Assessment of Submarine Groundwater Discharge (SGD) as a Source of Dissolved Radium and Nutrients to Moorea (French Polynesia) Coastal Waters

Previous work has documented large fluxes of freshwater and nutrients from submarine groundwater discharge (SGD) into the coastal waters of a few volcanic oceanic islands. However, on the majority of such islands, including Moorea (French Polynesia), SGD has not been studied. In this study, we used radium (Ra) isotopes and salinity to investigate SGD and associated nutrient inputs at five coastal sites and Paopao Bay on the north shore of Moorea. Ra activities were highest in coastal groundwater, intermediate in coastal ocean surface water, and lowest in offshore surface water, indicating that high-Ra groundwater was discharging into the coastal ocean. On average, groundwater nitrate and nitrite (N + N), phosphate, ammonium, and silica concentrations were 12, 21, 29, and 33 times greater, respectively, than those in coastal ocean surface water, suggesting that groundwater discharge could be an important source of nutrients to the coastal ocean. Ra and salinity mass balances indicated that most or all SGD at these sites was saline and likely originated from a deeper, unsampled layer of Ra-enriched recirculated seawater. This high-salinity SGD may be less affected by terrestrial nutrient sources, such as fertilizer, sewage, and animal waste, compared to meteoric groundwater; however, nutrient-salinity trends indicate it may still have much higher concentrations of nitrate and phosphate than coastal receiving waters. Coastal ocean nutrient concentrations were virtually identical to those measured offshore, suggesting that nutrient subsidies from SGD are efficiently utilized.     

Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering

The aim of this paper is to explore the possibility of using a fuzzy divisive clustering technique to the classification of pulsating stars according to the shape of their light curves. The considered sample contains Cepheides, RR Lyrae stars, and high amplitude Scuti and SX Phoenicis stars. Our investigations proved the ability of this method to identify morphological groups in a given class of pulsating stars. The method is also useful for establishing the membership of an unknown variable star in a given class.     

Submarine Groundwater Discharge-Derived Nutrient Loads to San Francisco Bay: Implications to Future Ecosystem Changes

Submarine groundwater discharge (SGD) was quantified at select sites in San Francisco Bay (SFB) from radium (²²³Ra and ²²⁴Ra) and radon (²²²Rn) activities measured in groundwater and surface water using simple mass balance box models. Based on these models, discharge rates in South and Central Bays were 0.3?C7.4?m³?day^?1?m^?1. Although SGD fluxes at the two regions (Central and South Bays) of SFB were of the same order of magnitude, the dissolved inorganic nitrogen (DIN) species associated with SGD were different. In the South Bay, ammonium (NH ₄ ⁺ ) concentrations in groundwater were three-fold higher than in open bay waters, and NH ₄ ⁺ was the primary DIN form discharged by SGD. At the Central Bay site, the primary DIN form in groundwater and associated discharge was nitrate (NO ₃ ^? ). The stable isotope signatures (??¹⁵N_NO3 and ??¹⁸O_NO3) of NO ₃ ^? in the South Bay groundwater and surface waters were both consistent with NO ₃ ^? derived from NH ₄ ⁺ that was isotopically enriched in ¹⁵N by NH ₄ ⁺ volatilization. Based on the calculated SGD fluxes and groundwater nutrient concentrations, nutrient fluxes associated with SGD can account for up to 16?% of DIN and 22?% of DIP in South and Central Bays. The form of DIN contributed to surface waters from SGD may impact the ratio of NO ₃ ^? to NH ₄ ⁺ available to phytoplankton with implications to bay productivity, phytoplankton species distribution, and nutrient uptake rates. This assessment of nutrient delivery via groundwater discharge in SFB may provide vital information for future bay ecological wellbeing and sensitivity to future environmental stressors.     

