File:Spencer Gulf (MODIS 2021-12-28).jpg

English: On December 23, 2021, the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of a sunny summer day over Spencer Gulf, Australia. The large, V-shaped Spencer Gulf spans a length of about 200 miles (322 km) and measures 80 miles (129 km) at the mouth. Spencer is the largest of the two gulfs seen in this image and is separated from the Gulf of St. Vincent by the long Yorke Peninsula.

With the deep blue waters opening to the Great Australian Bight, Spencer Gulf is surrounded by large coastal salt marshes, mud flats and mangrove forests, and supports large seagrass meadows. These features create a vibrant and diverse ecosystem that supports a wide range of species, including the Giant Cuttlefish. An area in the northwest part of Spencer Gulf, near the town of Whyalla, is the only place on Earth where this species breeds in large numbers.

The swirls of color floating in Spencer and St. Vincent Gulfs are most likely sediment, stirred from the sea floor by currents and tides. The color could also be caused by phytoplankton, which are microscopic plant-like organisms that float on the surface of the water year-round. When conditions are right (correct amount of nutrients, water temperature and sunlight length), phytoplankton can reproduce dramatically to create floating blooms that are easily seen from space.