Alternating Effects of Climate Drivers on Altamaha River Discharge to Coastal Georgia,USA

Freshwater delivery is an important factor determining estuarine character and health and may be influenced by large-scale climate oscillations. Variability in freshwater delivery (precipitation and discharge) to the Altamaha River estuary (GA, USA) was examined in relation to indices for several climate signals: the Bermuda High Index (BHI), the Southern Oscillation Index (SOI), the Improved El Niño Modoki Index (IEMI), the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO), and the Pacific/North American Pattern (PNA). Discharge to this estuary has been linked to key ecosystem properties (e.g., salinity regime, water residence time, nutrient inputs, and marsh processes), so understanding how climate patterns affect precipitation and river discharge will help elucidate how the estuarine ecosystem may respond to climate changes. Precipitation patterns in the Altamaha River watershed were described using empirical orthogonal functions (EOFs) of the combined multidecadal time series of precipitation at 14 stations. The first EOF (67 % of the variance) was spatially uniform, the second EOF (11 %) showed a spatial gradient along the long axis of the watershed (NW–SE), and the third EOF (6 %) showed a NE–SW pattern. We compared the principal components (PCs) associated with these EOFs, monthly standardized anomalies of Altamaha River discharge at the gauge closest to the estuary, and the climate indices. Complex, seasonally alternating patterns emerged. The BHI was correlated with June–January discharge and precipitation PC 1. The SOI was correlated with January–April discharge and precipitation PC 2, and also weakly correlated with PC 1 in November–December. The AMO was correlated with river discharge and precipitation PC 3 mainly in December–February and June. The correlation patterns of precipitation PCs with PDO and PNA were similar to those with SOI, but weaker. There were no consistent relationships with two NAO indices or IEMI. Connections between climate signals and estimates of nutrient loading were consistent with the connections to discharge. The occurrence of tropical storms in the region was strongly related to the BHI but not to the other climate indices, possibly representing the influence of storm tracking more than the rate of storm formation. Comparison with the literature suggests that the patterns found may be typical of southeastern USA estuaries but are likely to be different from those outside the region.     

Spatio-temporal analysis of rockfall pre-failure deformation using Terrestrial LiDAR

We present a long-term spatio-temporal analysis of rock slope evolution using a Terrestrial LiDAR aiming to improve our understanding of the link between pre-failure deformation and the spatial prediction of rockfalls. We monitored the pilot study area located at the Puigcercós cliff (Catalonia, Spain) over a period of 1,705 days and detected the deformation of nine different cliff regions together with a high rockfall activity. An exact match was observed between the progressively deformed areas and the regions recently affected by three of the highest magnitude rockfall events, demonstrating a causal relationship between pre-failure deformation and rockfall occurrence. These findings allowed us to make a forward spatial prediction of future failures, hypothesizing a high probability of failure in the six remaining regions. We observed an exponential acceleration of the deformation close to failure, in accordance with tertiary creep theory. However, the temporal analysis of the deformed areas showed a complex and variable behavior, so no exact prediction of the date of failure can yet be made. Our findings have broadened our understanding of the pre-failure behavior of rockfalls and have clear implications for the future implementation of early warning systems.     

AMSR‐E algorithm for snowmelt onset detection in sub‐arctic heterogeneous terrain

The onset of snowmelt in the upper Yukon River basin, Canada, can be derived from brightness temperatures (T_b) obtained by the Advanced Microwave Scanning Radiometer for EOS (AMSR‐E) on NASA's Aqua satellite. This sensor, with a resolution of 14 × 8 km² for the 36·5 GHz frequency, and two to four observations per day, improves upon the twice‐daily coverage and 37 × 28 km² spatial resolution of the Special Sensor Microwave Imager (SSM/I). The onset of melt within a snowpack causes an increase in the average daily 36·5 GHz vertically polarized T_b as well as a shift to high diurnal amplitude variations (DAV) as the snow melts during the day and re‐freezes at night. The higher temporal and spatial resolution makes AMSR‐E more sensitive to sub‐daily T_b oscillations, resulting in DAV that often show a greater daily range compared to SSM/I. Therefore, thresholds of T_b > 246 K and DAV > ± 10 K developed for use with SSM/I have been adjusted for detecting the onset of snowmelt with AMSR‐E using ground‐based surface temperature and snowpack wetness relationships. Using newly developed thresholds of T_b > 252 K and DAV > ± 18 K, AMSR‐E derived snowmelt onset correlates well with SSM/I observations in the small subarctic Wheaton River basin through the 2004 and 2005 winter/spring transition. In addition, the onset of snowmelt derived from AMSR‐E data gridded at a higher resolution than the SSM/I data indicates that finer‐scale differences in elevation and land cover affect the onset of snowmelt and are detectable with the AMSR‐E sensor. On the basis of these observations, the enhanced resolution of AMSR‐E is more effective than SSM/I at delineating spatial and temporal snowmelt dynamics in the heterogeneous terrain of the upper Yukon River basin. Copyright © 2007 John Wiley & Sons, Ltd.     

