Selected topics in arctic atmosphere and climate

This paper summarizes the main elements of four IPY projects that examine the Arctic Atmosphere. All four projects focus on present conditions with a view to anticipating possible climate change. All four investigate the Arctic atmosphere, ocean, ice, and land interfacial surfaces. One project uses computer models to simulate the dynamics of the Arctic atmosphere, storms, and their interactions with the ocean and ice interface. Another project uses statistical methods to infer transports of pollutants as simulated in large-scale global atmospheric and oceanic models verifying results with available observations. A third project focuses on measurements of pollutants at the ice-ocean?Catmosphere interface, with reference to model estimates. The fourth project is concerned with multiple, high accuracy measurements at Eureka in the Canadian Archipelago. While these projects are distinctly different, led by different teams and interdisciplinary collaborators, with different technical approaches and methodologies, and differing objectives, they all strive to understand the processes of the Arctic atmosphere and climate, and to lay the basis for projections of future changes. Key findings include: ? Decreased sea ice leads to more intense storms, higher winds, reduced surface albedo, increased surface air temperature, and enhanced vertical mixing in the upper ocean. ? Arctic warming may affect toxic chemicals by remobilizing persistent organic pollutants and augmenting mercury deposition/retention in the environment. ? Changes in sea ice can dramatically change processes in and at the ice surface related to ozone, mercury and bromine oxide and related chemical/physical properties. ? Structure and properties of the Arctic atmospheric??troposphere to stratosphere??and tracking of transport of pollution and smoke plumes from mid-latitudes to the poles.     

Oxygen isotopic composition and U-Pb discordance in zircon

We have investigated U-Pb discordance and oxygen isotopic composition of zircon using high-spatial resolution δ¹⁸O measurement by ion microprobe. δ¹⁸O in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance. Our results suggest that three characteristics of zircon are interrelated: (1) U-Pb systematics and concomitant age discordance, (2) δ¹⁸O and the water-rock interactions implied therein, and (3) zircon texture, as revealed by cathodoluminescence and BSE imaging. A key observation is that U-Pb-disturbed zircons are often also variably depleted in ¹⁸O, but the relationship between discordance and δ¹⁸O is not systematic. δ¹⁸O values of discordant zircons are generally lighter but irregular in their distribution. Textural differences between zircon grains can be correlated with both U-Pb discordance and δ¹⁸O. Discordant grains exhibit either a recrystallized, fractured, or strongly zoned CL texture, and are characteristic of ¹⁸O depletion. We interpret this to be a result of metamictization, leading to destruction of the zircon lattice and an increased susceptibility to lead loss. Conversely, grains that are concordant have less-expressed zoning and a smoother CL texture and are enriched in ¹⁸O. From this it is apparent that various stages of water-rock interaction, as evidenced by systematic variations in δ¹⁸O, leave their imprint on both the texture and U-Pb systematics of zircon.     

Environmental co-operation in the Baltic Sea region: A Lithuanian perspective

International co-operation is vital if the ecological crisis in the Baltic Sea is to be reversed. Organisations such as the Baltic Co-operation Council and HELCOM and agreements such as the Helsinki Convention, the Baltic Sea Declaration, and the Gdansk Convention, already exist to facilitate co-operation. Successful implementation of these conventions requires commitment at the national level. Lithuania's commitment is hampered by internal economic, and political problems which must be surmounted if the country is to reduce its impact on the Baltic Sea.Part of the following article is published in Baltic Studies in Australia II: AABS; Melbourne, 1993 — the proceedings from the 7th bi-annual Conference of the Association for the Advancement of Baltic Studies (Australasian Section) held in Melbourne, September, 1993.     

Responses of Native and Invasive Floating Aquatic Plant Communities to Salinity and Desiccation Stress in the Southeastern US Coastal Floodplain Forests

Low-lying coastal ecosystems along the northern Gulf of Mexico are already experiencing the effects of elevated salinity from sea-level rise and are predicted to face extreme events such as extended saltwater inundation, intense Atlantic hurricanes, and episodic drought. The ability of coastal plant communities to survive stresses from these events depends largely on how these communities respond to the stresses. Our understanding of how plant communities dominated by native vs. invasive plants respond to extreme events is limited. Utilizing controlled greenhouse experiments, we assessed the responses of floating aquatic macrophyte communities, dominated by native or invasive plants, of the coastal floodplains, Louisiana, USA, to a gradient of chronic salinity, mimicking sea-level rise; a gradient of acute salinity, mimicking hurricane storm surges; and a gradient of desiccation stress, mimicking episodic drought. We found that salinity and desiccation stress effects on plant communities depended on the degree of plant invasion; plant community cover decreased precipitously as severity of stress increased. Specifically, extreme salinity led to a decrease in plant cover of >?90% when communities were dominated by invasive plants, whereas increased desiccation stress led to decreased plant cover of 100% when communities were dominated by native species. At low to moderate salinity, invasive dominated plant communities performed better than native dominated. These responses to salinity and desiccation stress may drive large-scale shifts in plant community structure, including loss of species. Our results underscore the importance of evaluating plant community responses to environmental extremes to determine the potential for future effects on dynamics and functioning of low-lying coastal floodplain ecosystems experiencing effects of climate change.     

