Half of the phytoplankton in the oceans is hidden from satellites

Oct. 31 () –

The biomass of phytoplankton on Earth amounts to around 343 million tons, equivalent to about 250 million elephants. At least half is hidden from satellites.

It is the result of research published in the journal Proceedings of the National Academy of Sciences (PNAS), based on a network of underwater robots.

Phytoplankton (microscopic plant-like organisms) are the foundation of the marine food web, supporting everything from tiny fish to multi-ton whales, in addition to playing a fundamental role in removing carbon dioxide from the atmosphere.

Accurately monitoring Earth’s phytoplankton is essential, especially when it comes to understanding the effects of global warming or potential carbon removal initiatives. The ability to track phytoplankton has relied heavily on space satellites that observe the sea surface. However, phytoplankton can grow below the surface where satellites cannot detect it, leaving a significant gap in the way we monitor one of Earth’s most important primary producers, which are the organisms that carry out photosynthesis and form the base of the food web.

Researchers at Dalhousie University have drawn on a growing global network of underwater robots known as Biogeochemical-Argo floats. These devices travel below the ocean surface and measure phytoplankton where satellites cannot. As part of the BGC-Argo program, the floats are deployed around the world in an international effort to monitor the biology, geology and chemistry of the ocean.

Adam Stoer, a graduate student and lead author of the paper, says the research represents a major advance in tracking the world’s “hidden” phytoplankton. and is needed to better track the effects of climate change on the ocean.

“What our paper highlights is that this global fleet of robots will be incredibly valuable in monitoring Earth’s phytoplankton as a whole, so that we can understand how they might respond as the ocean continues to warm,” he says. in a statement about work.

“This fleet of robots has grown to a point where we can quantify how much phytoplankton there is and monitor where they are and when they ‘bloom,’ which is becoming increasingly necessary given how quickly the climate is changing our oceans.” .

The Dalhouise researchers used around 100,000 water column profiles from the floats to describe the carbon biomass of Earth’s phytoplankton and its spatiotemporal variability. The floats measure phytoplankton below the sea surface year-round and throughout the ocean, which was not feasible before they were available.

SATELLITE OBSERVATION IS NOT ENOUGH

While researchers routinely go out on research ships to collect seawater samples, quantifying phytoplankton biomass on a global scale is not possible this way.. There simply aren’t enough people, ships or funds to collect enough samples given the vastness of the ocean.say the authors.

Researchers have long relied on satellite observations of ocean color to describe phytoplankton on a global scale. From these satellite observations, chlorophyll-a, a commonly used indicator for carbon biomass, can be estimated. However, it is an imperfect way to represent carbon biomass because the growth conditions of phytoplankton (e.g. availability of sunlight) generate great variations in the relationship between the two.

“Another important result of this study is that we document the substantial mismatch between the seasonal cycles of carbon biomass and surface chlorophyll-a. This dissociation is present in two-thirds of the global ocean,” says Dr. Katja Fennel, director of the Department of Oceanography at Dal and lead author of the study.