Posts Tagged 'Antarctic'

Towards an intensified summer CO2 sink behaviour in the Southern Ocean coastal regions

Highlights

• We analysed the FCO2 and CO2 system in an important region of the Southern Ocean.

• The Gerlache Strait acts as a stronger CO2 sink than nearby open ocean areas during the austral summer.

• We identified both strong and near-equilibrium sink scenarios for FCO2.

• The pattern of variability of FCO2 has changed since 2012 to a higher frequency of years with a strong CO2 sink.

Abstract

The Southern Ocean is a globally important carbon sink region. However, the austral coastal zones are usually not considered in global estimations due to their general undersampling and large regional dynamics. Thus, estimations of carbon uptake in the Southern Ocean may differ considerably from current values, i.e., without accounting for coastal regions. Here, we conducted a case study in the Gerlache Strait, an ecologically important Antarctic coastal zone. We show that the net sea-air CO2 flux (FCO2) in the strait may reach the same or greater magnitudes than those in large open sea regions around Antarctica during summer, despite having a much smaller area. A large mean FCO2 of –31 ± 19 mmol m–2 d–1 was observed in the strong CO2 sink years (i.e., FCO2 < –12 mmol m–2 d–1), in contrast to –1 ± 7 mmol m–2 d–1 in CO2 near-equilibrium conditions (i.e., CO2 sea–air difference ≈ 0). This variability is mainly modulated by phytoplankton activity and likely upwelling processes. We also identified two cycles of variability with 2-year and 4-year periodicities from 1999 to 2017. The 2-year periodicity becomes stronger after 2012, intensifying the strong CO2 sink scenario in the Gerlache Strait. Our findings reinforce the importance of polar coastal zones as CO2 sinks during the austral summer and the need to broaden our understanding of the role of these regions at other time scales.

Continue reading ‘Towards an intensified summer CO2 sink behaviour in the Southern Ocean coastal regions’

A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification

Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in atmospheric processes and climate. Therefore, it is important to increase our understanding of how DMS production in these regions may respond to climate change. The polar oceans are particularly vulnerable to ocean acidification (OA). However, our understanding of the polar DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS concentrations decreased with increasing acidity. Here, we report on our findings from seven summertime shipboard microcosm experiments undertaken in a variety of locations in the Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short-term OA on the net production of DMS by planktonic communities. This is in contrast to similar experiments from temperate north-western European shelf waters where surface ocean communities responded to OA with significant increases in dissolved DMS concentrations. A meta-analysis of the findings from both temperate and polar waters (n=18 experiments) reveals clear regional differences in the DMS response to OA. Based on our findings, we hypothesize that the differences in DMS response between temperate and polar waters reflect the natural variability in carbonate chemistry to which the respective communities of each region may already be adapted. If so, future temperate oceans could be more sensitive to OA, resulting in an increase in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS emissions from the polar oceans may remain relatively unchanged. By demonstrating that DMS emissions from geographically distinct regions may vary in their response to OA, our results may facilitate a better understanding of Earth’s future climate. Our study suggests that the way in which processes that generate DMS respond to OA may be regionally distinct, and this should be taken into account in predicting future DMS emissions and their influence on Earth’s climate.

Continue reading ‘A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification’

Ocean freshening and acidification differentially influences mortality and behavior of the Antarctic amphipod Gondogeneia antarctica

Highlights

• Glacier retreat induced by global warming can decrease pH and salinity of the Antarctic ocean.

• The Antarctic amphipod Gondogeneia antarctica was exposed to low pH (7.6) and low salinity (27 psμ) conditions.

• Low pH increased mortality, impaired food detection, reduced shelter-use during daytime. .

• Low salinity increased cannibalism and induced abnormal swimming.

• Ocean acidification and freshening act as independent stressors influencing behavior and physiology of Antarctic amphipods.

Abstract

The Western Antarctic Peninsula (WAP) has experienced rapid atmospheric and ocean warming over the past few decades and many marine-terminating glaciers have considerably retreated. Glacial retreat is accompanied by fresh meltwater intrusion, which may result in the freshening and acidification of coastal waters. Marian Cove (MC), on King George Island in the WAP, undergoes one of the highest rates of glacial retreat. Intertidal and shallow subtidal waters are likely more susceptible to these processes, and sensitive biological responses are expected from the organisms inhabiting this area. The gammarid amphipod Gondogeneia antarctica is one of the most abundant species in the shallow, nearshore Antarctic waters, and it occupies an essential ecological niche in the coastal marine WAP ecosystem. In this study, we tested the sensitivity of G. antarctica to lowered salinity and pH by meltwater intrusion following glacial retreat. We exposed G. antarctica to four different treatments combining two salinities (34 and 27 psμ) and pH (8.0 and 7.6) levels for 26 days. Mortality, excluding cannibalized individuals, increased under low pH but decreased under low salinity conditions. Meanwhile, low salinity increased cannibalism, whereas low pH reduced food detection. Shelter use during the daytime decreased under each low salinity and pH condition, indicating that the two stressors act as disruptors of amphipod behavior. Under low salinity conditions, swimming increased during the daytime but decreased at night. Although interactions between low salinity and low pH were not observed during the experiment, the results suggest that each stressor, likely induced by glacial melting, causes altered behaviors in amphipods. These environmental factors may threaten population persistence in Marian Cove and possibly other similar glacial embayments.

