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Dimethylsulfoniopropionate (DMSP) is produced in surface seawater by phytoplankton. Phytoplankton culture experiments have shown that nanoeucaryotes (NANO) display much higher mean DMSP-to-Carbon or DMSP-to-Chlorophyll (Chl) ratios than Prochlorococcus (PRO), Synechococcus (SYN) or diatoms (DIAT). Moreover, the DMSP-lyase activity of algae which cleaves DMSP into dimethylsulfide (DMS) is even more group specific than DMSP itself. Ship-based observations have shown at limited spatial scales, that sea surface DMS-to-Chl ratios (DMS:Chl) are dependent on the composition of phytoplankton groups. Here we use satellite remote sensing of Chl (from SeaWiFS) and of Phytoplankton Group Dominance (PGD from PHYSAT) with ship-based sea surface DMS concentrations (8 cruises in total) to assess this dependence on an unprecedented spatial scale. PHYSAT provides PGD (either NANO, PRO, SYN, DIAT, Phaeocystis (PHAEO) or coccolithophores (COC)) in each satellite pixel (1/4° horizontal resolution). While there are identification errors in the PHYSAT method, it is important to note that these errors are lowest for NANO PGD which we typify by high DMSP:Chl. In summer, in the Indian sector of the Southern Ocean, we find that mean DMS:Chl associated with NANO + PHAEO and PRO + SYN + DIAT are 13.6±8.4 mmol g-1 (n = 34) and 7.3±4.8 mmol g -1 (n = 24), respectively. That is a statistically significant difference (P

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.12.008 Byline: Thomas Gorgues (a), C. Menkes (b), L. Slemons (c), O. Aumont (d), Y. Dandonneau (e), M.-H. Radenac (f), S. Alvain (g), C. Moulin (g) Keywords: La NiA[+ or -]a; ENSO; Equatorial Pacific; Phytoplankton; Blooms; 1997-1998; Iron; Model Abstract: A biogeochemical model of the tropical Pacific has been used to assess the impact of interannual variability in a western Pacific iron source on the iron-limited ecosystem of the central and eastern Pacific during the 1997-1998 El NiA[+ or -]o. A reference simulation and two simulations with an iron source in the western Pacific have been performed. The two 'source' simulations differed only in the temporal variability of the iron source. In the variable source simulation, the iron concentration in the source region was proportional to the velocity of the New Guinea Coastal Undercurrent (NGCUC). In the constant source simulation, the same time-averaged concentration of iron was imposed with no temporal variability. The variable source was designed to mimic variations of iron flux from the northeast slope of New Guinea to the NGCUC due to modulation of sedimentary iron resuspension as previously hypothesized. Through the comparison of these simulations, it appeared that: (i) an iron source in the NGCUC, regardless of its source variability, increases biomass in the eastern equatorial Pacific because of the greater eastward iron flux by the Equatorial Undercurrent and (ii) a variable NGCUC iron source does not change the temporal variability of eastern Pacific chlorophyll, and in particular the timing and intensity of the June 1998 bloom. To explain eastern Pacific biological variability, local rather than remote processes are needed, such as wind-driven upwelling, the local depth of the thermocline, tropical instability waves and biological processes such as high grazing pressure. Therefore, while the western Pacific sources of dissolved iron are important in our model to sustain annually integrated equatorial Pacific production, they are unlikely to strongly constrain the timing of blooms in the central and eastern Pacific such as during the 1998 La NiA[+ or -]a. Author Affiliation: (a) IUEM - LPO, Centre IRD de bretagne, 29280 Plouzane, France (b) LOCEAN - IRD Noumea, BP A5, Noumea, 98848, New Caledonia (c) School of Oceanography, University of Washington, Seattle, WA98105, United States (d) LPO, Centre IRD de bretagne, 29280 Plouzane, France (e) LOCEAN/IPSL,75252 PARIS Cedex 05, France (f) LEGOS, 31400 Toulouse, France (g) ISPL/LSCE, CEA-CNRS-UVSQ, 91191 Gif-sur-Yvette, France Article History: Received 29 May 2009; Revised 22 December 2009; Accepted 27 December 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.01.011 Byline: S. Alvain (a), C. Moulin (a), Y. Dandonneau (b), H. Loisel (c), F.-M. Breon (a) Abstract: The PHYSAT method, which enables identification of four different phytoplankton groups from their impact on the normalized water-leaving radiance (nLw) spectra, is applied to coincident in situ measurements of both chlorophyll a concentration (Chl a) and nLw. Observations show that measurements acquired in waters dominated by haptophytes, diatoms and Synechococcus-like cyanobacteria have optical properties that deviate significantly from the mean OC4V4 bio-optical model, which is currently used as the standard for global ocean color processing. A specific OC4v4-like relationship, i.e., Chl a as a 4th-order polynomial of the 'maximum band ratio', was fitted for each dominant phytoplankton group identified by PHYSAT. The resulting OC4-SD bio-optical model thus starts from a classification of the dominant phytoplankton group, followed by a species-dependent estimate of Chl a. It has been applied to global daily SEAWIFS data of the year 2001. Monthly mean maps of Chl a derived from OC4-SD or OC4v4 show large regional differences that can reach 50% at high latitudes. The new algorithm leads to lower concentrations in regions where the standard model retrievals are known to be too high, such as the Mediterranean Sea. Conversely, higher concentrations are retrieved in regions dominated by diatom blooms, such as the northern North Atlantic in summer, where previous studies have demonstrated a low bias in standard SEAWIFS Chl a. Author Affiliation: (a) IPSL/LSCE, CNRS-CEA, Gif-sur-Yvette, France (b) IPSL/LODYC, IRD-CNRS-UPMC, Paris, France (c) ELICO, ULCO, Wimereux, France Article History: Received 1 July 2005; Revised 6 January 2006; Accepted 7 January 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2005.06.015 Byline: S. Alvain (a), C. Moulin (a), Y. Dandonneau (b), F.M. Breon (a) Keywords: Water color; Remote sensing; Phytoplankton; In situ measurements; SeaWiFs; Optical properties; Global; North Atlantic; Equatorial Pacific Abstract: Ocean color sensors enable a quasi-permanent monitoring of the chlorophyll a concentration (Chl a) in surface waters. This ubiquitous photosynthetic pigment cannot, however, be used to distinguish between phytoplankton species. Distinguishing phytoplankton groups from space is nevertheless necessary to better study some biochemical processes such as carbon fixation at the global scale, and is thus one of the major challenges of ocean color research. In situ data have shown that the water-leaving radiances (nLw), measured by ocean color sensors at different wavelengths in the visible spectrum, vary significantly for a given Chl a. This natural variability is due partly to differences in optical properties of phytoplankton species. Here, we derive relationships between nLw and phytoplankton species by using a large set of quantitative inventories of phytoplankton pigments collected during nine cruises from Le Havre (France) to Noumea (New Caledonia) in the framework of the GeP&CO program. Coincident SeaWiFS nLw data between 412 and 555nm are extracted and normalized to remove the effect of Chl a. These normalized spectra vary significantly with in situ pigment composition, so that four major phytoplankton groups, i.e., haptophytes, Prochlorococcus, Synechococcus-like cyanobacteria and diatoms, can be distinguished. This classification (PHYSAT) is applied to the global SeaWiFS dataset for year 2001, and global maps of phytoplankton groups are presented. Haptophytes and diatoms are found mostly in high latitudes and in eutrophic regions. Diatoms show a strong seasonal cycle with large-scale blooms during spring and summer. These results, obtained with only five channels in the visible spectrum, demonstrate that ocean color measurements can be used to discriminate between dominant phytoplankton groups provided that sufficient data are available to establish the necessary empirical relationships. Author Affiliation: (a) IPSL/LSCE, CEA Saclay, Gif-sur-Yvette 91191, France (b) IRD-IPSL/LOCEAN, 4 place Jussieu, Paris 75252, France Article History: Received 12 July 2004; Revised 6 May 2005; Accepted 6 June 2005

