Modelling high-latitude explosive eruptions and their atmospheric and environmental impacts

<p>Large explosive volcanic eruptions inject sulphur into the stratosphere where it is converted to sulphur dioxide and sulphate aerosols. Due to atmospheric circulation patterns, aerosols from high-latitude eruptions typically remain concentrated in the hemisphere in which they are injected. Eruptions in the high-latitude Northern Hemisphere could thus lead to a stronger hemispheric radiative forcing and surface climate response than tropical eruptions, a claim that is supported by a previous study based on proxy records and the coupled aerosol-general circulation model MAECHAM5-HAM. Additionally, the subsequent surface deposition of volcanic sulphate is potentially harmful to humans and ecosystems, and an improved understanding of the deposition over polar ice sheets can contribute to better reconstructions of historical volcanic forcing. On this basis, we model Icelandic explosive eruptions in a pre-industrial atmosphere, taking both volcanic sulphur and halogen loading into account. We use the fully coupled Earth system model CESM2 with the atmospheric component WACCM6, which extends to the lower thermosphere and has prognostic stratospheric aerosols and full chemistry. In order to study the volcanic impacts on the atmosphere, environment, and sulphate deposition, we vary eruption parameters such as sulphur and halogen loading, and injection altitude and season. The modelled volcanic sulphate deposition is compared to the deposition in ice cores following comparable historical eruptions. Furthermore, we evaluate the potential environmental impacts of sulphate deposition. To study inter-model differences, we also compare the CESM2-WACCM6 simulations to similar Icelandic eruption experiments simulated with MAECHAM5-HAM. </p>

Forecast of the deposition of sulfate salts, taking into account the content of strontium, in the exploitation of oil deposits

Based on the experience of developing an oil fieled on the Caspian Sea shelf, which was initially operated with injection of seawater into oil-bearing seams to maintain reservoir pressure, a forecast was made for the deposition of sulfate salts in reservoir conditions. The forecast of sulphate deposition is carried out in two ways: analytical calculations by the method of J.E. Oddo and M.B. Thomson and computer modeling. The prognosis took into account the strontium content in the reservoir waters of the deposit, which is usually ignored in oilfield practice. It has been established that computer modeling gives a more accurate prediction, in particular, considerably expands the temperature limits of anhydrite precipitation. The determination of the amount of potentially sulphate salts potentially found in computer simulations has shown that the mass of deposited calcium and strontium sulfates is large enough that it can significantly reduce the permeability of the reservoir.

Aerosol flux measurements above a mixed forest at Borden, Ontario

Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. Chemically speciated flux measurements were made at a height of 29 m at the same location between 19 July and 2 August, 2006 using a Quadrupole Aerosol Mass Spectrometer (Q-AMS). The Q-AMS measured an average sulphate deposition velocity of 0.3 mm s−1 and an average nitrate deposition velocity of 4.8 mm s−1. The FMPS, mounted at a height of 33 m (approximately 10 m above the canopy top) and housed in a temperature controlled enclosure, measured size-resolved particle concentrations from 3 to 410 nm diameter at a rate of 1 Hz. For the size range 18 < D < 452 nm, 60 % of fluxes were upward. The exchange velocity was between −0.5 and 2.0 mm s−1, with median values near 0.5 mm s−1 for all sizes between 22 and 310 nm. The size distribution of the apparent production rate of particles at 33 m peaked at a diameter of 75 nm. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day.

Assessing pH changes since pre-industrial times in 51 low-alkalinity lakes in Nova Scotia, Canada

Diatom-based paleolimnological techniques were used to reconstruct lake acidification trends in 51 low-alkalinity Nova Scotia lakes that spanned gradients of dissolved organic carbon (DOC) concentrations and sulphate deposition. Pre-industrial, diatom-inferred pH values of these lakes were <6.8, with 31 lakes having pre-industrial pH < 6.0 and two lakes having pH < 5.5. Lakes in Kejimkujik National Park documented the greatest pH decline (–0.4 pH unit (±0.2)) since the 19th century, whereas those in northern parts of the province (e.g., Cape Breton Highlands National Park) experienced little or no acidification, with a net mean pH decline = –0.1 pH unit (±0.2). While the sulphate deposition and diatom-inferred pH changes have not been as great as those observed in other acidified areas of northeastern North America (e.g., Adirondack region of New York or New England), Nova Scotia lakes have experienced biological changes toward more acidophilous diatom assemblages, especially in lakes with low pre-industrial pH values (currently with high DOC concentrations) located in Kejimkujik National Park, which receives the highest loading of sulphate deposition in Nova Scotia. However, the generally low pre-industrial pH values inferred for most of the study lakes suggest that many of these lakes were somewhat naturally acidic, but acidified further as a result of atmospheric deposition.