Sargasso Sea Expeditions

The Sargasso Sea, some 1,300 kilometers southeast of North Carolina, lies in the middle of the North Atlantic Gyre, a system of clockwise rotating currents that are related to global climate patterns. It covers an area roughly the size of the United States and is uniquely bounded by the surrounding currents, not land. Early explorers were vexed by its stagnant winds and the characteristic mats of floating brown seaweed that hindered their progress.

The large patches of the seaweed Sargassum are floating habitat islands in the otherwise nutrient-deficient conditions of the Sargasso Sea. Over the years, scientists have cataloged an array of life associated with Sargassum, from microscopic bacteria to commercially important fish. Many species are found only with the Sargassum in the Sargasso Sea and have unique adaptations. In the current study, MBARI scientists and collaborators seek to unlock some of the mysteries of this habitat and what it can reveal about the Earth’s changing climate.


Research Objectives

MBARI Senior Scientist Ken Smith studied the Sargassum community of plankton, seaweeds, and animals more than 30 years ago, before the impact of global warming was identified in the surface ocean. Over a period of two years, Smith, co-chief scientist Alana Sherman, and their team will conduct four research cruises in the area in order to observe how this community has been altered by warmer surface waters and increased acidity. They will also study how the effects of climate variation on the surface life ultimately affect the food supply of the area’s deep-sea ecosystems. The research team will collect samples within Sargassum patches on the transit from southeastern Bermuda to the Bahamas. While at sea, they will receive updated satellite images of the area from John Ryan at MBARI and consult with him and colleagues to hone in on sites with large seaweed aggregations. Smith and Sherman’s team will collect samples to measure species composition (who is there?), species abundance (how many of each kind?), and biomass (volume of living material).

Smith and Sherman will also deploy a benthic observatory at a 5,400-meter-deep site. They will return to collect data from amd then redeploy the observatory every six months for two years. The system has sediment traps to collect sinking particulate matter through the water and a time-lapse camera system to record observations of the seafloor. This Sargasso Sea station gives the researchers a contrasting ocean basin with which to compare data from a similar observatory that they have maintained in the Pacific Ocean for more than 20 years. Data from the Pacific observatory at “Station M” have revealed changes over time in the amount of food reaching the deep sea. This variation in food has been related to changes in climate and surface ocean conditions.