Search

ABSTRACT Understanding observed changes to the global water cycle is key to predicting future climate changes and their impacts. While many datasets document crucial variables such as precipitation, ocean salinity, [...]

Variation in the release and recruitment of larvae of estuarine invertebrates affects the distribution and abundance of adults, as well as trophic interactions in both the plankton and the benthos. Larval release and supply are often timed to environmental cycles such as the diel and tidal cycles. Here, we determined using plankton tows whether the abundance of larvae spanning salt marsh and mangrove habitats across the intertidal landscape varied with diel and tidal cycles. Using three different sampling designs across two sites and within each of two estuaries over a 12-month period, we covered a range of spatial and temporal scales. This allowed us to test the general prediction that densities of meroplankton in the water column would be greater during nocturnal ebb tides than during other phases of the diel or tidal cycle. As predicted, nocturnal ebb tides yielded the highest densities of meroplanktonic larvae and were dominated by first-stage crab zoeae and this finding was most pronounced in the salt marsh. Throughout the course of the year, greater numbers of meroplankters consistently occurred during the ebb tide compared with the flood tide. The densities of other taxa (e.g. gastropods and polychaetes) showed no clear trends with diel or tidal cycles. This study highlights the effects of these pervasive physical cycles on the timing of larval release and supply in the salt marsh-mangrove complex, and emphasises their contribution to the trophic interactions and the dynamics of benthic populations within estuaries., Introduction Larval release and supply (the availability of larvae to settle) are important processes for the future structuring of adult populations of marine invertebrates (Underwood and Fair-weather 1989; Minchinton and [...]

Titan has a methane cycle akin to Earth's water cycle. It has lakes in polar regions (1,2), preferentially in the north (3); dry low latitudes with fluvial features (4,5) and occasional rainstorms (6,7); and tropospheric clouds mainly (so far) in southern middle latitudes and polar regions (8-15). Previous models have explained the low-latitude dryness as a result of atmospheric methane transport into middle and high latitudes (16). Hitherto, no model has explained why lakes are found only in polar regions and preferentially in the north; how low-latitude rainstorms arise; or why clouds cluster in southern middle and high latitudes. Here we report simulations with a three-dimensional atmospheric model coupled to a dynamic surface reservoir of methane. We find that methane is cold-trapped and accumulates in polar regions, preferentially in the north because the northern summer, at aphelion, is longer and has greater net precipitation than the southern summer. The net precipitation in polar regions is balanced in the annual mean by slow along-surface methane transport towards mid-latitudes, and subsequent evaporation. In low latitudes, rare but intense storms occur around the equinoxes, producing enough precipitation to carve surface features. Tropospheric clouds form primarily in middle and high latitudes of the summer hemisphere, which until recently has been the southern hemisphere. We predict that in the northern polar region, prominent clouds will form within about two (Earth) years and lake levels will rise over the next fifteen years., Explanations for Titan's tropospheric clouds range from control by local topography and cryovolcanism (11,12) to control by a seasonally varying global Hadley circulation with methane condensation in its ascending branch [...]

The management of water resources in arid and semiarid areas has long been a challenge, from ancient Mesopotamia to the modern southwestern United States. As our understanding of the hydrological and climatological cycles has improved, and our ability to manipulate the hydrologic cycle has increased, so too have the challenges associated with managing a limited natural resource for a growing population. Modern civilization has made remarkable progress in water management in the past few centuries. Burgeoning cities now survive in desert regions, relying on a mix of simple and complex technologies and management systems to bring adequate water and remove wastewater. These systems have permitted agricultural production and urban concentrations to expand in regions previously thought to have inadequate moisture. However, evidence is also mounting that our current management and use of water is unsustainable. Physical, economic, and ecological limits constrain the development of new supplies and additional water withdrawals, even in regions not previously thought vulnerable to water constraints. New kinds of limits are forcing water managers and policy makers to rethink previous assumptions about population, technology, regional planning, and forms of development. In addition, new threats, especially the challenges posed by climatic changes, are now apparent. Sustainably managing and using water in arid and semiarid regions such as the southwestern United States will require new thinking about water in an interdisciplinary and integrated way. The good news is that a wide range of options suggest a roadmap for sustainable water management and use in the coming decades. climate change | soft path | freshwater | sustainability | water management doi/ 10.1073/pnas.1005473107