Continue reading ‘Ocean freshening and acidification differentially influences mortality and behavior of the Antarctic amphipod Gondogeneia antarctica’

Report card: Potential tipping points for life in the Southern Ocean

There is now clear scientific evidence that the increasing magnitude and rate of anthropogenic carbon dioxide (CO2) emissions are causing rapid and unprecedented changes to the global ocean. These will have potentially serious impacts during the 21st century on the sustainability and management of many marine and coastal ecosystems. Research has shown that the Southern Ocean, in particular, is encountering significant changes linked to climate change. The changes in pH, temperature, circulation and sea ice – along with potential for increased fishing pressure – are all likely to have far-reaching consequences for all species that currently inhabit the Southern Ocean.

One of the fundamental questions for marine scientists studying the Southern Ocean is how climate change will alter the growth of key prey species including phytoplankton, zooplankton and krill. Phytoplankton are the base Baleen whale. iStock of the marine food web, and even seemingly small changes in sea-ice, ocean circulation, chemistry and temperature will affect which species live, thrive and die in the ocean. The biological outcomes from these changes will be determined by the environment, timing, rate and magnitude of change in each stressor, the order in which the changes occur, and the potential for consequences to be compounded when multiple stressors change concurrently.

Hence, understanding the impacts of climate change on Southern Ocean life requires us to consider which key species will be more sensitive to change, if change will have benefical or detrimental effects on marine life, and how change will vary from region to region. These new scientific insights will have important implications for management of fish stocks and high conservation value species throughout the region.

Continue reading ‘Report card: Potential tipping points for life in the Southern Ocean’

Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios

Antarctic krill (Euphausia superba, hereafter ‘krill’) are lipid-rich euphausiids with an important role in the Southern Ocean, including as the primary prey of Antarctic megafauna (whales, seals, penguins), fish, squid and seabirds. They contain high levels of nutritious long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA), specifically eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). The sheer abundance of krill in the Southern Ocean means that the ecosystem is largely driven by energy derived from krill lipids. In addition to their ecological importance, a Scotia Sea krill fishery harvests krill, including for commercial use of their LC-PUFA. The existence of this year-round krill fishery provides a unique opportunity to collect krill samples for research over large spatial and temporal scales, which is unfeasible using scientific research vessels.

In this thesis, fishery caught krill samples were used to investigate the fatty acid content and composition of krill, during all seasons and over consecutive years (2013 – 2016). This research (presented in Chapter 2) aimed to fill knowledge gaps on the seasonal diet of krill (particularly in winter) in the Scotia Sea region, using fatty acids as dietary biomarkers. Krill were primarily herbivorous in summer (higher levels of 20:5n-3 and 22:6n-3, and low 18:1n-9c/18:1n-7c ratios) and became more omnivorous from autumn to spring (increasing ratios of 18:1n-9c/18:1n-7c and percentages of Σ 20:1 + 22:1 isomers). Seasonal proportions of herbivory and omnivory differed between years, and fatty acid composition differed between fishing locations. Selected samples were also used to investigate the composition of fatty acids in the structural (phospholipids) and storage lipids (triacylglycerols) of krill (Chapter 3). Triacylglycerol fatty acids (thought to better represent recent diet), reflected omnivorous feeding with highest percentages of flagellate biomarkers (18:4n-3) occurring in summer, diatom biomarkers (16:1n-7c) from autumn-spring, and greater carnivory (higher Σ 20:1 + 22:1 and 18:1n-9c/18:1n-7c ratios) in autumn. Phospholipid fatty acids were less variable and were higher in the essential membrane fatty acids 20:5n-3 and 22:6n-3. Percentages of the major krill sterol, cholesterol, were significantly higher in winter and spring compared with summer and autumn. Results presented in Chapters 2 and 3 highlighted the dynamic nature of krill lipids, and the flexible diet of krill, which likely contributes to their huge biomass and success as one of the most abundant organisms on Earth.

