Latitudinal Distributions and Controls of Bacterial Community Composition during the Summer of 2017 in Western Arctic Surface Waters (from the Bering Strait to the Chukchi Borderland)

www.nature.com/scientificreports OPEN Latitudinal Distributions and Controls of Bacterial Community Composition during the Summer of 2017 in Western Arctic Surface Waters (from the Bering Strait to the Chukchi Borderland) Jiyoung Lee1, Sung-Ho Kang2, Eun Jin Yang2, Alison M. Macdonald3, Hyoung Min Joo2, Junhyung Park4, Kwangmin Kim4, Gi Seop Lee5, Ju-Hyoung Kim6, Joo-Eun Yoon7, Seong-Su Kim 7, Jae-Hyun Lim 8 & Il-Nam Kim7* The western Arctic Ocean is experiencing some of the most rapid environmental changes in the Arctic. However, little is known about the microbial community response to these changes. Employing observations from the summer of 2017, this study investigated latitudinal variations in bacterial community composition in surface waters between the Bering Strait and Chukchi Borderland and the factors driving the changes. Results indicate three distinctive communities. Southern Chukchi bacterial communities are associated with nutrient rich conditions, including genera such as Sulfitobacter, whereas the northern Chukchi bacterial community is dominated by SAR clades, Flavobacterium, Paraglaciecola, and Polaribacter genera associated with low nutrients and sea ice conditions. The frontal region, located on the boundary between the southern and northern Chukchi, is a transition zone with intermediate physical and biogeochemical properties; however, bacterial communities differed markedly from those found to the north and south. In the transition zone, Sphingomonas, with as yet undetermined ecological characteristics, are relatively abundant. Latitudinal distributions in bacterial community composition are mainly attributed to physical and biogeochemical characteristics, suggesting that these communities are susceptible to Arctic environmental changes. These findings provide a foundation to improve understanding of bacterial community variations in response to a rapidly changing Arctic Ocean. Arctic air temperatures have risen twice as fast as the global average (~0.7 °C) since the mid-20th century1,2. Recent Arctic warming is strongly linked to declining sea ice extent, suggesting a strong positive ice-temperature feedback1,3. As a result, annual sea ice extent has declined rapidly (3.5–4.1% per decade since 1979), which has resulted in physical and biogeochemical changes in the Arctic Ocean2. For instance, freshening of the upper Arctic Ocean enhances stratification and inhibits vertical mixing2,4–6, which in turn limits the transfer of deep 1 Marine Environment Research Division, National Institute of Fisheries Science, Busan, 46083, South Korea. Korea Polar Research Institute, Incheon, 21990, South Korea. 3Woods Hole Oceanographic Institution, MS 21, 266 Woods Hold Rd., Woods Hole, MA, 02543, USA. 43BIGS, Hwaseong, 18454, South Korea. 5Marine Bigdata Center, Korea Institute of Ocean Science and Technology, Busan, 49111, South Korea. 6Faculty of Marine Applied Biosciences, Kunsan National University, Gunsan, 54150, South Korea. 7Department of Marine Science, Incheon National University, Incheon, 22012, South Korea. 8Fisheries Resources and Environmental Research Division, East Sea Fisheries Research Institute, National Institute of Fisheries Science, Gangneung, 25435, South Korea. *email: 2 Scientific Reports | (2019) 9:16822 | https://doi.org/10.1038/s41598-019-53427-4 1 www.nature.com/scientificreports/ www.nature.com/scientificreports Figure 1. Map of the August 2017 Ice Breaking RV Araon western Arctic Ocean sampling stations used in this study. The location of each sampling site has been superimposed onto the Chl-a concentration contour (blue to red background colors). Pink, green, and blue circles represent stations in the Southern Chukchi (SC), Frontal Zone (FZ), and Northern Chukchi (NC) regions, respectively. Note that as satellite Chl-a data during August 2017 contained a large gap over the study area due to cloud/ice interferences, we show the mean state of summer Chl-a concentrations averaged from satellite Chl-a data obtained during August 2002–2017. ocean nutrients into the euphotic zone7. Ultimately, these physical changes will have a critical impact on Arctic primary productivity8–12. The Arctic Ocean is comprised of two distinct oceanic regions, distinguished by the presence (western Arctic) or absence (eastern Arctic) of Pacific water within the halocline. The western Arctic Ocean is geographically comprised of the Chukchi, East Siberian and Beaufort Seas, the Canadian Arctic Archipelago, and the Canadian Basin (Fig. 1)13. This ocean has experienced the most rapid sea ice retreat14, which has been driven by heat transport from Pacific waters15–17. Relatively warm, fresh, and nutrient-rich Pacific waters enter the western Arctic Ocean through the Bering Strait to the Chukchi Sea, which is a shallow (average depth 50 m) and wide (surface area 620 × 103 km2) sea18–20. During the summer open water season, latitudinal differences in the physical and biogeochemical features of the western Arctic surface water are apparent from the Bering Strait to the Chukchi Borderland5,21. Relatively low latitude regions (i.e., the Bering Strait to the Chukchi Shelf) are primarily driven by Pacific waters that supply nutrients and heat, and are among the world’s most productive ocean regions22–24. Conversely, the higher latitude regions (i.e., Chukchi Borderland and Canada Basin) are relatively cold, fresh, and oligotrophic because the surface layer is highly influenced by freshwater inputs from melting ice and rivers through the Beaufort Gyre. Intermixing of the two surface water masses in the western Arctic has produced a physicochemical frontal zone in the Chukchi Sea5. The latitudinal gradient of surface water physical and biogeochemical features in the western Arctic also affects the marine planktonic ecosystem8,21,25–27. Previous studies have shown that large-size phytoplankton groups and a high chlorophyll-a (Chl-a) biomass are associated with high nutrient Pacific waters in lower latitude regions, while small-size phytoplankton groups and a low Chl-a biomass are attributed to the oligotrophic conditions of higher latitude regions12,21. A latitudinal gradient of abundance and diversity in the summer zooplankton community of the western Arctic has also been reported26. Bacterial communities are a key component of the marine ecosystem because they are responsible for modifying and decomposing organic matter, supporting higher trophic levels and driving biogeochemical cycles28–32. Recent studies have reported that the composition and relative abundance of bacterial communities in the western Arctic Ocean are largely determined by physical and biogeochemical water properties, such as temperature, salinity, and nutrients, indicating that microbial communities are highly susceptible to environmental changes33–37. However, little is known about changes in the latitudinal distribution of bacterial community compositions in response to western Arctic (...truncated)