Description: Lake Tahoe is an ultra-oligotrophic subalpine lake that is renowned for its clarity. The region experiences little cloud cover and is one of the most UV transparent lakes in the world. As such, it is an ideal environment to study the role of UV radiation in aquatic ecosystems. Long-term trends in Secchi depths showed that water transparency to visible light has decreased in recent decades, but limited data are available on the UV transparency of the lake. Here we examine how ultraviolet radiation varies relative to longer-wavelength photosynthetically active radiation (PAR, 400-700 nm, visible wavelengths) horizontally along inshore-offshore transects in the lake and vertically within the water column as well as temporally throughout 2007. UV transparency was more variable than PAR transparency horizontally across the lake and throughout the year. Seasonal patterns of Secchi transparency differed from both UV and PAR, indicating that different substances may be responsible for controlling transparency to UV, PAR, and Secchi. In surface waters, UVA (380 nm) often attenuated more slowly than PAR, a pattern visible in only exceptionally transparent waters with very low dissolved organic carbon. On many sampling dates, UV transparency decreased progressively with depth suggesting surface photobleaching, reductions in particulate matter, increasing chlorophyll a, or some combination of these increased during summer months. Combining these patterns of UV transparency with data on visible light provides a more comprehensive understanding of ecosystem structure, function, and effects of environmental change in highly transparent alpine and subalpine lakes such as Tahoe.

Description: During the SAMUM field campaign in southern Morocco in May and June 2006 density currents generated by evaporative cooling after convective precipitation were frequently observed at the Sahara side of the Atlas Mountain chain. The associated strong surface cold-air outflow during such events has been observed to lead to dust mobilization in the foothills. Here a regional model system is used to simulate a density current case on 3 June 2006 and the subsequent dust emission. The model studies are performed with different parameterization schemes for convection, and with different horizontal model grid resolutions to examine to which extent the model system can be used for reproducing dust emissions in this region. The effect of increasing the horizontal model grid resolution from 14 km to 2.8 km on the strength on the density currents and thus on dust emission is smaller than the differences due to different convection parameterization schemes in this case study. While the results in reproducing the observed density current at the Atlas Mountain varied with different convection parameterizations, the most realistic representation of the density current is obtained at 2.8 km grid resolution at which no parameterization of deep convection is needed.

Description: Jamaica Bay, NY, is a highly urbanized estuary within the boroughs of New York City conspicuously lacking published information on dissolved trace metal concentrations. The current study examines the distribution and cycling of trace metals in that embayment with data gathered during cruises in November 2004, April 2005, and June 2006. Most of the metal distributions (Fe, Zn, Co, Ag, Cu, Pb, Ni) in the water column are explained by the input of substantial volumes of treated wastewater effluent. However, several lines of evidence suggest that submarine groundwater discharge (SGD) is also an important source of dissolved Fe, Zn, Co, Ni, and isotopically distinct stable Pb ratios (206Pb, 207Pb, 208Pb) in the Bay. Conversely, the recirculated seawater component of SGD is an apparent sink for dissolved Mo. This study provides the first measurements of dissolved trace metals in the Jamaica Bay water column and subterranean estuary and provides evidence for trace metal input due to SGD.

Description: The main physical and biological processes that control the seasonal cycle of the plankton dynamics over the Western Black Sea were explored by means of a three‐dimensional, 7‐compartment, on‐line coupled biophysical model that was developed for this study. Adopting high frequency forcing in terms of air‐sea interaction and Danube river inputs, we performed a simulation of the coupled model during the 2002–2003 period. A series of 8‐day Chl‐a SeaWiFS images provided a validation tool that guided us, along with available in situ measurements, to the improvement of model parameterizations and the calibration of the biological parameters. The simulation of the seasonal phytoplankton variability over the entire Western Black Sea, extending from the highly eutrophic river influenced area to the open sea area, was a major challenge that made necessary the representation of both the spatial and time variability of several processes. Despite the model simplicity, the simulated Chl‐a patterns presented a good agreement as compared to the SeaWiFS and in situ data. During winter, phytoplankton in coastal areas was shown to be limited by light availability, primarily due to the increased particulate matter concentrations, as a result of resuspension from the sediment and the increased river loads. During summer, the primary production was mostly sustained by riverine nutrients and regeneration processes and thus was strongly linked to the evolution of the Danube plume. The limiting nutrients showed deviations from the observed concentrations, indicating the necessity for a more realistic phytoplankton growth model.

