Autonomous in situ measurements of seawater alkalinity

Total alkalinity (AT) is an important parameter for describing the marine inorganic carbon system and understanding the effects of atmospheric CO2 on the oceans. Measurements of AT are limited, however, because of the laborious process of collecting and analyzing samples. In this work we evaluate the performance of an autonomous instrument for high temporal resolution measurements of seawater AT. The Submersible Autonomous Moored Instrument for alkalinity (SAMI-alk) uses a novel tracer monitored titration method where a colorimetric pH indicator quantifies both pH and relative volumes of sample and titrant, circumventing the need for gravimetric or volumetric measurements. The SAMI-alk performance was validated in the laboratory and in situ during two field studies. Overall in situ accuracy was −2.2 ± 13.1 μmol kg–1 (n = 86), on the basis of comparison to discrete samples. Precision on duplicate analyses of a carbonate standard was ±4.7 μmol kg–1 (n = 22). This prototype instrument can measure in situ AT hourly for one month, limited by consumption of reagent and standard solutions.

Continue reading ‘Autonomous in situ measurements of seawater alkalinity’

Ocean acidification wrecks sharks’ smellovision

Picture by brandXpictures

Picture by brandXpictures

Scarier than any movie shark that can smell a drop of blood miles away (they can’t, by the way) is this week’s news about sharks’ sense of smell. A team of Australian and American scientists has just shown that smooth dogfishes (also called dusky smooth-hound sharks) can’t smell food as well after living in ocean acidification conditions expected for the year 2100. These “future” sharks could correctly track food smells only 15% of the time, compared to a 60% accuracy rate for unexposed sharks. In fact, the acidification-exposed sharks even avoided food smells!

Continue reading ‘Ocean acidification wrecks sharks’ smellovision’

Acid–base physiology response to ocean acidification of two ecologically and economically important holothuroids from contrasting habitats, Holothuria scabra and Holothuria parva

Sea cucumbers are dominant invertebrates in several ecosystems such as coral reefs, seagrass meadows and mangroves. As bioturbators, they have an important ecological role in making available calcium carbonate and nutrients to the rest of the community. However, due to their commercial value, they face overexploitation in the natural environment. On top of that, occurring ocean acidification could impact these organisms, considered sensitive as echinoderms are osmoconformers, high-magnesium calcite producers and have a low metabolism. As a first investigation of the impact of ocean acidification on sea cucumbers, we tested the impact of short-term (6 to 12 days) exposure to ocean acidification (seawater pH 7.7 and 7.4) on two sea cucumbers collected in SW Madagascar, Holothuria scabra, a high commercial value species living in the seagrass meadows, and H. parva, inhabiting the mangroves. The former lives in a habitat with moderate fluctuations of seawater chemistry (driven by day–night differences) while the second lives in a highly variable intertidal environment. In both species, pH of the coelomic fluid was significantly negatively affected by reduced seawater pH, with a pronounced extracellular acidosis in individuals maintained at pH 7.7 and 7.4. This acidosis was due to an increased dissolved inorganic carbon content and pCO2 of the coelomic fluid, indicating a limited diffusion of the CO2 towards the external medium. However, respiration and ammonium excretion rates were not affected. No evidence of accumulation of bicarbonate was observed to buffer the coelomic fluid pH. If this acidosis stays uncompensated for when facing long-term exposure, other processes could be affected in both species, eventually leading to impacts on their ecological role.

Continue reading ‘Acid–base physiology response to ocean acidification of two ecologically and economically important holothuroids from contrasting habitats, Holothuria scabra and Holothuria parva’

Faster recovery of a diatom from UV damage under ocean acidification

Diatoms are the most important group of primary producers in marine ecosystems. As oceanic pH declines and increased stratification leads to the upper mixing layer becoming shallower, diatoms are interactively affected by both lower pH and higher average exposures to solar ultraviolet radiation. The photochemical yields of a model diatom, Phaeodactylum tricornutum, were inhibited by ultraviolet radiation under both growth and excess light levels, while the functional absorbance cross sections of the remaining Photosystem II increased. Cells grown under ocean acidification (OA) were less affected during UV exposure. The recovery of PSII under low photosynthetically active radiation was much faster than in the dark, indicating that photosynthetic processes were essential for the full recovery of Photosystem II. This light dependent recovery required de novo synthesized protein. Cells grown under ocean acidification recovered faster, possibly attributable to higher CO2 availability for the Calvin cycle producing more resources for repair. The lower UV inhibition combined with higher recovery rate under ocean acidification could benefit species such as Phaeodactylum tricornutum, and change their competitiveness in the future ocean.

