High-quality pH measurements are essential for observing ocean acidification and interpreting its chemical and ecological effects. Spectrophotometric measure is the preferred method for pH analysis of seawater because of its high reproducibility and excellent precision. Meta-cresol purple (mCP) is one of the most used indicator dyes for spectrophotometric pH determination. Impurities in indicator salts can significantly bias spectrophotometric pH determinations, and therefore the use of purified mCP is recommended. This work describes the use of a fast, simple, and green-friendly High-Performance-Liquid Chromatography (HPLC) procedure for purification of mCP dye solution. A C18 reversed phase column was used, and different compositions of the mobile phase were considered. The selected mobile phase was 85% Milli-Q water and 15% CH3CN pH 8.0 that allowed reasonable run time and a suitable purified mCP retention time (4.65 ± 0.005 min). Aliquots of purified mCP were mixed and evaporated by rotary evaporator that resulted in the fastest preconcentration procedure among those considered in this study. Purified mCP was used for measuring the pH in seawater samples collected in the Ross Sea (Antarctica) and the values ranged between 8.202 and 7.983, with the highest values at the surface.
Continue reading ‘HPLC-DAD purification and characterization of meta-cresol-purple for spectrophotometric seawater pH measurements’Posts Tagged 'Antarctic'
HPLC-DAD purification and characterization of meta-cresol-purple for spectrophotometric seawater pH measurements
Published 2 November 2021 Science ClosedTags: Antarctic, chemistry, field
Calcium carbonate saturation states along the West Antarctic Peninsula
Published 1 November 2021 Science ClosedTags: Antarctic, chemistry, field
The waters along the West Antarctic Peninsula (WAP) have experienced warming and increased freshwater inputs from melting sea ice and glaciers in recent decades. Challenges exist in understanding the consequences of these changes on the inorganic carbon system in this ecologically important and highly productive ecosystem. Distributions of dissolved inorganic carbon (CT), total alkalinity (AT) and nutrients revealed key physical, biological and biogeochemical controls of the calcium carbonate saturation state (Ωaragonite) in different water masses across the WAP shelf during the summer. Biological production in spring and summer dominated changes in surface water Ωaragonite (ΔΩaragonite up to +1.39; ~90%) relative to underlying Winter Water. Sea-ice and glacial meltwater constituted a minor source of AT that increased surface water Ωaragonite (ΔΩaragonite up to +0.07; ~13%). Remineralization of organic matter and an influx of carbon-rich brines led to cross-shelf decreases in Ωaragonite in Winter Water and Circumpolar Deep Water. A strong biological carbon pump over the shelf created Ωaragonite oversaturation in surface waters and suppression of Ωaragonite in subsurface waters. Undersaturation of aragonite occurred at < ~1000 m. Ongoing changes along the WAP will impact the biologically driven and meltwater-driven processes that influence the vulnerability of shelf waters to calcium carbonate undersaturation in the future.
Continue reading ‘Calcium carbonate saturation states along the West Antarctic Peninsula’Emiliania huxleyi biometry and calcification response to the Indian sector of the Southern Ocean environmental gradients
Published 26 October 2021 Science ClosedTags: Antarctic, biological response, calcification, laboratory, morphology, phytoplankton
Highlights
- E. huxleyi morphotypes morphological variations in the SO
- E. huxleyi extracellular overcalcification prominent in high latitude SO
- E. huxleyi overcalcified coccosphers show extracellular Ca + Mg precipitation.
- E. huxleyi may pre-adapted to changing carbonate chemistry.
Abstract
An increase in the atmospheric pCO2 and temperature is expected to reduce ocean CO32− concentration, make oceans warmer and alter ocean circulation patterns. This will also affect the production and biogeographic distribution of marine calcifying organisms including coccolithophores. The lowering of oceanic CO32− is expected to interfere with the coccolithophore calcification process and cause malformation of coccoliths, whereas changes in the oceanic temperature and circulation patterns may shift their biogeographic boundaries. In this study, we have investigated Emiliania huxleyi coccolith and coccosphere size response to the wide-ranging physico-chemical conditions of the Indian sector of the Southern Ocean between latitudes 38oS and 58oS during the austral summer of 2010 (January–February). This study helps to understand the response of E. huxleyi coccolith/coccosphere morphometry and mass changes to the fluctuating temperature, salinity, CO32−, pCO2, and nutrient values. Our results show that in the Indian sector of the Southern Ocean, E. huxleyi coccoliths are larger and coccospheres are smaller in the Subtropical Zone (STZ). In contrast, coccoliths size is smaller and coccospheres size is larger in the Subantarctic Zone (SAZ), which is due to the decrease in Sea Surface Temperature, Sea Surface Salinity and increase in nutrient concentrations. In the Indian sector of the Southern Ocean, E. huxleyi shows a north-to-south morphotype shift from the heavily calcified ‘Group A’ (E. huxleyi morphotype A) to the weakly calcified ‘Group B’ (E. huxleyi morphotypes B/C, C) forms. We demonstrate that although weakly calcified E. huxleyi morphotypes (morphotypes B/C and C) comprise less mass than that of the E. huxleyi morphotype A, due to the large-sized coccospheres and numerous coccoliths per coccosphere, ‘Group B’ coccospheres precipitate large amount of CaCO3 in the SAZ compared to ‘Group A’ coccospheres located in the STZ. We have documented the presence of large E. huxleyi overcalcified coccospheres with large-sized coccoliths in the southernmost cold, high pCO2, and nutrient-rich waters which show extracellular calcite precipitation. The energy dispersive spectrometry analysis indicates the presence of a large amount of Mg in the overcalcified E. huxleyi specimens. We suspect that E. huxleyi in the colder nutrient-rich waters, with future projected changes in the carbonate chemistry, may adapt to low pH, high pCO2 conditions through extracellular Ca and Mg mineralization.
