Posts Tagged 'Antarctic'

Near-future ocean acidification does not alter the lipid content and fatty acid composition of adult Antarctic krill

Euphausia superba (Antarctic krill) is a keystone species in the Southern Ocean, but little is known about how it will respond to climate change. Ocean acidification, caused by sequestration of carbon dioxide into ocean surface waters (pCO2), alters the lipid biochemistry of some organisms. This can have cascading effects up the food chain. In a year-long laboratory experiment adult krill were exposed to ambient seawater pCO2 levels (400 μatm), elevated pCO2 levels mimicking near-future ocean acidification (1000, 1500 and 2000 μatm) and an extreme pCO2 level (4000 μatm). Total lipid mass (mg g−1 DM) of krill was unaffected by near-future pCO2. Fatty acid composition (%) and fatty acid ratios associated with immune responses and cell membrane fluidity were also unaffected by near-future pCO2, apart from an increase in 18:3n-3/18:2n-6 ratios in krill in 1500 μatm pCO2 in winter and spring. Extreme pCO2 had no effect on krill lipid biochemistry during summer. During winter and spring, krill in extreme pCO2 had elevated levels of 18:2n-6 (up to 1.2% increase), 20:4n-6 (up to 0.8% increase), lower 18:3n-3/18:2n-6 and 20:5n-3/20:4n-6 ratios, and showed evidence of increased membrane fluidity (up to three-fold increase in phospholipid/sterol ratios). These results indicate that the lipid biochemistry of adult krill is robust to near-future ocean acidification.

Continue reading ‘Near-future ocean acidification does not alter the lipid content and fatty acid composition of adult Antarctic krill’

Acidification diminishes diatom silica production in the Southern Ocean

Diatoms, large bloom-forming marine microorganisms, build frustules out of silicate, which ballasts the cells and aids their export to the deep ocean. This unique physiology forges an important link between the marine silicon and carbon cycles. However, the effect of ocean acidification on the silicification of diatoms is unclear. Here we show that diatom silicification strongly diminishes with increased acidity in a natural Antarctic community. Analyses of single cells from within the community reveal that the effect of reduced pH on silicification differs among taxa, with several species having significantly reduced silica incorporation at CO2 levels equivalent to those projected for 2100. These findings suggest that, before the end of this century, ocean acidification may influence the carbon and silicon cycle by both altering the composition of the diatom assemblages and reducing cell ballasting, which will probably alter vertical flux of these elements to the deep ocean.

Continue reading ‘Acidification diminishes diatom silica production in the Southern Ocean’

Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean

The Scotia Sea (Southern Ocean) is a hotspot of biodiversity, however, it is one of the fastest warming regions in the world alongside one of the first to experience ocean acidification (OA). Thecosome (shelled) pteropods are planktonic gastropods which can dominate the Scotia Sea zooplankton community, form a key component of the polar pelagic food web and are important contributors to carbon and carbonate fluxes. Pteropods have been identified as sentinel species for OA, since their aragonitic shells are vulnerable to dissolution in waters undersaturated with respect to aragonite.

In this thesis I investigate the impact of a changing ocean on the physiology and life history of pteropods in the Scotia Sea. Firstly, I culture early stage pteropods within OA and warming conditions predicted to occur in 2100 (Chapter 2). I demonstrate that larval shell morphology and survival rates are detrimentally affected in these conditions. Secondly, I constrain the life cycle and population dynamics of pteropods collected over a year from a sediment trap deployed on a moored platform (Chapter 3). I show that Limacina helicina and Limacina retroversa both have distinct life history strategies, although, spawning of both species corresponds to phytoplankton blooms. Thirdly, I establish a baseline vertical and biogeographical distribution of pteropods using historical samples (Chapter 4). I elucidate the geographical range edges of L. retroversa and L. helicina, as well as vertical migration patterns in relation to predation threat. Finally, I examine in-situ pteropod shell condition in relation to carbonate chemistry using net and oceanographic samples collected during two recent cruises (Chapter 5). I demonstrate that larval shells are susceptible to dissolution on exposure to aragonite undersaturation, however, later life stages display some resilience, since shell dissolution is confined to breaches in the periostracum. Overall, I recommend that continued monitoring, combined with bioassays and mesocosm work, will be essential in identifying the continued threat to pteropods from rapid environmental changes.