Continue reading ‘Faster recovery of a diatom from UV damage under ocean acidification’

A seawater filtration method suitable for total dissolved inorganic carbon and pH analyses

High biomass and heavy particle loads may interfere with carbonate chemistry analyses of samples from experimental aquaria and cultures used to investigate the impact of ocean acidification on organisms, as well as from biologically productive coastal regions. For such samples, a filtration method is needed that does not change the dissolved CO2 content, and consequently does not alter the total dissolved inorganic carbon and pH of the sample. Here, a filtration method is presented in which the sample seawater is pumped by a peristaltic pump through a replaceable 0.45 mu m filter in a 50 mm polycarbonate filter holder and then into the sample bottle. Seawater samples of known carbonate composition were filtered to confirm that the filtration method did not alter the CO2 content, and compromise the subsequent sample analysis and data usefulness. Seawater samples with added phytoplankton concentrations in the range of 1-5 x 10(5) cells mL(-1) were also filtered successfully. Finally, seawater with added biogenic CaCO3 was tested to prove that the method could successfully filter out such particles and produce dependable results. This approach will help to ensure more consistent and reliable carbonate chemistry measurements in coastal environments and from ocean acidification aquaria and cultures, by providing a well-tested method for sample filtration.

Continue reading ‘A seawater filtration method suitable for total dissolved inorganic carbon and pH analyses’

Effect on pCO2 by phytoplankton uptake of dissolved organic nutrients in the Central and Northern Baltic Sea, a model study

Dissolved organic matter (DOM) has been added to an existing biogeochemical model and the phytoplankton were allowed to utilize the dissolved organic nutrients for primary production. The results show typical vertical structures for dissolved organic carbon (DOC), and improved or maintained model skill for both mean vertical profiles and mean seasonal variation of biogeochemical variables, evaluated by objective skill metrics. Due to scarce DOM measurements in the Baltic Sea it was hard to validate the new variables, but the model can recreate the general magnitude and distribution of terrestrial and in situ produced DOC, DON, and DOP, as far as we know them. The improvements are especially clear for the total nutrient levels and in recreating the biological drawdown of CO2 in the Eastern Gotland basin. Without phytoplankton uptake of dissolved organic nitrogen and phosphate, CO2 assimilation is lower during the summer months and the partial pressure of CO2 increases by about 200 μatm in the Eastern Gotland Basin, while in the Bothnian Bay, both the duration and magnitude of CO2 assimilation are halved. Thus the phytoplankton uptake of dissolved organic nutrients lowers pCO2 in both basins. Variations in the river transported DOM concentration mainly affect the magnitude of the summer cyanobacteria bloom.

Continue reading ‘Effect on pCO2 by phytoplankton uptake of dissolved organic nutrients in the Central and Northern Baltic Sea, a model study’

Falling ocean pH levels means rising threats for coral reefs

The rate of acidification in coral reef ecosystems is more than three times faster than in the open ocean, say a team of Southern Cross University biogeochemists.

Led by recent graduate Dr Tyler Cyronak, the results highlight how coral reefs may be acidifying faster than expected.

The University’s Centre for Coastal Biogeochemistry Research has published its results, ‘Enhanced coral reef acidification driven by regional biogeochemical feedbacks’ by Dr Tyler Cyronak, Associate Professor Isaac Santos, Associate Professor Kai Schulz, and Professor Bradley Eyre, in the latest edition of the Geophysical Research Letters journal.

Ocean acidification, or the lowering of the ocean pH due to anthropogenic inputs of carbon dioxide, has been well documented in the open ocean. However, this research looked back at studies done in coral reefs since the 1960s and found that the rate of acidification in coral reef ecosystems was more than three faster than in the open ocean.
Continue reading ‘Falling ocean pH levels means rising threats for coral reefs’


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Ocean acidification in the IPCC AR5 WG II

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