Continue reading ‘Emiliania huxleyi biometry and calcification response to the Indian sector of the Southern Ocean environmental gradients’Integrated assessment of ocean acidification risks to pteropods in the Northern high latitudes: regional comparison of exposure, sensitivity and adaptive capacity
Published 13 September 2021 Science ClosedTags: adaptation, Antarctic, biological response, chemistry, field, globalmodeling, laboratory, modeling, molecular biology, mollusks, North Pacific, otherprocess, physiology, South Pacific, zooplankton
Exposure to the impact of ocean acidification (OA) is increasing in high-latitudinal productive habitats. Pelagic calcifying snails (pteropods), a significant component of the diet of economically important fish, are found in high abundance in these regions. Pteropods have thin shells that readily dissolve at low aragonite saturation state (Ωar), making them susceptible to OA. Here, we conducted a first integrated risk assessment for pteropods in the Eastern Pacific subpolar gyre, the Gulf of Alaska (GoA), Bering Sea, and Amundsen Gulf. We determined the risk for pteropod populations by integrating measures of OA exposure, biological sensitivity, and resilience. Exposure was based on physical-chemical hydrographic observations and regional biogeochemical model outputs, delineating seasonal and decadal changes in carbonate chemistry conditions. Biological sensitivity was based on pteropod morphometrics and shell-building processes, including shell dissolution, density and thickness. Resilience and adaptive capacity were based on species diversity and spatial connectivity, derived from the particle tracking modeling. Extensive shell dissolution was found in the central and western part of the subpolar gyre, parts of the Bering Sea, and Amundsen Gulf. We identified two distinct morphotypes: L. helicina helicina and L. helicina pacifica, with high-spired and flatter shells, respectively. Despite the presence of different morphotypes, genetic analyses based on mitochondrial haplotypes identified a single species, without differentiation between the morphological forms, coinciding with evidence of widespread spatial connectivity. We found that shell morphometric characteristics depends on omega saturation state (Ωar); under Ωar decline, pteropods build flatter and thicker shells, which is indicative of a certain level of phenotypic plasticity. An integrated risk evaluation based on multiple approaches assumes a high risk for pteropod population persistence with intensification of OA in the high latitude eastern North Pacific because of their known vulnerability, along with limited evidence of species diversity despite their connectivity and our current lack of sufficient knowledge of their adaptive capacity. Such a comprehensive understanding would permit improved prediction of ecosystem change relevant to effective fisheries resource management, as well as a more robust foundation for monitoring ecosystem health and investigating OA impacts in high-latitudinal habitats.
Continue reading ‘Integrated assessment of ocean acidification risks to pteropods in the Northern high latitudes: regional comparison of exposure, sensitivity and adaptive capacity’Potential role of major phytoplankton communities on pCO2 modulation in the Indian sector of Southern Ocean
Published 31 August 2021 Science ClosedTags: Antarctic, chemistry, field
Spatial variations in the phytoplankton community compositions, carbon dioxide system and ancillary water column properties, were monitored across various frontal systems in the Indian Sector of Southern Ocean (ISSO) during austral summer 2013. Four major frontal systems, namely, the Agulhas Return Front (ARF), Southern Subtropical Front (SSTF), Subantarctic Front (SAF) and Polar Front (PF) were identified along the study area. Major groups of phytoplankton were distinguished adopting single marker pigment approach. Statistical computations showed the distribution of diatoms were influenced by the availability of inorganic nutrients (primarily silicate and nitrate) and mixed layer depths (MLD). Haptophytes were strongly dependent on phosphate availability, whereas, picoplankton flourished in water where regenerated nutrient ammonium was present. The lowest surface pCO2 (267.26–291.5 µatm) along with in situ oxygen production (> 10 µM) was encountered at the two warmer fronts, ARF and SSTF, dominated by haptophytes and picoplankton. The colder Antarctic fronts, SAF and PF were dominated by diatoms where surface pCO2 was relatively higher (> 350µatm). Poor statistical correlation among temperature and total chlorophyll with pCO2 revealed complex interplay of multiple factors. Contribution of major phytoplankton groups towards pCO2 drawdown was computed using a one-dimensional model describing the relative contributions of biological activities. In ISSO, calcifying and photosynthesizing haptophytes were observed to play a crucial role in the “biological pump” of CO2 drawdown at ARF, SSTF and SAF, while the silicifying micro phytoplankton diatoms and picoplankton were more effective at PF.
