Algorithm development and validation for satellite‐derived distributions of DOC and CDOM in the U.S. Middle Atlantic Bight

Abstract

Carbon is the basic building block of life, and the carbon cycle represents the cycle of all living organisms. Through the process of photosynthesis, plants on land or algae living in lakes and oceans take up carbon dioxide and convert this into living organic products (such as carbohydrates, proteins, fats, etc.). Through the process of respiration, organisms break down these organic compounds for energy, metabolizing them into various forms of chemical energy and regenerating the carbon dioxide. The level of carbon dioxide in the atmosphere plays an important role in earth's climate through the "greenhouse effect". Therefore, understanding the carbon cycle provides insight about life on earth as well as its role in climate change. The carbon component of interest here is dissolved organic carbon (DOC), which comprises >97% of the organic carbon in the ocean. The dissolved organic carbon in the coastal ocean originates from many sources, including land plant debris and pollution transported by rivers and material excreted from algae and other living organisms in the ocean. Our objective in this study was to quantify DOC from space through the portion of DOC that can be seen by satellite sensorscolored dissolved organic matter (CDOM). The substance that leaches from tea bags is an example of CDOM. Satellite instruments used to study ocean biology do not measure ocean constituents directly, but rather measure light leaving the ocean at multiple wavelengths (blue, green, red, etc.), which can be used to derive the concentration of ocean constituents, including chlorophyll and CDOM. In fact, the presence of high levels of CDOM in coastal waters reduces the accuracy of satellite chlorophyll measurements.We 'conducted multiple expeditionswithin the coastal ocean region along the U.S. MidAtlantic to collect measurements of DOC, CDOM, and light leaving the ocean to develop relationships to compute CDOM and DOC from NASA's MODIS and SeaWiFS satellite sensors. We also evaluated the accuracy of the satellite measurements through comparisons with independent measurements collected at sea. Our results demonstrate that the accuracies of satellite-derived measurements are within 9% for DOC and 20% for CDOM for our coastal ocean study region. These results compare very well with the 33% accuracy for satellite estimates of ocean chlorophyll globally. This study represents the first successful and verified satellite measurements of dissolved organic carbon and colored dissolved organic matter in the coastal ocean. These new satellite products can be applied to study coastal ocean processes such as the export of DOC from land to the ocean, the summer accumulation of DOC from algae and other organisms, and the summer bleaching of CDOM by sunlight. We can apply these satellite observations to investigate interannual and decadal-scale variability in surface ocean CDOM and DOC within coastal waters and monitor impacts of climate change and human activities on coastal ecosystems.https://ntrs.nasa.gov/search.jsp?R=20080040698 2019-03-2...

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