MOSCOW, August 6. /TASS/. The North Pole-42 drifting expedition participants explained how the internal biological clock of Arctic plankton works in complete darkness. In the polar night and the absence of sunlight, marine plankton particles establish biological rhythms based on the tides' ebb and flow, press service of the Arctic and Antarctic Research Institute (AARI) told TASS.

"Scientists have collected data on mesozooplankton concentrations and monitored their daily activity. They have demonstrated that even in the absence of sunlight in the Arctic, plankton continues to function according to its internal 'biological clock.' Spectral analysis of plankton concentrations revealed that its behavioral activity's 24-hour daily rhythm, typically associated with sunrise and sunset, persists even with the onset of polar night: the amplitude drops by approximately a third, but the rhythm still persists - the plankton continues to operate according to its internal 'biological clock.' The second rhythm -a tidal rhythm, with a period of 10.5-13 hours - is also consistently present in the spectrum. This rhythm manifests as a 'second harmonic' of the daily cycle and, apparently, helps the plankton maintain its biorhythm in the absence of light," the press service said.

Marine plankton particles serve as critical bio indicators of the Arctic ecosystem's well-being, scientists say. However, without a day-night cycle, their biological clocks in the Arctic must be disrupted. However, the plankton revealed that they have a backup "pendulum" - the tides. This changes the very logic of monitoring polar ecosystems: now, the rhythm of life under the ice may be measured and predicted even in places where the sun doesn't shine for months, scientists believe. A separate discovery was when scientists detected the single-celled phytoplankton at a depth of less than a meter under the ice, where sunlight is completely absent, and the nature of these organisms is still unclear and will be the subject of future expeditions, the institute said.

The discovery changes the very understanding of high-latitude polar ecosystems structure and life in the subglacial ocean, experts say. Over the research period, more than 58,000 underwater holograms were recorded and processed in real time, from which the scientists selected a validated set, including nearly 2,800 images of marine particles of various types representing the main Arctic taxa. This dataset will be used further on to train neural networks that recognize plankton and other marine particles.

Research equipment

"The holographic probe, tested during the North Pole-42 drifting expedition, is a domestic development product that, for the first time in the world, allowed observing the Arctic ecosystem in its natural environment in real time. Such technologies form the basis for future monitoring systems for a wide range of environments in climate-challenged and difficult-to-research conditions. Digital holography has the potential to become a reliable bio-indication tool in the Arctic, allowing scientists to monitor ocean conditions in polar regions more accurately, quickly, and much closer to real natural conditions," the press service quoted AARI's Director Alexander Makarov as saying.

The research was conducted aboard the North Pole research vessel from October 2024 through to March 2025. The Tomsk State University scientists developed specifically for that expedition the DHC-FOCL underwater probe with a digital holographic camera. The probe was lowered through a hole in the ice to depths of up to 50 meters. The equipment recorded the presence of plankton and other particles in the water and also captured their images directly at the observation site, without interfering with their vital functions. A digital holographic camera recorded all particles within its measurement range -including mesozooplankton, gas bubbles, settling inorganic particles, phytoplankton, and others.

About the expedition

The North Pole-42 expedition continued the drifting research program in the high Arctic, founded by Soviet scientists. The world's first polar research drifting Arctic station, dubbed North Pole, began operations on May 21, 1937. Since then, every subsequent expedition was given the name "North Pole" and a serial number. A total of 40 such expeditions have been organized. For 75 years, drifting stations conducted research in oceanography, meteorology, and marine biology; they monitored ice cover dynamics, and observed the planet's ionospheric and magnetic fields, allowing for conclusions about radio wave propagation.

In 2013, the team of scientists from the North Pole-40 drifting station was evacuated, and the program was suspended for nearly ten years: the critical ice conditions, including shifts, cracks, and breaks, made it impossible to maintain the ice camp. Since 2022, the drifting Arctic station program has resumed at a technologically advanced level - with the support of the North Pole unique research expedition vessel. This ice-resistant platform acts as a research center designed for year-round expeditions in the high latitudes of the Arctic Ocean.