FlowCAM®-ing the Microscopic Flora of the Amazon River Plume
Submitted by: Joaquim Goes, Lamont-Doherty Earth Observatory
The outflow of freshwater from the Amazon River is the largest of all of the world’s rivers. On average, the Amazon River empties around 120,000 m3 per second of freshwater into the western Atlantic Ocean, a rate that is roughly seven times higher than that of the Mississippi. Because the Amazon River flows through the world’s biggest and most densely-forested river basins, it carries with it massive amounts of sediments and nutrients, as well as particulate and dissolved organic material, which together impart a unique color to the freshwater being discharged, making it visible from space as a greenish-brown plume stretching several thousands of miles in the western north Atlantic Ocean.
The gradient of environmental conditions (light, nutrients, pCO2, dissolved organic matter, salinity, temperature, mixed layer depths, etc.) that evolve as the plume meanders northwards and mixes with the waters of the western North Atlantic Ocean has a profound influence on the composition and magnitude of phytoplankton communities within and outside of the plume. The focus of our research work was to investigate the structure of phytoplankton communities along the environmental gradient, their photo-physiology, and contribution to carbon drawdown into the western North Atlantic Ocean. Seawater samples were collected during three cruises in 2010, 2011, and 2012 corresponding with the peak low and peak flows respectively of the Amazon River.
Phytoplankton communities were identified microscopically and enumerated with a FlowCAM. One of the surprising findings was that pCO2 concentrations could have a significant influence on the distribution of phytoplankton communities. Ms. Therese Chen, an undergraduate from Barnard College, Ms. Marisol Diaz, a baccalaureate from Columbia University, and Ms. Tegan Gallina, a high-school senior from Bronx Science, are currently conducting follow up experiments with laboratory cultures of phytoplankton from the Amazon River Plume to investigate the role of pCO2 concentrations in regulating their physiology and growth rates. The FlowCAM was used as a major tool to investigate growth rates and species composition changes.
|Diatoms and dinoflagellates from Station 3||Diatoms from Station 4|
Diatoms from an underway sample in the Amazon River Plume
|Rhizosolenia setigera from Station 15|