Posts Tagged 'regionalmodeling'

Development of a biogeochemical and carbon model related to ocean acidification indices with an operational ocean model product in the North Western Pacific

We developed a biogeochemical and carbon model (JCOPE_EC) coupled with an operational ocean model for the North Western Pacific. JCOPE_EC represents ocean acidification indices on the background of the risks due to ocean acidification and our model experiences. It is an off-line tracer model driven by a high-resolution regional ocean general circulation model (JCOPE2M). The results showed that the model adequately reproduced the general patterns in the observed data, including the seasonal variability of chlorophyll-a, dissolved inorganic nitrogen/phosphorus, dissolved inorganic carbon, and total alkalinity. We provide an overview of this system and the results of the model validation based on the available observed data. Sensitivity analysis using fixed values for temperature, salinity, dissolved inorganic carbon and total alkalinity helped us identify which variables contributed most to seasonal variations in the ocean acidification indices, pH and Ωarg. The seasonal variation in the pHinsitu was governed mainly by balances of the change in temperature and dissolved inorganic carbon. The seasonal increase in Ωarg from winter to summer was governed mainly by dissolved inorganic carbon levels.

Continue reading ‘Development of a biogeochemical and carbon model related to ocean acidification indices with an operational ocean model product in the North Western Pacific’

Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform

The marine carbonate system is a critical component of global biogeochemical cycles. It determines a given marine region’s status as a source or sink for atmospheric CO2, and long-term changes (i.e. ocean acidification) that can affect key ecosystem functions. Carbonate system processes are highly-variable through space and time, which makes it difficult to fully characterize a region without either intensive sampling, or long-term deployment of high-precision instruments. Both of these are difficult in the Arctic, where challenging logistics limit sampling opportunities, and instruments must endure extreme conditions. In this work, we present the first high-resolution marine carbon system dataset covering a full Arctic cycle of sea ice growth and melt. We deployed a Satlantic SeaFET Ocean pH Sensor and a Pro-Oceanus CO2-Pro CV sensor for consecutive nearly year-long deployments onboard the Cambridge Bay Ocean Networks Canada Undersea Community Observatory from September 2015 – June 2018. The sensors measurements were compared to discrete sample references, and determined to require multipoint in situ calibration, but were representative of the greater sea surface mixed layer inside the bay through most of the year. Using a diagnostic box model approach, seasonal influencing processes on the marine carbon system at the platform were quantitatively determined. Air-sea gas exchange and biologic respiration/ remineralization were dominant in the fall, whereas following sea ice freeze-up brine rejection drove pCO2 to seasonal supersaturation with respect to the atmosphere, and the aragonite saturation state to become undersaturated. Shortly after the sun rose under the ice in the late winter, the ecosystem at the platform became net autotrophic at very low light levels, driving pCO2 to undersaturation. As sea ice melted, an under-ice phytoplankton bloom drew down a significant amount of carbon before the open water season, returning the aragonite saturation state to supersaturation at the platform. These observations show a dynamic system, where biological processes occur at times and rates previously unknown to the literature. These processes will need to be included in future biogeochemical modelling efforts, if we are to properly resolve the current, and future, role of the Arctic Ocean basin in global biogeochemical cycles.

Continue reading ‘Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform’

Identifying important species that amplify or mitigate the interactive effects of human impacts on marine food webs

Some species may have a larger role than others in the transfer of complex effects of multiple human stressors, such as changes in biomass, through marine food webs. We devised a novel approach to identify such species. We constructed annual interaction‐effect networks (IENs) of the simulated changes in biomass between species of the southeastern Australian marine system. Each annual IEN was composed of the species linked by either an additive (sum of the individual stressor response), synergistic (lower biomass compared with additive effects), or antagonistic (greater biomass compared with additive effects) response to the interaction effect of ocean warming, ocean acidification, and fisheries. Structurally, over the simulation period, the number of species and links in the synergistic IENs increased and the network structure became more stable. The stability of the antagonistic IENs decreased and became more vulnerable to the loss of species. In contrast, there was no change in the structural attributes of species linked by an additive response. Using indices common in food‐web and network theory, we identified the species in each IEN for which a change in biomass from stressor effects would disproportionately affect the biomass of other species via direct and indirect local, intermediate, and global predator–prey feeding interactions. Knowing the species that transfer the most synergistic or antagonistic responses in a food‐web may inform conservation under increasing multiple‐stressor impacts.

Continue reading ‘Identifying important species that amplify or mitigate the interactive effects of human impacts on marine food webs’

Riverine calcium end-members improve coastal saturation state calculations and reveal regionally variable calcification potential

