Posts Tagged 'modeling'

Shifting the balance: engaging students in using a modeling tool to learn about ocean acidification

Modeling is one of the core scientific and engineering practices described in A Framework for K-12 Science Education. Students are expected to construct, use, evaluate, and revise their models to make sense of phenomena or to find solutions to problems. Technology tools can support the development of students’ modeling practice when learning about environmental issues. This study investigates the incorporation of an online computational modeling tool in a middle school curricular unit focusing on ocean acidification. We present the advantages and challenges experienced by students and teachers while engaging in the unit and using the modeling tool. Our results indicate that integrating the modeling tool in the ocean acidification curricular unit facilitates students’ interest and engagement in environmental responsibility and focused students’ attention toward human involvement and impact on the environment. Students perceived the tool and the curricular unit to be relevant to their lives and important in promoting their content learning and modeling practice. However, students and teachers reported several challenges, mostly related to the complexity of using the modeling tool and working with the resulting graphs and charts. We discuss these advantages and challenges and suggest recommendations for supporting students’ modeling practice when learning about environmental issues.
Continue reading ‘Shifting the balance: engaging students in using a modeling tool to learn about ocean acidification’

Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia

The severity of carbonate chemistry changes from ocean acidification is predicted to increase greatly in the coming decades, with serious consequences for marine species-­ especially those reliant on calcium carbonate for structure and function (Fabry et al. 2008). The Northern California Current Ecosystem off the coast of US West Coast experiences seasonal variations in upwelling and downwelling patterns creating natural episodes of hypoxia and calcite/aragonite undersaturation, exacerbating global trends of increasing ocean acidification and hypoxia (OAH) (Chan et al. 2008) (Gruber et al. 2012). The goal of these experiments was to identify thresholds of tolerance and attempt to quantify a point at which variance in responses to stress collapses. This study focuses on two species: Cancer magister (Dungeness crab) and Haliotis rufescens (red abalone). These species were selected for this study based on their economic and ecological value, as well as their taxonomic differences. Respirometry was used as a proxy for metabolic activity at four different scenarios mimicking preindustrial, upwelling, contemporary upwelling, and distant future conditions by manipulating dissolved oxygen and inorganic carbon (DIC) concentrations. Both species showed a decrease in mean respiration rate as OAH stressors increase, including an effect in contemporary upwelling conditions. These results suggest that current exposure to ocean acidification (OA) and hypoxia do not confer resilience to these stressors for either taxa. In teasing apart the effects of OAH as multiple stressors, it was found that Dungeness crab response was more strongly driven by concentration of dissolved oxygen, while red abalone data suggested a strong interactive effect between OA and hypoxia. Not only did these two different taxa exhibit different responses to a multiple stressors, but the fact that the Dungeness crab were secondarily impacted by acidification could suggest that current management concerns may need to be focus more strongly on deoxygenation.

Continue reading ‘Quantifying sensitivity and adaptive capacity of shellfish in the Northern California Current Ecosystem to increasing prevalence of ocean acidification and hypoxia’

Modelling determinants of extinction across two Mesozoic hyperthermal events

The Late Triassic and Early Toarcian extinction events are both associated with greenhouse warming events triggered by massive volcanism. These Mesozoic hyperthermals were responsible for the mass extinction of marine organisms and resulted in significant ecological upheaval. It has, however, been suggested that these events merely involved intensification of background extinction rates rather than significant shifts in the macroevolutionary regime and extinction selectivity. Here, we apply a multivariate modelling approach to a vast global database of marine organisms to test whether extinction selectivity varied through the Late Triassic and Early Jurassic. We show that these hyperthermals do represent shifts in the macroevolutionary regime and record different extinction selectivity compared to background intervals of the Late Triassic and Early Jurassic. The Late Triassic mass extinction represents a more profound change in selectivity than the Early Toarcian extinction but both events show a common pattern of selecting against pelagic predators and benthic photosymbiotic and suspension-feeding organisms, suggesting that these groups of organisms may be particularly vulnerable during episodes of global warming. In particular, the Late Triassic extinction represents a macroevolutionary regime change that is characterized by (i) the change in extinction selectivity between Triassic background intervals and the extinction event itself; and (ii) the differences in extinction selectivity between the Late Triassic and Early Jurassic as a whole.

