Posts Tagged 'methods'

Ocean carbonate system computation for anoxic waters using an updated CO2SYS program

Highlights

  • In anoxic waters hydrogen sulfide (H2S) influences the ocean carbonate equilibrium.
  • H2S and ammonia (NH3) are added to the popularly used CO2SYS program.
  • The new software is made available to the community and is recommended for use.


Abstract

In anoxic/hypoxic waters, the presence of hydrogen sulfide (H2S) and ammonia (NH3) influences results of the computation of parameters in the ocean carbonate system. To evaluate their influences, H2S and NH3 contributions to total alkalinity are added to CO2SYS, which is a most often used publicly available software package that calculates oceanic carbonate parameters. We discuss how these two metabolites affect the carbonate parameters and compare the differences in total alkalinity, dissolved inorganic carbon, pH, fCO2, and aragonite saturation state between the CO2SYS packages with and without considering the acid-base systems of H2S and NH3. The results show that, without considering these two acid-base systems, even low to moderate concentrations (e.g., 2–20 μmol kg−1) of these metabolites cause errors in the calculated carbonate parameters larger than the accuracies of the best measurements, and thus it is important to include contributions from these metabolites. The outputs from this updated version of CO2SYS agree well with outputs from AquaEnv, which is the only other computation program for the ocean carbonate system that includes the acid-base systems of H2S and NH3. Users are encouraged to use the updated version of CO2SYS to calculate carbonate parameters in anoxic/hypoxic waters.

Continue reading ‘Ocean carbonate system computation for anoxic waters using an updated CO2SYS program’

Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

Continue reading ‘Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast’

Multiple phases of mg-calcite in crustose coralline algae suggest caution for temperature proxy and ocean acidification assessment: lessons from the ultrastructure and biomineralisation in Phymatolithon (Rhodophyta, Corallinales)

Magnesium content, strongly correlated with temperature, has been developed as a climate archive for the late Holocene without considering anatomical controls on Mg content. In this paper we explore the ultrastructure and cellular scale Mg-content variations within four species of North Atlantic crust-forming Phymatolithon. The cell wall has radial grains of Mg-calcite whereas the interfilament (middle lamella) has grains aligned parallel to the filament axis. The proportion of interfilament and cell wall carbonate varies by tissue and species. Three distinct primary phases of Mg-calcite are identified: interfilament Mg-calcite (mean 8.9 mol% MgCO3), perithallial cell walls Mg-calcite (mean 13.4 mol% MgCO3), and hypothallium Mg-calcite (mean 17.1 mol% MgCO3). Magnesium content for the bulk crust, an average of all phases present, shows a strongly correlated (R2= 0.975) increase of 0.31 mol% MgCO3/°C. Of concern for climate reconstructions is the potential for false warming signals from undetected post-grazing wound repair carbonate that is substantially enriched in Mg, unrelated to temperature. Within a single crust, component carbonates can range from Mg content as stable as aragonite (8 mol% MgCO3), up to 150% higher (20 mol% MgCO3) a predicted unstable high magnesium calcite. It is unlikely that existing current predictions of ocean acidification impact on coralline algae, based on saturation states calculated using average Mg contents, provide an environmentally-relevant estimate.

Continue reading ‘Multiple phases of mg-calcite in crustose coralline algae suggest caution for temperature proxy and ocean acidification assessment: lessons from the ultrastructure and biomineralisation in Phymatolithon (Rhodophyta, Corallinales)’

Conceptualizing ecosystem tipping points within a physiological framework

Connecting the nonlinear and often counterintuitive physiological effects of multiple environmental drivers to the emergent impacts on ecosystems is a fundamental challenge. Unfortunately, the disconnect between the way “stressors” (e.g., warming) is considered in organismal (physiological) and ecological (community) contexts continues to hamper progress. Environmental drivers typically elicit biphasic physiological responses, where performance declines at levels above and below some optimum. It is also well understood that species exhibit highly variable response surfaces to these changes so that the optimum level of any environmental driver can vary among interacting species. Thus, species interactions are unlikely to go unaltered under environmental change. However, while these nonlinear, species-specific physiological relationships between environment and performance appear to be general, rarely are they incorporated into predictions of ecological tipping points. Instead, most ecosystem-level studies focus on varying levels of “stress” and frequently assume that any deviation from “normal” environmental conditions has similar effects, albeit with different magnitudes, on all of the species within a community. We consider a framework that realigns the positive and negative physiological effects of changes in climatic and nonclimatic drivers with indirect ecological responses. Using a series of simple models based on direct physiological responses to temperature and ocean pCO2, we explore how variation in environment-performance relationships among primary producers and consumers translates into community-level effects via trophic interactions. These models show that even in the absence of direct mortality, mismatched responses resulting from often subtle changes in the physical environment can lead to substantial ecosystem-level change.