Continue reading ‘Potential role of major phytoplankton communities on pCO2 modulation in the Indian sector of Southern Ocean’Warming, not CO2-acidified seawater, alters otolith development of juvenile Antarctic emerald rockcod (Trematomus bernacchii)
Published 13 August 2021 Science ClosedTags: Antarctic, biological response, fish, laboratory, morphology, multiple factors, physiology, temperature
The combustion of fossil fuels is currently causing rapid rates of ocean warming and acidification worldwide. Projected changes in these parameters have been repeatedly observed to stress the physiological limits and plasticity of many marine species from the molecular to organismal levels. High latitude oceans are among the fastest changing ecosystems; therefore, polar species are projected to be some of the most vulnerable to climate change. Antarctic species are particularly sensitive to environmental change, having evolved for millions of years under stable ocean conditions. Otoliths, calcified structures found in a fish’s inner ear used to sense movement and direction, have been shown to be affected by both warming and CO2-acidified seawater in temperate and tropical fishes but there is no work to date on Antarctic fishes. In this study, juvenile emerald rockcod (Trematomus bernacchii) were exposed to projected seawater warming and CO2-acidification for the year 2100 over 28 days. Sagittal otoliths were analyzed for changes in area, perimeter, length, width and shape. We found ocean warming increased the growth rate of otoliths, while CO2-acidified seawater and the interaction of warming and acidification did not have an effect on otolith development. Elevated temperature also altered the shape of otoliths. If otolith development is altered under future warming scenarios, sensory functions such as hearing, orientation, and movement may potentially be impaired. Changes in these basic somatic abilities could have broad implications for the general capabilities and ecology of early life stages of Antarctic fishes.
Continue reading ‘Warming, not CO2-acidified seawater, alters otolith development of juvenile Antarctic emerald rockcod (Trematomus bernacchii)’Editorial: Microbial response to a rapidly changing marine environment: global warming and ocean acidification
Published 9 August 2021 Science ClosedTags: Antarctic, biological response, community composition, Mediterranean, North Pacific, photosynthesis, physiology, phytoplankton, primary production, prokaryotes, review, South Pacific, virus
The World Ocean is undergoing rapid and substantial changes, particularly, in terms of warming and acidification. Global sea surface temperatures have risen by 0.7°C in recent years (2005–2014) relative to pre-industrial times (1870–1899) (Gattuso et al., 2015). The ocean pH is decreasing in response to the increasing anthropogenic CO2 emissions (Ocean Acidification; OA). This clear trend of ocean warming and acidification was documented in the fifth Assessment Report (AR5) by Intergovernmental Panel on Climate Change (IPCC). The warming of the surface ocean could increase stratification, suppress transport of nutrients into the upper photic zone and alter hydrographic properties or patterns of ocean circulation. The effects of OA include the changes of seawater carbonate chemistry such as an increase in partial pressure of seawater CO2 (pCO2) concentration and a decrease in calcium carbonate (CaCO3) saturation state (Royal Society, 2005; IPCC, 2014). Consequently, the warming and acidification will have substantial impacts on the growth and survival of marine organisms (e.g., Brander, 2010; Doney et al., 2012; Hollowed et al., 2013). In particular, microbes, as a vital component of the marine ecosystem that includes microalga (phytoplankton), protists, fungi, viruses, and the two main groups of prokaryotes (Bacteria and Archaea), are vulnerable to these environmental changes. Since these microscopic organisms drive major biogeochemical cycles and support higher food webs globally, physiological, and ecological alterations in microbial communities caused by marine environmental changes can herald changes not only in pathways of energy transfer through the food web but also in global biogeochemical cycles. Considering the microbial communities’ pivotal roles in the marine ecosystem and biogeochemical cycles, it is important to understand recent changes in microbial communities and how future changes might arise under the ongoing environmental forcing of the warming and acidifying oceans.
The goal of this Research Topic was to collect studies on present and future possible changes in microbial communities with respect to environmental change and their consequences within various oceans. The topic contains 10 diverse scientific contributions on many fundamental questions related to microbial communities in oceanic environments, and report on physiological and ecological responses of microbial communities to environmental changes. The studies from a range of geographic regions were collected, from more coastal systems to open oceans, and include Tera Nova Bay in Antarctica, Mediterranean waters, the East/Japan Sea, the South China Sea, the Western Pacific Ocean, the South Pacific Ocean, and the Ross Sea of the Southern Ocean. In the context of taxonomic diversity, heterotrophic bacteria, viruses, microalga, and other prokaryotes were included in this Research Topic.