Cold seeps in Monterey Bay, California: Geochemistry of pore waters and relationship to benthic foraminiferal calcite

An extensive geochemical and biogeochemical examination of CH₄ seeps in the Clam Flats area of Monterey Bay provides insight into the character of relationships between seep geochemistry and benthic foraminiferal geochemistry. The area is characterized by sulfide-rich fluids. Sulfide increases are associated with large increases in alkalinity, as well as small decreases in dissolved Ca and Mg. In addition, only small increases in NH₄ are observed, but values of δ¹³C of dissolved inorganic C are as low as −60‰ at shallow depths (<3 cm). These observations indicate that all these processes are related to the bacterial oxidation of CH₄, which is transported upward by slow seepage of pore fluids. The geochemistry of the pore fluids should be relevant to the geochemistry of the carbonate tests of living and dead foraminifera. However, a profound disequilibrium of approximately an order of magnitude occurs between the δ¹³C values of stained (cytoplasm-containing) foraminiferal carbonate and the C isotope values of ambient pore water dissolved inorganic C. Reasons are unclear for this isotopic disequilibrium, but have important implications for interpretations of foraminiferal carbonate as a paleoenvironmental proxy. Much fine scale work is needed to fully understand the relationships between the biogeochemistry of benthic foraminifera and the geochemistry of the pore waters where they live.     

Li, Be, B concentrations and δ7Li values in plagioclase phenocrysts of dacites from Nea Kameni (Santorini, Greece)

Li, Be, B and δ⁷Li SIMS analyses of plagioclase phenocrysts from the 1040–1941 Niki dacite lava (Nea Kameni, Santorini, Greece) exhibit varied processes. From their anorthite contents alone, the crystals may be segregated into four main types: type-N shows the normal decline in An during crystallisation (An_62–40); type-O has only oscillatory zoning accompanied by resorption surfaces (An_58–39); type-C is complex with high-An cores (subtype C1: An_64–58, subtype C2: An_88–73) and normal rims (An_55–42). Type-A plagioclase with high An content (An_92–82) is found within mafic enclaves. On the basis of their Li concentrations, type-O crystals may be subdivided into subtype O1 with flat Li concentration profiles and subtype O2 with decreasing Li concentration from core to rim. The concentrations of Be and B of all four types show a negative correlation with anorthite content (An), but Li concentration profiles differ amongst the different plagioclase types. Types N and O1, and the cores of type-C, are equilibrated in Li concentration. Types O2 and A, and the mantles of type-C display an initial enrichment in Li, probably from volatile influx into the melt. Consistent with the propensity towards equilibrium with the melt, these crystals display dramatic rim-ward declines in Li concentration. All analysed plagioclase crystals, except for the xenocrystic type-A, have nearly the same Li, Be and B concentrations at their rims. These coincide with the composition of plagioclase microlites in the groundmass, thereby affording estimates of plagioclase-melt partitioning for the light elements: K _Li = 0.19–0.28, K _Be = 0.24–0.38 and K _B = 0.007–0.009. δ⁷Li profiles in type-O2 and type-A phenocrysts manifest an unmistakable inverse relation to Li concentration, with variations of up to ~39 ‰, revealing preferential kinetic diffusion. This may have been driven by Li loss from the melt, most likely through degassing during decompression, perhaps in the course of magma ascent to subsequent eruption. Considering the rapid diffusion of Li in plagioclase, in situ phenocryst analyses may yield useful information about processes leading up to, or even causing, eruptions.     

Impacts of climate change on water resources in the Mediterranean Basin: a case study in Catalonia,Spain

Abstract

Most climate change projections show important decreases in water availability in the Mediterranean region by the end of this century. We assess those main climate change impacts on water resources in three medium-sized catchments with varying climatic conditions in northeastern Spain. A combination of hydrological modelling and climate projections with B1 and A2 IPCC emission scenarios is performed to infer future streamflows. The largest reduction (34%) in mean streamflows (for 2076–2100) is expected in the headwaters of the two wettest catchments, while lower decreases (25% of mean value for 2076–2100) are expected in the drier one. In all three catchments, autumn and summer are the seasons with the most notable projected decreases in streamflow, of 50% and 30%, respectively. Thus, ecological flows in the study area might be noticeably influenced by climate change, especially in the headwaters of the wet catchments.     

Variation in transparent exopolymer particles in relation to biological and chemical factors in two contrasting lake districts

In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L⁻¹ in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L⁻¹. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column.