Posts Tagged 'chemistry'

Climatic modulation of surface acidification rates through summertime wind forcing in the Southern Ocean

While the effects of the Southern Annular Mode (SAM), a dominant climate variability mode in the Southern Ocean, on ocean acidification have been examined using models, no consensus has been reached. Using observational data from south of Tasmania, we show that during a period with positive SAM trends, surface water pH and aragonite saturation state at 60°–55° S (Antarctic Zone) decrease in austral summer at rates faster than those predicted from atmospheric CO2 increase alone, whereas an opposite pattern is observed at 50°–45° S (Subantarctic Zone). Together with other processes, the enhanced acidification at 60°–55° S may be attributed to increased westerly winds that bring in more “acidified” waters from the higher latitudes via enhanced meridional Ekman transport and from the subsurface via increased vertical mixing. Our observations support climatic modulation of ocean acidification superimposed on the effect of increasing atmospheric CO2.

Continue reading ‘Climatic modulation of surface acidification rates through summertime wind forcing in the Southern Ocean’

Simulation of coastal processes affecting pH with impacts on carbon and nutrient biogeochemistry

Naturally occurring microbial decomposition of organic matter (OM) in coastal marine environments cause increased acidity in deeper layers similar or even exceeding the future predictions for global ocean acidification (OA). Experimental studies in coastal areas characterized by increased inputs of OM and nutrients, coping with intermittent hypoxic/anoxic conditions, provide decrease. Laboratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected from thdecrease. Labouratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected form the deepest part of Elefsis Bay (Saronikos Gulf, Eastern Mediterranean) focusing to study the co-evolution of processes affected by the decline of dissolved oxygen and pH induced by (a) OM remineralization and (b) the future anthropogenic increase of atmospheric CO2. Under more acidified conditions, a significant increase of total alkalinity was observed partially attributed to the sedimentary carbonate dissolution and the reactive nitrogen species shift towards ammonium. Nitrate and nitrite decline, in parallel with ammonium increase, demonstrated a deceleration of ammonium oxidation processes along with decrease in nitrate production. The decreased DIN:DIP ratio, the prevalence of organic nutrient species against the inorganic ones, the observations of constrained DON degradation and nitrate production decline and the higher DOC concentrations revealed the possible inhibition of OM decomposition under lower pH values. Finally, our results highlight the need for detailed studies of the carbonate system in coastal areas dominated by hypoxic/anoxic conditions, accompanied by other biogeochemical parameters and properly designed experiments to elucidate the processes sequence or alterations due to pH reduction.

Continue reading ‘Simulation of coastal processes affecting pH with impacts on carbon and nutrient biogeochemistry’

What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?

Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean DIC, which generally increases polewards. Here, we revisit this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project Version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from low to high latitudes. These are: (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) high latitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explains the majority of the surface nDIC latitudinal gradient (182 out of 223μmolkg−1 in the high-latitude Southern Ocean). Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air-sea CO2 exchange, is to raise Southern Ocean nDIC by 208μmolkg−1 above the average low latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74μmolkg−1 above the low latitude average.

Continue reading ‘What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?’

Seasonal trends in surface pCO2 and air‐sea CO2 fluxes in Apalachicola Bay, Florida from VIIRS ocean color

Estuaries have been recognized as important sources of carbon dioxide (CO2) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO2 distribution and air‐sea CO2 fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico, that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time‐series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH–pCO2 relationships for obtaining surface pCO2 estimates and air‐sea CO2 fluxes from VIIRS ocean color data. Monthly and seasonal maps of pCO2 and air‐sea CO2 fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO2 fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO2 with large seasonal and spatial variability and a mean annual CO2 flux to the atmosphere of 3.4 ± 3.1 mol m‐2 y‐1 (9.4 ± 8.5 mmol m‐2 d‐1), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates.

Continue reading ‘Seasonal trends in surface pCO2 and air‐sea CO2 fluxes in Apalachicola Bay, Florida from VIIRS ocean color’

A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger

Herein, we present a small and versatile optode system with integrated battery and logger for monitoring of O2, pH, and pCO2 in seawater. Three sensing materials designed for seawater measurements are optimized with respect to dynamic measurement range and long‐term stability. The spectral properties of the sensing materials were tailored to be compatible with a commercially available laboratory oxygen logger that was fitted into a pressure housing. Interchangeable sensor caps with appropriate “sensing chemistry” are conveniently attached to the end of the optical fiber. This approach allows using the same instrument for multiple analytes, which offers great flexibility and minimizes hardware costs. Applications of the new optode system were demonstrated by recording depth profiles for the three parameters during a research cruise in the Baltic Sea and by measuring surface water transects of pH. The optode was furthermore used to monitor the concentration of dissolved oxygen in a seagrass meadow in the Limfjord, Denmark, and sensor packages consisting of pO2, pH, and pCO2 were deployed in the harbors of Kiel, Germany, and Southampton, England, for 6 d. The measurements revealed that the system can resolve typical patterns in seawater chemistry related to spatial heterogeneities as well as temporal changes caused by biological and tidal activity.