Out of the 10 works published, seven of them are focused on the phytoplankton communities, or single species of microalgae, or environmental drivers. Kim et al. describe the seasonal variability in the macromolecular composition of the sea surface in front of the Korean station in Terra Nova Bay, Ross Sea, Antarctica. They show changes in organic matter composition mainly derived by changes in phytoplankton metabolism between the productive and the non-productive season. Their study helps us to understand the effect of future climate change on the composition of organic matter derived from phytoplankton in the polar oceans. Biochemical compositions such as macromolecular and amino acids of phytoplankton in the Ross Sea, Antarctica was investigated by Jo et al.. They found distinct differences in the biochemical composition between two major bloom-forming phytoplankton groups (diatoms and Phaeocystis antarctica). They discuss how these different compositions may highlight the different strategies of these two phytoplankton communities to cope with ongoing environmental changes in the Antarctic Ocean. Kang et al. demonstrate the differences in carbon uptake rates and intracellular biochemical compositions between two different size fractions of phytoplankton to understand the ecological roles of the small phytoplankton in terms of food quantity and quality in the East/Japan Sea where the water temperature has rapidly increased. Their findings show that the increase of small phytoplankton under the warming ocean conditions could negatively affect the primary productivity and caloric content, with further consequences on the marine food webs. The photosynthetic responses to oceanic physio-chemical conditions and phytoplankton communities in the oligotrophic Western Pacific Ocean were presented by Wei et al.. Their study found that the important biotic variables influencing Fv/Fm are diatoms, Prochlorococcus, and picoeukaryotes, whilst the maximum of primary production is closely related to cyanobacteria, dinoflagellates, and Synechococcus. The detailed investigation of a chromophytic phytoplankton community using high-throughput sequencing of rbcL genes in the Western Pacific Ocean was presented by Pujari et al.. The authors found that the diversity of RuBisCO encoding rbcL gene varies with depth and across latitudes in the Western Pacific Ocean. The variation observed in chromophytic phytoplankton suggests the strong influence of environmental variables on biological production induced by oceanographic features. Thangaraj et al. investigated comprehensive proteomic profiling of diatom Skeletonema dohrnii with a change of temperature and silicate deprivation based on the iTRAQ proteomic approach, to understand the effect of the temperature and nutrient on the physiology of marine diatoms growth and photosynthesis. Their study shows that the proteome analysis for environmental stress-response of diatoms could extend our understanding for the potential impacts of climate change on the physiological adjustment to the metabolic process of phytoplankton. Sow et al. present a clear and concise description of the biogeography of Phaeocystis along a transect from the ice edge to the equator in the South Pacific Ocean, by way of high-throughput 18S rRNA gene sequencing. Their study shows that Phaeocystis could be occasionally highly abundant and diverse in the South Pacific Ocean, whereas the oceanic fronts could be the driving force for the distribution and structure of Phaeocystis assemblages in the ocean. Their work greatly expands our knowledge about the biodiversity patterns and abundances of Phaeocystis as a globally important nano-eukaryote.
Three of the 10 published works have focused on the response of viruses, prokaryotes or microbial communities to environmental stress. The response of viruses to two anthropogenic stressors (OA and eutrophication) was presented by Malits et al.. Their study demonstrates that the effect of OA on viral dynamics and viral-mediated mortality varies depending on the nutrient regime of the studied systems. It helps us to understand how viral-mediated mortality of microbes (VMMM) can be modified with environmental forcing. Another work looks into the contribution of grazers and viruses in controlling ecologically distinct prokaryotic sub-groups (i.e., high nucleic acid (HNA) and low nucleic acid (LNA) cells) along a cross-shore nutrient gradient in the northern South China Sea (Hu et al.). Their study shows how the nutrient regime influences the fate of ecologically relevant prokaryotic groups in the actual context of global warming and the anticipated oligotrophication of the future ocean. Sörenson et al. address the resilience of a marine microbial community, cultivated in an outdoor photobioreactor, when exposed to a naturally occurring seasonal stress. Differential gene expression analyses suggest that community function at warm temperatures is based on concomitant utilization of inorganic and organic carbon assigned to autotrophs and heterotrophs, while at colder temperatures, the uptake of organic carbon was performed primarily by autotrophs. Overall, the microbial community maintains a similar level of diversity and function within and across autotrophic and heterotrophic levels, confirming the cross-scale resilience theory.
The topics of the papers published in this Research Topic range from viruses, prokaryotes to phytoplankton and cover microbial communities from the various oceans. The studies confirm that the changes already occurring in ocean environments affect the metabolism and physiology of microbial communities, and further suggest that future changes will impact the physiological and ecological function or strategy of the microbial community in the marine ecosystem. Since most of these studies focus on the response of a single taxonomic population of microbes to environmental changes, our special issue highlights the need for studies to understand how ecological interactions occurring within and among the microbial community in the changing ocean will affect ecosystem structure and function. Finally, we hope that the group of papers that we have drawn together here will be a valuable addition to the accumulating observational evidence of how microbial communities are responding to the climate-related changes and consequently useful for evaluating and predicting the ongoing and future responses of marine ecosystems associated with the global climate change.