Climate models robustly predict that the climate of southwestern North America, defined as the area from the western Great Plains to the Pacific Ocean and from the Oregon border to southern Mexico, will dry throughout the current century as a consequence of rising greenhouse gases. This regional drying is part of a general drying of the subtropics and poleward expansion of the subtropical dry zones. Through an analysis of 15 coupled climate models it is shown here that the drying is driven by a reduction of winter season precipitation associated with increased moisture divergence by the mean flow and reduced moisture convergence by transient eddies. Due to the presence of large amplitude decadal variations of presumed natural origin, observations to date cannot confirm that this transition to a drier climate is already underway, but it is anticipated that the anthropogenic drying will reach the amplitude of natural decadal variability by midcentury. In addition to this drop in total precipitation, warming is already causing a decline in mountain snow mass and an advance in the timing of spring snow melt disrupting the natural water storage systems that are part of the region's water supply system. Uncertainties in how radiative forcing will impact the tropical Pacific climate system create uncertainties in the amplitude of drying in southwest North America with a La Nina-like response creating a worst case scenario of greater drying. climate change | decadal variability | hydrological cycle | southwest drying drought doi/ 10.1073/pnas.0910856107

Freshwater discharge from the continents is a key component of Earth's water cycle that sustains human life and ecosystem health. Surprisingly, owing to a number of socioeconomic and political obstacles, a comprehensive global river discharge observing system does not yet exist. Here we use 13 years (1994-2006) of satellite precipitation, evaporation, and sea level data in an ocean mass balance to estimate freshwater discharge into the global ocean. Results indicate that global freshwater discharge averaged 36,055 [km.sup.3]/y for the study period while exhibiting significant interannual variability driven primarily by El Nino Southern Oscillation cycles. The method described here can ultimately be used to estimate long-term global discharge trends as the records of sea level rise and ocean temperature lengthen. For the relatively short 13-year period studied here, global discharge increased by 540 [km.sup.3]/[y.sup.2], which was largely attributed to an increase of global-ocean evaporation (768 [km.sup.3]/[y.sup.2]). Sustained growth of these flux rates into long-term trends would provide evidence for increasing intensity of the hydrologic cycle. climate | global water cycle | hydrology | remote sensing | observations doi/ 10.1073/pnas.1003292107

ABSTRACT. Arctic wetland environments are sensitive to ongoing climate change as seen by the recent loss of lakes and ponds in southern Alaska, Siberia, and northern Ellesmere Island, Canada. A [...]

Changes in climate during the 20th century differ from region to region across the United States. We provide strong evidence that spatial variations in US temperature trends are linked to the hydrologic cycle, and we also present unique information on the seasonal and latitudinal structure of the linkage. We show that there is a statistically significant inverse relationship between trends in daily temperature and average daily precipitation across regions. This linkage is most pronounced in the southern United States (30-40[degrees]N) during the May-June time period and, to a lesser extent, in the northern United States (40-50[degrees]N) during the July-August time period. It is strongest in trends in maximum temperatures ([T.sub.max]) and 90th percentile exceedance trends (90PET), and less pronounced in the [T.sub.max] 10PET and the corresponding [T.sub.min] statistics, and it is robust to changes in analysis period. Although previous studies suggest that areas of increased precipitation may have reduced trends in temperature compared with drier regions, a change in sign from positive to negative trends suggests some additional cause. We show that trends in precipitation may account for some, but not likely all, of the cause point to evidence that shows that dynamical patterns (El Nino/Southern Oscillation, North Atlantic Oscillation, etc.) cannot account for the observed effects during May-June. We speculate that changing aerosols, perhaps related to vegetation changes, and increased strength of the aerosol direct and indirect effect may playa role in the observed linkages between these indices of temperature change and the hydrologic cycle. atmosphere | trends