Continue reading ‘Modelling determinants of extinction across two Mesozoic hyperthermal events’

Drivers of carbon and oxygen dynamics in disparate marine ecosystems

Determining the change of sea surface CO2 fugacity (fCO2) is important as the fCO2 gradient between the atmosphere and the ocean dictates the direction of CO2 flux and the fate of this greenhouse gas. While substantial efforts have been dedicated to the study of fCO2 trends in the open ocean, little is known regarding how fCO2 levels change in ocean margins. Meanwhile, hypoxia (i.e., dissolved oxygen concentration, or DO, less than 2 mg L-1) is becoming an increasing global threat in coastal areas. Elucidating the carbon sources that consume DO is important because it helps to make proper mitigation plans. In Chapter II, I used a newly available, community-based global CO2 database (Surface Ocean CO2 Atlas version 3) to develop a new statistical approach based on Generalized Additive Mixed Modeling (GAMM) to interpret oceanic fCO2 changes in ocean margins. This method utilized Julian day of year, sea surface salinity, sea surface temperature, and sampling date as predictors. Using the GAMM method, I was able to derive multi-decadal fCO2 trends with both improved precision and greater robustness to data gaps compared to the existing method. In Chapter III, I used the GAMM method on global ocean margins (within 400 km from the shore and 30°S-70°N) and found that fCO2 trends closely followed the atmospheric fCO2 increase rate. Further analysis suggested that fCO2 trends in Western Boundary Current- and Eastern Boundary Current-influenced areas differed in response to thermal (temperature) and nonthermal (chemical and biological) effects. These differences were due to heterogonous physical, chemical, and biological responses under climate change forcing, leading to divergent trends in CO2 sinks and sources among different ocean margins. To address the hypoxia formation mechanism question, I adopted the stable carbon isotope (δ13C) of dissolved inorganic carbon (or DIC, the end product of organic carbon degradation) as a proxy to trace back the δ13C of remineralized organic carbon that was responsible for DO consumption in the northern Gulf of Mexico (Chapter IV) and two semi-arid coastal bays in south Texas (Baffin Bay and Oso Bay) (Chapter V), the two areas that both experience seasonal bottom water hypoxia. My findings suggested that terrestrial carbon contributed to oxygen consumption in limited extent and mostly focused in areas where river water influence was significant in the northern Gulf of Mexico, while for the vast shelf areas marine-produced organic carbon was the dominant contributor to hypoxia formation. In Baffin Bay and Oso Bay, however, phytoplankton, seagrass/marsh organic carbon, and refractory terrestrial organic carbon all contributed to the DO loss under different hydrological conditions. This study provided a comprehensive data-driven analysis on ocean margin fCO2 changes on a multi-decadal timescale and revealed different behaviors of the two types of boundary current-dominated systems. Regarding the hypoxia formation mechanism in the different coastal and estuarine environments, my study suggested that eutrophication remained the top stressor that could lead to hypoxia formation. Therefore, sustained efforts that focus on reducing nutrient pollution should still be carried out to mitigate the hypoxia stress for the both ecologically and economically important coastal and estuarine systems.

Continue reading ‘Drivers of carbon and oxygen dynamics in disparate marine ecosystems’

Modeling impact of varying pH due to carbondioxide on the dynamics of prey–predator species system

In this paper, we have considered a nonlinear mathematical model to investigate the effect of pH on prey–predator dynamics with Holling type II functional response. In the model, capture rate, handling time, growth rate and death rate are considered to be pH dependent. From the analysis of the model, it has been observed that as pH level goes below the normal tolerance limit of prey species then the equilibrium density of prey population decreases due to increase in capture rate and decrease in handling time by predator. Further, we have shown that as the growth rate of prey population decreases due to lowering of pH then the density of predator population also decreases and both the populations may tend to extinction if growth rate of prey population becomes negative due to lowering of pH on account of elevated carbondioxide concentration in the aquatic body. Moreover, it is noticed from the simulation that if the mortality of predator population increases because of decrease in pH level then the prey population gets advantage and in-turn their population increases.

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Modeling the variability, trends and future changes in ocean acidification in the Humboldt Current System