Continue reading ‘Editorial: Microbial response to a rapidly changing marine environment: global warming and ocean acidification’The effects of combined ocean acidification and nanoplastic exposures on the embryonic development of Antarctic krill
Published 4 August 2021 Science ClosedTags: Antarctic, biological response, crustaceans, laboratory, multiple factors, reproduction, toxicants
In aquatic environments, plastic pollution occurs concomitantly with anthropogenic climate stressors such as ocean acidification. Within the Southern Ocean, Antarctic krill (Euphausia Superba) support many marine predators and play a key role in the biogeochemical cycle. Ocean acidification and plastic pollution have been acknowledged to hinder Antarctic krill development and physiology in singularity, however potential multi-stressor effects of plastic particulates coupled with ocean acidification are unexplored. Furthermore, Antarctic krill may be especially vulnerable to plastic pollution due to their close association with sea-ice, a known plastic sink. Here, we investigate the behaviour of nanoplastic [spherical, aminated (NH2), and yellow-green fluorescent polystyrene nanoparticles] in Antarctic seawater and explore the single and combined effects of nanoplastic (160 nm radius, at a concentration of 2.5 μg ml–1) and ocean acidification (pCO2 ∼900, pHT 7.7) on the embryonic development of Antarctic krill. Gravid female krill were collected in the Atlantic sector of the Southern Ocean (North Scotia Sea). Produced eggs were incubated at 0.5 °C in four treatments (control, nanoplastic, ocean acidification and the multi-stressor scenario of nanoplastic presence, and ocean acidification) and their embryonic development after 6 days, at the incubation endpoint, was determined. We observed that negatively charged nanoplastic particles suspended in seawater from the Scotia Sea aggregated to sizes exceeding the nanoscale after 24 h (1054.13 ± 53.49 nm). Further, we found that the proportion of embryos developing through the early stages to reach at least the limb bud stage was highest in the control treatment (21.84%) and lowest in the multi-stressor treatment (13.17%). Since the biological thresholds to any stressors can be altered by the presence of additional stressors, we propose that future nanoplastic ecotoxicology studies should consider the changing global ocean under future climate scenarios for assessments of their impact and highlight that determining the behaviour of nanoplastic particles used in incubation studies is critical to determining their toxicity.
Continue reading ‘The effects of combined ocean acidification and nanoplastic exposures on the embryonic development of Antarctic krill’Molecular mechanisms underlying responses of the Antarctic coral Malacobelemnon daytoni to ocean acidification
Published 27 July 2021 Science 1 CommentTags: Antarctic, biological response, corals, laboratory, molecular biology, physiology
Highlights
- Gene expression profiles of the sea pen Malacobelemnon daytoni revealed an important number of transcripts upregulated in response to short-term and long-term Low pH conditions.
- The biomineralization in this coral is not acclimated after two months in the Low pH condition, indicating that the pennatulid would be striving to produce its calcium carbonate structure.
- Malacobelemnon daytoni is working extra hard at the molecular level to maintain the same enzyme activity levels.
Abstract
Benthic organisms of the Southern Ocean are particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. OA most strongly affects animals with calcium carbonate skeletons or shells, such as corals and mollusks. We exposed the abundant cold-water coral Malacobelemnon daytoni from an Antarctic fjord to low pH seawater (LpH) (7.68 ± 0.17) to test its physiological responses to OA, at the level of gene expression (RT-PCR) and enzyme activity. Corals were exposed in short- (3 days) and long-term (54 days) experiments to two pCO2 conditions (ambient and elevated pCO2 equaling RCP 8.5, IPCC 2019, approximately 372.53 and 956.78 μatm, respectively).
Of the eleven genes studied through RT-PCR, six were significantly upregulated compared with control in the short-term in the LpH condition, including the antioxidant enzyme superoxide dismutase (SOD), Heat Shock Protein 70 (HSP70), Toll-like receptor (TLR), galaxin and ferritin. After long-term exposure to low pH conditions, RT-PCR analysis showed seven genes were upregulated. These include the mannose-binding C-Lectin and HSP90. Also, the expression of TLR and galaxin, among others, continued to be upregulated after long-term exposure to low pH. Expression of carbonic anhydrase (CA), a key enzyme involved in calcification, was also significantly upregulated after long-term exposure. Our results indicated that, after two months, M. daytoni is not acclimatized to this experimental LpH condition. Gene expression profiles revealed molecular impacts that were not evident at the enzyme activity level. Consequently, understanding the molecular mechanisms behind the physiological processes in the response of a coral to LpH is critical to understanding the ability of polar species to cope with future environmental changes. Approaches integrating molecular tools into Antarctic ecological and/or conservation research make an essential contribution given the current ongoing OA processes.
