Phytoplankton Under Antarctic Sea Ice Could be Supporting a Whole Ecosystem

Scientists have discovered evidence of phytoplankton blooms lurking beneath Antarctic sea ice using NASA's Earth-observing system. They assert that a complex ecosystem may be supported by these algal blooms.

The Southern Ocean, also known as the Antarctic Ocean, has been thought by scientists to be completely dark because of the dense sea ice that covers it. As a result, there was no room for phytoplankton, the microscopic algae that form the foundation of aquatic food webs.

As a result, there was no room for phytoplankton, the microscopic algae that form the foundation of aquatic food webs. This means that life below the ice is severely constrained by a lack of sunlight. However, studies motivated by rising Arctic under-ice phytoplankton blooms have revealed that Antarctic waters also harbor unexpected invertebrates, suggesting that ecological variability beneath the ice is underestimated.

Blooms and Retreats

Phytoplankton blooms are frequently observed as soon as the sea ice starts its seasonal retreat because they are supported by an abundance of light and freshwater with high iron content. However, a group led by Dr. Christopher Horvat from Brown University and the University of Auckland had a hunch that phytoplankton blooms might already be on the horizon.

To test this theory, the team explained how to estimate the availability of light beneath the ice using output from climate models and sampling gathered from independent BGC-Argo floats.

According to Horvat, they discovered that almost all instances of floats profiling beneath Antarctic sea ice document an increase in phytoplankton before sea ice retreat. His team frequently found sizeable blooms. Horvat also emphasized the possibility of hidden phytoplankton blooms with the potential to sustain other life out there because the floats only sampled a very small portion of the vast sea ice that might host these under-ice blooms.

Floats and a New NASA Satellite

The floats are abandoned at sea by research vessels and left to collect biogeochemical samples on their own; they are even able to detect conditions that are close to freezing at the water's surface and dive into the water to avoid being damaged by ice. The team used information gathered from 79 sequences of measurements from 51 floats between 2014 and 2021. During this time, there were a total of 2197 under-ice dives.

To understand how compact the ice is around Antarctica, Horvat's team used a new data product from the ICESat-2 laser altimeter, a new NASA satellite. They also took into account the amount of light that reached the upper ocean while using a variety of global climate models. Because sea ice in the Southern Ocean is made up of individual floes and there are only small pockets of open water, they discovered that at least half of the Antarctic under-ice might support under-ice algal blooms.

Under-Ice Algal Blooms

The researchers found that when they measured under compact sea ice that completely or almost completely covered the water below, 88% of measurement sequences showed an increase in phytoplankton before the sea ice retreated, and 26% met the requirements for an under-ice bloom.

According to Head Topics, the coordinates for the sample locations are not entirely accurate, the authors warned, because the floats could sample beneath the ice but couldn't return data from these locations.

Horvat said that possibly, some of the periods of high productivity were observed in areas with little sea ice. It is also possible that some of the phytoplankton originate from processes taking place outside of the sea ice zone since the time these algal blooms are observed is near to when sea ice retreats. However, given the overwhelming volume of high-productivity measurements they discovered, the team believes this is unlikely.

Possibility of Prey and Predator Beneath the Ice

Ecosystems in Antarctica may be significantly impacted.

Horvat emphasized that higher trophic levels relocate or migrate to areas with higher productivity, and if this occurs beneath the ice, one might anticipate that the food chain will follow. To determine how these hidden complex ecosystems function and whether phytoplankton blooms draw predators and prey below the ice, more investigation will be required, SciTech Daily reports.

The study by Horvat, Bisson, and their colleagues was published recently in the journal Frontiers in Marine Science.