How soil moisture mediates the influence of transpiration on streamflow at hourly to interannual scales in a forested catchment

The water balance equation dictates that streamflow may be reduced by transpiration. Yet temporal disequilibrium weakens the relationship between transpiration and streamflow in many cases where inputs and outputs are unbalanced. We address two critical knowledge barriers in ecohydrology with respect to time, scale dependence and lags. Study objectives were to correlate components of the water balance equation at hourly to annual scales, quantify time lags, and simplify critical components of the water budget during wet and dry conditions. We tested interrelationships among precipitation, vapour pressure deficit, transpiration, soil moisture, and streamflow within the confines of a 60‐hectare forested watershed in the western Cascades of Oregon. The Pacific Northwest is an ideal location to compare wet and dry seasons because of its Mediterranean climate. Soil moisture explained more than 80% of the variation in streamflow at all temporal scales investigated. Streamflow was most strongly coupled to soil moisture in the wet season because of gravitational drainage patterns; strong coupling of transpiration to vapour pressure deficit was dominant in the dry season and driven by low humidity. We observed progressively longer hourly time lags between soil moisture and streamflow in the dry season, which relates to an increasing soil moisture deficit that took an average of 48 days to refill after the onset of winter rains. We propose that transpiration drives seasonal patterns in soil moisture that relate to patterns in streamflow only after long time lags. In other words, soil moisture mediates the influence of transpiration on streamflow. Copyright © 2011 John Wiley & Sons, Ltd.     

River management response to multi-decade changes in timing of reservoir inflows,Columbia River Basin,USA

Around the world, long-term changes in the timing and magnitude of streamflow are testing the ability of large managed water resource systems constructed in the 20th century to continue to meet objectives in the 21st century. Streamflow records for unregulated rivers upstream of reservoirs can be combined with records downstream of reservoirs using a paired-watershed framework and concepts of water resource system performance to assess how reservoir management has responded to long-term change. Using publicly available data, this study quantified how the intra-annual timing of inflows and outflows of 25 major reservoirs has shifted, how management has responded, and how this has influenced reliability and vulnerability of the water resource system in the 668,000 km² Columbia River basin from 1950 to 2012. Reservoir inflows increased slightly in early spring and declined in late spring to early fall, but reservoir outflows increased in late summer from 1950 to 2012. Average inflows to reservoirs in the low flow period exceeded outflows in the1950s, but inflows are now less than outflows. Reservoirs have increased hedging, that is, they have stored more water during the spring, in order to meet the widening gap between inflows and outflows during the summer low flow period. For a given level of reliability (the fraction of time flow targets were met), vulnerability (the maximum departure from the flow target) was greater during periods with lower than average inflows. Thus, the water management system in this large river basin has adjusted to multi-decade trends of declining inflows, but vulnerability, that is, the potential for excess releases in spring and shortfalls in summer, has increased. This study demonstrates the value of combining publicly available historical data on streamflow with concepts from paired-watershed analyses and metrics of water resource performance to detect, evaluate, and manage water resource systems in large river basins.     

In situ cosmogenic exposure ages from the Isle of Skye,northwest Scotland: implications for the timing of deglaciation and readvance from 15 to 11 ka

We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Mesozoic origins and antecedents of Australia's Eastern Highlands

Australia's Eastern Highlands are a conspicuous manifestation of a tectonic regime that has been previously shown to go back at least 65 Ma. This review of the Mesozoic stratigraphy of eastern Australia gives evidence of a very different regime before 95 Ma, related to the presence of a plate boundary close to the present east coast of the continent.

During the prior regime, cratonic sedimentation in eastern Australia was dominated by labile sediment from an andesitic orogen coincident with the coast north of Brisbane during the Cretaceous, and further offshore in the Jurassic. Whereas the plate boundary north of Brisbane appears to have been simply convergent, that south to Bass Strait may have experienced prolonged oblique‐slip, manifested in the Jurassic by alkaline volcanism within the SE Highlands terrain.