Evaporation and groundwater fluxes are thought to regulate hydrologic variability in lakes of the northern Great Plains, but little is known of how the relative importance of these processes may vary in time or space. To address this issue, we measured the isotopic composition of water ([[delta].sup.18]]O, [[delta].sup.2]H) from 70 closed-basin lakes in southern Saskatchewan, Canada. All lakes occupied endorheic basins along a long gradient of salinity (0.2-115 g total dissolved solids [L.sup.-1]). Lakes exhibited synchronous seasonal changes in salinity (synchrony, S = 0.78) and [[delta].sup.18]]O (S = 0.84) during the dry summer of 2003 (~195 mm rain), whereas coherence was reduced to 0.56 and 0.22, respectively, during the wet summer of 2004 ~295 mm rain). However, despite evaporative enrichment of isotopic ratios during dry summers, hydrologic balances were regulated mainly by changes in water inflow (I) rather than evaporation (E) in both wet and dry years, with particularly strong influence of inflow (lowest E : I ratio) in dry southwestern regions. Analysis of isotopic composition also identified winter precipitation or groundwater as the most influential source of water to most lakes, despite only ~30% of annual precipitation being delivered during winter. Therefore, although seasonal variability in lake chemistry was influenced by evaporation during summer, long-term mean chemical characteristics of prairie lakes were regulated mainly by changes in winter precipitation or groundwater influx.

Aerosol- and moonsoon-related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. In recent years, thanks to improved satellite and in situ observations, and better models, great strides have been made in aerosol and monsoon research, respectively. There is now a growing body of evidence suggesting that interaction of aerosol forcing with monsoon dynamics may alter the redistribution of energy in the atmosphere and at the Earth's surface, thereby influencing monsoon water cycle and climate. In this article, the authors describe the scientific rationale and challenges for an integrated approach to study the interactions between aerosol and monsoon water cycle dynamics. A Joint Aerosol-Monsoon Experiment (JAMEX) is proposed for 2007-11, with enhanced observations of the physical and chemical properties, sources and sinks, and long-range transport of aerosols, in conjunction with meteorological and oceanographic observations in the Indo-Pacific continental and oceanic regions. JAMEX will leverage on coordination among many ongoing and planned national research programs on aerosols and monsoons in China, India, Japan, Nepal, Italy, and the United States, as well as international research programs of the World Climate Research Program (WCRP) and the World Meteorological Organization (WMO).

It has previously been noted that there are drops in global sea level (GSL) after some major volcanic eruptions. However, observational evidence has not been convincing because there is substantial variability in the global sea level record over periods similar to those at which we expect volcanoes to have an impact. To quantify the impact of volcanic eruptions we average monthly GSL data from 830 tide gauge records around five major volcanic eruptions. Surprisingly, we find that the initial response to a volcanic eruption is a significant rise in sea level of 9 [+ or -] 3 mm in the first year after the eruption. This rise is followed by a drop of 7 [+ or -] 3 mm in the period 2-3 years after the eruption relative to preeruption sea level. These results are statistically robust and no particular volcanic eruption or ocean region dominates the signature we find. Neither the drop nor especially the rise in GSL can be explained by models of lower oceanic heat content. We suggest that the mechanism is a transient disturbance of the water cycle with a delayed response of land river runoff relative to ocean evaporation and global precipitation that affects global sea level. The volcanic impact on the water cycle and sea levels is comparable in magnitude to that of a large El Nino-La Nina cycle, amounting to [approximately equal to] 5% of global land precipitation. climate | evaporation | heat content | ocean | precipitation

A modified definition of precipitation efficiency (PE) is proposed based on either cloud microphysics precipitation efficiency (CMPE) or water cycling processes including water vapor and hydrometeor species [large-scale precipitation efficiency (LSPE)]. These PEs are examined based on a two-dimensional cloud-resolving simulation. The model is integrated for 21 days with the imposed large-scale vertical velocity, zonal wind, and horizontal advections obtained from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). It is found that the properly defined PEs include all moisture and hydrometeor sources associated with surface rainfall processes so that they range from 0% to 100%. Furthermore, the modified LSPE and CMPE are highly correlated. Their linear correlation coefficient and root-mean-squared difference are insensitive to the spatial scales of averaged data and are moderately sensitive to the time period of averaged data.