Description: A flow-injection (FI)-based instrument under Lab VIEW control for monitoring iron in marine waters is described. The instrument incorporates a miniature, low-power photomultiplier tube (PMT), and a number of microelectric and solenoid actuated valves and peristaltic pumps. The software allows full control of all flow injection components and processing of the data from the PMT. The optimised system is capable of 20 injections per hour, including preconcentration and wash steps. The detection limit (3 sd of the blank) is 21 pM at sea and the linear range is 21-2000 pM with a 60-second sample load time. Typical precision between replicate FI peaks is 5.9 ± 3.2 (n = 4) over the linear range. © 2005 Hindawi Publishing Corporation.

Description: A 2-year record of mixed layer measurements of CO2 partial pressure (pCO2), nitrate, and other physical, chemical, and biological parameters at a time series site in the northeast Atlantic Ocean (49N/16.5W) is presented. The data show average undersaturation of surface waters with respect to atmospheric CO2 levels by about 40 ± 15 matm, which gives rise to a perennial CO2 sink of 3.2 ± 1.3 mol m2 a1. The seasonal pCO2 cycle is characterized by a summer minimum (winter maximum), which is due to the dominance of biological forcing over physical forcing. Our data document a rapid transition from deep mixing to shallow summer stratification. At the onset of shallow stratification, up to one third of the mixed layer net community production during the productive season had already been accomplished. The combination of high prestratification productivity and rapid onset of tratification appears to have caused the observed particle flux peak early in the season. Mixed layer deepening during fall and winter reventilated CO2 from subsurface respiration of newly exported organic matter, thereby negating more than one third of the carbon drawdown by net community production in the mixed layer. Chemical signatures of both net community production and respiration are indicative of carbon overconsumption, the effects of which may be restricted, though, to the upper ocean. A comparison of the estimated net community production with satellite-based estimates of net primary production shows fundamental discrepancies in the timing of ocean productivity.

Description: Requirements for understanding the relationships between ocean color and suspended and dissolved materials within the water column, and a rapidly emerging photonics and materials technology base for performing optical based analytical techniques have generated a diverse offering of commercial sensors and research prototypes that perform optical measurements in water. Through inversion, these tools are now being used to determine a diverse set of related biogeochemical and physical parameters. Techniques engaged include measurement of the solar radiance distribution, absorption, scattering, stimulated fluorescence, flow cytometry, and various spectroscopy methods. Selective membranes and other techniques for material isolation further enhance specificity, leading to sensors for measurement of dissolved oxygen, methane, carbon dioxide, common nutrients and a variety of other parameters. Scientists are using these measurements to infer information related to an increasing set of parameters and wide range of applications over relevant scales in space and time.

Description: Studies of the pantophysin (Pan I*) locus in Atlantic cod Gadus morhua and other marine gadoids indicate that the locus is under positive selection; in Atlantic cod, genotypic variation at this locus has been linked to differences in growth. Here, we present preliminary data comparing the growth and condition of different Atlantic cod Pan I* genotypes within families held under seminatural mesocosm conditions. Larvae from three full-sibling families carrying Pan I*bb or Pan I*ab genotypes were reared for 10 weeks in two mesocosms. Multivariate analysis of variance indicated that larvae carrying the Pan I*ab genotype exhibited significantly higher standard length, dry weight, and RNA: DNA ratio (condition factor) than did larvae that carried the Pan I*bb genotype, potentially indicating selection. The influence of linked loci cannot be excluded; indeed, the absence of a significant correlation between genotype and growth in one family may substantiate this. The lack of differences in survival among genotypes indicates that moderate selective effects are acting primarily through size-specific mortality and fecundity. The proposed putative fitness effects, together with documented marked geographic differentiation in the wild, have implications for Atlantic cod population structure, effective migration rates, recruitment, and local adaptation, which are of particular relevance in a species threatened by continuing exploitation and rising sea temperatures.

