The cool, rising waters support a variety of marine life and occasionally attract unusual photographers to the Bonny Shores area. When satellites passed over the Bonny Coast of South Australia in January 2024, they captured images showing blue and green spots swirling in the surface water. These colorful phytoplankton threads are in their prime. These tiny plant-like creatures thrive here in the summer when cold, nutrient-rich water emerges from the ocean's depths.
This image captured by the VIIRS (Visible Infrared Imaging Radiometer Suite) sensor on the SuomiNPP satellite shows a competing phytoplankton bloom on January 10, 2024. Images collected by NASA's Terra and Aqua satellites show that the algal bloom will be visible from space for the first time in late December 2023.
Jochen Kaempf, an oceanographer at Flinders University, said: "The green filaments we see in the picture are definitely phytoplankton blooms that extend along the continental shelf break and exist at a depth of about 150 meters. The bluer signals may be sediments located in very shallow water, or they may be different phytoplankton species."
Confirming the species of phytoplankton requires collecting water samples from the sea surface. However, a recent study by Kampf shows that diatoms often dominate large blooms in this area.
Temperature anomalies and upwelling events
Signs of cold water upwelling are also evident in satellite observations. Sea surface temperature data from NASA's Multiscale Ultra-Resolution Sea Surface Temperature Project (MURSST) show that water temperatures along much of the Bonny Coast on January 10 were about 3 degrees Celsius (5.4 degrees Fahrenheit) cooler than the long-term average temperature for that day (2003-2014).
The cooler waters are caused by the Great South Australian Coastal Upwelling System, a seasonal phenomenon that stretches from Ceduna in South Australia to Portland in Victoria - a distance of about 800 kilometers (500 miles). Upwelling in the area occurs in the summer (December to May), when seasonal winds from the southeast blow parallel to the coastline. These winds push coastal surface water offshore through a process called Ekman transport, pulling in cold water from depths of about 300 meters.
Importance of upwelling to marine life
Water deep in the ocean is often rich in nutrients because the remains of dead sea creatures continue to sink to the bottom and decompose. The nutrients released, especially nitrogen and phosphorus, are critical to phytoplankton growth. When nutrient-rich seawater reaches the light-rich upper layers of the ocean (the photic zone), it promotes the growth of phytoplankton, causing blooms of phytoplankton like this and increasing the surface concentration of chlorophyll-a, a green pigment involved in photosynthesis, tenfold.
Phytoplankton blooms support a variety of marine life. Marine biologists estimate that upwellings off the coast of Bonny attract about 80 blue whales each year to feast on the diatoms. Due to the abundance of phytoplankton, many species of filter feeders and crabs thrive here, as well as sardines, anchovies, tuna and other types of fish.
The National Oceanic and Atmospheric Administration (NOAA) estimates that upwelling zones account for only 1% of the ocean, but support about 50% of fish species. The rich marine life here even attracts so many great white sharks that parts of the original movie "Jaws" were filmed on nearby reefs.
Compiled from /ScitechDaily