The Mackenzie Global Energy and Water Cycle Experiment (GEWEX) Study (MAGS) is one of the continental-scale experiments approved specifically by GEWEX to better understand and model water and energy cycling at high latitudes. The project has gone through two phases since its inception in 1994 and conclusion in December 2005. Many scientific results have been achieved through MAGS research to advance our understanding of the Mackenzie River basin climate system. This article is a synthesis of its atmospheric research achievements through an integrative description of the basin's climate system, along with highlights of MAGS research that has advanced our knowledge and understanding of various key aspects of the system. In particular, the significance of MAGS research is discussed in the context of how it contributes to enhancing knowledge of the basin's hydroclimate with focuses on i) the large-scale atmospheric processes that control the transport of water and energy into the basin, and ii) the interactions of the large-scale atmospheric flows with physical features of the basin's environment in affecting the weather and climate of the basin.

The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was developed and provided to the National Aeronautics and Space Administration's EOS Aqua satellite by the National Space Development Agency of Japan, as one of the indispensable instruments for Aqua's mission. AMSR-E is a modified version of AMSR that was launched December 2002 aboard the Advanced Earth Observing Satellite-II (ADEOS-II). It is a six-frequency dual-polarized total-power passive microwave radiometer that observes water-related geophysical parameters supporting global change science and monitoring efforts. The hardware improvements over existing spaceborne microwave radiometers for earth imaging include the largest main reflector of its kind and addition of 6.925-GHz channels. These improvements provide finer spatial resolution and the capability to retrieve sea surface temperature and soil moisture information on a global basis. This paper provides an overview of the instrument characteristics, mission objectives, and data products. Index Terms--Climate, earth, microwave radiometry, remote sensing.

Aqua is a major satellite mission of the Earth Observing System (EOS), an international program centered at the U.S. National Aeronautics and Space Administration (NASA). The Aqua satellite carries six distinct earth-observing instruments to measure numerous aspects of earth's atmosphere, land, oceans, biosphere, and cryosphere, with a concentration on water in the earth system. Launched on May 4, 2002, the satellite is in a sun-synchronous orbit at an altitude of 705 km, with a track that takes it north across the equator at 1:30 P.M. and south across the equator at 1:30 A.M. All of its earth-observing instruments are operating, and all have the ability to obtain global measurements within two days. The Aqua data will be archived and available to the research community through four Distributed Active Archive Centers (DAACs). Index Terms--Aqua, Earth Observing System (EOS), remote sensing, satellites, water cycle.

In northern Chile, precipitation in the High Andes (>3500 m) recharges groundwater systems that flow down the Pacific slope and feed large aquifers in the hyperarid Atacama Desert. Wetlands, which are often found along the base of the Andes, mark locations where the water table intersects the land surface. At these locations, paleo--wetland deposits, which are present as terraces between 3 and 20 m above modern wetlands, record past water-table heights along the Andean front and are used to reconstruct changes in groundwater discharge. Paleo--wetland deposits in the central Atacama Desert (lat 22[degrees]-24[degrees]S) record an episode (>15.4-9 ka) of high water tables followed by an episode (8-3 ka) of moderately high water tables. Elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the Andes. The concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations. This interpretation is supported by close agreement with other paleoclimatic records in the region. The periods of greater groundwater discharge were separated by episodes (9-8 and 3-0 ka) of significant groundwater lowering and stream incision, implying greatly diminished discharge. The central Atacama and Andes (lat 22[degrees]-24[degrees]S) receive precipitation mainly from moist air masses transported from the Amazon Basin by the South American Summer Monsoon (SASM). Increases in groundwater recharge are therefore thought to reflect an increase in the frequency and/or moisture content of SASM air masses crossing the Andes. Fluctuations in SASM precipitation have previously been linked to summer insolation in the Southern Hemisphere. The wettest period in the central Atacama (>15.4-9 ka), however, coincides with a minimum in austral-summer insolation at 10 ka, suggesting that regional summer insolation is not a dominant influence on the SASM. Instead, intensification of the SASM may be linked to extraregional forcings such as the Walker Circulation. Keywords: Atacama Desert, wetlands, springs, paleohydrology, South America.