Continue reading ‘Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean’

Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates

High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNF), nano- and picophytoplankton, and prokaryotes in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥ 634 μatm, HNF abundance was reduced, coinciding with significantly increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNF. Nanophytoplankton abundance was significantly elevated in the 634 and 953 μatm treatments, suggesting that moderate increases in CO2 may stimulate growth. Changes in predator-prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean. Based on these results, it is likely that the phytoplankton community composition in these waters will shift to communities dominated by prokaryotes, nano- and picophytoplankton. This may intensify organic matter recycling in surface waters, leading to a decline in carbon flux, as well as a reducing the quality and quantity of food available to higher trophic organisms.

Continue reading ‘Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates’

Robustness of Adamussium colbecki shell to ocean acidification in a short-term exposure


• Adamussium colbecki shell crystals deposition is not affected by low pH exposure.

• A. colbecki shell resulted robust to low pH exposure in terms of micro and nano-mechanics.

• Larger resilience of Antarctic communities to predation than foreseen in a Global Change scenario.


Atmospheric pCO2 has increased since the industrial revolution leading to a lowering of the ocean surface water pH, a phenomenon called ocean acidification (OA). OA is claimed to be a major threat for marine organisms and ecosystems and, particularly, for Polar regions. We explored the impact of OA on the shell mechanical properties of the Antarctic scallop Adamussium colbecki exposed for one month to acidified (pH 7.6) and natural conditions (unmanipulated littoral water), by performing Scanning Electron Microscopy, nanoindentation and Vickers indentation on the scallop shell. No effect of pH could be detected either in crystal deposition or in the mechanical properties. A. colbecki shell was found to be resistant to OA, which suggests this species to be able to face a climate change scenario that may threat the persistence of the endemic Antarctic species. Further investigation should be carried out in order to elucidate the destiny of this key species in light of global change.

Continue reading ‘Robustness of Adamussium colbecki shell to ocean acidification in a short-term exposure’

Calcification and distribution of extant coccolithophores across the Drake Passage during late austral summer 2016

Coccolithophores are globally distributed microscopic marine algae that exert a major influence on the global carbon cycle through calcification and primary productivity. There is recent interest in coccolithophore polar communities, however field observations regarding their biogeographic distribution are scarce for the Southern Ocean. This study documents the latitudinal variability in the coccolithophore assemblage composition and the coccolith mass variation of the ecologically dominant Emiliania huxleyi across the Drake Passage. Ninety-six water samples were taken between 10 and 150 m water depth from 18 stations during POLARSTERN Expedition PS97 (February–April, 2016). A minimum of 200 coccospheres per sample were classified in scanning electron microscope and coccolith mass was estimated with light microscopy, using the C-Calcita software. We find that coccolithophore abundance and diversity decrease southwards marking different oceanographic fronts as ecological boundaries. We characterize three zones: (1) the Chilean margin, where E. huxleyi type A (normal and overcalcified) and type R are present; (2) the Subantarctic Zone (SAZ), where E. huxleyi reaches maximum values of 212.5×103cells/L and types B/C, C, O are dominant. (3) The Polar Front Zone (PFZ), where E. huxleyi types B/C and C dominate. We link the decreasing trend in E. huxleyi coccolith mass to the poleward latitudinal succesion from type A to type B group. Remarkably, we find that coccolith mass is strongly anticorrelated to total alkalinity, total CO2, bicarbonate ion and pH. We speculate that low temperatures are a greater limiting factor than carbonate chemistry in the Southern Ocean. However, further in situ oceanographical data is needed to verify the proposed relationships. We hypothesize that assemblage composition and calcification modes of E. huxleyi in the Drake Passage will be strongly influenced by the ongoing climate change.

Continue reading ‘Calcification and distribution of extant coccolithophores across the Drake Passage during late austral summer 2016’

Degradation of internal organic matter is the main control on pteropod shell dissolution after death

The potential for preservation of thecosome pteropods is thought to be largely governed by the chemical stability of their delicate aragonitic shells in seawater. However, sediment trap studies have found that significant carbonate dissolution can occur above the carbonate saturation horizon. Here we present the results from experiments conducted on two cruises to the Scotia Sea to directly test whether the breakdown of the organic pteropod body influences shell dissolution. We find that, on the timescales of three to thirteen days, the oxidation of organic matter within the shells of dead pteropods is a stronger driver of shell dissolution than the saturation state of seawater. Three to four days after death, shells became milky white and nano‐SEM images reveal smoothing of internal surface features and increased shell porosity, both indicative of aragonite dissolution. These findings have implications for the interpretation of the condition of pteropod shells from sediment traps and the fossil record, as well as for understanding the processes controlling particulate carbonate export from the surface ocean.

Continue reading ‘Degradation of internal organic matter is the main control on pteropod shell dissolution after death’

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Ocean acidification in the IPCC AR5 WG II

OUP book