Because krill are so important in the Southern Ocean food web, any decreases in krill biomass could result in a major ecological regime shift. Very little is known about how climate change will affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Long-term laboratory studies are needed to understand how keystone species such as krill may respond to predicted future pCO2 levels. A long term experiment was conducted to test whether rising ocean pCO2 is likely to impact krill physiology and biochemistry (Chapters 4 and 5). Adult krill were exposed to near-future ocean acidification (1000 – 2000 μatm pCO2) for one year in the laboratory. Krill reared in near-future pCO2 conditions were able to survive, grow, store fat, mature, and maintain normal respiration rates. Haemolymph pH, lipid and fatty acid composition were also maintained at the same levels as krill in ambient pCO2 (400 μatm). Negative effects on physiology and lipid biochemistry were only observed in extreme pCO2 conditions (4000 μatm), which krill will not experience in the wild. These results place adult krill among the most resilient species in ocean acidification studies to date.

In summary, results in this thesis highlight the remarkable adaptability of krill in a changing environment, from short-term seasonal or annual scales, to longer-term decadal scales. Their flexible phenotype may aid their survival in an ocean that is rapidly changing with increasing anthropogenic CO2 emissions. The data obtained in this thesis can be used for fisheries management to guide fishing activities, and in fisheries models to predict how krill biomass may be affected by climate change. Krill lipid energy fuels the Southern Ocean ecosystem and to date, lipid data has not been included in Antarctic ecosystem models. The large scale of lipid data in this study makes it ideal for inclusion in such models, and it has important implications for the health of the wider Southern Ocean ecosystem.

Continue reading ‘Lipid biochemistry and physiology of Antarctic krill (Euphausia superba) in the present day and under future ocean acidification scenarios’

Elevated temperature and decreased salinity both affect the biochemical composition of the Antarctic sea-ice diatom Nitzschia lecointei, but not increased pCO2

Areas in western Antarctica are experiencing rapid climate change, where ocean warming results in more sea ice melt simultaneously as oceanic CO2 levels are increasing. In this study, we have tested how increased temperature (from −1.8 to 3 °C) and decreased salinity (from 35 to 20 and 10) synergistically affect the growth, photophysiology and biochemical composition of the Antarctic sea-ice diatom Nitzschia lecointei. In a separate experiment, we also addressed how ocean acidification (from 400 to 1000 µatm partial pressure of CO2) affects these key physiological parameters. Both positive and negative changes in specific growth rate, particulate organic carbon to particulate organic nitrogen ratio, chl a fluorescence kinetics, lipid peroxidation, carbohydrate content, protein content, fatty acid content and composition were observed when cells were exposed to warming and desalination. However, when cells were subjected to increased pCO2, only Fv/Fm, non-photochemical quenching and lipid peroxidation increased (by 3, 16 and 14%, respectively), and no other of the abovementioned biochemical properties were affected. These results suggest that changes in temperature and salinity may have more effects on the biochemical composition of N. lecointei than ocean acidification. Sea-ice algae are important component of polar food webs, and their nutritional quality may be affected as a result of altered environmental conditions due to climate change and sea ice melt.

Continue reading ‘Elevated temperature and decreased salinity both affect the biochemical composition of the Antarctic sea-ice diatom Nitzschia lecointei, but not increased pCO2’

Hidden biogeochemical anonymities under Antarctic fast ice

Climate change is negatively affecting the extent of summer sea ice and the global oceanic oxygen concentrations, it is therefore imperative to decipher the life processes under the Antarctic fast ice. The biogeochemical parameters like dissolved oxygen, inorganic carbon, macronutrients, phytoplankton, and chlorophyll a (Chl a) were studied under the fast ice (by drilling 1.8 m thick ice) around Larsemann Hills, East Antarctica during India’s Scientific Expedition to Antarctica (31-ISEA-2011/12 and 33-ISEA-2013/14). The waters under ice cover were characterized by hyperoxia (up to 10.6 ml/L). Macronutrient concentrations under sea ice were depleted (<0.1 M NO3, PO4 and <2 M SiO4); this could be ascribed to the nutrient demand from under ice algae. The water under the ice cover exhibited higher algal biomass (Chl a up to 6.1 mg/m3) and CO2 under saturation (pCO2 <10 atm). This is reflected through the Spearman rank correlation indicating a negative correlation between Chl a and pCO2 (). The strong negative correlation between dissolved oxygen and pCO2 () suggests that photosynthesis regulates the concentrations of both these climatically important gases. The waters under the sea ice cover had brownish mucilaginous aggregates comprised of tube-forming diatoms Berkeleya adelienses and Nitzschia lecointei. These unusual biogeochemical changes were seen only at the ice water interface, and not at deeper depths. This study suggests that with global warming and sea ice melting, Antarctica might witness phytoplankton community shifts.

Continue reading ‘Hidden biogeochemical anonymities under Antarctic fast ice’


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Ocean acidification in the IPCC AR5 WG II

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