Impacts of Temperature, CO2, and Salinity on Phytoplankton Community Composition in the Western Arctic Ocean

Koji Sugie,Sohiko Kameyama,Shigeto Nishino,Amane Fujiwara,Naomi Harada

doi:10.3389/fmars.2019.00821

Koji Sugie, Sohiko Kameyama + Show 3 more

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https://doi.org/10.3389/fmars.2019.00821

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Abstract

The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better understand the impacts of rapid environmental changes on the Arctic ecosystem. Two temperature conditions (control: <3°C and 5°C above the control), two CO2 levels (control: ~300 μatm and 300/450 μatm above the control; i.e., 600/750 μatm), and two salinity conditions (control: 29 in 2015 and 27 in 2016, and 1.4 below the control) conditions were fully factorially manipulated in eight treatments. Higher temperatures enhanced almost all phytoplankton traits in both experiments in terms of chl-a, accessory pigments and diatom biomass. The diatom diversity index decreased due to the replacement of chain-forming Thalassiosira spp. by solitary Cylindrotheca closterium or Pseudo-nitzschia spp. under higher temperature and lower salinity in combination. Higher CO2 levels significantly increased the growth of small-sized phytoplankton (<10 μm) in both years. Decreased salinity had marginal effects but significantly increased the growth of small-sized phytoplankton under higher CO2 levels in terms of chl-a in 2015. Our results suggest that the smaller phytoplankton tend to dominate in the shelf edge region of the Chukchi Sea in the western Arctic Ocean under multiple environmental perturbations.

Highlights

The ocean mitigates global climate change by absorbing heat and atmospheric CO2, resulting in warming and acidification of the sea surface
These results indicate that when freshwater input such as sea ice melt occurs simultaneously with the other environmental perturbations, the only 1.4 unit change in salinity has an important role in the ecosystem function of the western Arctic Ocean
The photosynthetically active radiation (PAR) levels were about three times higher in the MR16exp., the fertilization effect of higher CO2 levels on the growth rate of many non-diatom phytoplankton appeared only in the MR16-exp. (Table 2). These results suggest that the interactive effect of higher CO2 and light levels on photophysiological processes varied between phytoplankton communities in the respective regions, and thereby that is not an important factor affecting phytoplankton dynamics in the western Arctic Ocean during autumn

Summary

Introduction

The ocean mitigates global climate change by absorbing heat and atmospheric CO2, resulting in warming and acidification of the sea surface. Arctic Phytoplankton Under Multiple Environmental Perturbations gas (e.g., carbon dioxide: CO2) emissions continues (Overland et al, 2014). The impact of CO2induced acidification is most severe in the Arctic Ocean, especially in terms of the saturation state of calcium carbonate (AMAP, 2013; Yamamoto-Kawai et al, 2016). Freshwater input to the Arctic Ocean has increased because of the increase in sea ice melt and meteoric water as a result of warming (Comiso et al, 2008; Koenigk et al, 2013). Organisms in the Arctic Ocean must cope with multiple environmental perturbations. The effects of these environmental changes on the ecosystem processes in the Arctic Ocean are poorly understood

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