Diatom flux reflects water-mass conditions on the southern Northwind Abyssal Plain, Arctic Ocean

J Onodera,N Harada,E Watanabe,M C Honda

doi:10.5194/bg-12-1373-2015

J Onodera, N Harada + Show 2 more

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https://doi.org/10.5194/bg-12-1373-2015

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Abstract

Abstract. We studied time-series fluxes of diatom particles from 4 October 2010 to 18 September 2012 using bottom-tethered moorings with two sediment traps deployed at 180 and 1300 m depths at Station NAP (75° N, 162° W; 1975 m water depth) in the western Arctic Ocean. This paper discusses on the relationship of time-series diatom fluxes to satellite-based sea-ice motion and simulated hydrographic variations. We observed clear maxima of the diatom valve flux in November–December of both 2010 and 2011, and in August 2011. Diatoms in samples were categorized into 98 taxa. The diatom flux maxima were characterized by many resting spores in November–December and by the sea-ice-associated diatom Fossula arctica in August 2011. These assemblages along with abundant clay minerals in the samples suggest a significant influence of shelf-origin materials transported by mesoscale eddies, which developed along the Chukchi Sea shelf break. In contrast, the fluxes of total mass and diatoms were reduced in summer 2012. We hypothesize that this suppression reflects the influx of oligotrophic water originating from the central Canada Basin. A physical oceanographic model demonstrated that oligotrophic surface water from the Beaufort Gyre was supplied to Station NAP from December 2011 to the early half of 2012.

Highlights

There are numerous studies reporting the significant influence of the recent declining trend in Arctic sea-ice extent (Stroeve et al, 2012) on marine ecosystems (i.e., Grebmeier et al, 2010; Wassmann and Reigstad, 2011; Wassmann et al, 2011)
Station NAP is located at the southwestern edge of the Beaufort Gyre (Fig. 1), and is occasionally influenced by relatively oligotrophic waters of the Beaufort Gyre (Nishino et al, 2011a)
Station NAP is located in a seasonal sea-ice zone, and is covered by sea ice from late October through July (Fig. 2b)

Summary

Introduction

There are numerous studies reporting the significant influence of the recent declining trend in Arctic sea-ice extent (Stroeve et al, 2012) on marine ecosystems (i.e., Grebmeier et al, 2010; Wassmann and Reigstad, 2011; Wassmann et al, 2011). Interannual monitoring to observe the influences of hydrographic variations on primary productivity and the microplankton assemblage is key to estimating the future direction of lower-trophic levels of marine ecosystems and biogeochemical cycles in the Arctic Ocean. In the Canada Basin of the western Arctic Ocean, the shift in wind patterns has promoted downward Ekman pumping and consequent Beaufort Gyre circulation seen in recent decades (McPhee, 2013). The enhanced Ekman forcing under decreasing sea-ice cover results in deepening of the nutricline in the central part of the Beaufort Gyre (McLaughlin and Carmack, 2010; Nishino et al, 2011a), limiting the biological pump effect in this area (Nishino et al., 2011a).

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