Refining P nuclear magnetic resonance spectroscopy for marine particulate samples: Storage conditions and extraction recovery

Solution ³¹P nuclear magnetic resonance (NMR) spectroscopy has recently been used to characterize phosphorus species within marine particles. However, the effects of sample collection, storage and preparation have not been thoroughly examined. In this study, samples of settling particulates collected from a 1200-m sediment trap located in Monterey Bay, California, were subjected to various storage options (i.e., no storage, refrigeration, freezing, and oven-drying and grinding) prior to extraction for solution ³¹P-NMR spectroscopy. Freezing, refrigerating and drying samples for periods of up to 6 months prior to extraction with 0.25 M NaOH + 0.05 M Na₂EDTA increased the concentration of extracted P by an average of 16% relative to samples extracted without storage. Pre-extraction storage also introduced some minor changes in P speciation, by increasing the percentage of orthophosphate by up to 15% and decreasing the percentage of pyrophosphate by up to 5%, relative to the abundances of these P species in samples extracted without storage. Drying caused the biggest changes in speciation, specifically decreasing more extensively the relative percentage of pyrophosphate compared to other treatments. Nevertheless, observed changes in speciation due to sample storage within a specific sample were small relative to differences observed among samples collected sequentially in the same area, or reported differences among samples collected at different locations. Samples were also analyzed by solid-state ³¹P-NMR spectroscopy before and after extraction, to examine extraction-related changes in P speciation. Comparison of solution with solid-state ³¹P NMR indicates that extraction with NaOH–EDTA removes the majority of organic esters, but only a variable portion of phosphonates (39–67%). In addition, there was preferential extraction of Ca-associated phosphate over Mg-, Fe- and Al-associated phosphate. Solution ³¹P NMR enables much higher resolution of P species within samples, particularly when it is important to speciate orthophosphate monoesters and diesters, or if polyphosphates are present. However, combining solid-state ³¹P NMR with solution ³¹P NMR spectroscopy for marine particles should be conducted when examining inorganic P speciation and the abundance of phosphonates.     

Evaluating digital elevation models for glaciologic applications: An example from Nevado Coropuna, Peruvian Andes

This paper evaluates the suitability of readily available elevation data derived from recent sensors – the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) – for glaciological applications. The study area is Nevado Coropuna (6426 m), situated in Cordillera Ampato of Southern Peru. The glaciated area was 82.6 km² in 1962, based on aerial photography. We estimate the glacier area to be ca. 60.8 km² in 2000, based on analysis of the ASTER L1B scene.We used two 1:50,000 topographic maps constructed from 1955 aerial photography to create a digital elevation model with 30 m resolution, which we used as a reference dataset. Of the various interpolation techniques examined, the TOPOGRID algorithm was found to be superior to other techniques, and yielded a DEM with a vertical accuracy of ± 14.7 m. The 1955 DEM was compared to the SRTM DEM (2000) and ASTER DEM (2001) on a cell-by-cell basis. Steps included: validating the DEM's against field GPS survey points on rock areas; visualization techniques such as shaded relief and contour maps; quantifying errors (bias) in each DEM; correlating vertical differences between various DEM's with topographic characteristics (elevation, slope and aspect) and subtracting DEM elevations on a cell-by-cell basis.The RMS error of the SRTM DEM with respect to GPS points on non-glaciated areas was 23 m. The ASTER DEM had a RMS error of 61 m with respect to GPS points and displayed 200–300 m horizontal offsets and elevation ‘spikes’ on the glaciated area when compared to the DEM from topographic data.Cell-by-cell comparison of SRTM and ASTER-derived elevations with topographic data showed ablation at the toes of the glaciers (− 25 m to − 75 m surface lowering) and an apparent thickening at the summits. The mean altitude difference on glaciated area (SRTM minus topographic DEM) was − 5 m, pointing towards a lowering of the glacier surface during the period 1955–2000. Spurious values on the glacier surface in the ASTER DEM affected the analysis and thus prevented us from quantifying the glacier changes based on the ASTER data.     

Locally modified surface winds on linear dunes as derived from directional raingauges

The study deals with local airflow patterns induced by 12–16 m high, partly vegetated dunes, under various prevailing wind conditions. Detailed empirical data were derived by means of an unconventional use of directional raingauges. The utility and accuracy of the method have been previously tested in a combined empirical and numerical study over ridges on a similar scale. Results are presented on the nature, extent and intensity of locally modified patterns of surface flow and on their dependence on wind conditions and slope inclination. Results may serve to verify or refine existing perceptions or models of the flow affecting sand movement over dunes. For example, deflected surface wind flow and even stationary vortices were found to form under winds with resultant angles of incidence of only 5–10° relative to the axes of the dunes, and on slopes inclined only 12–15°, i.e. lower angles than often assumed in previous studies of dune morphology. Various effects of the resulting surface flow on the dune ecosystem are also referred to, e.g. the distribution of settling dust and seed dispersal. Copyright © 2002 John Wiley & Sons, Ltd.     

