Multivariate approach for the retrieval of phytoplankton size structure from measured light absorption spectra in the Mediterranean Sea (BOUSSOLE site)

Models based on the multivariate partial least squares (PLS) regression technique are developed for the retrieval of phytoplankton size structure from measured light absorption spectra (BOUSSOLE site, northwestern Mediterranean Sea). PLS-models trained with data from the Mediterranean Sea showed good accuracy in retrieving, over the nine-year BOUSSOLE time series, the concentrations of total chlorophyll a [Tchl a], of the sum of seven diagnostic pigments and of pigments associated with micro, nano, and picophytoplankton size classes separately. PLS-models trained using either total particle orphytoplankton absorption spectra performed similarly, and both reproduced seasonal variations of biomass and size classes derived by high performance liquid chromatography. Satisfactory retrievals were also obtained using PLS-models trained with a data set including various locations of the world’s oceans, with however a lower accuracy. These results open the way to an application of this method to absorption spectra derived from hyperspectral and field satellite radiance measurements

Spring coccolithophore production and dispersion in the temperate eastern North Atlantic Ocean

Production and dispersion of coccolithophores are assessed within their ecologic and hydrographic context across enhanced spring chlorophyll production in the surface eastern North Atlantic. Within a 4 day period from 12 to 16 March 2004, a N-S transect from 47 degrees N to 33 degrees N was sampled along 20 degrees W. Water samples from defined depths down to 200 m were analyzed for coccolithophores from 0.45 mu m polycarbonate filters by scanning electron microscopy. At 47 degrees N coccolithophores flourished when euphotic conditions allowed new production at deep mixing, low temperatures, and high nutrient concentrations. Emiliania huxleyi flourished at high turbulence during an early stage of the phytoplankton succession and contributed half of the total coccolithophore assemblage, with up to 150 x 10(3) cells L(-1) and up to 12 x 10(9) cells m(-2) when integrated over the upper 200 m of the water column. Maximum chlorophyll concentrations occurred just north of the Azores Front, at 37 degrees N-39 degrees N, at comparatively low numbers of coccolithophores. To the south, at 35 degrees N-33 degrees N, coccolithophores were abundant within calm and stratified Subtropical Mode Waters, and E. huxleyi was the dominant species again. Although the cell densities of coccolithophores observed here remained below those typical of plankton blooms visible from satellite images, the depth-integrated total mass makes them significant producers of calcite and contributors to the total carbon sedimentation at a much wider range of ecological conditions during late winter and early spring than hitherto assumed

Partitioning of the Open Waters of the Gulf of Mexico Based on the Seasonal and Interannual Variability of Chlorophyll Concentration

The seasonal and interannual variability of chlorophyll in the Gulf of Mexico open waters is studied using a three‐dimensional coupled physical‐biogeochemical model. A 5 years hindcast driven by realistic open‐boundary conditions, atmospheric forcings, and freshwater discharges from rivers is performed. The use of recent in situ observations allowed an in‐depth evaluation of the model nutrient and chlorophyll seasonal distributions, including the chlorophyll vertical structure. We find that different chlorophyll patterns of temporal variability coexist in the deep basin which thereby cannot be considered as a homogeneous region with respect to chlorophyll dynamics. A partitioning of the Gulf of Mexico open waters based on the winter chlorophyll concentration increase is then proposed. This partition is basically explained by the amount of nutrients injected into the euphotic layer which is highly constrained by the dynamic of the winter mixed layer. The seasonal and interannual variability appears to be affected by the variability of atmospheric fluxes and mesoscale dynamics (Loop Current eddies in particular). Finally, estimates of primary production in the deep basin are provided

Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean

Eddies are generated in the eastern tropical Pacific (3 degrees S-23 degrees N, 75 degrees-105 degrees W) by winds blowing through Central American mountain passes from the Atlantic. We used Coastal Zone Color Scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery complemented with monthly in situ sea surface temperature and wind series from the Comprehensive Ocean-Atmosphere Data Set (COADS) to study these eddies and their effect on pigment concentrations in the region. Pigment values in the Gulf of Tehuantepec generally reach higher values in November-March before those in the Gulf of Papagayo. The eddies generated in the Gulf of Tehuantepec are associated with passages of cold fronts across the Gulf of Mexico from the north, while the eddies off Papagayo and Panama are associated with increases in trade wind intensity. CZCS images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and AVHRR observations or numerical simulations. We counted 13 eddies in 1979-1980, 8 in 1984-1985, and 6 in 1985-1986, The eddies transfer both energy and biological constituents from the continental margin to the offshore tropical Pacific. The eddies frequently moved distances in excess of 1500 km from their point of origin. Both anticyclonic and cyclonic eddies are generated, but in general, there are more anticyclones. Anticyclonic eddies generally moved to the southwest. Some cyclonic eddies moved to the south and southeast along the Central American coast and appeared to be trapped by the cyclonic Costa Rica thermal dome. Eddies traveled at speeds varying between 9 and 21 cm s(-1) and had diameters of 100-500 km. Phytoplankton concentrations associated with the eddies varied from similar to 2 to \u3e10 mg m(-3) within similar to 70 km of the coast to similar to 1 mg m(-3) up to 600 km of the coast. Between late April and October, fewer eddies were observed, and phytoplankton concentrations were lower

Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean

Eddies are generated in the eastern tropical Pacific (3° S-23° N, 75°-105° W) by winds blowing through Central American mountain passes from the Atlantic. We used Coastal Zone Color Scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery complemented with monthly in situ sea surface temperature and wind series from the Comprehensive Ocean-Atmosphere Data Set (COADS) to study these eddies and their effect on pigment concentrations in the region. Pigment values in the Gulf of Tehuantepec generally reach higher values in November-March before those in the Gulf of Papagayo. The eddies generated in the Gulf of Tehuantepec are associated with passages of cold fronts across the Gulf of Mexico from the north, while the eddies off Papagayo and Panama are associated with increases in trade wind intensity. CZCS images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and AVHRR observations or numerical simulations. We counted 13 eddies in 1979-1980, 8 in 1984-1985, and 6 in 1985-1986. The eddies transfer both energy and biological constituents from the continental margin to the offshore tropical Pacific. The eddies frequently moved distances in excess of 1500 km from their point of origin. Both anticyclonic and cyclonic eddies are generated, but in general, there are more anticyclones. Anticyclonic eddies generally moved to the southwest. Some cyclonic eddies moved to the south and southeast along the Central American coast and appeared to be trapped by the cyclonic Costa Rica thermal dome. Eddies traveled at speeds varying between 9 and 21 cm s-1 and had diameters of 100-500 km. Phytoplankton concentrations associated with the eddies varied from ∼2 to \u3e10 mg m-3 within ∼70 km of the coast to ∼1 mg m-3 up to 600 km of the coast. Between late April and October, fewer eddies were observed, and phytoplankton concentrations were lower (\u3c0.25 mg m-3) and more uniform over the region. Copyright 2000 by the American Geophysical Union

Exploring future directions of control

Control system research is entering a new era, which may be considered a milestone in the history of Systems and Control. The traditional framework of a control system structure — i.e. plant, sensor, actuator and a controller — presents a number of limitations to some current research, i.e. (a) System to be controlled comprise network of subsystems; (b) Control task is achieved by a network of distributed local controllers (agents); (c) New research topics on control of networked behaviour, including consensus, formation and synchronisation, are clearly beyond the scope of the traditional “one controller” framework. It is worth noting that with these new trends some new concepts are emerging, e.g. consensusability, formationability, computability. The intended contributions of this paper are: (1) A new framework of control research represented by a new block diagram and its mathematical treatment. It is pointed out that, many current different studies can be considered as some special cases under this general framework; (2) a brief overview of various research fitting the proposed framework and some open questions. This paper is largely motivated by past, current and future applications of power system control, and is based on a recent invited presentation, of the first author, at a special workshop on “Bridging the Gap — Control Theory and Control Engineering Practice”

Satellite-derived total and new phytoplankton production in the Gulf of Mexico

408-417Integrated total (PTint) and new production (Pnewint) (gC m⁻² d⁻¹) were calculated for the Gulf of Mexico with semi-analytical models from the literature, using chlorophyll a concentrations (Chlsat) and the vertical attenuation coefficients of light (K₄₉₀) from monthly composites of the satellite sensor SeaWIFS (1997–2004). The phytoplankton biomass vertical distribution associated with Chlsat, and the vertical distribution of the f-ratio [f(z) = Pnew(z)/PT(z)], were deduced from historic oceanographic data. Based on bathimetry, surface T ºC, Chl and nutrients, the Gulf was partitioned into three regions: Yucatan, Deep-waters, and Mississippi. The year was divided into two periods for the Deep-waters region, “cool” and “warm.” The whole year was treated as a single period for the Yucatan and Mississippi regions. Average values for PTint had a significant seasonal variation for the Deep-waters region (0.37-0.44 and 0.22-0.24 gC m⁻² d⁻¹, for the “cool” and “warm” periods, respectively), and similarly for Pnewint (0.023-0.026 and 0.013-0.014 gC m⁻² d⁻¹). Ranges for the average PTint values were 1.18 – 1.22, and 1.60 – 1.68 gC m⁻² d⁻¹, for the Yucatan and Mississippi regions, respectively. Ranges for Pnewint were 0.97 – 1.05, and 1.38 – 1.44 gC m⁻² d⁻¹. The present, limited data, do not show a significant interannual PTint and Pnewint variability in any region of the Gulf. Longer satellite time series for more complete future work may lead to the description of significant interannual primary production variability in the Gulf