21st century. This increase will reduce the concentration of [CO3]2- of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage. Using the large 2650 m3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcification of coral reef organisms at the community scale. Our experimental design was to obtain a long (3.8 years) time series of the net calcification of the complete system and all relevant physical and chemical variables (temperature, salinity, light, nutrients, Ca2+,pCO2, TCO2, and total alkalinity). Periodic additions of NaHCO3, Na2CO3, and/or CaCl2 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcification in response to our manipulations of the saturation state. We show that the net community calcification rate responds to manipulations in the concentrations of both Ca2+ and [CO3]2- and that the rate is well described as a linear function of the ion concentration product, [Ca2+]0.69[[CO3]2-]. This suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcification on coral reefs at the ecosystem level. We compare the sensitivity of calcification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification between the years 1880 and 2065 A.D. based on our long-term results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. In the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.

Phytoplankton calcification as an effective mechanism to alleviate cellular calcium poisoning

Marine phytoplankton has developed the remarkable ability to tightly regulate the concentration of free calcium ions in the intracellular cytosol at a level of ~ 0.1 µmol /l in the presence of seawater Ca2+ concentrations of 10 mmol/1. The low cytosolic calcium ion concentration is of utmost importance for proper cell signalling function. While the regulatory mechanisms responsible for the tight control of intracellular Ca2+ concentration are not completely understood, phytoplankton taxonomic groups appear to have evolved different strategies, which may affect their ability to cope with changes in seawater Ca2+ concentrations in their environment on geological time scales. For example, the Cretaceous (145 to 66 Ma ago), an era known for the high abundance of coccolithophores and the production of enormous calcium carbonate deposits, exhibited seawater calcium concentrations up to four times present-day levels. We show that calcifying coccolithophore species (Emiliania huxleyi, Gephyrocapsa oceanica and Coccolithus braarudii) are able to maintain their relative fitness (in terms of growth rate and photosynthesis) at simulated Cretaceous seawater calcium concentrations, whereas these rates are severely reduced under these conditions in some non-calcareous phytoplankton species (Chaetoceros sp., Ceratoneis closterium and Heterosigma akashiwo). Most notably, this also applies to a non-calcifying strain of E. huxleyi which displays a calcium-sensitivity similar to the non-calcareous species. We hypothesize that the process of calcification in coccolithophores provides an efficient mechanism to alleviate cellular calcium poisoning and thereby offered a potential key evolutionary advantage, responsible for the proliferation of coccolithophores during times of high seawater calcium concentrations. The exact function of calcification and the reason behind the highly-ornate physical structures of coccoliths remain elusive.

Factors affecting counteraction by methylamines of urea effects on aldose reductase

The concentration of urea in renal medullary cells is high enough to affect enzymes seriously by reducing Vmax or raising Km, yet the cells survive and function. The usual explanation is that the methylamines found in the renal medulla, namely glycerophosphocholine and betaine, have actions opposite to those of urea and thus counteract its effects. However, urea and methylamines have the similar (not counteracting) effects of reducing both the Km and Vmax of aldose reductase (EC 1.1.1.21), an enzyme whose function is important in renal medullas. Therefore, we examined factors that might determine whether counteraction occurs, namely different combinations of assay conditions (pH and salt concentration), methylamines (glycerophosphocholine, betaine, and trimethylamine N-oxide), substrates (dl-glyceraldehyde and d-xylose), and a mutation in recombinant aldose reductase protein (C298A). We find that Vmax of both wild-type and C298A mutant generally is reduced by urea and/or the methylamines. However, the effects on Km are much more complex, varying widely with the combination of conditions. At one extreme, we find a reduction of Km of wild-type enzyme by urea and/or methylamines that is partially additive, whereas at the other extreme we find that urea raises Km for d-xylose of the C298A mutant, betaine lowers the Km, and the two counteract in a classical fashion so that at a 2:1 molar ratio of betaine to urea there is no net effect. We conclude that counteraction of urea effects on enzymes by methylamines can depend on ion concentration, pH, the specific methylamine and substrate, and identity of even a single amino acid in the enzyme.

