160 research outputs found
Arsenic and Phosphorus Biogeochemistry in the Ocean: Arsenic Species as Proxies for P-Limitation
Arsenic and phosphorus are biochemically very similar, and hence arsenate (As5+) is toxic by interfering with the energy metabolism, in particular during P limitation. However, many phytoplankton detoxify As by reducing arsenate to arsenite (As3+), and/or methylating it to mono and dimethyl As. Such As detoxification becomes operative in oligotrophic waters when phosphate concentrations are below those for As; therefore, we evaluated the potential use of these detoxification products as indicators of P-limitation by measuring As speciation during the US GEOTRACES North Atlantic transect. The distribution of As3+ concentrations in surface waters is similar to that of N : P ratios and alkaline phosphatase activity (APA), two conventional proxies for P-limitation. As3+ concentrations have a very similar relationship to phosphate as APA to phosphate, and therefore indicate the potential of As3+ as proxy for P-limitation. From the relationship to phosphate we derived threshold values of As3+ concentration to indicate moderate and extreme P-limitation. We then applied these threshold values to assess P-limitation with high horizontal resolution in the North Atlantic, improving on the contradictory assessments using the conventional proxies. Our new evaluation is consistent with the general concept that the North Atlantic is moderately to extremely limited in phosphate
Quasi-uncoupled rotational diffusion of phospholipid headgroups from the main molecular frame
Organizing TTF-based supramolecular polymers through non-covalent p-p interactions with SWCNTs
A marine biogenic source of atmospheric ice nucleating particles
The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties1,2. The formation of ice in clouds is facilitated by the presence of airborne ice nucleating particles1,2. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice3-11. Sea spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer12-19. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice nucleating material is likely biogenic and less than ~0.2 ÎŒm in size. We find that exudates separated from cells of the marine diatom T. Pseudonana nucleate ice and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol in combination with our measurements suggest that marine organic material may be an important source of ice nucleating particles in remote marine environments such as the Southern Ocean, North Pacific and North Atlantic
Ki-67 is strongly prognostic in synovial sarcoma: analysis based on 86 patients from the Scandinavian Sarcoma Group Register
PCBs and PAHs in sea-surface microlayer and sub-surfacewater samples of the Venice Lagoon (Italy)
Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are two classes of micropollutants intensively monitored
and regulated due to their toxicity, persistency and wide diffusion. Their concentrations have been investigated in sea-microlayer
(SML) and sub-surface water (SSW) samples collected at two sites of the Venice Lagoon, a fragile ecosystem highly influenced by industrial
and anthropogenic emissions. The total PPCB concentration varies from 0.45 ng/l to 2.1 ng/l in SSW while a clear enrichment is
observed in the SML, where it ranges from 1.2 ng/l to 10.5 ng/l. The total PPAH concentration shows marked differences between the
two stations and varies from 12.4 ng/l to 266.8 ng/l in SSW; in SML it is more uniform and ranges from 19.6 ng/l to 178.9 ng/l. The
enrichment factors are not larger than 1 for both pollutants in the dissolved phase, while they are most significant for the particulate
phase (PPCB: 5â9; PPAH: 4â14).
2005 Elsevier Ltd. All rights reserved
Introduction to special section on Recent Advances in the Study of Optical Variability in the Near-Surface and Upper Ocean
Optical variability occurs in the near-surface and upper ocean on very short time and space scales (e.g., milliseconds and millimeters and less) as well as greater scales. This variability is caused by solar, meteorological, and other physical forcing as well as biological and chemical processes that affect optical properties and their distributions, which in turn control the propagation of light across the air-sea interface and within the upper ocean. Recent developments in several technologies and modeling capabilities have enabled the investigation of a variety of fundamental and applied problems related to upper ocean physics, chemistry, and light propagation and utilization in the dynamic near-surface ocean. The purpose here is to provide background for and an introduction to a collection of papers devoted to new technologies and observational results as well as model simulations, which are facilitating new insights into optical variability and light propagation in the ocean as they are affected by changing atmospheric and oceanic conditions
The Potential Use of Organically Grown Dye Plants in the Organic Textile Industry: Experiences and Results on Cultivation and Yields of Dyer's Chamomile ( Anthemis tinctoria
n-Alkanes, PAHs and surfactants in the sea surface microlayer and sea water samples of the Gerlache Inlet sea (Antarctica)
Sea surface microlayer (SML) and sea water samples (SSW) collected in the Gerlache Inlet Sea (Antarctica)
were analysed for n-alkanes and polycyclic aromatic hydrocarbons (PAHs). The SML is a potential enrichment
site of hydrophobic organic compounds compared to the underlying water column. Total concentration
ranges of n-alkanes and PAHs (dissolved and particulate) in subsurface water (â0.5 m depth) were 272â
553 ng lâ1 (mean: 448 ng lâ1) and 5.27â9.43 ng lâ1 (mean: 7.06 ng lâ1), respectively. In the SML, the
concentration ranges of n-alkanes and PAHs were 353â968 ng lâ1 (mean: 611 ng lâ1) and 7.32â23.94 ng lâ1
(mean: 13.22 ng lâ1), respectively. To evaluate possible PAH contamination sources, specific PAH ratios were
calculated. The ratios reflected a predominant petrogenic input. A characterisation of surface active
substances was also performed on SML and SSW samples, both by gas bubble extraction, and by dynamic
surface tension measurements. Results showed a good correlation between n-alkanes, PAHs and refractory
organic matter
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