Continue reading ‘Molecular mechanisms underlying responses of the Antarctic coral Malacobelemnon daytoni to ocean acidification’The variable circulation and carbonate chemistry of ocean upwelling systems
Published 11 June 2021 Science ClosedTags: Antarctic, chemistry, North Pacific
Ocean upwelling is a process in which winds drive deep waters to the surface ocean. The biogeochemical state of these waters causes upwelling regions to have some of the strongest air-sea fluxes of carbon dioxide (CO2) and most productive fisheries in the global oceans. In this dissertation, I use Earth System models to investigate the variability and projected impacts of climate change on upwelling systems. I first use the Community Earth System Model Large Ensemble (CESM-LE) to project the impacts of climate change on upwelling in the California Current. The CESM-LE provides an ensemble of potential trajectories of the climate system that differ due to internal climate variability. I find that upwelling is expected to weaken over the next century in the summer and intensify poleward in the spring due to anthropogenic climate change. Next, I use the CESM-LE to highlight the role of internal climate variability in modulating air-sea CO2 fluxes in the major Eastern Boundary Upwelling Systems (EBUS). I identify the major mode of internal variability that influences air-sea CO2 flux in each EBUS. I then quantify how the given mode of variability modifies local conditions, which in turn leads to the anomalous air-sea CO2 fluxes. Following this, I use a version of the CESM-LE that is configured for climate prediction to examine predictability of ocean acidification in the California Current. I find that our system makes skillful forecasts of surface pH out to fourteen months relative to observations and has a potential ceiling of skillful prediction out to five years in some regions. Finally, I use the Model for Prediction Across Scales Ocean (MPAS-O) to investigate the pathways over which carbon upwells in the Southern Ocean. I seed a high-resolution version of MPAS-O with 1,000,000 Lagrangian floats and find that regions with complex ocean topography have a disproportionate influence on bringing carbon-rich waters from the deep Southern Ocean to the surface. The results of this dissertation highlight the value of using ensemble methods and the Lagrangian perspective in Earth System models to better understand the dynamic and variable biogeochemistry in ocean upwelling systems.
Continue reading ‘The variable circulation and carbonate chemistry of ocean upwelling systems’Responses of Southern ocean seafloor habitats and communities to global and local drivers of change
Published 17 May 2021 Science ClosedTags: Antarctic, policy, review, socio-economy
Knowledge of life on the Southern Ocean seafloor has substantially grown since the beginning of this century with increasing ship-based surveys and regular monitoring sites, new technologies and greatly enhanced data sharing. However, seafloor habitats and their communities exhibit high spatial variability and heterogeneity that challenges the way in which we assess the state of the Southern Ocean benthos on larger scales. The Antarctic shelf is rich in diversity compared with deeper water areas, important for storing carbon (“blue carbon”) and provides habitat for commercial fish species. In this paper, we focus on the seafloor habitats of the Antarctic shelf, which are vulnerable to drivers of change including increasing ocean temperatures, iceberg scour, sea ice melt, ocean acidification, fishing pressures, pollution and non-indigenous species. Some of the most vulnerable areas include the West Antarctic Peninsula, which is experiencing rapid regional warming and increased iceberg-scouring, subantarctic islands and tourist destinations where human activities and environmental conditions increase the potential for the establishment of non-indigenous species and active fishing areas around South Georgia, Heard and MacDonald Islands. Vulnerable species include those in areas of regional warming with low thermal tolerance, calcifying species susceptible to increasing ocean acidity as well as slow-growing habitat-forming species that can be damaged by fishing gears e.g., sponges, bryozoan, and coral species. Management regimes can protect seafloor habitats and key species from fishing activities; some areas will need more protection than others, accounting for specific traits that make species vulnerable, slow growing and long-lived species, restricted locations with optimum physiological conditions and available food, and restricted distributions of rare species. Ecosystem-based management practices and long-term, highly protected areas may be the most effective tools in the preservation of vulnerable seafloor habitats. Here, we focus on outlining seafloor responses to drivers of change observed to date and projections for the future. We discuss the need for action to preserve seafloor habitats under climate change, fishing pressures and other anthropogenic impacts.
Continue reading ‘Responses of Southern ocean seafloor habitats and communities to global and local drivers of change’Combined effects of ocean acidification and elevated temperature on feeding, growth, and physiological processes of Antarctic krill Euphausia superba
Published 30 April 2021 Science ClosedTags: Antarctic, biological response, crustaceans, growth, laboratory, mortality, multiple factors, performance, physiology, temperature, zooplankton
Antarctic krill Euphausia superba is a key species in the Southern Ocean, where its habitat is projected to undergo continued warming and increases in pCO2. Experiments during 2 summer field seasons at Palmer Station, Antarctica, investigated the independent and interactive effects of elevated temperature and pCO2 (decreased pH) on feeding, growth, acid-base physiology, metabolic rate, and survival of adult Antarctic krill. Ingestion and clearance rates of chlorophyll were depressed under low pH (7.7) compared to ambient pH (8.1) after a 48 h acclimation period, but this difference disappeared after a 21 d acclimation. Growth rates were negligible and frequently negative, but were significantly more negative at high (3°C, -0.03 mm d-1) compared to ambient temperature (0°C, -0.01 mm d-1) with no effect of pH. Modest elevations in tissue total CO2 and tissue pH were apparent at low pH but were short-lived. Metabolic rate increased with temperature but was suppressed at low pH in smaller but not larger krill. Although effects of elevated temperature and/or decreased pH were mostly sublethal, mortality was higher at high temperature/low pH (58%) compared to ambient temperature/pH or ambient temperature/low pH (>90%). This study identified 3 dominant patterns: (1) shorter-term effects were primarily pH-dependent; (2) krill compensated for lower pH relatively quickly; and (3) longer-term effects on krill growth and survival were strongly driven by temperature with little to no pH effect.
