THE REMOTE SENSING OF SAND DUNES IN BAJA CALIFONIA, MEXICO

Within the Gulf of California, coastal sand dunes and dune fields are potential sinks for carbon in the form of biologically produced calcium carbonate. For example, the small dune field at San Nicholas holds about 350,000 m³ of sand and sequesters approximately 3.2 X 10¹¹ grams of carbon. Carbonate–rich dunes (eolianites) are found in coastal zones or on islands between 20-40 degrees of latitude in both hemispheres. The Gulf of California fits these criteria and has a climate conducive to marine production of skeletal calcium carbonate and the onshore winds necessary to transfer those materials inland. Dunes with 70% carbonate sand by volume have been reported previously from the Pinacate dune field at the north end of the Gulf of California. Dunes with a range of carbonate content have also been described from Punta Chivato (54-86%), San Nicholas (36-51%) and Punta El Gallo (5-15%) on the peninsular coast. Eolianites have also been found on the midriff islands of Coronados (86%), Carmen (68%) and Monserrate.

Using image data from the LANDSAT and ASTER satellite systems is an effective way to geologically survey rugged, low-vegetation areas such as the Baja California peninsula. Within a given image, carbonate-rich dunes appear brighter than their low-carbonate equivalents. We used the remote sensing software ENVI 4.2 to measure the area of dune fields from satellite images in order to estimate carbon content. Higher resolution panchromatic, or comparable multi-band data in the visible range, is now available for many of these dune fields through the Google Earth mapping service. We used Google Earth to enhance our coastal dune study, measure more accurately the average wind direction for dune fields, and identify previously undescribed sheet dunes from the Gulf of California coast, interior mountain basins of the Baja peninsula, and Isla Tiburon. A comparison of the intermountain sheet dunes with the classic sheet dunes from the Mohave Desert region, using Google Earth, suggests that these sand sheets have a similar pluvial origin.