Stable isotope analysis of Porites coral core from the Andaman Islands

North Atlantic climate variations are reflected in sedimentary records from the northern Indian Ocean in which two basins, the Arabian Sea and the Bay of Bengal, are strongly affected by the monsoon. Contrary to the Bay of Bengal the Arabian Sea plays an important role in the global marine nitrogen cycle. In its mid-water oxygen minimum zone (OMZ) bioavailable fixed nitrogen is reduced to nitrogen gas (NO3- - > N2), whereas oxygen concentrations are slightly above the threshold of nitrate reduction in the OMZ of the Bay of Bengal. A coral colony (Porites lutea) growing south of Port Blair on the Andaman Islands in the Bay of Bengal was studied for its response to changes in the monsoon system and its link to temperature changes in the North Atlantic Ocean, between 1975 and 2006. Its linear extension rates, d13C and d18O values measured within the coral skeleton reveal a strong seasonality, which seems to be caused by the monsoon-driven reversal of the surface ocean circulation. The sampling site appears to be influenced by low salinity Bay of Bengal Water during the NE monsoon (boreal winter) and by the high salinity Arabian Sea Water during the SW monsoon in summer. The high salinity Arabian Sea Water circulates along with the Summer Monsoon Current (S-MC) from the Arabia Sea into the Bay of Bengal. Decreasing d18O and reconstructed salinity values correlate to the increasing SSTs in the North Atlantic Ocean indicating a reduced influence of the S-MC at the sampling site in the course of northern hemispheric warming. During such periods oxygen-depletion became stronger in the OMZ of the Arabian Sea as indicated by the sedimentary records. A reduced propagation of oxygen-depleted high salinity Arabian Sea Water into the Bay of Bengal could be a mechanism maintaining oxygen concentration above the threshold of nitrate reduction in the OMZ of the Bay of Bengal in times of global warming.

Global Ocean Colour for Carbon Cycle Research (full product set)

In 2005, the International Ocean Colour Coordinating Group (IOCCG) convened a working group to examine the state of the art in ocean colour data merging, which showed that the research techniques had matured sufficiently for creating long multi-sensor datasets (IOCCG, 2007). As a result, ESA initiated and funded the DUE GlobColour project (http://www.globcolour.info/) to develop a satellite based ocean colour data set to support global carbon-cycle research. It aims to satisfy the scientific requirement for a long (10+ year) time-series of consistently calibrated global ocean colour information with the best possible spatial coverage. This has been achieved by merging data from the three most capable sensors: SeaWiFS on GeoEye's Orbview-2 mission, MODIS on NASA's Aqua mission and MERIS on ESA's ENVISAT mission. In setting up the GlobColour project, three user organisations were invited to help. Their roles are to specify the detailed user requirements, act as a channel to the broader end user community and to provide feedback and assessment of the results. The International Ocean Carbon Coordination Project (IOCCP) based at UNESCO in Paris provides direct access to the carbon cycle modelling community's requirements and to the modellers themselves who will use the final products. The UK Met Office's National Centre for Ocean Forecasting (NCOF) in Exeter, UK, provides an understanding of the requirements of oceanography users, and the IOCCG bring their understanding of the global user needs and valuable advice on best practice within the ocean colour science community. The three year project kicked-off in November 2005 under the leadership of ACRI-ST (France). The first year was a feasibility demonstration phase that was successfully concluded at a user consultation workshop organised by the Laboratoire d'Océanographie de Villefranche, France, in December 2006. Error statistics and inter-sensor biases were quantified by comparison with insitu measurements from moored optical buoys and ship based campaigns, and used as an input to the merging. The second year was dedicated to the production of the time series. In total, more than 25 Tb of input (level 2) data have been ingested and 14 Tb of intermediate and output products created, with 4 Tb of data distributed to the user community. Quality control (QC) is provided through the Diagnostic Data Sets (DDS), which are extracted sub-areas covering locations of in-situ data collection or interesting oceanographic phenomena. This Full Product Set (FPS) covers global daily merged ocean colour products in the time period 1997-2006 and is also freely available for use by the worldwide science community at http://www.globcolour.info/data_access_full_prod_set.html. The GlobColour service distributes global daily, 8-day and monthly data sets at 4.6 km resolution for, chlorophyll-a concentration, normalised water-leaving radiances (412, 443, 490, 510, 531, 555 and 620 nm, 670, 681 and 709 nm), diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. Error statistics from the initial sensor characterisation are used as an input to the merging methods and propagate through the merging process to provide error estimates for the output merged products. These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into ocean simulations. An intensive phase of validation has been undertaken to assess the quality of the data set. In addition, inter-comparisons between the different merged datasets will help in further refining the techniques used. Both the final products and the quality assessment were presented at a second user consultation in Oslo on 20-22 November 2007 organised by the Norwegian Institute for Water Research (NIVA); presentations are available on the GlobColour WWW site. On request of the ESA Technical Officer for the GlobColour project, the FPS data set was mirrored in the PANGAEA data library.