Description: We measured halogen concentrations and I-129/I ratios in five drilling sites of Integrated Ocean Drilling Program Expedition 311 (offshore Vancouver Island, Canada) in order to identify potential sources of fluids and methane in gas hydrate fields. Iodine is dominated by organic decomposition and transports with fluids in reducing environments and the presence of the cosmogenic radioisotope I-129 (T-1/2 = 15.7 Ma) allows the age determination of organic sources for iodine. Here we report halogen concentrations in 135 pore water samples, I concentrations in 48 sediment samples, and I-129/I ratios measured in a subset of 20 pore water samples. Most I-129/I ratios fall into a range around 500 x 10(-15), corresponding to a minimum age of 25 Ma and the lowest ratio of 188 x 10(-15) (T-min = 47 Ma) was observed at 208 m below sea floor (mbsf) in Site 1326. These ages are considerably older than that of the local sediments in the gas hydrate fields and that of the subducting sediments on the Juan de Fuca plate, indicating that old, accreted sediments in the accretionary wedge contribute a significant amount of iodide and, by association, of methane to the gas hydrate occurrences. A geochemical transport-reaction model was applied to simulate the advection of deeply sourced fluids and the release of iodide, bromide, and ammonia in the host sediments due to organic matter degradation. The model was first tested with data from two well studied areas, Ocean Drilling Program Site 1230 (Peru margin) and Site 1245 (Hydrate Ridge). The model results for the Expedition 311 sites indicate that the in situ release of young iodine is relatively minor in comparison to the contribution of migrating fluids, carrying large amounts of old iodine from deep sources. The comparison between the sites demonstrates that the total organic content has a strong effect on the rate of in situ iodine release and that lateral flows along fractures can have a significant influence on pore water chemistry, especially at the Cascadia margin. The iodine results indicate that mobilization and transport of methane from sources in the upper plate of active margins is an important process which can also play a substantial role in the formation of gas hydrate fields.

Description: Trimix scuba divers discovered coelacanths in Jesser Canyon at a depth of 104 m on the northern KwaZulu-Natal (KZN) coast (Sodwana Bay) in October 2000. The existence of these animals at such a shallow depth and in the swift and powerful Agulhas Current led to a suggestion that this might be an isolated group swept well away from the main population in the Comoros, where they live at depths of 200-350 m with little current. Subsequent observations from three manned submersible surveys and one remotely operated vehicle expedition together with recreational diver observations indicate that the South African population of coelacanths has at least 26 individuals, mostly occupying the depth range of 104-140 m in canyons. Seventeen CTD sections collected during four cruises in 2002 and 2003 indicate the temperature range in this habitat to be similar to that found in the Comoros Islands (that is, 15-22〈sup〉o〈/sup〉C cf. 15-19〈sup〉o〈/sup〉C in the Comoros). However, a 2.5-month-long time series of hourly data collected by a thermistor array deployed near a known coelacanth cave in Wright Canyon indicated greater variation than anticipated, with temperature changes between 16〈sup〉o〈/sup〉C and 24〈sup〉o〈/sup〉C occurring in a day. Dissolved oxygen levels in this depth zone were found to range between 3.0 ml l〈sup>-1〈/sup> and 4.8 ml l〈sup>-1〈/sup> compared to 3.5 ml l〈sup>-1〈/sup> in the Comoros. The low oxygen values along this coast are a result of the shallow oxygen minimum, which becomes shallower in the southwest Indian Ocean, particularly in the Agulhas Current, than in tropical latitudes. Current velocities measured using a ship-borne ADCP in the depth range 100-140 m at Sodwana were considerably higher than those measured in the Comoros habitat (20-60 cm s〈sup>-1〈/sup> cf. 3-4 cm s〈sup〉-1〈/sup〉) and may be an important factor explaining the coelacanths' occupation of the canyons found along the northern KZN shelf-break.