Submarine Groundwater Discharge to a High-Energy Surf Zone at Stinson Beach,California, Estimated Using Radium Isotopes

Two 14-day experiments conducted in the dry summer (July 2006) and wet winter (March 2007) seasons, respectively, examined tidal, wave-driven, and seasonal variability of submarine groundwater discharge (SGD) at Stinson Beach, CA, using natural radium tracers. Tide stage, tide range, breaker height, and season each explained a significant degree of radium variability in the surf zone. A mass balance of excess radium in the surf zone was used to estimate SGD for each season, confirming larger discharge rates during the wet season. Our results indicate median groundwater discharge rates of 6 to 8 L min⁻¹ m⁻¹ in July 2006 and 38 to 43 L min⁻¹ m⁻¹ in March 2007. SGD from 200 m of Stinson Beach in March 2007 contributed a flux of phosphate and dissolved inorganic nitrogen approximately equal to that associated with all local creeks and streams within 6 km of the study site at that time.     

Late Holocene environmental change in Celestun Lagoon,Yucatan, Mexico

Journal of Paleolimnology - Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence...     

Kalman filter-based algorithms for monitoring the ionosphere and plasmasphere with GPS in near-real time

Data collected from a GPS receiver located at low latitudes in the American sector are used to investigate the performance of the WinTEC algorithm [Anghel et al., 2008a, Kalman filter-based algorithm for near realtime monitoring of the ionosphere using dual frequency GPS data. GPS Solutions, accepted for publication; for different ionospheric modeling techniques: the single-shell linear, quadratic, and cubic approaches, and the multi-shell linear approach. Our results indicate that the quadratic and cubic approaches perform much better than the single-shell and multi-shell linear approaches in terms of post-fit residuals. The performance of the algorithm for the cubic approach is then further tested by comparing the vertical TEC predicted by WinTEC and USTEC [Spencer et al., 2004. Ionospheric data assimilation methods for geodetic applications. In: Proceedings of IEEE PLANS, Monterey, CA, 26–29 April, pp. 510–517] at five North American stations. In addition, since the GPS-derived total electron content (TEC) contains contributions from both ionospheric and plasmaspheric sections of the GPS ray paths, in an effort to improve the accuracy of the TEC retrievals, a new data assimilation module that uses background information from an empirical plasmaspheric model [Gallagher et al., 1988. An empirical model of the Earth's plasmasphere. Advances in Space Research 8, (8)15–(8)24] has been incorporated into the WinTEC algorithm. The new Kalman filter-based algorithm estimates both the ionospheric and plasmaspheric electron contents, the combined satellite and receiver biases, and the estimation error covariance matrix, in a single-site or network solution. To evaluate the effect of the plasmaspheric component on the estimated biases and total TEC and to assess the performance of the newly developed algorithm, we compare the WinTEC results, with and without the plasmaspheric term included, at three GPS receivers located at different latitudes in the American sector, during a solar minimum period characterized by quiet and moderate geomagnetic conditions. We also investigate the consistency of our plasmaspheric results by taking advantage of the specific donut-shaped geometry of the plasmasphere and applying the technique at 12 stations distributed roughly over four geomagnetic latitudes and three longitude sectors.     

The release of dissolved actinium to the ocean: A global comparison of different end-members

The measurement of short-lived ²²³Ra often involves a second measurement for supported activities, which represents ²²⁷Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of ²²⁷Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles ²²⁷Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of ²²⁷Ac near its potential sources.The average ²²⁷Ac activities of nearshore marine end-members range from 0.4 dpm m^− 3 at the Gulf of Mexico to 3.0 dpm m^− 3 in the coastal waters of the Korean Strait. In analogy to ²²⁸Ra, we find the extension of adjacent shelf regions to play a substantial role for ²²⁷Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean ²²⁷Ac inventory of 1.35 * 10¹⁸ dpm ²²⁷Ac_ex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm m⁻² y^− 1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of ²²⁷Ac of 4.5 * 10¹⁵ dpm, which cannot be converted directly into a flux value, as the regional loss term of ²²⁷Ac to the open ocean would have to be included.Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to ²³¹Pa_ex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in ²²⁷Ac/²²⁸Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including ²²⁷Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution.