Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi (TW1), 2003

Precipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange of CO2 at the ocean-atmosphere interface. Previous experiments have demonstrated that, under nutrient-sufficient conditions, doubling the partial pressure of CO2 (pCO2) in seawater-a likely scenario for the end of the century-can significantly decrease both the rate of calcification by coccolithophorids and the ratio of inorganic to organic carbon production. The present work investigates the effects of high pCO2 on calcification by the coccolithophore Emiliania huxleyi (Strain TW1) grown under nitrogen-limiting conditions, a situation that can also prevail in the ocean. Nitrogen limitation was achieved in NO3-limited continuous cultures renewed at the rate of 0.5 d-1 and exposed to a saturating light level. pCO2 was increased from 400 to 700 ppm and controlled by bubbling CO2-rich or CO2-free air into the cultures. The pCO2 shift has a rapid effect on cell physiology that occurs within 2 cell divisions subsequent to the perturbation. Net calcification rate (C) decreased by 25% and, in contrast to previous studies with N-replete cultures, gross community production (GCP) and dark community respiration (DCR) also decreased. These results suggest that increasing pCO2 has no noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited.

Seawater carbonate chemistry, processes and elements during experiments with planktonic foraminifera Orbulina universa, 2004

We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO3[2-]] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 +/- 7% per 100 µmol [CO3[2-]] kg**-1, as seawater [CO3[2-]] increases from 110 to 470 µmol kg**-1. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ~+40% at the same environmental [CO3[2-]]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO3[2-]] was 110 +/- 70 µmol kg**-1 and 80 +/- 40 µmol kg**-1 higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO3[2-]] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean's carbonate concentration.

Seawater carbonate chemistry and photosynthesis of a coccolithophorid in a laboratory experiment

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 µatm) and low, current (390 µatm) CO2 levels, under regimes of fluctuating irradiances with or without UVR. Under both CO2 levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO2 showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO2-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.

Ocean acidification mediates photosynthetic response to UV radiation and temperature increase in the diatom Phaeodactylum tricornutum

Increasing atmospheric CO2 concentration is responsible for progressive ocean acidification, ocean warming as well as decreased thickness of upper mixing layer (UML), thus exposing phytoplankton cells not only to lower pH and higher temperatures but also to higher levels of solar UV radiation. In order to evaluate the combined effects of ocean acidification, UV radiation and temperature, we used the diatom Phaeodactylum tricornutum as a model organism and examined its physiological performance after grown under two CO2 concentrations (390 and 1000 µatm) for more than 20 generations. Compared to the ambient CO2 level (390 µatm), growth at the elevated CO2 concentration increased non-photochemical quenching (NPQ) of cells and partially counteracted the harm to PS II (photosystem II) caused by UV-A and UV-B. Such an effect was less pronounced under increased temperature levels. The ratio of repair to UV-B induced damage decreased with increased NPQ, reflecting induction of NPQ when repair dropped behind the damage, and it was higher under the ocean acidification condition, showing that the increased pCO2 and lowered pH counteracted UV-B induced harm. As for photosynthetic carbon fixation rate which increased with increasing temperature from 15 to 25 °C, the elevated CO2 and temperature levels synergistically interacted to reduce the inhibition caused by UV-B and thus increase the carbon fixation.

Seawater carbonate chemistry, nutrients, particulate carbon and growth rate of Emiliania huxleyi (AC472), Calcidiscus leptoporus (AC370) and Syracosphaera pulchra (AC418) during experiments, 2011

The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H. Blackman) J. Schiller, andSyracosphaera pulchra Lohmann to elevated partial pressure of carbon dioxide (pCO2) was investigated in batch cultures. We reported on the response of both haploid and diploid life stages of these three species. Growth rate, cell size, particulate inorganic carbon (PIC), and particulate organic carbon (POC) of both life stages were measured at two different pCO2 (400 and 760 parts per million [ppm]), and their organic and inorganic carbon production were calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO2, the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO2, but the response of other processes varied among species. Calcification rate of C. leptoporusand of S. pulchra did not change at elevated pCO2, whereas it increased in E. huxleyi. POC production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO2. It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO2 has a significant effect on these three coccolithophore species, the haploid stage being more sensitive. This effect must be taken into account when predicting the fate of coccolithophores in the future ocean.

Seawater carbonate chemistry and biological processes during experiments with haploid and diploid life stages of Emiliania huxleyi, Calcidiscus leptoporus and Syracosphaera pulchra

The response of Emiliania huxleyi (Lohmann), Calcidiscus leptoporus (Murray and Blackman), and Syracosphaera pulchra (Lohmann) to elevated partial pressure of carbon dioxide (pCO2) was investigated in batch cultures. For the first time, we reported on the response of the non-calcifying (haploid) life stage of these three species. Growth rate, cell size, particulate inorganic (PIC) and particulate organic carbon (POC) of both life stages were measured at two different pCO2 (400 and 760 ppm) and their organic and inorganic carbon production calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO2, the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO2 but the response of other processes varied among species. Calcification rate of C. leptoporus and of S. pulchra did not change at elevated pCO2 while it increased in E. huxleyi. Particulate organic carbon production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO2. It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO2 has a significant effect on these three coccolithophores species, the haploid stage being more sensitive. This must be taken into account when predicting the fate of coccolithophores in the future ocean.

