Variabilité, circulation et chlorophylle dans la région du Dôme d'Angola en février-mars 1971

In February-March 1971 the hydrological conditions off Angola did not display the thermal dome mapped by Mazeika's averages (1967). Cold water cells observed are connected at the surface to a sinuous boundary between low-salinity coastal waters and high-salinity tropical oceanic waters. That boundary coincides rather regularly with an area where trades and SW winds alternate; photosynthesis growths rapidly in a thermoclinal layer that rises until 10 m of the surface but never outcrops. Below a poor and permanent homogeneous surface layer, chlorophyll concentrations show a distribution which is typical of divergence areas. Geostrophical and measured currents show off a transient process in horizontal and vertical movements, however the general curvature of the circulation is propitious to upwelling. Oxygen oversaturations of about 110%, suggest a moderate potential primary production which confirms slowness and alternation of movements. Also, the regular range of the various chemical and biological levels and moderate chlorophyll concentrations suggest an ecosystem where nutrients supply rapidly equilibrate phytoplankton consumption and not at all a 'phytoplankton bloom' area as that which exists in coastal upwelling. Values of Richardson's number show that instability becomes visible at the bottom of the euphotic layer. An evaluation of the vertical motion is inferred by the peculiar distribution and diurnal alternance of the winds shows that 'doming' structures may be sustained by local meteorological events

Aspects principaux des variations du phytoplancton sur le plateau continental ivorien

21 surveys over the whole Ivorian continental shelf lead to a description of the phytoplankton repartition according to the different seasons: great and small cold seasons, discharge seasons, and warm seasons. Yearly means of surface cells concentrations range from 1000 to 30000 cells per liter, corresponding to a daily production of 386 to 1166 mg C/m2, according to regression analysis. These values make Côte d'Ivoire a rather rich region, which is subjected to wide standing crop variations

An algorithm for detecting <i>Trichodesmium</i> surface blooms in the South Western Tropical Pacific

<i>Trichodesmium</i>, a major colonial cyanobacterial nitrogen fixer, forms large blooms in NO₃-depleted tropical oceans and enhances CO₂ sequestration by the ocean due to its ability to fix dissolved dinitrogen. Thus, its importance in C and N cycles requires better estimates of its distribution at basin to global scales. However, existing algorithms to detect them from satellite have not yet been successful in the South Western Tropical Pacific (SP). Here, a novel algorithm (TRICHOdesmium SATellite) based on radiance anomaly spectra (RAS) observed in SeaWiFS imagery, is used to detect <i>Trichodesmium</i> during the austral summertime in the SP (5° S–25° S 160° E–170° W). Selected pixels are characterized by a restricted range of parameters quantifying RAS spectra (e.g. slope, intercept, curvature). The fraction of valid (non-cloudy) pixels identified as <i>Trichodesmium</i> surface blooms in the region is low (between 0.01 and 0.2 %), but is about 100 times higher than deduced from previous algorithms. At daily scales in the SP, this fraction represents a total ocean surface area varying from 16 to 48 km² in Winter and from 200 to 1000 km² in Summer (and at monthly scale, from 500 to 1000 km² in Winter and from 3100 to 10 890 km² in Summer with a maximum of 26 432 km² in January 1999). The daily distribution of <i>Trichodesmium</i> surface accumulations in the SP detected by TRICHOSAT is presented for the period 1998–2010 which demonstrates that the number of selected pixels peaks in November–February each year, consistent with field observations. This approach was validated with in situ observations of <i>Trichodesmium</i> surface accumulations in the Melanesian archipelago around New Caledonia, Vanuatu and Fiji Islands for the same period

An algorithm for detecting Trichodesmium surface blooms in the South Western Tropical Pacific

Trichodesmium, a major colonial cyanobacterial nitrogen fixer, forms large blooms in NO₃-depleted tropical oceans and enhances CO₂ sequestration by the ocean due to its ability to fix dissolved dinitrogen. Thus, its importance in C and N cycles requires better estimates of its distribution at basin to global scales. However, existing algorithms to detect them from satellite have not yet been successful in the South Western Tropical Pacific (SP). Here, a novel algorithm (TRICHOdesmium SATellite) based on radiance anomaly spectra (RAS) observed in SeaWiFS imagery, is used to detect Trichodesmium during the austral summertime in the SP (5° S–25° S 160° E–170° W). Selected pixels are characterized by a restricted range of parameters quantifying RAS spectra (e.g. slope, intercept, curvature). The fraction of valid (non-cloudy) pixels identified as Trichodesmium surface blooms in the region is low (between 0.01 and 0.2 %), but is about 100 times higher than deduced from previous algorithms. At daily scales in the SP, this fraction represents a total ocean surface area varying from 16 to 48 km² in Winter and from 200 to 1000 km² in Summer (and at monthly scale, from 500 to 1000 km² in Winter and from 3100 to 10 890 km² in Summer with a maximum of 26 432 km² in January 1999). The daily distribution of Trichodesmium surface accumulations in the SP detected by TRICHOSAT is presented for the period 1998–2010 which demonstrates that the number of selected pixels peaks in November–February each year, consistent with field observations. This approach was validated with in situ observations of Trichodesmium surface accumulations in the Melanesian archipelago around New Caledonia, Vanuatu and Fiji Islands for the same period

Cirene : air-sea iInteractions in the Seychelles-Chagos thermocline ridge region

Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 90 (2009): 1337-1350, doi:10.1175/2008BAMS2499.1.The Vasco—Cirene program ex-plores how strong air—sea inter-actions promoted by the shallow thermocline and high sea surface temperature in the Seychelles—Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and air—sea flux observations in this region in Jan-uary—February 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers. Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles—Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.CNES funded the Vasco part of the experiment; INSU funded the Cirene part. R/V Suroît is an Ifremer ship. The contributions from ODU, WHOI, and FOI (Sweden) are supported by the National Science Foundation under Grant Number 0525657. The participation of the University of Miami group was funded though NASA (NNG04HZ33C). PMEL participation was supported through NOAA’s Office of Climate Observation

SEIS: Insight's Seismic Experiment for Internal Structure of Mars.

By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01&nbsp;Hz to 50&nbsp;Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1&nbsp;sps and a continuous compound VBB/SP vertical axis at 10&nbsp;sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ∼ 2500 at 1&nbsp;Hz and ∼ 200 000 at 0.1&nbsp;Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w ∼ 3 at 40 ∘ epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.Electronic supplementary materialThe online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users

Fishery-Independent Data Reveal Negative Effect of Human Population Density on Caribbean Predatory Fish Communities

BACKGROUND: Understanding the current status of predatory fish communities, and the effects fishing has on them, is vitally important information for management. However, data are often insufficient at region-wide scales to assess the effects of extraction in coral reef ecosystems of developing nations. METHODOLOGY/PRINCIPAL FINDINGS: Here, I overcome this difficulty by using a publicly accessible, fisheries-independent database to provide a broad scale, comprehensive analysis of human impacts on predatory reef fish communities across the greater Caribbean region. Specifically, this study analyzed presence and diversity of predatory reef fishes over a gradient of human population density. Across the region, as human population density increases, presence of large-bodied fishes declines, and fish communities become dominated by a few smaller-bodied species. CONCLUSIONS/SIGNIFICANCE: Complete disappearance of several large-bodied fishes indicates ecological and local extinctions have occurred in some densely populated areas. These findings fill a fundamentally important gap in our knowledge of the ecosystem effects of artisanal fisheries in developing nations, and provide support for multiple approaches to data collection where they are commonly unavailable