Arctic Deep Sea Teems with Microbes

"Time to sample!" With this call from Ding Weikang, a researcher aboard the Xuelong (Snow Dragon), China's icebreaking research vessel, the midship laboratory instantly bustled with activity. Members from the 16th Chinese Arctic Expedition's oceanographic survey group hurried to the CTD (conductivity, temperature and depth) sampling room.

CTD sampling is a routine oceanographic survey procedure, often likened to giving the ocean a "physical checkup." The 24 water sampling bottles at the CTD unit can each hold 10 liters of seawater.

"Water collected from different depths serves different research objectives. Since different researchers require varying amounts of water from specific layers, I must coordinate everyone's needs individually and make an overall plan before each CTD operation," Zheng Xinyu, a researcher and member of the oceanographic survey group, said.

Although she is now thoroughly familiar with the entire CTD sampling process, the depths where dissolved oxygen minima or chlorophyll maxima occur do not always fall within standard ranges. Consequently, the sampling bottle numbers must be dynamically adjusted based on actual depths.

Before each operation, she drafts a preliminary schedule of the sample requirements and the sampling sequence. After the operation, she compiles a detailed breakdown of sample allocations for each researcher and their respective water layers.

To prevent contamination, team members wear masks and gloves before the operation begins and affix a fine-pored, microscopic filter membrane — as thin as a cicada's wing — over the bottle mouths, which are just a few centimeters wide. This task demands immense patience and meticulousness. The membrane must fit the filter holder perfectly; the slightest misalignment can cause leakage and contaminate the samples, which would compromise the entire set of experimental data.

Once the water samples are retrieved, the most urgent task is filtration. To preserve the samples' original state, filtration should be completed without delay. After seawater is poured into the filtration system, the microorganisms and other particles, the most valuable yield of the process, are trapped on the surface of the tiny filter membranes. These membranes are then wrapped in aluminum foil and taken to the land-based laboratory for analysis.

Currently, humans understand only about two percent of all existing microorganisms, and research on Arctic microorganisms is particularly scarce. Zhang Xinran, another team member, focuses on marine microorganisms.

Conventional microbiological research relies on gene fragments to determine the composition of microbial communities in water. While longer gene fragment sequences allow for more accurate species identification, they also entail higher costs. To manage expenses, researchers typically use shorter gene fragments. However, this approach makes it difficult to detect microorganisms with low abundance or small populations.

"Obtaining detailed and comprehensive data on microbial communities requires filtering large volumes of water," said Zhang. At some sampling stations, she has filtered up to 320 liters of water. On several occasions, she worked through the night, finishing just in time to catch breakfast at the mess hall.

The northernmost CTD sampling station of this expedition is located near 86° North latitude. Zhang was surprised to find that these high-latitude waters were far from barren. Even in the deep sea, at depths of 3,000 meters, vast numbers of microorganisms thrive.

"The polar regions are not as barren as we imagine. On the contrary, a highly active microbial ecosystem exists in the deep sea," Zhang remarked.

Source: Science and Technology Daily