Continue reading ‘Conceptualizing ecosystem tipping points within a physiological framework’

Organic matter export to the seafloor in the Baltic Sea: Drivers of change and future projections

The impact of environmental change and anthropogenic stressors on coastal marine systems will strongly depend on changes in the magnitude and composition of organic matter exported from the water column to the seafloor. Knowledge of vertical export in the Baltic Sea is synthesised to illustrate how organic matter deposition will respond to climate warming, climate-related changes in freshwater runoff, and ocean acidification. Pelagic heterotrophic processes are suggested to become more important in a future warmer climate, with negative feedbacks to organic matter deposition to the seafloor. This is an important step towards improved oxygen conditions in the near-bottom layer that will reduce the release of inorganic nutrients from the sediment and hence counteract further eutrophication. The evaluation of these processes in ecosystem models, validated by field observations, will significantly advance the understanding of the system’s response to environmental change and will improve the use of such models in management of coastal areas.

Continue reading ‘Organic matter export to the seafloor in the Baltic Sea: Drivers of change and future projections’

Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy

Quantifying the saturation state of aragonite (ΩAr) within the calcifying fluid of corals is critical for understanding their biomineralisation process and sensitivity to environmental changes including ocean acidification. Recent advances in microscopy, microprobes, and isotope geochemistry allow determination of calcifying fluid pH and [CO32−], but direct quantification of ΩAr (where ΩAr =[CO32−][Ca2+]/Ksp) has proved elusive. Here we test a new technique for deriving ΩAr based on Raman spectroscopy. First, we analysed abiogenic aragonite crystals precipitated under a range of ΩAr from 10 to 34, and found a strong dependence of Raman peak width on ΩAr that was independent of other factors including pH, Mg/Ca partitioning, and temperature. Validation of our Raman technique for corals is difficult because there are presently no direct measurements of calcifying fluid ΩAr available for comparison. However, Raman analysis of the international coral standard JCp-1 produced ΩAr of 12.3 ± 0.3, which we demonstrate is consistent with published skeletal Sr/Ca, Mg/Ca, B/Ca, δ44Ca, and δ11B data. Raman measurements are rapid (≤ 1 s), high-resolution (< 1 μm), precise (derived ΩAr ±1 to 2), and require minimal sample preparation; making the technique well suited for testing the sensitivity of coral calcifying fluid ΩAr to ocean acidification and warming using samples from natural and laboratory settings. To demonstrate this, we also show a high-resolution time series of ΩAr over multiple years of growth in a Porites skeleton from the Great Barrier Reef, and we evaluate the response of ΩAr in juvenile Acropora cultured under elevated CO2 and temperature.

Continue reading ‘Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy’

Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish

Ocean acidification threatens marine ecosystems by altering ocean chemistry and calcification processes in marine organisms. This study investigated the effects of predicted future CO2 levels, under varying temperature levels, on otolith development (size and shape) and chemistry, with the latter aimed at developing a chemical tracer of environmental pCO2. Juvenile barramundi (Lates calcarifer), a diadromous fish species, were reared in ambient (pCO2: 640 μatm; pH: 7.9) and elevated (pCO2: 1490 μatm; pH: 7.5) pCO2 treatments representing current and projected coastal systems crossed with three temperature levels (26 °C, 30 °C and 34 °C) for 42 days. Otolith shape and size parameters (length, width, perimeter and area) were measured and element concentrations (Na, Mg, Sr, Ba, Li, Mn and B) were quantified using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS). There was an interactive effect of elevated pCO2 and temperature on otolith shape and perimeter, whereas otolith chemistry did not vary among treatments. This study demonstrates that combined elevated pCO2 and temperature can affect the development of important internal structures in diadromous fish, but also suggests that otolith elemental chemistry was not a suitable tracer for pCO2 histories in fish. Future climate change conditions affect an important auditory and balance organ; consequently, rising CO2 levels may interfere with sensory function.

Continue reading ‘Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish’


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Ocean acidification in the IPCC AR5 WG II

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