Carbonate-rich groundwater discharged from springs, seeps, and spring-fed rivers on carbonate platforms creates environments of potential refuge for calcifying organisms in coastal waters by supplying higher [Ca2+] and [CO32-] along with typically lower nutrient concentrations. The benefits associated with carbonate terrains are maximized in the presence of submerged aquatic vegetation (SAV), especially seagrasses. To improve the accuracy of carbonate saturation state (Ω) determinations, calculated values of [CO32-] and Ksp∗ were paired with [Ca2+] values determined using a model that incorporates directly measured riverine calcium end-members (model A). This model results in Ω values larger than those calculated by assuming that [Ca2+] is directly proportional to salinity (model B; e.g., using CO2SYS, CO2calc). As an example, for salinity (S) between 13.5 and 24, improvements in saturation states calculated as differences (ΔΩ) between model A and model B saturation states in the tidal mixing zone of the Weeki Wachee River (Florida, United States) ranged from 0.39 to 1.00 (aragonite) and 0.61–1.65 (calcite). Saturation state ratios (Ω(A)/Ω(B)) for coastal waters with enhanced [Ca2+] originating from carbonate-rich groundwater can be calculated from end-member calcium concentrations and salinity. Applied to several river systems in the conterminous United States, Ω(A)/Ω(B) values calculated at S = 20 lead to Ω(A)/Ω(B) ratios of 1.12 (Weeki Wachee), 1.09 (Anclote), 1.06 (Mississippi), and 1.03 (Columbia). These increases in saturation states can be used to identify potential calcification refugia for subsequent high resolution field studies that focus on, for example, the long-term viability of oyster communities and other calcifying organisms in brackish coastal waters.

Continue reading ‘Riverine calcium end-members improve coastal saturation state calculations and reveal regionally variable calcification potential’

Quasi‐real‐time and high‐resolution spatiotemporal distribution of ocean anthropogenic CO2

Increasing marine uptake of anthropogenic CO2 (Cant) causes global ocean acidification. To obtain a high‐resolution spatiotemporal distribution of oceanic carbon chemistry, we developed new parameterizations of the seawater total alkalinity (TA), and dissolved inorganic carbon (DIC) from the ocean’s surface to 2000 m depth by using dissolved oxygen (DO), water temperature (T), salinity (S), and pressure (P) data. Using the values of TA and DIC predicted by DO, T, S, and P data derived from autonomous biogeochemical Argo floats (BGC‐Argo), we described the distribution of oceanic Cant in the 2000s in the subarctic North Pacific at high spatiotemporal resolution. The Cant was found about 300 m deeper than during the 1990s; its average inventory to 2000 m was 24.8 ± 10.2 mol m–2, about 20% higher than the 1990s average. Future application of parameterizations to global BGC‐Argo data should allow the detailed global mapping of spatiotemporal distributions of CO2 parameters.

Continue reading ‘Quasi‐real‐time and high‐resolution spatiotemporal distribution of ocean anthropogenic CO2’

Decadal-scale acidification trends in adjacent North Carolina estuaries: competing role of anthropogenic CO2 and riverine alkalinity loads

Decadal-scale pH trends for the open ocean are largely monotonic and controlled by anthropogenic CO2 invasion. In estuaries, though, such long-term pH trends are often obscured by a variety of other factors, including changes in net metabolism, temperature, estuarine mixing, and riverine hydrogeochemistry. In this study, we mine an extensive biogeochemical database in two North Carolina estuaries, the Neuse River estuary (NeuseRE) and New River estuary (NewRE), in an effort to deconvolute decadal-scale trends in pH and associated processes. By applying a Generalized Additive Mixed Model (GAMM), we show that temporal changes in NewRE pH were insignificant, while pH decreased significantly throughout much of the NeuseRE. In both estuaries, variations in pH were accompanied by increasing river discharge, and were independent of rising temperature. Decreases in bottom-water pH in the NeuseRE coincided with elevated primary production in surface waters, highlighting the importance of eutrophication on long-term acidification trends. Next, we used a simple mixing model to illustrate the impact of changing river discharge on estuarine carbonate chemistry. We found that increased riverine alkalinity loads to the NewRE likely buffered the impact of CO2-intrusion-induced acidification. In the NeuseRE, however, elevated dissolved inorganic carbon loads further decreased the buffering capacity, exacerbating the effects of CO2-intrusion-driven acidification. Taken together, the findings of this study show that future trajectories in estuarine pH will be shaped by complex interactions among global-scale changes in climate, regional-scale changes in precipitation patterns, and local-scale changes in estuarine biogeochemistry.

Continue reading ‘Decadal-scale acidification trends in adjacent North Carolina estuaries: competing role of anthropogenic CO2 and riverine alkalinity loads’

Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean

Models project that with current CO2 emission rates, the Southern Ocean surface will be undersaturated with respect to aragonite by the end of this century1,2,3,4. This will result in widespread impacts on biogeochemistry and ocean ecosystems5,6,7, particularly the health of aragonitic organisms, such as pteropods7, which can dominate polar surface water communities6. Here, we quantify the depth of the present-day Southern Ocean aragonite saturation horizon using hydrographic and ocean carbon chemistry observations, and use a large ensemble of simulations from the Community Earth System Model (CESM)8,9 to track its evolution. A new, shallow aragonite saturation horizon emerges in many Southern Ocean locations between now and the end of the century. While all ensemble members capture the emergence, internal climate variability may affect the year of emergence; thus, its detection may have been overlooked by ensemble average analysis in the past. The emergence of the new horizon is driven by the slow accumulation of anthropogenic CO2 in the Southern Ocean thermocline, where the carbonate ion concentration exhibits a local minimum and approaches undersaturation. The new horizon is also apparent under an emission-stabilizing scenario indicating an inevitable, sudden decrease in the volume of suitable habitat for aragonitic organisms.

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Ocean acidification in the IPCC AR5 WG II

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