October 9, 2018 - Phytoplankton Bloom off Argentina

Phytoplankton Bloom off Argentina

Jewel-toned colors tinted the blue waters of the South Pacific Ocean just off the coast of Argentina in early October 2018. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite acquired a true-color image of the Valdez Peninsula and surrounding waters on October 4.

The remarkable colors are caused by two different phenomena: in open ocean, the brilliant tones are a result of the rapid growth of microscopic organisms, while close to shore the cause is more likely due to sediment.

In the far north of the image sits Bahia Blanca, a large triangular-shaped estuary that receives water from several inland creeks, streams, and rivers, including the Sauce Chico River and Naposta Grande Creek which are main contributors. Not only does the estuary receive sediment carried by these sources, sediment is also constantly stirred up by the strong tidal action on the thick, muddy bottom of the shallow estuary. As a result, tan sediment fills the estuary and pours into the ocean, flowing southward. As the sediment sinks under water, the reflective characteristics change so the colors as they appear from space change from tan near the surface to blues and greens as the level of the sediment deepens. To complicate matters, the waters that carry sediment may also carry nutrients that spur the growth of colorful microorganisms.

Further away from the coast, the ocean color is likely the result of a phytoplankton bloom. When conditions are right, these microscopic plant-like organisms can reproduce explosively, creating blooms (colonies) big enough to be seen from space. To grow this robustly, phytoplankton need abundant sunlight, carbon dioxide, dissolved nutrients, and favorable temperatures. All of these conditions frequently occur off the Argentine coast. The Malvina (Falkland) Current flows northward along Argentina’s continental shelf and winds may promote upwelling that bring nutrient-rich water to the surface. October is springtime in this region, and the increasing sunlight also promotes such blooms.

Image Facts
Satellite: Terra
Date Acquired: 10/4/2018
Resolutions: 1km (340.8 KB), 500m (790.5 KB), 250m (589 KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC