ESA Contributes To
Ocean Carbon Cycle Research
(5 May 2008) The Earth's oceans play a vital role in the carbon cycle, making it imperative that we understand marine biological activity enough to predict how our planet will react to the extra 25 000 million tonnes of carbon dioxide humans are pumping into the atmosphere annually.
A GlobColour chlorophyll product showing the distribution of phytoplankton in the Atlantic Ocean and Mediterranean Sea. (courtesy: globcolour.info)
The colour of oceanic seawater depends
largely on the number of microscopic phytoplankton, marine plants that live in
the well-lit surface layer. Just like land-based plants, phytoplankton
accumulate carbon dioxide during photosynthesis and store it in their tissues,
making them potentially important carbon sinks.
While phytoplankton
themselves are individually microscopic, the chlorophyll they collectively
contain colours the ocean's waters, which provides a means of detecting these
tiny organisms from space with dedicated ocean colour sensors.
Marine phytoplankton seen through a microscope. (courtesy: N. Sullivan, US National Oceanic & Atmospheric Administration/Department of Commerce)
To support ocean carbon cycle research,
ESA's GlobColour project has merged 55 terabytes of data from three
state-of-the-art instruments aboard different satellites, including MERIS
aboard ESA's Envisat, MODIS aboard NASA's Aqua and SeaWiFS aboard GeoEye's
Orbview-2, to produce a 10-year dataset of global ocean colour stretching to
2007.
"I am quite impressed by the work ESA has done so far within
GlobColour," said Dr Cyril Moulin of the International Ocean Carbon
Co-ordination Project (IOCCP). "This
10-year dataset is going to be very
useful for carbon studies and global modelling."
The ocean colour
datasets are freely available to the public via the GlobColour website. A new
web interface, Hermes, is available which allows users to select a time period,
spatial region and product type. Based on this input, the system extracts the
appropriate ocean colour products for users to download.
By combining
observations from multiple sensors, GlobColour brings several benefits over
existing products, such as better sampling of the daily variability, smaller
errors because of the larger amount of data and reduced instrumental
biases.
To guarantee the data set is of good quality, the data have
undergone an intensive validation process by comparing measurements from
in-situ buoys. The conclusion was that the error statistics of the merged data
are better than data from the three individual sensors.
Envisat's MERIS reduced-resolution image from 3 May 2007 showing a bloom of phytoplankton (primarily coccolithophores) along the edge of the continental shelf south west of Ireland and to the west of the English Channel, and suspended sediments in the Irish Sea, Bristol Channel and English Channel. (courtesy: ESA)
In addition to aiding carbon cycle research,
ocean colour data can provide oceanographers with the information they need to
monitor the state of the oceans for other applications, such as for the
fisheries and aquaculture industries.
GlobColour, part of ESA's Data
User Element (DUE), will begin providing near-real time ocean colour
observations to support this type of operational oceanography from
mid-2008.
This service will continue well into the future, thanks to the
European Commission (EC), who will continue production of the GlobColour time
series from 2009 as part of the Marine Core Service of the GMES (Global
Monitoring for Environment and Security) initiative.
"We need to sustain
an international effort to make sure we can link one satellite dataset to
another to build the long-time series that we need to distinguish change from
cycles, and GlobColour is definitely a significant step in that perspective,"
said Dr James Yoder, Chair of the International Ocean-Colour Co-ordinating
Group (IOCCG).
Marine Core Service and GMES
The Marine Core
Service will deliver systematic reference information on the state of the
global ocean and European Union seas by providing observational and model data,
real-time predictions and ocean scenario simulations.
GMES - a joint
initiative of the EC and ESA - responds to Europe's needs for geo-spatial
information services by bringing together the capacity of Europe to collect and
manage data and information on the environment and civil security, for the
benefit of European citizens.
(source: ESA)
