César Fuentes-Yaco, José Eduardo Valdez-Holguín, Trevor Platt, Shubha Sathyendranath, Jochen Halfar, Lucio Godinez Orta, José Manuel Borges, Emmanuel Devred
Strong winds associated with hurricanes generate upwelling of cold water and transfer nutrients to the sea surface, supporting the development of significant phytoplankton blooms. Here we study the effect of the passage of hurricanes on the fields of sea surface temperature and chlorophyll-a in the pelagic ocean. A case-study is given for Hurricane Ignacio, the first storm of the 2003 season in the Eastern Tropical Pacific Ocean, on the south-eastern waters of Baja California Peninsula. The net reduction of in situ water temperature was -10° C and the phytoplankton pigment increase was 10 fold. Detailed features of the distribution of both characteristics of the sea surface are evident in the synoptic satellite imagery (MODIS/Aqua), with extreme thermal changes of -6 °C and increases up to 25 fold in chlorophyll-a. The satellite-derived averaged changes computed in the area of impact (~45,000 km^2) show temperature reduction of -1.3 °C and 1.5 fold increase of phytoplankton biomass. The physical and biological features studied for Hurricane Ignacio are crucial for understanding the ecosystem function around the southern Baja California peninsula, a region with strong dynamics in the carbon cycle. The study demonstrates how hurricanes induce phytoplankton blooms, a critical resource in the food chain, in particular for the pelagic fisheries. Systematic use of satellite remote-sensing may be advantageous to quantify at short, middle and long term, the impact of hurricanes on ocean biology at spatial and temporal scales of local and regional interest.
In this work, we present a new method for dynamic assignment of
the boundaries of the ecological provinces of the North West Atlantic. The results are compared with the distribution of diatoms in the study area. Both analyses rely on ocean-colour data for the region. Diatoms were identified using remoteely-sensed data on the basis of their species-dependent absorption characteristics, which were embedded in a simple reflectance model(Sathyendranath et al., 2004). Maps of diatom distributions were produced for the area. Satellite-derived chlorophyll biomass and sea surface temperature (MODIS data) for the same period were used to redefine, in a dynamic way, the static borders of the ecological provinces (Sathyendranath et al., 1995; Longhurst 1998). The analyses were carried on two-week composite images, at different times of the year (April-May, July and October), to examine seasonal variability in the boundaries. The boundaries of provinces and the occurrence of diatoms were spatially coherent. Diatoms were favoured in rich waters on the continental shelf and in cold waters at high latitudes. In provinces labelled as
oligotrophic (subtropical gyre and Gulf Stream), very negligible fractions of diatoms were found at any time of the year.
Remote sensing has improved our capacity to study the passage of hurricanes in the coastal zone. These transient events lead to upwelling of cold, nutrient-rich waters into the mixed layer that promotes increased primary production and therefore higher phytoplankton biomass. The Northwest Atlantic, an area with rich fisheries resources, experiences several hurricanes each year. We report on the response of the fields of chlorophyll and temperature to the passage of Hurricane Fabian using satellite images of ocean colour (SeaWiFS, analysed with local modifications to the standard NASA method) and sea-surface temperature (NOAA/AVHRR). Data from a band of 700 km width along the storm track were extracted from composite images of the fields before and after the storm passage. Concurrent changes in the temperature and chlorophyll-a (Chl-a) fields were observed along and across the storm track. There is an imbalance in the distribution of the differences in both SST and Chl-a, with changes being smaller on the left side of the storm path, than on the right side. We also examined changes in the taxonomic composition of phytoplankton communities promoted by the physical forcing, since it is known that diatoms have fast growth rates in relatively turbulent and nutrient-rich waters. This step was carried on using an algorithm that allows to distinguish between diatoms and other phytoplankton populations. Our results showed that after the passage of Hurricane Fabian, a new phytoplankton succession cycle was initiated, led by diatoms.
The in water penetration of the solar light is described by the attenuation coefficient Kd. Kd depends upon (i) the solar angle, (ii) the state of the sky, and (iii) the water composition. Knowing the above parameters as well as the inherent optical properties of the atmosphere ad of the water, a radiative transfer code can be run to derive Kd at different wavelengths.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.