Posts Tagged 'regionalmodeling'

Climate change impacts on natural sulfur production: ocean acidification and community shifts

Utilizing the reduced-complexity model Hector, a regional scale analysis was conducted quantifying the possible effects climate change may have on dimethyl sulfide (DMS) emissions within the oceans. The investigation began with a review of the sulfur cycle in modern Earth system models. We then expanded the biogeochemical representation within Hector to include a natural ocean component while accounting for acidification and planktonic community shifts. The report presents results from both a latitudinal and a global perspective. This new approach highlights disparate outcomes which have been inadequately characterized via planetary averages in past publications. Our findings suggest that natural sulfur emissions (ESN) may exert a forcing up to 4 times that of the CO2 marine feedback, 0.62 and 0.15 Wm−2, respectively, and reverse the radiative forcing sign in low latitudes. Additionally, sensitivity tests were conducted to demonstrate the need for further examination of the DMS loop. Ultimately, the present work attempts to include dynamic ESN within reduced-complexity simulations of the sulfur cycle, illustrating its impact on the global radiative budget.

Continue reading ‘Climate change impacts on natural sulfur production: ocean acidification and community shifts’

Rapid changes in anthropogenic carbon storage and ocean acidification in the intermediate layers of the Eurasian Arctic Ocean: 1996‐2015

The extended multiple linear regression (eMLR) technique is used to determine changes in anthropogenic carbon in the intermediate layers of the Eurasian Basin based on occupations from four cruises between 1996 and 2015. The results show a significant increase in basin‐wide anthropogenic carbon storage in the Nansen Basin (0.44‐0.73 ± 0.14 mol C m−2 yr−1) and the Amundsen Basin (0.63‐1.04 ± 0.09 mol C m−2 yr−1). Over the last two decades, inferred changes in ocean acidification (0.020‐0.055 pH units) and calcium carbonate desaturation (0.05‐0.18 units) are pronounced and rapid. These results, together with results from carbonate‐dynamic box model simulations and 129I tracer distribution simulations, suggest that the accumulation of anthropogenic carbon in the intermediate layers of the Eurasian Basin are consistent with increasing concentrations of anthropogenic carbon in source waters of Atlantic origin entering the Arctic Ocean followed by interior transport. The dissimilar distributions of anthropogenic carbon in the interior Nansen and Amundsen Basins are likely due to differences in the lateral ventilation of the intermediate layers by the return flows and ramifications of the boundary current along the topographic boundaries in the Eurasian Basin.

Continue reading ‘Rapid changes in anthropogenic carbon storage and ocean acidification in the intermediate layers of the Eurasian Arctic Ocean: 1996‐2015’

Treated wastewater changes the export of dissolved inorganic carbon and its isotopic composition and leads to acidification in coastal oceans

Human-induced changes to carbon fluxes across the land-ocean interface can influence the global carbon cycle, yet the impacts of rapid urbanization and establishment of wastewater treatment plants (WWTPs) on coastal ocean carbon cycles are poorly known. This is unacceptable as at present ~64% of global municipal wastewater is treated before discharge. Here, we report surface water dissolved inorganic carbon (DIC) and sedimentary organic carbon concentrations and their isotopic compositions in the rapidly urbanized Jiaozhou Bay in northeast China as well as carbonate parameters in effluents of three large WWTPs around the bay. Using DIC, δ13CDIC and total alkalinity (TA) data and a tracer model, we determine the contributions to DIC from wastewater DIC input, net community production, calcium carbonate precipitation and CO2 outgassing. Our study shows that high-DIC and low-pH wastewater effluent represents an important source of DIC and acidification in coastal waters. In contrast to the traditional view of anthropogenic organic carbon export and degradation, we suggest that with the increase of wastewater discharge and treatment rates, wastewater DIC input may play an increasingly more important role in the coastal ocean carbon cycle.

Continue reading ‘Treated wastewater changes the export of dissolved inorganic carbon and its isotopic composition and leads to acidification in coastal oceans’

The spatial and temporal variability of air-sea CO2 fluxes and the effect of net coral reef calcification in the Indonesian Seas: a numerical sensitivity study

A numerical model system was developed and applied to simulate air-sea fluxes of CO2 and coral reef calcification in the Indonesian Seas and adjacent ocean basin for the period 1960–2014 on a fine resolution grid (ca. 11 km) in order to study their response to rising sea water temperatures and CO2 concentrations in the atmosphere. Results were analyzed for different sub-regions on the Sunda Shelf (Gulf of Thailand, Malacca Strait, Java Sea) and show realistic and different levels, signs and pronounced temporal variability in air-sea CO2 flux. The Gulf of Thailand changes from an atmospheric CO2 sink during the boreal winter to a CO2 source in summer due to higher water temperatures, while other sub-regions as well as the entire averaged Sunda Shelf act as a continuous source of CO2 for the atmosphere. However, increasing atmospheric CO2 concentrations weakened this source function during the simulation period. In 2007, the model simulations showed even a first flux inversion, in course of which the Java Sea took up CO2. The simulated trends suggest that the entire Sunda Shelf will turn into a permanent sink for atmospheric CO2 within the next 30–35 years if current trends remain constant. Considering the period between 2010 and 2014, coral reef calcification enhanced the average CO2 emission of the Sunda Shelf by more than 10% from 15 to 17 Tg C yr−1 due to lowering the pH and increasing the partial pressure of CO2 in surface water. During the entire period of simulation, net reef calcification decreased although increasing seawater temperature mitigated effects of reduced CO2 emission and the resulting decrease of the pH values on reef calcification. Our realistic simulation results already without consideration of any biological processes suggest that biological processes taking up and releasing CO2 are currently well balanced in these tropical regions. However, the counteracting effects of climate change on the reef calcification, on other biological processes and the carbonate system need to be investigated in more detail. SST increased by about 0.6°C during the last 55 years, while SSS decreased by about 0.7 psu.