The selective HN[O.sub.3] nitration of di-n-octylcrown-6 calix[4]arene using different conditions, studied with LCMS and NMR ([1.sup]H and [13.sup]C) spectroscopic techniques, lead to the identification of most of the expected nitro derivative isomeric compounds. The formation of these isomers under acidic and radiolytic conditions is discussed with the help of molecular modelling. Key words: calix crown compounds, nitration of calixarenes, NMR of isomeric nitrocalixarenes, LC-ESI-MS. Resume : La nitration selective au HN[O.sub.3] du di-n-octylcouronne-6 calix[4]arbne dans differentes conditions, etudiee par des techniques spectroscopiques de LC-MS et de RMN ([1.sup]H et [13.sup]C), conduisent a l'identification de la plupart des isomeres de derives nitro attendus. La formation de ces isombres dans des conditions acides et radiolytiques est discutee avec l'aide de la mode1isation moleculaire. Mots cles : composes calix couronne, nitration de calixarenes, RMN des nitrocalixarenes isomeres, LC-ESI-MS.

X-ray absorption near-edge spectroscopy was used to study structural changes due to thermal poling treatment in a Herasil silica glass.

Electrospray ionization mass spectrometry was tested for its potential use in the quantification of monobutyl phosphate (H(sub 2)MBP) and dibutyl phosphate (HDBP), two degradation products of tributyl phosphate (TBP), the extractant used in the nuclear fuel reprocessing known as the PUREX process. Detection and quantification of these phosphate esters by electrospray in positive and negative ionization mode are reported in this study. This fast and reliable method, which does not require any preliminary sample extraction, appears to be very attractive for process control. Negative ionization mode gave abundant [M - H](super -) ions for both HDBP and H(sub 2)MBP products. Thus, the concentration of H(sub 2)MBP between 0.1 and 10 g/L in concentrated aqueous nitrate solutions can be precisely determined. Moreover, the concentration of HDBP up to 1 g/L in a TBP matrix was evaluated in this mode. For HDBP concentrations below 1 g/L, detection in the positive ionization mode appeared to be attractive. TBP and HDBP cluster detection allowed quantitative HDBP determination. Indeed, small amounts of HDBP in commercial TBP (60 mg/L) could be directly quantified using the specific [2TBP, HDBP + H](super +) cluster at m/z 743.