The largest buffer against climate change is the oceanic sink of anthropogenic CO2. However, this important ecosystem service to humanity leads to the reduction of pH and the saturation state of the biologically relevant calcium carbonate minerals aragonite and calcite  (Ωarag and Ωcalc). This process, known as anthropogenic ocean acidification, is a major marine ecosystem stressor and has negative impacts that range from reduced calcification to changes in population dynamics of important fisheries. Some of the most productive regions of the world, the Eastern Boundary Upwelling Systems (EBUS), are also among the most vulnerable to become undersaturated in the next decades due to the natural occurrence of low pH and Ω values at shallow depths and the projected further uptake of anthropogenic CO2. While extensive research on ocean acidification has been conducted in the California Current upwelling System, little is known about the dynamics of the marine carbonate chemistry in the much more productive Humboldt Current Upwelling System (HumCS), in the west coast of South America. To fill this gap, I used the high resolution Regional Ocean Modelling System (ROMS) and two different ecosystem models to study the progression of ocean acidification in the HumCS and the natural fluctuations superimposed to this anthropogenic perturbation. Results from a preindustrial simulation (year 1870) show that even then, pH and Ωarag values in the HumCS were respectively ⇠ 0.3 and 1 units lower than the preindustrial global average. The simulated evolution of ocean acidification to the end of the century showed that the continuous uptake of anthropogenic CO2 will push the nearshore off Peru to even lower values, from a present-day pH of 7.8 and Ωarag of 1.8 to year-round undersaturated conditions in year 2090 in at least 60 % of the top layer of the water column in the nearshore off Peru. Aragonite undersaturation in the following decades is already a committed change regardless of the amount of carbon emitted to the atmosphere in the future. However, a striking difference arises between following a “high CO2 emissions” scenario (RCP8.5, pCO2 values 840 μatm by year 2090) or a “low CO2 emissions” scenario (RCP2.6, pCO2 values of 428 μatm). In the former, water corrosive to calcite, a less soluble form of calcium carbonate than aragonite, will be found in the first 15 km off Peru and will potentially impact a larger range of calcifying organisms. On the other hand, this can be avoided the RCP2.6 scenario is followed, and strong CO2 mitigation measures are established and executed. In the high CO2 emissions scenario, an overall decrease of 0.9 ± 0.1 units in Ωarag from present day to the end of the century is projected in the nearshore off Peru, and a similar trend in the nearshore off Chile. On top of this long-term trend, natural climate variability off Peru can lead to strong year-to-year variations in the progression of ocean acidification. The largest contribution to Ωarag variability in the HumCS is on the interannual timescale, mainly forced by remotely forced tropical oscillations (e.g. El Ni˜no/Southern Oscillation) but also by local and regional phenomena (e.g., El Ni˜no costero). Analysis from a hindcast simulation for the period of 1979-2016 reveals that under present day conditions, the magnitude of such variability is comparable to the anthropogenic trend. Interannual changes in Ω are mainly driven by variations in the thermocline structure and wind patterns. Off Peru, the deepening of the thermocline associated with warm, El Ni˜no-like events, is translated into an increase in Ωarag in the surface layer of 0.4 units, while a shallower thermocline driven by cold interannual events (e.g., La Ni˜na) leads to a decrease in Ωarag values of 0.3 units. These natural interannual variations account for ⇠ 30 to and 40 % of the magnitude of the expected anthropogenic change, potentially bringing forward of delaying by some decades the pervasive appearance of aragonite undersaturated waters in the surface layer of the most productive EBUS of the Pacific: the Humboldt Current.

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Boric acid and borate incorporation in inorganic calcite inferred from B/Ca, boron isotopes and surface kinetic modeling

The boron concentration (B/Ca ratio) and isotopic composition (δ11B) of biogenic calcite are widely applied to reconstruct past changes in seawater carbonate chemistry. Knowledge of B incorporation pathways into calcite is critical for these applications and for improving the theoretical basis of B proxies. While the canonical interpretation of δ11B holds that B in calcite predominantly derives from dissolved borate anion in seawater, recent studies of the B content, coordination, and isotopic composition in calcite suggest more complex B incorporation pathways. To provide new insights into these pathways, here we present δ11B of inorganic calcite precipitated from saline solutions of varying pH, calcium and dissolved inorganic carbon (DIC) concentration for which B/Ca data were previously reported by Uchikawa et al. (2015). Results show that calcite δ11B significantly increases with increasing pH and decreases with increasing [Ca2+] and [DIC]. In combination, these experiments show that the difference in δ11B between solid calcite and aqueous borate linearly decreases with increasing calcite precipitation rate. To interpret these data, we present the first application of surface kinetic modeling (SKM) to boron incorporation. The SKM can simultaneously explain rate-dependent B/Ca and δ11B patterns observed in our and previously published inorganic calcite precipitation experiments when both aqueous borate and boric acid contribute to boron in inorganic calcite. If the B incorporation mechanism shown here for inorganic calcite is applicable to biogenic calcite, precipitation rate variations could modify δ11B patterns by changing the contributions of aqueous boric acid and borate to boron in calcite. However, better knowledge of biogenic calcite precipitation mechanisms and rates is needed to assess the importance of this effect for applications of B proxies in biogenic carbonates.

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Ocean acidification in the IPCC AR5 WG II

OUP book