Continue reading ‘Combined effects of ocean acidification and elevated temperature on feeding, growth, and physiological processes of Antarctic krill Euphausia superba’A review and meta-analysis of potential impacts of ocean acidification on marine calcifiers from the southern Ocean
Published 2 February 2021 Science ClosedTags: Antarctic, chemistry, echinoderms, mollusks, phytoplankton, review
Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the global oceans. Average surface seawater pH levels have already decreased by 0.1 and are projected to decline by ~0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many resident marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). Ocean warming could further exacerbate the effects of OA in these particular species. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make projections about how OA might affect a broad range of SO taxa. We consider a species’ geographic range, skeletal mineralogy, biological traits, and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate illustrates that the response variation is largely dependent on mineralogical composition. Species-specific responses due to mineralogical composition indicate that taxa with calcitic, aragonitic, and HMC skeletons, could be at greater risk to expected future carbonate chemistry alterations, and low-Mg calcite (LMC) species could be mostly resilient to these changes. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits, and physiological processes are also expected to influence species-specific responses.
Continue reading ‘A review and meta-analysis of potential impacts of ocean acidification on marine calcifiers from the southern Ocean’Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean
Published 18 November 2020 Science ClosedTags: algae, Antarctic, brachiopods, calcification, dissolution, echinoderms, mollusks, morphology, phytoplankton, reproduction, review, survival, zooplankton
Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the oceans. Seawater pH levels have already decreased by 0.1 and are predicted to decline by ~ 0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). These negative effects may become even exacerbated by increasing sea temperatures. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make predictions about how OA might affect different taxa. We consider their geographic range, skeletal mineralogy, biological traits and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate shows response variation depending on mineralogical composition. Species-specific responses due to mineralogical composition suggest taxa with calcitic, aragonitic and HMC skeletons may be more vulnerable to the expected carbonate chemistry alterations, and low magnesium calcite (LMC) species may be mostly resilient. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits and physiological processes are also expected to influence species specific responses.
Continue reading ‘Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean’Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica
Published 27 October 2020 Science ClosedTags: Antarctic, biological response, crustaceans, laboratory, mortality, multiple factors, performance, salinity
Highlights
- Glacial retreat induced by global warming can decrease salinity and pH of the Antarctic ocean.
- The Antarctic amphipod Gondogeneia antarctica was exposed to low salinity (27 psu) and low pH (7.6) conditions.
- Low salinity increased cannibalism and induced adjusted swimming.
- Low pH increased mortality, impaired food detection and reduced daytime shelter use.
- Ocean freshening and acidification 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 psu) 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 influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica’Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna
Published 27 October 2020 Science ClosedTags: Antarctic, biological response, dissolution, laboratory, mollusks, mortality, multiple factors, performance, physiology, salinity
Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, to two different pH (8.00 and 7.55) and salinity (34.0 and 27.0 psu) levels and measured their righting ability after being flipped over, mortality, condition factor, and shell dissolution. During the 35-day exposure, there was no significant difference in behavior and mortality between different treatments. However, the condition factor was negatively affected by low salinity. Both low pH and low salinity negatively influenced shell formation by decreasing the aragonite saturation state (Ωarg) and enhancing shell dissolution. Our results suggest that, though limpets can tolerate short-term low pH and salinity conditions, intrusions of meltwater accompanied by the glacial retreat may act as a serious threat to the population of N. concinna.
Continue reading ‘Effects of low pH and low salinity induced by meltwater inflow on the behavior and physical condition of the Antarctic limpet, Nacella concinna’Effects of ocean acidification on acid-base physiology, skeleton properties, and metal contamination in two echinoderms from vent sites in Deception Island, Antarctica
Published 13 October 2020 Science ClosedTags: Antarctic, biological response, chemistry, echinoderms, field, morphology, otherprocess, physiology, vents
Highlights
- Acid-base characteristics of adult Antarctic echinoderms are similar to those of tropical and temperate echionderms
- Skeleton properties of both species were weaker than those of tropical and temperate echinoderms
- Reduced seawater pH and metals had no impact on the skeleton mechanical properties of the two investigated species
- Reduced pH was correlated to increased contamination by most metals but this relation was weak
Abstract
Antarctic surface waters are expected to be the first to experience severe ocean acidification (OA) with carbonate undersaturation and large decreases in pH forecasted before the end of this century. Due to the long stability in environmental conditions and the relatively low daily and seasonal variations to which they are exposed, Antarctic marine organisms, especially those with a supposedly poor machinery to eliminate CO2 and protons and with a heavily calcified skeleton like echinoderms, are hypothesized as highly vulnerable to these environmental shifts. The opportunities offered by the natural pH gradient generated by vent activities in Deception Island caldera, Western Antarctic Peninsula, were used to investigate for the first time the acid-base physiologies, the impact of OA on the skeleton and the impact of pH on metal accumulation in the Antarctic sea star Odontaster validus and sea urchin Sterechinus neumayeri. The two species were sampled in four stations within the caldera, two at pH (total scale) 8.0- 8.1 and two at reduced pH 7.8. Measured variables were pH, alkalinity, and dissolved inorganic carbon of the coelomic fluid; characteristic fracture force, stress and Young’s modulus using Weibull statistics and Cd, Cu, Fe, Pb and Zn concentrations in the integument, gonads and digestive system. Recorded acid-base characteristics of both studied species fit in the general picture deduced from temperate and tropical sea stars and sea urchins but conditions and possibly confounding factors, principally food availability and quality, in the studied stations prevented definitive conclusions. Reduced seawater pH 7.8 and metals had almost no impact on the skeleton mechanical properties of the two investigated species despite very high Cd concentrations in O. validus integument. Reduced pH was correlated to increased contamination by most metals but this relation was weak. Translocation and caging experiments taking into account food parameters are proposed to better understand future processes linked to ocean acidification and metal contamination in Antarctic echinoderms.
