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  • 1
    Online Resource
    Online Resource
    Sea level measured by tide gauges from global oceans - the Joint Archive for Sea Level holdings (NCEI Accession 0019568), Version 5.5, NOAA National Centers for Environmental Information
    Copernicus GmbH ; 2017
    In:  Biogeosciences Vol. 14, No. 4 ( 2017-02-24), p. 817-826
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 14, No. 4 ( 2017-02-24), p. 817-826
    Abstract: Abstract. The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, the first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data show that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure, at least during low tide periods. Altimetry data were used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such an event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-14-817-2017
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 2158181-2
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  • 2
    Online Resource
    Online Resource
    Investigating links between rainfall variations in the Ogooué River basin and ENSO in the Pacific Ocean over the period 1940–1999
    Copernicus GmbH ; 2021
    In:  Proceedings of the International Association of Hydrological Sciences Vol. 384 ( 2021-11-16), p. 181-186
    Details
    In: Proceedings of the International Association of Hydrological Sciences, Copernicus GmbH, Vol. 384 ( 2021-11-16), p. 181-186
    Abstract: Abstract. This paper investigates links between rainfall variability in the Ogooué River Basin (ORB) and El Niño Southern Oscillation (ENSO) in the Pacific Ocean. Recent hydroclimatology studies of the ORB and surrounding areas resulting in contrasting conclusions about links between rainfall variability and ENSO. Thus, to make the issue clearer, this study investigates the links between ENSO and rainfall in the ORB over the period 1940–1999. The principal component analysis of monthly rainfall in the ORB was done. The temporal mode of the first component corresponds to the interannual variations of rainfall on the ORB. Also, the pattern of the spatial mode of the first component shows that the ORB is a homogeneous hydroclimatic zone. However, no leading mode is significantly correlated to the ENSO index. A cross-wavelet analysis of the time series of basin-scale rainfall and the ENSO index was therefore carried out. The result is a set of periodogram structures corresponding to some ENSO episodes recorded over the study period. And wavelet coherence analysis of both time series confirms that there are significant links between ENSO and rainfall in the ORB.
    Type of Medium: Online Resource
    ISSN: 2199-899X
    URL: Article
    DOI: 10.5194/piahs-384-181-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2827925-6
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  • 3
    Online Resource
    Online Resource
    Coastal sea level rise at Senetosa (Corsica) during the Jason altimetry missions
    Copernicus GmbH ; 2020
    In:  Ocean Science Vol. 16, No. 5 ( 2020-10-07), p. 1165-1182
    Details
    In: Ocean Science, Copernicus GmbH, Vol. 16, No. 5 ( 2020-10-07), p. 1165-1182
    Abstract: Abstract. In the context of the ESA Climate Change Initiative project, we are engaged in a regional reprocessing of high-resolution (20 Hz) altimetry data of the classical missions in a number of the world's coastal zones. It is done using the ALES (Adaptive Leading Edge Subwaveform) retracker combined with the X-TRACK system dedicated to improve geophysical corrections at the coast. Using the Jason-1 and Jason-2 satellite data, high-resolution, along-track sea level time series have been generated, and coastal sea level trends have been computed over a 14-year time span (from July 2002 to June 2016). In this paper, we focus on a particular coastal site where the Jason track crosses land, Senetosa, located south of Corsica in the Mediterranean Sea, for two reasons: (1) the rate of sea level rise estimated in this project increases significantly in the last 4–5 km to the coast compared to what is observed further offshore, and (2) Senetosa is the calibration site for the TOPEX/Poseidon and Jason altimetry missions, which are equipped for that purpose with in situ instrumentation, in particular tide gauges and a Global Navigation Satellite System (GNSS) antenna. A careful examination of all the potential errors that could explain the increased rate of sea level rise close to the coast (e.g., spurious trends in the geophysical corrections, imperfect inter-mission bias estimate, decrease of valid data close to the coast and errors in waveform retracking) has been carried out, but none of these effects appear able to explain the trend increase. We further explored the possibility that it results from real physical processes. Change in wave conditions was investigated, but wave setup was excluded as a potential contributor because the magnitude was too low and too localized in the immediate vicinity of the shoreline. A preliminary model-based investigation about the contribution of coastal currents indicates that it could be a plausible explanation of the observed change in sea level trend close to the coast.
    Type of Medium: Online Resource
    ISSN: 1812-0792
    URL: Article
    DOI: 10.5194/os-16-1165-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2183769-7
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  • 4
    Online Resource
    Online Resource
    Observability of fine-scale ocean dynamics in the northwestern Mediterranean Sea
    Copernicus GmbH ; 2017
    In:  Ocean Science Vol. 13, No. 1 ( 2017-01-13), p. 13-29
    Details
    In: Ocean Science, Copernicus GmbH, Vol. 13, No. 1 ( 2017-01-13), p. 13-29
    Abstract: Abstract. Technological advances in the recent satellite altimeter missions of Jason-2, SARAL/AltiKa and CryoSat-2 have improved their signal-to-noise ratio, allowing us to observe finer-scale ocean processes with along-track data. Here, we analyse the noise levels and observable ocean scales in the northwestern Mediterranean Sea, using spectral analyses of along-track sea surface height from the three missions. Jason-2 has a higher mean noise level with strong seasonal variations, with higher noise in winter due to the rougher sea state. SARAL/AltiKa has the lowest noise, again with strong seasonal variations. CryoSat-2 is in synthetic aperture radar (SAR) mode in the Mediterranean Sea but with lower-resolution ocean corrections; its statistical noise level is moderate with little seasonal variation. These noise levels impact on the ocean scales we can observe. In winter, when the mixed layers are deepest and the submesoscale is energetic, all of the altimeter missions can observe wavelengths down to 40–50 km (individual feature diameters of 20–25 km). In summer when the submesoscales are weaker, SARAL can detect ocean scales down to 35 km wavelength, whereas the higher noise from Jason-2 and CryoSat-2 blocks the observation of scales less than 50–55 km wavelength. This statistical analysis is completed by individual case studies, where filtered along-track altimeter data are compared with co-located glider and high-frequency (HF) radar data. The glider comparisons work well for larger ocean structures, but observations of the smaller, rapidly moving dynamics are difficult to co-locate in space and time (gliders cover 200 km in a few days, altimetry in 30 s). HF radar surface currents at Toulon measure the meandering Northern Current, and their good temporal sampling shows promising results in comparison to co-located SARAL altimetric currents. Techniques to separate the geostrophic component from the wind-driven ageostrophic flow need further development in this coastal band.
    Type of Medium: Online Resource
    ISSN: 1812-0792
    URL: Article
    DOI: 10.5194/os-13-13-2017
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 2183769-7
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