Posts Tagged 'Antarctic'

High resolution microscopy reveals significant impacts of ocean acidification and warming on larval shell development in Laternula elliptica

Environmental stressors impact marine larval growth rates, quality and sizes. Larvae of the Antarctic bivalve, Laternula elliptica, were raised to the D-larvae stage under temperature and pH conditions representing ambient and end of century projections (-1.6°C to +0.4°C and pH 7.98 to 7.65). Previous observations using light microscopy suggested pH had no influence on larval abnormalities in this species. Detailed analysis of the shell using SEM showed that reduced pH is in fact a major stressor during development for this species, producing D-larvae with abnormal shapes, deformed shell edges and irregular hinges, cracked shell surfaces and even uncalcified larvae. Additionally, reduced pH increased pitting and cracking on shell surfaces. Thus, apparently normal larvae may be compromised at the ultrastructural level and these larvae would be in poor condition at settlement, reducing juvenile recruitment and overall survival. Elevated temperatures increased prodissoconch II sizes. However, the overall impacts on larval shell quality and integrity with concurrent ocean acidification would likely overshadow any beneficial results from warmer temperatures, limiting populations of this prevalent Antarctic species.

Continue reading ‘High resolution microscopy reveals significant impacts of ocean acidification and warming on larval shell development in Laternula elliptica’

Effects of CO2 concentration on a late summer surface sea ice community

Annual fast ice at Scott Base (Antarctica) in late summer contained a high biomass surface community of mixed phytoflagellates, dominated by the dinoflagellate, Polarella glacialis. At this time of the year, ice temperatures rise close to melting point and salinities drop to less than 20. At the same time, pH levels can rise above 9 and nutrients can become limiting. In January 2014, the sea ice microbial community from the top 30 cm of the ice was exposed to a gradient of pH and CO2 (5 treatments) that ranged from 8.87 to 7.12 and 5–215 µmol CO2 kg−1, respectively, and incubated in situ. While growth rates were reduced at the highest and lowest pH, the differences were not significant. Likewise, there were no significant differences in maximum quantum yield of PSII (Fv/Fm) or relative maximum electron transfer rates (rETRmax) among treatments. In a parallel experiment, a CO2 gradient of 26–230 µmol CO2 kg−1 (5 treatments) was tested, keeping pH constant. In this experiment, growth rates increased by approximately 40% with increasing CO2, although differences among treatments were not significant.. As in the previous experiment, there was no significant response in Fv/Fm or rETRmax. A synchronous grazing dilution experiment found grazing rates to be inconclusive These results suggest that the summer sea ice brine communities were not limited by in situ CO2 concentrations and were not adversely affected by pH values down to 7.1.

Continue reading ‘Effects of CO2 concentration on a late summer surface sea ice community’

Global variability and changes in ocean total alkalinity from Aquarius satellite data

This work demonstrates how large-scale Aquarius satellite salinity data have provided an unprecedented opportunity when combined with total alkalinity (TA) equations as a function of salinity and temperature to examine global changes in the CO2 system. Alkalinity is a gauge on the ability of seawater to neutralize acids. TA correlates strongly with salinity. Spatial variability in alkalinity and salinity exceed temporal variability. Northern Hemisphere has more spatial variability in TA and salinity, while less variability in Southern Ocean TA is due to less salinity variability and upwelling of waters enriched in alkalinity. For the first time it is shown that TA in subtropical regions has increased as compared with climatological data; this is reflective of large-scale changes in the global water cycle. Thus, as temperature and salinity increase in subtropical regions, the resultant increase in TA and ocean acidification is reinforcing that from oceanic uptake of atmospheric CO2.