The eccentricities of the barium stars

We investigate the eccentricities of barium (Ba  ii ) stars formed via a stellar wind accretion model. We carry out a series of Monte Carlo simulations using a rapid binary evolution algorithm, which incorporates full tidal evolution, mass loss and accretion, and nucleosynthesis and dredge-up on the thermally pulsing asymptotic giant branch. We follow the enhancement of barium in the envelope of the accreting main-sequence companion and dilution into its convective envelope once the star ascends the giant branch.
The observed eccentricities of Ba  ii stars are significantly smaller than those of an equivalent set of normal red giants but are nevertheless non-zero. We show that such a distribution of eccentricities is consistent with a wind accretion model for Ba  ii star production with weak viscous tidal dissipation in the convective envelopes of giant stars. We successfully model the distribution of orbital periods and the number of observed Ba  ii stars. The actual distribution of eccentricities is quite sensitive to the strength of the tides, so that we are able to confirm that this strength is close to, but less than, what is expected theoretically and found with alternative observational tests. Two systems – one very short-period but eccentric, and one long-period and highly eccentric – still lie outside the envelope of our models, and so require a more exotic formation mechanism. All our models, even those which were a good fit to the observed distributions, overproduced the number of high-period barium stars, a problem that could not be solved by some combination of the three parameters: tidal strength, tidal enhancement and wind accretion efficiency.     

Very short-term spatio-temporal wind power prediction using a censored Gaussian field

Wind power is a renewable energy resource, that has relatively cheap installation costs and it is highly possible that will become the main energy resource in the near future. Wind power needs to be integrated efficiently into electricity grids, and to optimize the power dispatch, techniques to predict the level of wind power and the associated variability are critical. Ideally, one would like to obtain reliable probability density forecasts for the wind power distributions. We aim at contributing to the literature of wind power prediction by developing and analysing a spatio-temporal methodology for wind power production, that is tested on wind power data from Denmark. We use anisotropic spatio-temporal correlation models to account for the propagation of weather fronts, and a transformed latent Gaussian field model to accommodate the probability masses that occur in wind power distribution due to chains of zeros. We apply the model to generate multi-step ahead probability predictions for wind power generated at both locations where wind farms already exist but also to nearby locations.     

Evaluation of hydrologic impact of an irrigation curtailment program using Landsat satellite data

Upper Klamath Lake (UKL) is the source of the Klamath River that flows through southern Oregon and northern California. The UKL Basin provides water for 81,000+ ha (200,000+ acres) of irrigation on the U.S. Bureau of Reclamation Klamath Project located downstream of the UKL Basin. Irrigated agriculture also occurs along the tributaries to UKL. During 2013–2016, water rights calls resulted in various levels of curtailment of irrigation diversions from the tributaries to UKL. However, information on the extent of curtailment, how much irrigation water was saved, and its impact on the UKL is unknown. In this study, we combined Landsat-based actual evapotranspiration (ETa) data obtained from the Operational Simplified Surface Energy Balance model with gridded precipitation and U.S. Geological Survey station discharge data to evaluate the hydrologic impact of the curtailment program. Analysis was performed for 2004, 2006, 2008–2010 (base years), and 2013–2016 (target years) over irrigated areas above UKL. Our results indicate that the savings from the curtailment program over the June to September time period were highest during 2013 and declined in each of the following years. The total on-field water savings was approximately 60 hm³ in 2013 and 2014, 44 hm³ in 2015, and 32 hm³ in 2016 (1 hm3 = 10,000 m³ or 810.7 ac-ft). The instream water flow changes or extra water available were 92, 68, 45, and 26 hm³, respectively, for 2013, 2014, 2015, and 2016. Highest water savings came from pasture and wetlands. Alfalfa showed the most decline in water use among grain crops. The resulting extra water available from the curtailment contributed to a maximum of 19% of the lake inflows and 50% of the lake volume. The Landsat-based ETa and other remote sensing datasets used in this study can be used to monitor crop water use at the irrigation district scale and to quantify water savings as a result of land-water management changes.     

Multi‐scale classification of fluvial architecture: An example from the Palaeocene–Eocene Bighorn Basin,Wyoming

Fluvial channel geometry classification schemes are commonly restricted in relation to the scale at which the study took place, often due to outcrop limitations or the need to conduct small‐scale detailed studies. A number of classification schemes are present in the literature; however, there is often limited consistency between them, making application difficult. The aim of this study is to address this key problem by describing channel body geometries across a depositional basin to ensure that a wide range of architectures are documented. This was achieved by studying 28 locations over 4000 m of vertical succession in Palaeocene‐aged and Early Eocene‐aged deposits within the Bighorn Basin, Wyoming, USA. Five different channel body geometries have been defined based on the external geometric form, and internal arrangement and nature of storey contacts. These include the massive channel body geometry, semi‐amalgamated channel body geometry, internally amalgamated channel body geometry and offset stacked channel body geometry, which are considered to be subdivisions of the sheet geometry of many other classifications. An isolated channel body geometry has also been recognized alongside splay channel and sheet sandstone geometries in the floodplain facies associations. Field evidence, including the stacking style of storey surfaces, suggests that the different geometries form a continuum. The nature and degree of amalgamation at the storey scale are important in producing the different geometries and are related to the degree of channel migration. It is speculated that this is the result of differences in sediment supply and available accommodation. In contrast to previous schemes, the classification scheme presented here recognizes the importance of transitional geometries. This geometrical range has been recognized because of the basin‐scale nature of the study.