Timing of sea ice retreat can alter phytoplankton community structure in the western Arctic Ocean

A Fujiwara,K Suzuki,I Imai,S.-I Saitoh,T Hirawake

doi:10.5194/bg-11-1705-2014

A Fujiwara, K Suzuki + Show 3 more

Open Access

https://doi.org/10.5194/bg-11-1705-2014

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Abstract

Abstract. This study assesses the response of phytoplankton assemblages to recent climate change, especially with regard to the shrinking of sea ice in the northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of phytoplankton groups in the late summers of 2008–2010 were analysed based on HPLC pigment signatures and, the following four major algal groups were inferred via multiple regression and cluster analyses: prasinophytes, diatoms, haptophytes and dinoflagellates. A remarkable interannual difference in the distribution pattern of the groups was found in the northern basin area. Haptophytes dominated and dispersed widely in warm surface waters in 2008, whereas prasinophytes dominated in cold water in 2009 and 2010. A difference in the onset date of sea ice retreat was evident among years–the sea ice retreat in 2008 was 1–2 months earlier than in 2009 and 2010. The spatial distribution of early sea ice retreat matched the areas in which a shift in algal community composition was observed. Steel-Dwass's multiple comparison tests were used to assess the physical, chemical and biological parameters of the four clusters. We found a statistically significant difference in temperature between the haptophyte-dominated cluster and the other clusters, suggesting that the change in the phytoplankton communities was related to the earlier sea ice retreat in 2008 and the corollary increase in sea surface temperatures. Longer periods of open water during the summer, which are expected in the future, may affect food webs and biogeochemical cycles in the western Arctic due to shifts in phytoplankton community structure.

Highlights

The acceleration of warming and the shrinking of sea ice in the Arctic Ocean have been observed since the late 1990s (Steele et al, 2008; Perovich and Richter-Menge, 2009)
Our study revealed the surface distribution of major phytoplankton groups during the summer in the western Arctic and differences in the environmental conditions they favour
Because we could use in situ data from only three years, and we analysed only the surface phytoplankton pigments, variability across long periods of time and the vertical phytoplankton community structure were not evaluated here

Summary

Introduction

The acceleration of warming and the shrinking of sea ice in the Arctic Ocean have been observed since the late 1990s (Steele et al, 2008; Perovich and Richter-Menge, 2009). Reductions in sea ice cover are significant on the Pacific side of the western Arctic (e.g., Perovich and Richter-Menge, 2009). Such reductions in sea ice have caused the freshening of seawater, along with a recent increase in river discharge into the Canada basin (Peterson et al, 2002; Yamamoto-Kawai et al, 2009). It has been reported that a thinning or/and shrinking of sea ice enhanced underwater light availability, which stimulated higher primary productivity, where phytoplankton were not strongly limited by nutrient availability (Lee and Whitledge, 2005; Nishino et al, 2011; Arrigo et al, 2012)

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