Continue reading ‘Global variability and changes in ocean total alkalinity from Aquarius satellite data’

Calculating surface ocean pCO2 from biogeochemical Argo floats equipped with pH: an uncertainty analysis

More than 74 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10-day intervals have been deployed throughout the Southern Ocean. Calculating the surface ocean partial pressure of carbon dioxide (pCO2sw) from float pH has uncertainty contributions from the pH sensor, the alkalinity estimate, and carbonate system equilibrium constants, resulting in a relative standard uncertainty in pCO2sw of 2.4% (or 10 µatm at pCO2sw of 400 µatm). The calculated pCO2sw from several floats spanning a range of oceanographic regimes are compared to existing climatologies. In some locations, such as the Subantarctic zone, the float data closely match the climatologies, but in the Polar Antarctic Zone significantly higher pCO2sw are calculated in the wintertime implying a greater air-sea CO2 efflux estimate. Our results based on four representative floats suggest that despite their uncertainty relative to direct measurements the float data can be used to improve estimates for air-sea carbon flux, as well as to increase knowledge of spatial, seasonal, and interannual variability in this flux.

Continue reading ‘Calculating surface ocean pCO2 from biogeochemical Argo floats equipped with pH: an uncertainty analysis’

Mobile diatoms flourish in acid ocean

Thick mats of single celled microalgae, ‘pulsing’ in the seafloor sediments under the Antarctic sea ice, could flourish as ocean acidification intensifies.

Pyper W., 2016. Mobile diatoms flourish in acid ocean. Australian Antarctic Magazine 31:20-21. Article (subscription required).

An in situ incubation method for measuring the productivity and responses of under-ice algae to ocean acidification and warming in polar marine habitats

During the Antarctic spring, algae grows under extensive areas of sea-ice and is a fundamental source of primary production. Understanding how under-ice (bottom-ice) algae will be affected by ocean warming and acidification is critically important in determining the probable future flow-on effects to the ecological communities this algae supports. To investigate this we designed and built a customised experimental system to assess the in situ responses of under-ice algae to changes in both seawater pH and temperature. We conducted two trials in 2013 followed by a successful 14-day incubation experiment in 2014 in the Ross Sea, Antarctica, using the system described here. Assessment of our main control parameters indicated we could reliably control and monitor both pH and temperature in transparent under-ice chambers. The “plug-and-play” nature of our novel system meant it was easy for divers to deploy and maintain in the very cold temperatures experienced under the sea-ice. Moreover, the system could be remotely sampled from a surface laboratory. This enabled robust monitoring and analyses of manipulated seawater conditions (e.g., pH and temperature), and of responses of the associated biological communities (e.g., fluxes in dissolved oxygen and nutrient levels).

Continue reading ‘An in situ incubation method for measuring the productivity and responses of under-ice algae to ocean acidification and warming in polar marine habitats’

Southern Ocean phytoplankton in a changing climate

Phytoplankton are the base of the Antarctic food web, sustain the wealth and diversity of life for which Antarctica is renowned, and play a critical role in biogeochemical cycles that mediate global climate. Over the vast expanse of the Southern Ocean (SO), the climate is variously predicted to experience increased warming, strengthening wind, acidification, shallowing mixed layer depths, increased light (and UV), changes in upwelling and nutrient replenishment, declining sea ice, reduced salinity, and the southward migration of ocean fronts. These changes are expected to alter the structure and function of phytoplankton communities in the SO. The diverse environments contained within the vast expanse of the SO will be impacted differently by climate change; causing the identity and the magnitude of environmental factors driving biotic change to vary within and among bioregions. Predicting the net effect of multiple climate-induced stressors over a range of environments is complex. Yet understanding the response of SO phytoplankton to climate change is vital if we are to predict the future state/s of the ecosystem, estimate the impacts on fisheries and endangered species, and accurately predict the effects of physical and biotic change in the SO on global climate. This review looks at the major environmental factors that define the structure and function of phytoplankton communities in the SO, examines the forecast changes in the SO environment, predicts the likely effect of these changes on phytoplankton, and considers the ramifications for trophodynamics and feedbacks to global climate change. Predictions strongly suggest that all regions of the SO will experience changes in phytoplankton productivity and community composition with climate change. The nature, and even the sign, of these changes varies within and among regions and will depend upon the magnitude and sequence in which these environmental changes are imposed. It is likely that predicted changes to phytoplankton communities will affect SO biogeochemistry, carbon export, and nutrition for higher trophic levels.

Continue reading ‘Southern Ocean phytoplankton in a changing climate’

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Ocean acidification in the IPCC AR5 WG II

OUP book