Stable isotope values of shallow groundwater emerging from springs in a high-elevation basin in the central Sierra Nevada of California decrease with increasing geochemical groundwater ages. From water recharged in 1960 to water recharged in 1990, a 1.2 [per thousand] and 11 [per thousand] increase occurs in [[delta].sup.18]O and [delta]D, respectively. Historic temperature records from surrounding areas show a 1.3[degrees]C increase in mean annual air temperature over the same time period. This temperature change alone is not great enough to explain the observed increase in [[delta].sup.18]O. We suggest that changes in atmospheric circulation patterns, which have been documented in this region, account for the remaining increase in [[delta].sup.18]O. The time scale of these climatic changes, recorded in both the historical and the hydrological records, is extremely short (decadal scale) and suggests that the [[delta].sup.18]O of groundwater can be a useful tool for studying climatic and atmospheric circulation changes over very short time intervals. It also suggests that circulation changes must be considered along with temperature when interpreting paleoclimate data. Keywords: springs, stable isotopes, California, climate, groundwater, dating.

Research concerning reaction of phosphites with dimethyl acetylenedicarboxylate and C (sub)60 to produce phosphite ylides has been conducted. Hydrolysis of these ylides used to introduce phosphonate ester, phosphine oxide and phosphonic acid to a fullerene moiety is described.

The influence of lake hydrology on carbon dioxide and methane dynamics is discussed, based on research conducted at two lakes in north-central Minnesota, in the Shingobee River watershed. Topics include temperature and dissolved gas concentrations, lake CH4 and CO2 storage, methane oxidation, C gas flux across the air-water interface, and annual carbon inputs and losses.

Most Precambrian Shield forested catchments have some wetland component. Even small riparian wetlands are important modifiers of stream chemistry. Dissolved organic matter (DOM) is one of the most important products exported by wetlands in streams. Stratigraphic control of hydraulic conductivity generally leads to decreasing conductivity with depth. Thus important flowpaths occur in the uppermost organic rich layers and are reflected in chemical profiles of dissolved organic carbon (DOC). Accumulation of DOC in peal porewaters is the net effect of production, consumption and transport. DOC profiles vary with degree of interaction with the surrounding upland catchment and distance from the edge of the wetland as well as internal processes within the wetland. In wetlands, DOM production is offset by flushing resulting in decreasing DOC concentrations with increasing flows. Despite old carbon (2,000 to 3,000 years) at relatively shallow depths, 14C activity in DOC exported from wetlands is mostly modern (recent carbon), consistent with shallow flowpaths and export of DOM from shallow organic rich horizons. In contrast, the source area for DOM in upland catchments with developed B horizon soils increases with antecedent soil moisture conditions resulting in increasing DOC concentrations with higher stream flows. Activity of 14C in stream DOC from upland catchments span a range from low activities (older carbon) similar to B horizon soil water during dry moisture conditions to values slightly less than modern (more recent carbon) during high moisture conditions. The more modern carbon activities reflect the increased contribution of the organic rich litter and A horizon soil layers in the area immediately bordering the stream under wet antecedent moisture conditions. Reduced hydrologic export or loss of wetlands trader drier climatic conditions may result in in larger fluctuations in stream DOC concentrations and reduced DOM loads to lakes. keywords: wetlands, forested catchments, dissolved organic carbon, carbon cycling