Turbidity (Kd490) Average Annual Frequency of Anomalies, 1998-2018 - American Samoa

Spectrally resolved water-leaving radiances (ocean color) and inferred chlorophyll concentration are key to studying phytoplankton dynamics at seasonal and inter-annual scales, for a better understanding of the role of phytoplankton in marine biogeochemistry; the global carbon cycle; and the response of marine ecosystems to climate variability, change, and feedback processes. Ocean color data also have a critical role in operational observation systems monitoring coastal eutrophication, harmful algal blooms, and sediment plumes. The contiguous ocean color record reached 21 years in 2018. However, it is comprised of a number of one-off missions such that creating a consistent time series of ocean color data requires merging of the individual sensors without introducing artifacts.

The diffuse attenuation coefficient at 490 nm (Kd490) indicates the turbidity of the water column: i.e., how well visible light in the blue to green region of the spectrum penetrates the water column. The value of Kd490 represents the rate at which light at 490 nm is attenuated with depth. For example, a Kd490 of 0.1 per meter means that light intensity is reduced by one natural log within 10 meters of water. Thus, for a Kd490 of 0.1, one attenuation length is 10 meters. Higher Kd490 values mean shallower attenuation depths and thus higher turbidity, or lower clarity, of ocean water. This layer represents the annual average number of anomalies of Kd490 (m-1) from 1998-2018, with values presented as fraction of a year.

Data products generated by the Ocean Colour component of the European Space Agency (ESA) Climate Change Initiative (CCI) project. These files are 8-day 4-km composites of merged sensor products: Global Area Coverage (GAC), Local Area Coverage (LAC), MEdium Resolution Imaging Spectrometer (MERIS), Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua, Ocean and Land Colour Instrument (OLCI), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and Visible Infrared Imaging Radiometer Suite (VIIRS).

The Kd490 average annual frequency of anomalies was calculated by taking the average number of times that the 8-day time series exceeded the maximum monthly climatological Kd490 value from 1998-2018 for each pixel. A quality control mask was applied to remove spurious data associated with shallow water, following Gove et al., 2013. Nearshore map pixels with no data were filled with values from the nearest neighboring valid offshore pixel by using a grid of points and the Near Analysis tool in ArcGIS then converting points to raster.

Data source: https://oceanwatch.pifsc.noaa.gov/erddap/griddap/esa-cci-kd-8d-v5-0.graph

Tags: american samoa, aquatic ecosystems, biosphere, coastal areas, coastal processes, coral reef, coral reefs, earth science, ecosystems, human dimensions, human settlements, kd490, manua, marine ecosystems, ocean, ocean optics, oceans, ofu, olosega, pacific islands ocean observing system, pacific ocean, pacioos, polynesia, reef, reef habitat, rose atoll, south pacific ocean, swains, tau, turbidity, tutuila, water quality
Organization: National Oceanic and Atmospheric Administration, Department of Commerce