Genetic analysis of calcium spiking responses in nodulation mutants of Medicago truncatula

The symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti results in the formation of nitrogen-fixing nodules on the roots of the host plant. The early stages of nodule formation are induced by bacteria via lipochitooligosaccharide signals known as Nod factors (NFs). These NFs are structurally specific for bacterium–host pairs and are sufficient to cause a range of early responses involved in the host developmental program. Early events in the signal transduction of NFs are not well defined. We have previously reported that Medicago sativa root hairs exposed to NF display sharp oscillations of cytoplasmic calcium ion concentration (calcium spiking). To assess the possible role of calcium spiking in the nodulation response, we analyzed M. truncatula mutants in five complementation groups. Each of the plant mutants is completely Nod− and is blocked at early stages of the symbiosis. We defined two genes, DMI1 and DMI2, required in common for early steps of infection and nodulation and for calcium spiking. Another mutant, altered in the DMI3 gene, has a similar mutant phenotype to dmi1 and dmi2 mutants but displays normal calcium spiking. The calcium behavior thus implies that the DMI3 gene acts either downstream of calcium spiking or downstream of a common branch point for the calcium response and the later nodulation responses. Two additional mutants, altered in the NSP and HCL genes, which show root hair branching in response to NF, are normal for calcium spiking. This system provides an opportunity to use genetics to study ligand-stimulated calcium spiking as a signal transduction event.

A simple light-driven transmembrane proton pump.

Light-induced lipophilic porphyrin/aqueous acceptor charge separation across a single lipid-water interface can pump protons across the lipid bilayer when the hydrophobic weak acids, carbonylcyanide m-chlorophenylhydrazone and its p-trifluoromethoxyphenyl analogue, are present. These compounds act as proton carriers across lipid bilayers. In their symmetric presence across the bilayer, the positive currents and voltages produced by the photogeneration of porphyrin cations are replaced by larger negative currents and voltages. The maximum negative current and voltage occur at the pH of maximum dark conductance. The reversed larger current and voltage show a positive ionic charge transport in the same direction as the electron transfer. This transport can form an ion concentration gradient. The movement of protons is verified by an unusual D2O isotope effect that increases the negative ionic current by 2- to 3-fold. These effects suggest that an interfacial pK shift of the weak acid caused by the local electric field of photoformed porphyrin cations/acceptor anions functions as the driving force. The estimated pumping efficiency is 10-30%. Time-resolved results show that proton pumping across the bilayer occurs on the millisecond time scale, similar to that of biological pumps. This light-driven proteinless pump offers a simple model for a prebiological energy transducer.

Identification of receptor ligands and receptor subtypes using antagonists in a capillary electrophoresis single-cell biosensor separation system.

A capillary electrophoresis system with single-cell biosensors as a detector has been used to separate and identify ligands in complex biological samples. The power of this procedure was significantly increased by introducing antagonists that inhibited the cellular response from selected ligand-receptor interactions. The single-cell biosensor was based on the ligand-receptor binding and G-protein-mediated signal transduction pathways in PC12 and NG108-15 cell lines. Receptor activation was measured as increases in cytosolic free calcium ion concentration by using fluorescence microscopy with the intracellular calcium ion indicator fluo-3-acetoxymethyl ester. Specifically, a mixture of bradykinin (BK) and acetylcholine (ACh) was fractionated and the components were identified by inhibiting the cellular response with icatibant (HOE 140), a selective antagonist to the BK B2 receptor subtype (B2BK), and atropine, an antagonist to muscarinic ACh receptor subtypes. Structurally related forms of BK were also identified based on inhibiting B2BK receptors. Applications of this technique include identification of endogenous BK in a lysate of human hepatocellular carcinoma cells (Hep G2) and screening for bioactivity of BK degradation products in human blood plasma. The data demonstrate that the use of antagonists with a single-cell biosensor separation system aids identification of separated components and receptor subtypes.

Planktonic foraminifera of sediment trap samples

Biweekly sediment trap samples and concurrent hydrographic measurements collected between March 2005 and October 2008 from the Cariaco Basin, Venezuela, are used to assess the relationship between [CO3]2- and the area densities (ho A) of two species of planktonic foraminifera (Globigerinoides ruber (pink) and Globigerinoides sacculifer). Calcification temperatures were calculated for each sample using species-appropriate oxygen isotope (d18O) temperature equations that were then compared to monthly temperature profiles taken at the study site in order to determine calcification depth. Ambient [CO3]2- was determined for these calcification depths using alkalinity, pH, temperature, salinity, and nutrient concentration measurements taken during monthly hydrographic cruises. The rho A, which is representative of calcification efficiency, is determined by dividing individual foraminiferal shell weights (±0.43 µg) by their associated silhouette areas and taking the sample average. The results of this study show a strong correlation between rho A and ambient [CO3]2- for both G. ruber and G. sacculifer (R**2 = 0.89 and 0.86, respectively), confirming that [CO3]2- has a pronounced effect on the calcification of these species. Though the rho A for both species reveal a highly significant (p < 0.001) relationship with ambient [CO3]2-, linear regression reveals that the extent to which [CO3]2- influences foraminiferal calcification is species specific. Hierarchical regression analyses indicate that other environmental parameters (temperature and [PO4]3-) do not confound the use of G. ruber and G. sacculifer rho A as a predictor for [CO3]2-. This study suggests that G. ruber and G. sacculifer rho A can be used as reliable proxies for past surface ocean [CO3]2?-