Seawater carbonate chemistry and community calcification during a Molokai reef (Hawaii) study 2006

The severity of the impact of elevated atmospheric pCO2 to coral reef ecosystems depends, in part, on how seawater pCO2 affects the balance between calcification and dissolution of carbonate sediments. Presently, there are insufficient published data that relate concentrations of pCO2 and CO3 to in situ rates of reef calcification in natural settings to accurately predict the impact of elevated atmospheric pCO2 on calcification and dissolution processes. Rates of net calcification and dissolution, CO3 concentrations, and pCO2 were measured, in situ, on patch reefs, bare sand, and coral rubble on the Molokai reef flat in Hawaii. Rates of calcification ranged from 0.03 to 2.30 mmol CaCO3 m**-2 h**-1 and dissolution ranged from -0.05 to -3.3 mmol CaCO3 m**-2 h**-1. Calcification and dissolution varied diurnally with net calcification primarily occurring during the day and net dissolution occurring at night. These data were used to calculate threshold values for pCO2 and CO3 at which rates of calcification and dissolution are equivalent. Results indicate that calcification and dissolution are linearly correlated with both CO3 and pCO2. Threshold pCO2 and CO3 values for individual substrate types showed considerable variation. The average pCO2 threshold value for all substrate types was 654±195 µatm and ranged from 467 to 1003 µatm. The average CO3 threshold value was 152±24 µmol/kg, ranging from 113 to 184 µmol/kg. Ambient seawater measurements of pCO2 and CO3 indicate that CO3 and pCO2 threshold values for all substrate types were both exceeded, simultaneously, 13% of the time at present day atmospheric pCO2 concentrations. It is predicted that atmospheric pCO2 will exceed the average pCO2 threshold value for calcification and dissolution on the Molokai reef flat by the year 2100.

Seawater carbonate chemistry and biological processes during experiments with phytoplankton Emiliania huxleyi (CS369), 2009

Increasing atmospheric CO2 concentration affects calcification in most planktonic calcifiers. Both reduced or stimulated calcification under high CO2 have been reported in the widespread coccolithophore Emiliania huxleyi. This might affect the response of cells to photosynthetically active radiation (PAR; 400-700 nm) and ultraviolet radiation (UVR; 280-400 nm) by altering the thickness of the coccolith layer. Here we show that in the absence of UVR, the calcification rates in E. huxleyi decrease under lowered pH levels (pHNBS of 7.9 and 7.6; pCO2 of 81 and 178 Pa or 804 and 1759 ppmv, respectively) leading to thinned coccolith layers, whereas photosynthetic carbon fixation was slightly enhanced at pH 7.9 but remained unaffected at pH 7.6. Exposure to UVR (UV-A 19.5 W m**-2, UV-B 0.67 W m**-2) in addition to PAR (88.5 W m**-2), however, results in significant inhibition of both photosynthesis and calcification, and these rates are further inhibited with increasing acidification. The combined effects of UVR and seawater acidification resulted in the inhibition of calcification rates by 96% and 99% and that of photosynthesis by 6% and 15%, at pH 7.9 and 7.6, respectively. This differential inhibition of calcification and photosynthesis leads to significant reduction of the ratio of calcification to photosynthesis. Seawater acidification enhanced the transmission of harmful UVR by about 26% through a reduction of the coccolith layer of 31%. Our data indicate that the effect of a high-CO2 and low-pH ocean on E. huxleyi (because of reduced calcification associated with changes in the carbonate system) enhances the detrimental effects of UVR on the main pelagic calcifier.

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.

Seawater carbonate chemistry and community calcification during Miyako Island (Japan) coral reef studies, 1994

Coral reefs are characterized by enormous carbonate production of the organisms. It is known that rapid calcification is linked to photosynthesis under control of the carbonate equilibrium in seawater. We have established a model simulating the coexisting states of photosynthesis and calcification in order to examine the effects of photosynthesis and calcification on the carbonate system in seawater. Supposing that the rates of photosynthesis and calcification are proportional to concentrations of their inorganic carbon source, the model calculations indicate that three kinds of unique interactions of the organic and inorganic carbon productions are expected. These are photosynthetic enhancement of calcification, calcification which benefits photosynthesis and carbonate dissolution induced by respiration. The first effect appears when the photosynthetic rate is more than approximately 1.2 larger than that of calcification. This effect is caused by the increase of CO3 content and carbonate saturation degree in seawater. If photosynthesis use molecular carbon dioxide, the second effect occurs when the calcification rate is more than approximately 1.6 times larger than that of photosynthesis. Time series model experiments indicate that photosynthesis and calcification potentially enhance each other and that organic and inorganic carbon is produced more efficiently in the coexisting system than in the isolated reactions. These coexisting effects on production enhancement of photosynthesis and calcification are expected to appear not only in the internal pool of organisms but also in a reef environment which is isolated from the outer ocean during low tide. According to the measurements on the fringing type Shiraho Reef in the Ryukyu Islands, the diurnal change of water properties (pH, total alkalinity, total carbon dioxide and carbonate saturation degree) were conspicuous. This environment offers an appropriate condition for the appearance of these coexisting effects. The photosynthetic enhancement of calcification and the respiratory inducement of decalcification were observed during day-time and night-time slack-water periods, respectively. These coexisting effects, especially the photosynthetic enhancement of calcification, appear to play important roles for fluorishing coral reef communities.