Posts Tagged 'Antarctic'

Antarctic environmental change and biological responses

Antarctica and the surrounding Southern Ocean are facing complex environmental change. Their native biota has adapted to the region’s extreme conditions over many millions of years. This unique biota is now challenged by environmental change and the direct impacts of human activity. The terrestrial biota is characterized by considerable physiological and ecological flexibility and is expected to show increases in productivity, population sizes and ranges of individual species, and community complexity. However, the establishment of non-native organisms in both terrestrial and marine ecosystems may present an even greater threat than climate change itself. In the marine environment, much more limited response flexibility means that even small levels of warming are threatening. Changing sea ice has large impacts on ecosystem processes, while ocean acidification and coastal freshening are expected to have major impacts.

Continue reading ‘Antarctic environmental change and biological responses’

Changes in genome-wide methylation and gene expression in response to future pCO2 extremes in the Antarctic pteropod Limacina helicina antarctica

Epigenetic processes such as variation in DNA methylation may promote phenotypic plasticity and the rapid acclimatization of species to environmental change. The extent to which an organism can mount an epigenetic response to current and future climate extremes may influence its capacity to acclimatize or adapt to global change on ecological rather than evolutionary time scales. The thecosome pteropod Limacina helicina antarctica is an abundant macrozooplankton endemic to the Southern Ocean and is considered a bellwether of ocean acidification as it is highly sensitive to variation in carbonate chemistry. In this study, we quantified variation in DNA methylation and gene expression over time across different ocean acidification regimes. We exposed L. helicina antarctica to pCO2 levels mimicking present-day norms in the coastal Southern Ocean of 255 μatm pCO2, present-day extremes of 530 μatm pCO2, and projected extremes of 918 μatm pCO2 for up to 7 days before measuring global DNA methylation and sequencing transcriptomes in animals from each treatment across time. L. helicina antarctica significantly reduced DNA methylation by 29–56% after 1 day of exposure to 918 μatm pCO2 before DNA methylation returned to control levels after 6 days. In addition, L. helicina antarctica exposed to 918 μatm pCO2 exhibited drastically more differential expression compared to cultures replicating present-day pCO2 extremes. Differentially expressed transcripts were predominantly downregulated. Furthermore, downregulated genes were enriched with signatures of gene body methylation. These findings support the potential role of DNA methylation in regulating transcriptomic responses by L. helicina antarctica to future ocean acidification and in situ variation in pCO2 experienced seasonally or during vertical migration. More broadly, L. helicina antarctica was capable of mounting a substantial epigenetic response to ocean acidification despite little evidence of metabolic compensation or recovery of the cellular stress response in this species at future pCO2 levels.

Continue reading ‘Changes in genome-wide methylation and gene expression in response to future pCO2 extremes in the Antarctic pteropod Limacina helicina antarctica’

Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification

Microorganisms form the basis of ocean ecosystems yet the effects of perturbations such as decreasing pH on microbial community structure, interactions and functionality remain compared to multicellular organisms. Using an experimental manipulation of Southern Ocean seawater, we subjected bacterioplankton and mycoplankton to artificial pH decreases, which are predicted to occur in the future. We show that acidification led to substantial increases of bacterioplankton diversity, while in contrast it had no effect on mycoplankton diversity. Our analyses revealed a loss of putative keystone taxa and a decrease in predicted community interactions as a response to lower pH levels. Bacterioplankton shifted from generalist to specialist community members, suggesting a specific stress response to unfavourable conditions. In addition, enzyme activities involved in nitrogen acquisition were lower at reduced pH levels, suggesting altered organic matter cycling in a more acidic ocean. Our findings suggest that bacterioplankton and mycoplankton may respond differentially to future ocean acidification, with potentially negative impacts on community structure and biogeochemical cycling in the Southern Ocean.

Continue reading ‘Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification’

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’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book