Stable oxygen isotope records of different benthic foraminiferal species of core GeoB3004-1 from the western Arabian Sea

The stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western Arabian Sea was determined to evaluate deepwater oxygenation, organic matter remineralization, and early diagenetic processes during the past 190,000 years. The d18O records reveal species-specific metabolic effects, susceptibility to changes in carbonate ion concentration, and supralysoclinal calcite dissolution. The foraminiferal d13C records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon (d13CDIC) and in the microhabitat depth of infaunal species. Maximum d13CDIC offsets between bottom and pore waters ranged between mean values of 0.8 and 1.2% corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2.7 ml/l. Intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well-oxygenated deepwater masses during interglacials. During interglacial maxima the d13C difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes.

Environmental controls on the Emiliania huxleyi calcite mass

Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO3]2-, there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO3]2-. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO2 world and improve interpretation of paleorecords.

Figure 5. Trace metal analysis of sediment core PS1506-1

An increase in whole ocean alkalinity during glacial periods could account, in part, for the drawdown of atmospheric CO2 into the ocean. Such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity. We present evidence, based on down-core measurements of benthic foraminiferal B/Ca and Mg/Ca from a core in the Weddell Sea, that the deep ocean carbonate ion concentration, [CO3 2-], was elevated by ~25 µmol/kg during each glacial period of the last 800 kyrs. The heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the Atlantic and Pacific by the changing ventilation and chemistry of Weddell Sea waters. These waters are more corrosive than interglacial northern sourced waters, but not as undersaturated as interglacial southern sourced waters. Our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget, if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification. The Weddell records display low [CO3 2-] during deglaciations and peak interglacial warmth, coincident with maxima in %CaCO3 in the Atlantic and Pacific Oceans. Should the burial rate of alkalinity in the more alkaline glacial deepwaters outstrip the rate of alkalinity supply, then pelagic carbonate production by the coccolithophores, at the end of the glacial maximum could drive a decrease in ocean [CO3 2-] and act to trigger the deglacial rise in pCO2.

Chemical observations in the Red Sea and the inner Gulf of Aden during the International Indian Ocean Expedition 1964/65

The Red Sea has a special place among the adjacent seas of the world. High evaporation, exclusion of its deep water from contact with the Indian Ocean proper and complete absence of continental drainage may result special conditions of the chemistry of the Red Sea. This paper aims to describe and explain the peculiarity of the hydrochemical situation. The influence of the topography, of the inflow and outflow through the straights of Bab el Mandeb, of the evaporation, of the stability of the water layers, and of the circulation will be studied. An attempt is made to estimate the apparent oxygen ultilisation in order to obtain an indication of the biological activity. A further attempt is made toward the quantitative estimation of the circulation of the nutrients and also to obtain some information about transport, dissolution, and precipitation of calcium carbonate. The basis of these investigations are mainly observations of R. V. "Meteor" during the International Indian Ocean Expedition 1964/65. The determination of dissolved oxygen, dissolved inorganic phosphate, nitrate, nitrite, ammonia, pH, alkalinity, silicate as well as salinity and temperature forms the necessary basis for such an investigation of the chemical conditions. In the first chapter the methods and some modifications for the determination of the chemical properties as applied during the I.I.O.E. cruise of R. V. "Meteor" are described. The new methods, as worked out and tested under sea going conditions during several years by the author, are described in more detail. These are the methods for nitrate, silicate, the automatic determination of dissolved inorganic phosphate and silicate, the automated determination of total phosphorus, the in situ recording of the oxygen tension, and the modification for the determination of ammonia, calcium, and dissolved oxygen. With these revised methods more than 18,000 determinations have been carried out during the Indian Ocean cruise. The complete working up of the chemical data of the Indian Ocean Expedition of R. V. "Meteor" is devided into four sections: Contributions 1) to the Chemistry of the Red Sea and the Inner Gulf of Aden, 2) to the Gulf of Aden and the Somali Coast Region, 3) to the Western Indian Coast Region, and 4) to the Persian Gulf and the Straits of Oman. This paper presents the first contribution. The special hydrographical conditions are discussed. It can be shown, that the increase of salinity in the surface waters from the south to the north of the Red Sea is only to about 30 % due to evaporation. The remaining increase is presumed to be due to the admixture of deep water to the surface layers. A special rate for the consumption of oxygen (0.114 ml/ l/a) is derived for the deep water of the Red Sea at 1500 m. Based upon the distribution of the dissolved oxygen along the axii of the Red Sea, a chematic model for the longitudinal circulation of the Red Sea is constructed. This model should be considered as a first approximation and may explain the special distribution of phosphate, nitrate, and silicate. Based upon the evaluation of the residence time of the deep water a dissolution rate for silicate is estimated as 1 mygat/a. It seems possible to calculate residence times of water masses outside the Red Sea from the silicate content. The increase of silicate and the consumption of oxygen lead to residence times of the water below the thermocine of 30 to 48 years. The distribution of oxygen in the Straits of Bab el Mandeb is described and discussed. The rate of consumption of the oxygen in the outflowing Red Sea water is estimated to 8.5 ml/ l/a. This rather high rate is explained with reference to the special conditions in the outflowing water. The Red Sea water is characterized initially by a relative high content of oxygen and a low content of nutrients. The increase in nutrients and the decrease in the oxygen content is a secondary process of the Red Sea water on its way to the Arabian Sea. Based upon the vertical distribution of the dissolved inorganic phosphate vertical exchange coefficients of 1 - 4 g/cm/sec and vertical current speeds of 10**-5 to 10**-4 cm/sec are calculated for some stations in the Red Sea. The distribution of phosphate, silicate, nitrate, nitrite and ammonia for the Red Sea and the Straits of Bab el Mandeb are discussed. The special circulation is evaluated and the balance of the nutrients is estimated by means of the brutto transport. The nutrient deficit is assumed to be balanced by sporadic inflow of intermediate water from the Gulf of Aden. An example for such an inflow has been observed and is demonstrated. The silicate-salinity relationships are a suitable way for characterizing water masses in the Red Sea. Equations for the calculation of the different components from the carbonate system, the ion activities, and the calcium carbonate saturation are evaluated. The influence of temperature and pressure is taken into account. The carbonate saturation is calculated from the determined concentrations of calcium, alkalinity, and the hydrogen ion activity. Saturation values of 320 % are found for the surface layer and of 100% ± 1 for the deep water. The extraordinary equilibrium conditions may explain the constant Ca/Cl ratio and also the sedimentation of undissolved carbonate skelecons even in greater depths. A main sedimentation rate of 2 * 10**-3cm/year is evaluated from a total sedimentation of 10 * 106 to/a of calcium carbonate in the Red Sea. The appendix contains those data, which are not published in the data volume of the I.I.O.E. expedition of R. V. "Meteor".