Continue reading ‘The spatial and temporal variability of air-sea CO2 fluxes and the effect of net coral reef calcification in the Indonesian Seas: a numerical sensitivity study’

An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result

The amount of carbon dioxide (CO2) in the atmosphere has increased in the past 60 years and the technology of carbon capture and storage (CCS) has recently been extensively studied. One of the strategies of CCS is to directly inject a high dissolved inorganic carbon (DIC) concentration (or high partial pressure of carbon dioxide, pCO2) solution into the ocean. However, the carbonate dynamics and air-sea gas exchange are usually neglected in a CCS strategy. This study assesses the effect of a DIC-solution injection by using a simple two end-member model to simulate the variation of pH, DIC, total alkalinity (TA) and pCO2 between the river and sea mixing process for the Danshuei River estuary and Hoping River in Taiwan. We observed that the DIC-solution injection can contribute to ocean acidification and can also lead the pCO2 value to change from being undersaturated to oversaturated (with respect to the atmospheric CO2 level). Our model result also showed that the maximum Revelle factors (Δ[CO2]/[CO2])/(Δ[DIC]/[DIC]) among varied pH values (6–9) and DIC concentrations (0.5–3.5 mmol kg−1) were between pH 8.3 and 8.5 in fresh water and were between 7.3 and 7.5 in waters with a salinity of 35, reflecting the changing efficiency of dissolving CO2 gas into the DIC solution and the varying stability of this desired DIC solution. Finally, we suggest this uncoupled Revelle factor between fresh and salty water should be considered in the (anthropogenic) carbonate chemical weathering on a decade to century scale.

Continue reading ‘An assessment of direct dissolved inorganic carbon injection to the coastal region: a model result’

Reconstructing aragonite saturation state based on an empirical relationship for Northern California

Ocean acidification is a global phenomenon with highly regional spatial and temporal patterns. In order to address the challenges of future ocean acidification at a regional scale, it is necessary to increase the resolution of spatial and temporal monitoring of the inorganic carbon system beyond what is currently available. One approach is to develop empirical regional models that enable aragonite saturation state to be estimated from existing hydrographic measurements, for which greater spatial coverage and longer time series exist in addition to higher spatial and temporal resolution. We present such a relationship for aragonite saturation state for waters off Northern California based on in situ bottle sampling and instrumental measurements of temperature, salinity, and dissolved oxygen. Application of this relationship to existing datasets (5 to 200 m depth) demonstrates both seasonal and interannual variability in aragonite saturation state. We document a deeper aragonite saturation horizon and higher near surface aragonite saturation state in the summers of 2014 and 2015 (compared with 2010–2013), associated with anomalous warm conditions and decadal scale oscillations. Application of this model to time series data reiterates the direct association between low aragonite saturation state and upwelled waters and highlights the extent to which benthic communities on the Northern California shelf are already exposed to aragonite undersaturated waters.

Continue reading ‘Reconstructing aragonite saturation state based on an empirical relationship for Northern California’

Invariance of the carbonate chemistry of the South China Sea from the glacial period to the Holocene and its implications to the Pacific Ocean carbonate system

Highlights

  • The SCS carbonate chemistry didn’t change over the last glacial–interglacial cycle.
  • The SCS is not ocean dominated, or.
  • The Pacific carbonate chemistry did not change during the last GIT.
  • SCS CaCO3 content variations can be explained by altered lithogenic input.

Abstract

Substantial and correlated changes in marine carbonate (CaCO3) content of oceanic sediments commonly accompany the transitions from cold glacial periods to warm interglacial periods. The South China Sea (SCS) is said to be ocean-dominated at depth, and its CaCO3 records should reflect and preserve the effects of changes in the carbonate chemistry of the (western) Pacific Ocean. Using published and newly acquired CaCO3 data and a model for carbonate compensation dynamics, we show that a significant change with respect to carbonate saturation is unlikely to have occurred in the SCS during the last glacial–interglacial transition. Instead, the results from a carbonate deposition model argue that the saturation state of the SCS was largely invariant; a separate diagenetic model argues that changes in sediment CaCO3 content can be explained by alterations in lithogenic input. In turn, this could indicate that the carbonate ion concentration of the (western) Pacific at depths shallower than the sill to the SCS (ca. 2,400 m) has not changed appreciably between the last glacial period and the present interglacial.

Continue reading ‘Invariance of the carbonate chemistry of the South China Sea from the glacial period to the Holocene and its implications to the Pacific Ocean carbonate system’


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Ocean acidification in the IPCC AR5 WG II

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