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Dispatch 13: The Microbial Arctic

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Loic Jacquemot and Thomas Grevesse

September 24, 2019

Location: 77° 00’ N 150° 00’ W

Sea Conditions: 3828m water depth; open water.

Thomas Grevesse and I (Loïc Jacquemot) are PhD students hailing from Belgium and France. Thomas is studying at Concordia University in Montreal (Canada), and I am studying in Laval University in Québec city (Canada). Although we are coming from countries far removed from the Arctic, we are both interested in the same thing: microbial life in the Arctic.

As part as the JOIS expedition, what we do onboard is really simple, we collect microbes from wherever we can in the Arctic! Microbes are microscopic organisms (such as bacteria, viruses, and eukaryotes), and they exist virtually everywhere. We are interested in learning who these microbes are, what they are doing, and how they are affected by climate change in the Arctic. We are particularly interested in understanding these questions as they pertain to where we are right now, the Beaufort Sea. Among the other scientists aboard the CCGS Louis S. St-Laurent, we are the opportunistic guys. We wait until after everyone has sampled the water collected by the Niskin rosette. Then we scavenge as much leftover water as we can from Niskin bottles containing samples from various depths. Next, we use a peristaltic pump to run the water samples through a series of different sized filters where the microbes present in the water are collected by the filter media. Those samples are then preserved in a -80°C freezer. Additional samples are collected for microscopy and flow cytometry. This is a method used to quantify how many microorganisms there are per liter of sea water in the various samples collected from different locations and depths. Marine waters can contain in excess of 1 million microbes per liter of sea water, and it is very difficult to identify all of them exclusively using traditional methods such as microscopy. That’s why we use DNA sequencing to help us identify the multitude of microorganisms we encounter. Back in the lab, we can extract DNA from a filter medium, and obtain the sequence of all the microorganisms present on the filter. DNA sequences are unique to each microbial species, and can then be used as barcodes to identify the thousands of different species in each sample. We are then able to know the identity and abundance of each species across all the locations and depths that we sampled during the cruise. We then compare the diversity and distribution of each organism identified with data collected by the others scientists (salinity, temperature, nutrients, etc.) during the cruise to infer the conditions that drive the spatial distribution of microbes in the Beaufort Sea.

You could ask what’s the meaning of this? Microbes are microscopic organisms present everywhere in the oceans, and represent ~50% of the total ocean biomass. Being the basis of the marine food web, they provide energy to higher trophic levels, from the smallest animals (copepods for example) to the largest (whales). As the ice is melting in the Arctic Ocean, environmental conditions such as temperature, salinity, nutrient concentrations, and light availability are modified, and in turn affect the microorganisms living there. The influence of these changes has already been documented as having an influence on microbial communities. Loss of ice for example has been associated with the shift in size of the dominant phytoplankton communities in the Arctic. That shift in turn has implications on both carbon and energy transfers to the higher trophic levels. Tracking microorganism diversity in the Beaufort Sea can give scientists a window into how a community has evolved from past conditions and how they will evolve in a near future.

In addition to this sampling, we conducted experiments to study the impact of climate-change related modifications on the microbial communities in the Arctic. The Arctic ocean receives a high amount of fresh water from land sources compared to other oceans. With this water, comes a high amount of organic matter from terrestrial sources (plants, soil, etc.). Microbes feed on organic matter, and changes in the sources of organic matter has the potential to drastically modify the composition and function of microbial communities. With increased temperatures in the Arctic region, it is predicted that permafrost will massively thaw, which will bring a substantial amount of organic matter from terrestrial sources to the Arctic ocean. In order to mimic this process and predict future changes in the Arctic, we collected water at two sites: over the continental shelf, and in the basin. We stored this water in bottles on board and added some organic matter derived from the permafrost. Every day we filter some water to collect the microbes to study how their communities change over the course of the experiment using the same methods as described in the previous paragraphs. We hope to be able to forecast what will happen to microbial communities in a rapidly changing Arctic ocean and to understand what impact that will have on the ecosystem.

Last updated: September 30, 2019

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