Flux variations and vertical distributions of siliceous Rhizaria (Radiolaria and Phaeodaria) in the western Arctic Ocean: indices of environmental changes

T Ikenoue,K R Bjørklund,K Kimoto,S B Kruglikova,J Onodera,N Harada

doi:10.5194/bg-12-2019-2015

Abstract

Abstract. The vertical distribution of radiolarians was investigated using a vertical multiple plankton sampler (100–0, 250–100, 500–250, and 1000–500 m water depths, 62 μm mesh size) at the Northwind Abyssal Plain and southwestern Canada Basin in September 2013. To investigate seasonal variations in the flux of radiolarians in relation to sea ice and water masses, a time-series sediment trap system was moored at Station NAP (75°00´ N, 162°00´ W; bottom depth 1975 m) in the western Arctic Ocean during October 2010–September 2012. The radiolarian flux was comparable to that in the North Pacific Ocean. Amphimelissa setosa was dominant during the season with open water as well as at the beginning and end of the seasons with sea-ice cover. During the sea-ice-cover season, however, oligotrophic and cold-water-tolerant actinommids were dominant, productivity of Radiolaria was lower, and species diversity was greater. These suggest that the dynamics of sea ice are a major factor affecting the productivity, distribution, and composition of the radiolarian fauna.

Highlights

In recent years, summer sea-ice extent in the Arctic Ocean has decreased rapidly due to global climate change (Stroeve et al, 2007, 2012)
The abundance of living radiolarians at Station 56 was about 2 times higher than at Station 32 at each depth interval in the upper 500 m, the depth level at which the abundance of living radiolarians decreased with increasing water depth at both stations (Fig. 2a and b)
The annual means (2823 specimens m−2 day−1: upper trap; 4823 specimens m−2 day−1: lower trap) were comparable to those observed in several areas of the North Pacific Ocean (Fig. 8, Table S5)

Summary

Introduction

Summer sea-ice extent in the Arctic Ocean has decreased rapidly due to global climate change (Stroeve et al, 2007, 2012). The most remarkable sea-ice decrease was observed in the western Arctic Ocean, on the Pacific side (Shimada et al, 2006; Comiso et al, 2008; Markus et al, 2009). Melting of sea-ice can both enhance and reduce the efficiency of the biological pump in the Arctic Ocean, depending on ocean circulation (Nishino et al, 2011). In the Canada Basin, the Beaufort Gyre governs the upper ocean circulation (Proshutinsky et al, 2002), and it has strengthened recently due to the decreasing sea ice (Shimada et al, 2006; Yang, 2009). The efficiency of the biological pump is enhanced outside the gyre because of nutrient supply from shelves and improved light penetration (Nishino et al, 2011)

Methods

Results

Conclusion