Bio-Argo floats: Robots to monitor ocean biology and biogeochemistry
Hi there, my name is Giorgio Dall’Olmo and I am a scientist at the Plymouth Marine Laboratory. I want to tell you about a small revolution that is taking place in the field of biological and chemical oceanography.
By now you should have understood that scientists go on research cruises to gather information about the ocean, its organisms, its chemistry, and its physics. Satellites orbiting around the Earth provide us with a second important means to observe the ocean.
Both these observing systems, however, have important limitations. Research cruises can help determining the horizontal, temporal, and vertical distribution of various ocean properties, but are extremely expensive and thus limited in space and time. In contrast, satellite sensors scan the ocean at the global scale with a relatively high temporal and spatial resolution, but can only detect a limited set of parameters near the surface and under cloud-free conditions (some sensors can “see” through clouds).
Most biological, chemical, and physical processes develop in a three-dimensional ocean that continuously changes over time. So, what are we missing with the current observation methods?
The truth is that we do not know for sure.
Our understanding of ocean processes can be further improved by a third observational method: Argo floats (Figure 1). These are autonomous robotic platforms that carry scientific instruments and that can regulate their buoyancy. Once deployed, they spend most of the following 3-5 years at a “parking” depth of 1000 m in a dormant state. Every ten days or so, they turn on, sink to 2000 m, turn on their scientific instruments and collect data as they rise to the surface. From there, they transmit the data to land via a satellite link and then sink back to the parking depth where the cycle restarts. About 3500 Argo floats are currently recording temperature and salinity profiles that are fundamental for understanding ocean physics (see Argo web site). But what about biology and biogeochemistry?
Well, that is where the revolution is happening!
Argo floats have recently been equipped with sensors that can measure biological and chemical properties. We call these “Bio-Argo floats” and the data they are collecting are opening exciting new opportunities to further our understanding of ocean biology and biogeochemistry.
During AMT22, besides six “traditional” Argo floats, we also deployed eight Bio-Argo floats: four in the northern and four in the southern sub-tropical gyres. They will contribute data to a larger project lead by Dr. Herve’ Claustre at the Laboratoire d’Oceanographie de Villefrance-sur-mer (France, http://www.OAO.obs-vlfr.fr/).
Besides temperature, salinity and depth, the instruments on these floats also measure chlorophyll fluorescence (a proxy of phytoplankton pigment concentration), optical scattering (a proxy of particle concentration), dissolved oxygen (produced by photosynthesis and consumed by living organisms), nutrients (needed by all ocean organisms), as well as light (the main ocean fuel, Figure 2).
Importantly, these floats will monitor the gyres after the passage of the cruise. We will thus be able to better understand how the ship-based “snapshot view” of these ecosystem will evolve with time.