Following a Cenomanian (95–90 Ma) phase of transition, during which the eastern Australian plate boundary may have resembled that margining western North America at present, the plate boundary migrated away from mainland Australia, as is evidenced by the subsequent dominance of quartzose sedimentation on the craton, and the fission‐track and palaeomagnetic evidence of rapidly falling geotherms in the Late Cretaceous. The Eastern Highlands were initiated around 90 Ma ago, and the crestline subsequently migrated west from an initial location at the present coastline.

The geography and history of the Eastern Highlands are inconsistent with concepts of continental margin development based on analogues outside the Pacific realm. The Highlands are an intrinsic element of a continent formerly fronting the Pacific Ocean, but now abutting a back‐arc basin.     

Timing,pace and controls on ice sheet retreat: an introduction to the BRITICE-CHRONO transect reconstructions of the British–Irish Ice Sheet

Motivated to help improve the robustness of predictions of sea level rise, the BRITICE-CHRONO project advanced knowledge of the former British–Irish Ice Sheet, from 31 to 15 ka, so that it can be used as a data-rich environment to improve ice sheet modelling. The project comprised over 40 palaeoglaciologists, covering expertise in terrestrial and marine geology and geomorphology, geochronometric dating and the modelling of ice sheets and oceans. A systematic and directed campaign, organised across eight transects from the continental shelf edge to a short distance (10s of kilometres) onshore, was used to collect 914 samples which yielded 639 new ages, tripling the number of dated sites constraining the timing and rates of change of the collapsing ice sheet. This special issue synthesises these findings of ice advancing to the maximum extent and its subsequent retreat for each of the eight transects to produce definitive palaeogeographic reconstructions of ice margin positions across the marine to terrestrial transition. These results are used to understand the controls that drove or modulated ice sheet retreat. A further paper reports on how ice sheet modelling experiments and empirical data can be used in combination, and another probes the glaciological meaning of ice-rafted debris.     

Timing and pace of ice-sheet withdrawal across the marine–terrestrial transition west of Ireland during the last glaciation

Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a⁻¹) and reduced (8 m a⁻¹) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets.     

Pliocene trace fossils from oyster substrates in the Nijar Basin,Betic Cordillera,southern Spain

The Almería-Níjar Basin is a Neogene, intermontane depression marginal to the Mediterranean in southern Spain in the vicinity of El Argamasón, Andalucia. The Pliocene Cuevas Formation rests unconformably on the Upper Messinian rock succession in the Carboneras Fault Zone. The Cuevas Formation is a coarse-grained, bioclastic-rich, calcarenite to calcirudite shoreface deposit. Oysters, namely Saccostrea cucullata (Born), are locally common and preserve a moderate diversity of borings: Caulostrepsis taeniola Clarke; Entobia isp.; Gastrochaenolites isp. aff. G. lapidicus Kelly and Bromley; Maeandropolydora isp. cf. M. sulcans Voigt; Oichnus paraboloides Bromley; and Talpina isp. aff. T. hirsuta Voigt. All represent domiciles except for the predatory O. paraboloides trace. This suite of ichnotaxa is assigned to the Entobia ichnofacies sensu Bromley and Asgaard; they are comparable, particularly, with the Boulder Assemblage of the Pliocene of Rhodes, Greece. Physical disturbance is an important parameter in favouring this pattern of infestation, whether the bored clasts are boulders or oyster valves.     

Various aspects of the petrogenesis of the Martian shergottite meteorites

Several controversies are associated with the age and origin of the shergottite meteorites, a suite of basaltic samples from Mars. Here, it will be argued that (1) the shergottites have a young igneous age, ≤600 Myr, (2) their parent magmas were relatively dry, (3) the range of initial isotopic compositions in shergottites is most likely due to assimilation of crustal materials by mantle‐derived basaltic magmas, and (4) the intercumulus liquid compositions of shergottites such as Shergotty and Zagami are relatively well constrained.