Shell preservation of Limacina inflata in surface sediments of the Central and South Atlantic

Over 300 surface sediment samples from the Central and South Atlantic Ocean and the Caribbean Sea were investigated for the preservation state of the aragonitic test of Limacina inflata. Results are displayed in spatial distribution maps and are plotted against cross-sections of vertical water mass configurations, illustrating the relationship between preservation state, saturation state of the overlying waters, and overall water mass distribution. The microscopic investigation of L. inflata (adults) yielded the Limacina dissolution index (LDX), and revealed three regional dissolution patterns. In the western Atlantic Ocean, sedimentary preservation states correspond to saturation states in the overlying waters. Poor preservation is found within intermediate water masses of southern origin (i.e. Antarctic intermediate water (AAIW), upper circumpolar water (UCDW)), which are distinctly aragonite-corrosive, whereas good preservation is observed within the surface waters above and within the upper North Atlantic deep water (UNADW) beneath the AAIW. In the eastern Atlantic Ocean, in particular along the African continental margin, the LDX fails in most cases (i.e. less than 10 tests of L. inflata per sample were found). This is most probably due to extensive "metabolic" aragonite dissolution at the sediment-water interface combined with a reduced abundance of L. inflata in the surface waters. In the Caribbean Sea, a more complex preservation pattern is observed because of the interaction between different water masses, which invade the Caribbean basins through several channels, and varying input of bank-derived fine aragonite and magnesian calcite material. The solubility of aragonite increases with increasing pressure, but aragonite dissolution in the sediments does not simply increase with water depth. Worse preservation is found in intermediate water depths following an S-shaped curve. As a result, two aragonite lysoclines are observed, one above the other. In four depth transects, we show that the western Atlantic and Caribbean LDX records resemble surficial calcium carbonate data and delta13C and carbonate ion concentration profiles in the water column. Moreover, preservation of L. inflata within AAIW and UCDW improves significantly to the north, whereas carbonate corrosiveness diminishes due to increased mixing of AAIW and UNADW. The close relationship between LDX values and aragonite contents in the sediments shows much promise for the quantification of the aragonite loss under the influence of different water masses. LDX failure and uncertainties may be attributed to (1) aragonite dissolution due to bottom water corrosiveness, (2) aragonite dissolution due to additional CO2 release into the bottom water by the degradation of organic matter based on an enhanced supply of organic matter into the sediment, (3) variations in the distribution of L. inflata and hence a lack of supply into the sediment, (4) dilution of the sediments and hence a lack of tests of L. inflata, or (5) redeposition of sediment particles.