Continue reading ‘Effects of ocean acidification on acid-base physiology, skeleton properties, and metal contamination in two echinoderms from vent sites in Deception Island, Antarctica’Seasonal variability of net sea-air CO2 fluxes in a coastal region of the northern Antarctic peninsula
Published 23 September 2020 Science ClosedTags: Antarctic, chemistry, field
We show an annual overview of the sea-air CO2 exchanges and primary drivers in the Gerlache Strait, a hotspot for climate change that is ecologically important in the northern Antarctic Peninsula. In autumn and winter, episodic upwelling events increase the remineralized carbon in the sea surface, leading the region to act as a moderate or strong CO2 source to the atmosphere of up to 40 mmol m–2 day–1. During summer and late spring, photosynthesis decreases the CO2 partial pressure in the surface seawater, enhancing ocean CO2 uptake, which reaches values higher than − 40 mmol m–2 day–1. Thus, autumn/winter CO2 outgassing is nearly balanced by an only 4-month period of intense ocean CO2 ingassing during summer/spring. Hence, the estimated annual net sea-air CO2 flux from 2002 to 2017 was 1.24 ± 4.33 mmol m–2 day–1, opposing the common CO2 sink behaviour observed in other coastal regions around Antarctica. The main drivers of changes in the surface CO2 system in this region were total dissolved inorganic carbon and total alkalinity, revealing dominant influences of both physical and biological processes. These findings demonstrate the importance of Antarctica coastal zones as summer carbon sinks and emphasize the need to better understand local/regional seasonal sensitivity to the net CO2 flux effect on the Southern Ocean carbon cycle, especially considering the impacts caused by climate change.
Effects of temperature and food concentration on pteropod metabolism along the Western Antarctic Peninsula
Published 17 September 2020 Science ClosedTags: Antarctic, biological response, laboratory, mollusks, physiology, zooplankton
Highlights
- Measured respiration and excretion of the Antarctic pteropod Limacina.
- Analyzed effects of future temperature and food conditions on pteropod metabolism.
- Highest metabolism occurred under higher temperatures with less response to food.
- Metabolic ratios of C, N, and P were all below the canonical Redfield ratio.
- Pteropod metabolism responsive to ocean change, affecting biogeochemical cycles.
Abstract
Pteropods (pelagic snails) are abundant zooplankton in the Southern Ocean where they are important grazers of phytoplankton, prey for higher trophic levels, and sensitive to environmental change. The Western Antarctic Peninsula (WAP) is a highly dynamic and productive region that has undergone rapid warming, but little is known about how environmental changes there will affect pteropod physiology. In this study, the effects of warming seawater temperatures and shifting food availability on Limacina helicina antarctica metabolism (respiration and excretion) were determined by conducting shipboard experiments that exposed pteropods to a range of temperatures and phytoplankton (food) concentrations. Highest respiration (up to 69 μmol O2 gDW−1 h−1) and usually highest excretion rates occurred under higher temperature with more limited metabolic response to food concentration, indicating these factors do not always have an additive effect on pteropod metabolism. The proportion of dissolved organic matter (DOM) to total organic and inorganic dissolved constituents was high and was also significantly affected by shifts in temperature and food. Dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP) were on average 27, 51, and 11.5% of the total C, N, and P metabolized, respectively. The proportion of total N excreted as DON and the proportion of total P excreted as DOP were significantly affected by a combination of shifting temperature and food concentrations. There were no effects of temperature or food on DOC excretion (mean 8.79 μmol C gDW−1 h−1; range 0.44 to 44) as a proportion of total C metabolized. Metabolic O2:N ratio ranged from 2 to 9 and decreased significantly with increasing temperature and food, indicating a shift toward increased protein catabolism. Metabolic ratios of C, N, and P were all below the canonical Redfield ratio, which has implications for phytoplankton nutrient uptake and bacterial production. Respiration rates at ambient conditions of other WAP pteropods, and excretion rates for Clio pyramidata, were also measured, with respiration rates ranging from 24.39 (Spongiobranchaea australis) to 28.86 (L. h. antarctica) μmol O2 gDW−1 h−1. Finally, a CO2 perturbation experiment measuring L. h. antarctica metabolism under pre-industrial and elevated dissolved pCO2 conditions showed no significant change in mean L. h. antarctica respiration or excretion rates with higher pCO2. These insights into the metabolic response of pteropods to ocean variability increase our understanding of the role of zooplankton in biogeochemical cycles and help predict future responses to climate change.