Continue reading ‘A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger’

Effects of biological production and vertical mixing on sea surface pCO2 variations in the Changjiang River plume during early autumn: A buoy‐based time series study

A month‐long, high‐resolution buoy time series from the surface ocean of the Changjiang River plume in early autumn 2013 (30‐min sampling frequency) show great variability in the partial pressure of carbon dioxide (pCO2), and other physical and biogeochemical parameters. Early in the deployment, surface pCO2 decreased by ~117 μatm in a single day (11–12 September, from an initial value of ~527 μatm); a similar decline of 62 μatm occurred 5 days later (to ~378 μatm). Both drawdown events were associated with strong vertical stratification, high chlorophyll a concentrations, and oxygen supersaturation. A one‐dimensional mass balance model suggests that biological production was responsible for more than half the pCO2 decrease observed during 10–23 September. Subsequently, in association with strong winds, the mixed layer rapidly deepened and surface pCO2 increased sharply (by about 108 μatm in late September and again in early October). Vertical mixing accounted for more than half of this pCO2 increase, which offset more than the earlier biologically‐driven CO2 drawdown. In the presence of such strong temporal variations of pCO2, sampling frequency exerts a substantial influence on air‐sea CO2 flux calculations for the Changjiang River plume and similar coastal areas. Compared to daily sampling, even weekly sampling would result in a bias of up to ±4.7 mmol C m−2 d−1, or ±63% error.

Continue reading ‘Effects of biological production and vertical mixing on sea surface pCO2 variations in the Changjiang River plume during early autumn: A buoy‐based time series study’

Determination of intracellular pH in phytoplankton using the fluorescent probe, SNARF, with detection by fluorescence spectroscopy

Highlights

•  Intracellular pH of phytoplankton was measured by fluorescence spectroscopy using SNARF.
•  Intracellular pH determined using SNARF was similar to pH measured using radioisotopic assays.
•  Variation in intracellular esterase activities did not negatively affect SNARF assays.

Abstract

The maintenance of pH homeostasis is critical for a variety of cellular metabolic processes. Although ocean acidification is likely to influence cellular metabolism and energy balance, the degree to which intracellular pH in phytoplankton differs from the external environment under varying environmental pH levels is not well characterized. While there are numerous existing methods for the determination of intracellular pH in the form of single peak emission (e.g., BCECF) and radioisotopic (e.g., 14C-DMO) indicators for use with phytoplankton, the fluorescent pH indicator seminaphtharhodafluor (SNARF) has not been established as a robust method for measuring in vivo pH in phytoplankton. SNARF has superior accuracy and sensitivity since it exhibits dual emission peaks from a single excitation wavelength and the ratio of the two are related to pH. The use of a ratio limiting variations in fluorescence due to dye loading, photobleaching, and instrument variation; moreover, like other fluorescence-based assays, it does not require the specialized equipment and permits that radioisotopic methods do. As a first step, we tested the performance of SNARF for measuring intracellular pH in vivo in a number of phytoplankton taxa. SNARF detection was accomplished using fluorescence spectroscopy (FS) and laser scanning microscopy (LSM). Since SNARF fluorescence is activated by cleavage of an ester group from the core fluorophore by non-specific esterases, we measured esterase activity using fluorescein diacetate (FDA) to characterize variability in esterase activity among phytoplankton taxa, with a view towards its influence on assay performance. Esterase activity cell volume; however, there was no indication that enzyme specificity and differences in individual esterase profiles adversely affected SNARF performance in phytoplankton. Assays of intracellular pH using SNARF were comparable to those made with 14C-labeled DMO, an accepted standard method. Thus, SNARF provides robust measurements of intracellular pH in phytoplankton, constituting a useful tool in investigations of the effects of ocean acidification and fluctuations in environmental pH on cellular physiology.

Continue reading ‘Determination of intracellular pH in phytoplankton using the fluorescent probe, SNARF, with detection by fluorescence spectroscopy’


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Ocean acidification in the IPCC AR5 WG II

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