NASA recently added a new data set to Giovanni-4 (Geospatial Interactive Online Visualization ANd aNalysis Infrastructure, Version 4). The data set derives from the most recent model run of the NASA Ocean Biogeochemical Model (NOBM). NOBM, developed by Watson Gregg and Cecile Rousseaux of the Global Modeling and Assimilation Office (GMAO), provides daily and monthly assimilated Total Chlorophyll concentrations, the concentrations of four phytoplankton functional groups, iron and nitrate concentrations, average sea ice cover, and mixed layer depth.
The new data set can be acquired from, in addition to Giovanni, the GES DISC Mirador data search and access system, OPeNDAP, Simple Subset Wizard, and Reverb/ECHO (See below for links.)
Previous versions of the NOBM model used chlorophyll concentrations from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) as model input. The new model run includes chlorophyll concentrations from both SeaWiFS and the Moderate Resolution Imaging Spectroradiometer (MODIS), using an approach that reduces the discrepancies between the two data sets (Gregg and Casey, 2010). This approach allows the modeled period to be extended to the end of 2012.
Refinements in the new version of the model also include a multivariate assimilation methodology to determine nutrient concentrations based primarily on the calculated changes in chlorophyll concentration. More information on the NOBM model can be found in the News article, New NASA Ocean Biogeochemical Data in Giovanni, and on the GMAO Web site:
Examples of Giovanni-4 visualization of NOBM data are shown in the following two figures. Figure 1 (above right and below) shows the Assimilated Total Chlorophyll for the North Atlantic Ocean in April 2008.
Figure 1. NOBM Assimilated Total Chlorophyll for the North Atlantic Ocean in April 2008. The annual spring bloom of phytoplankton in the North Atlantic Ocean takes place approximately from March through June, with the highest concentrations of phytoplankton progressing northward as spring advances. (Click to view full-size version.)
Figure 2 shows, with an expanded view of the region, where the four phytoplankton functional groups in the model are expected to occur during this month. Diatoms are found north of the Gulf Stream and in the central North Atlantic, consistent with the location of the highest chlorophyll concentrations in the North Atlantic. Chlorophytes are distributed north of the western Gulf Stream, while cyanobacteria are found south of the Gulf Stream front and in parts of the Sargasso Sea. Coccolithophores occur primarily in the eastern North Atlantic, with a “hot spot” for coccolithophore blooms in the Bay of Biscay west of France. Figure 3 shows a MODIS image of a coccolithophore bloom in the Bay of Biscay acquired on April 29, 2013. Coccolithophore blooms frequently recur in the Bay of Biscay.
Figure 2. Distributions of the four phytoplankton functional groups determined by the NOBM model, for the month of April 2008 in the North Atlantic Ocean. Note that chlorophytes and diatoms are expected to be located north of the Gulf Stream front, whereas cyanobacteria are located to the south of the front. Coccolithophores are distributed over the eastern part of the basin. Note the high concentration of coccolithophores in the Bay of Biscay, which is an area where bright coccolithophore blooms are frequently observed.
Figure 3. MODIS image of a coccolithophore bloom in the Bay of Biscay, acquired on April 29, 2013. The blue-green waters of the bloom can be easily distinguished from the greens and browns of coastal sediments and river outflow. Click to view larger image.
Links to NOBM data:
Gregg, W. W. and N. W. Casey (2010) Improving the consistency of ocean color data: A step toward climate data records. Geophysical Research Letters 37(4): L04605.
Gregg, W. W. and C. S. Rousseaux (2014) Decadal trends in global pelagic ocean chlorophyll: A new assessment combining multiple satellites, in situ data, and models. Journal of Geophysical Research, doi: 10.1002/2014JC010158.