From as high as hundreds of kilometers above the Earth, the waters around the Chatham Islands can suddenly appear as if painted. Mid-summer can see a ring of green and milky blue appear around the distant islandsand it is a sign in the ocean that indicates heavy blooms of microscopic life are taking place.
On January 10, 2026, a large, swirling patch of bloom ringed the islands, recorded by the Visible Infrared Imaging Radiometer Suite (VIIRS) on NOAA-20, 800 km east of New Zealand’s South Island. The swirling shapes in the bloom delineated surface eddies that entrapped and extended the drifting cells into threads, wisps, and arc shapes. These are important because they indicate not only where phytoplankton are, but also where water is being stirred and trapped.
The Chathams are situated at the top of the Chatham Rise, which is a large submarine plateau that stretches out from New Zealand to the east. The rise is where ocean fronts occur regularly as a result of the interaction between cold and nutrient-rich Antarctic waters and warmer and nutrient-poor subtropical waters. The topography assists in this process and provides enough light for quick photosynthesis due to long daylight during summer. The bloom is observable on color satellite images because of how chlorophyll alters the reflection of sunlight in certain bands such as blue and green bands used to determine concentrations of chlorophyll-a.
Chlorophyll maps are not only beautiful; they are an indicator of the working surface of the ocean.
NASA’s ocean color data series has been extended from past satellites to new satellites that observe more spectral detail. This is the case with the Ocean Color Instrument on the PACE mission, which observes in numerous spectral bands so that scientists might go from “how much chlorophyll” to “which communities are present.” Oceanographer Ivona Cetinić described the biological importance of swirling patterns in chlorophyll data: “Each of these eddies may have slightly different ecosystems.” This increased spectral detail allows scientists to distinguish among signals that might represent coccolithophores (which appear turquoise because they contain reflective calcium carbonate plates) versus green assemblages that might include diatoms.
As for New Zealand waters, satellite monitoring is increasingly being used for tracking the coastline and shelf seas between visits. Sampling on the coast is constrained by weather, logistics, and expense, so it tends not to capture transient events. A national synthesis on New Zealand coastal remote sensing states: While in-water monitoring is relatively sparse in some regions relative to the extent of the coastline, satellite monitoring is able to provide a broad-scale image on a time scale that is sufficient for establishing a seasonal cycle. A level of remoteness, for example in the Chathams, means that actual ground measurements might be sporadic.
The effects of the bloom do not end there but filter down through the food chain. With phytoplankton at the base of the food chain, a productive fishing ground and a variety of marine predators thrive in the area around the Chatham Islands. The area is also known for mass strandings of whales and dolphins in large groups, which has yet to be fully understood by a unified reason for such events in stranding biology summaries as Dr. Vanessa Pirotta of NPR explains: “It could be that these animals may have been fishing or transiting through the water and unfortunately came through a navigational hazard and ended up on the beach, and “The key point here is that any animal involved in a stranding does not want to be stranded.
Against this complexity, the bloom image is a reminder of what satellites do best: finding patterns that are either too large, too distant, or too brief to spot from a boat. “In a ring of ocean color around a few small islands, the topography of the seafloor, the interaction of water masses, and the biology of photosynthesis are visible at once.
