Late Glacial to Holocene relative sea-level change in Assynt, northwest Scotland, UK

Relative sea-level change (RSL), from the Late Glacial through to the late Holocene, is reconstructed for the Assynt region, northwest Scotland, based on bio- and lithostratigraphical analysis. Four new radiocarbon-dated sea-level index points help constrain RSL change for the Late Glacial to the late Holocene. These new data, in addition to published material, capture the RSL fall during the Late Glacial and the rise and fall associated with the mid-Holocene highstand. Two of these index points constrain the Late Glacial RSL history in Assynt for the first time, reconstructing RSL falling from 2.47 ± 0.59 m OD to 0.15 ± 0.59 m OD at c. 14,000–15,000 cal yr BP. These new data test model predictions of glacial isostatic adjustment (GIA), particularly during the early deglacial period which is currently poorly constrained throughout the British Isles. Whilst the empirical data from the mid- to late-Holocene to present matches quite well with the recent GIA model output, there is a relatively poor fit between the timing of the Late Glacial RSL fall and early Holocene RSL rise. This mismatch, also evident elsewhere in northwest Scotland, may result from uncertainties associated with both the global and local ice components of GIA models.</jats:p

Fish Distributions and Nutrient Cycling in Streams: Can Fish Create Biogeochemical Hotspots?

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6–176 molar). At the reach scale, fish excretion could meet \u3e75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool i

Fish Distributions And Nutrient Cycling In Streams: Can Fish Create Biogeochemical Hotspots

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117137/1/ecy20088982335.pd

Upwelling couples chemical and biological dynamics across the littoral and pelagic zones of Lake Tanganyika, East Africa

We studied the effects of upwelling on nutrient and phytoplankton dynamics in the pelagic and littoral zones of Lake Tanganyika near Kigoma, Tanzania. During the dry season of 2004, a rise in the thermocline and sudden drop in surface water temperatures indicated a substantial upwelling event. Increases in concentrations of nitrate, soluble reactive phosphorus, and silica in the surface waters occurred simultaneously after the temperature drop. Within days, chlorophyll a concentrations increased and remained elevated, while inorganic nutrient concentrations returned to preupwelling levels and organic nutrient concentrations peaked. We observed parallel temporal patterns of water temperature, nutrient concentrations, and phytoplankton chlorophyll in both the pelagic and the littoral zones, demonstrating that upwelling strongly affects the nearshore ecosystem as well as the pelagic zone. Concurrent records from 12 littoral sites indicated spatial variation in the timing, magnitude, and biological response to upwelling. There was no discernable latitudinal pattern in the timing of upwelling, suggesting that mixing did not result from a progressive wave. Our monitoring, as well as other multiyear studies, suggests that dry-season upwelling occurs during most years in northern Lake Tanganyika. The observed sensitivity of littoral nutrients and phytoplankton to upwelling suggests that reductions in upwelling due to global climate change could strongly affect the dynamics of the spectacular nearshore ecosystem of Lake Tanganyika, as has been proposed for the pelagic zone

Reducing adverse impacts of Amazon hydropower expansion

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth\u27s largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins

Ипотека морского судна в контексте восстановление отечественного торгового флота в Украине

Торговельне мореплавство – одна з тих галузей світової економіки, яка має найбільш швидкий розвиток у наш час. Перш за все, це пов’язано із прискоренням міжнародного товарообміну. Наростання обсягів міжнародної торгівлі, у якій прагне приймати участь також Україна, обумовлює необхідність адекватно швидкого зростання її транспортної галузі. Попри значний транспортний потенціал, що має Україна, багато в чому завдячуючи її географічному положенню, стан вітчизняного транспортного комплексу й, особливо, його морської ланки, потребує покращення. Це, в свою чергу, безпосередньо залежить від правового регулювання, що впорядковує такі процеси

Orbital control on late Miocene climate and the North African monsoon: insight from an ensemble of sub-precessional simulations

Orbital forcing is a key climate driver over multi-millennial timescales. In particular, monsoon systems are thought to be driven by orbital cyclicity, especially by precession. Here, we analyse the impact of orbital forcing on global climate with a particular focus on the North African monsoon, by carrying out an ensemble of 22 equally spaced (one every 1000 years) atmosphere–ocean–vegetation simulations using the HadCM3L model, covering one full late Miocene precession-driven insolation cycle with varying obliquity (between 6.568 and 6.589 Ma). The simulations only differ in their prescribed orbital parameters, which vary realistically for the selected time period. We have also carried out two modern-orbit control experiments, one with late Miocene and one with present-day palaeogeography, and two additional sensitivity experiments for the orbital extremes with varying CO2 forcing. Our results highlight the high sensitivity of the North African summer monsoon to orbital forcing, with strongly intensified precipitation during the precession minimum, leading to a northward penetration of vegetation up to ~ 21° N. The modelled summer monsoon is also moderately sensitive to palaeogeography changes, but it has a low sensitivity to atmospheric CO2 concentration between 280 and 400 ppm. Our simulations allow us to explore the climatic response to orbital forcing not only for the precession extremes but also on sub-precessional timescales. We demonstrate the importance of including orbital variability in model–data comparison studies, because doing so partially reduces the mismatch between the late Miocene terrestrial proxy record and model results. Failure to include orbital variability could also lead to significant miscorrelations in temperature-based proxy reconstructions for this time period, because of the asynchronicity between maximum (minimum) surface air temperatures and minimum (maximum) precession in several areas around the globe. This is of particular relevance for the North African regions, which have previously been identified as optimal areas to target for late Miocene palaeodata acquisition