Seasonal and interannual changes in particulate organic carbon export and deposition in the Chukchi Sea

Abstract

1] Particulate organic carbon (POC) export fluxes were estimated in the shelf-slope region of the Chukchi Sea using measurements of 234 Th À238 U disequilibria and the POC/ 234 Th ratio in large (>53-mm) particles. These export fluxes were used in conjunction with rates of primary productivity and benthic carbon respiration to construct a POC budget for this shelf-slope region. Samples were collected along a series of shelf-basin transects in the spring (May-June) and summer (July-August) of 2004. These stations were previously occupied during the ice covered (spring) and open water (summer) seasons of 2002, allowing for an interannual comparison of export flux. In contrast to 2002, when open water POC fluxes were significantly higher than in the ice-covered period, POC export fluxes in 2004 were similar during the spring (average = 19.7 ± 24.8 mmol C m À2 d À1 ) and summer (average = 20.0 ± 14.5 mmol C m À2 d À1 ). The high POC fluxes measured during the spring are attributed to a plankton bloom, as evidenced by exceptionally high rates of primary productivity (average = 124.4 ± 88.1 mmol C m À2 d À1 ). The shelf-slope budget of particulate organic carbon indicates that 10-20% of primary productivity was exported below 50 m but was not consumed during benthic carbon respiration or burial and oxidation in underlying sediments. Furthermore, a water columnÀsediment budget of 234 Th indicates that particulate material is retained in shelf sediments on a seasonal basis.

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

“…200 m depth. Whereas Lepore et al (2007) suggested a lack of spring-tosummer signal for years of enhanced primary production and export in Chukchi Sea, here, the seasonal increase in both Chl a and total sediment pigment concentration was highest at sites A-CW and FB (Table 2). We would have expected a more evident increase for A-NW in this context, but the late summer sampling date (August) may have allowed for a more complete degradation of algal material, since the spring bloom at this site.…”

“…In 2004, however, POC export and benthic carbon respiration were only slightly less under ice cover than in summer open-water conditions ; Lepore et al 2007). The findingselevated chlorophyll a (Chl a) concentrations under ice ), more than twice as high absolute export rates but only slightly higher benthic respirationsuggest that there was a distinct spring bloom but lateral advection of organic matter into the central Arctic Ocean, which resulted in a lack of a seasonal benthic activity boost (Lepore et al 2007). Enhanced benthic respiration has been related to higher nutritive quality of the phytodetritus reaching the seabed Sun et al 2009).…”

“…During the Shelf-Basin Interaction Study (SBI) in the Chukchi Sea, vertical export and benthic response were measured in spring and summer in 2002 and 2004 (Lepore et al 2007). In 2002, the export of particulate organic carbon (POC) was much higher in summer than in spring and coincided with an, albeit less pronounced, increase in benthic respiration (Moran et al 2005).…”

“…In 2002, the export of particulate organic carbon (POC) was much higher in summer than in spring and coincided with an, albeit less pronounced, increase in benthic respiration (Moran et al 2005). In 2004, however, POC export and benthic carbon respiration were only slightly less under ice cover than in summer open-water conditions ; Lepore et al 2007). The findingselevated chlorophyll a (Chl a) concentrations under ice ), more than twice as high absolute export rates but only slightly higher benthic respirationsuggest that there was a distinct spring bloom but lateral advection of organic matter into the central Arctic Ocean, which resulted in a lack of a seasonal benthic activity boost (Lepore et al 2007).…”

The Barents and Chukchi Seas: Comparison of two Arctic shelf ecosystems

“…Working in the northeastern corner of the Chukchi Sea in and near Barrow Canyon, Moran et al (2005Moran et al ( ) estimated that, in 2002 and 37% of primary production was exported to the benthos, and Lepore et al (2007) estimated that, in 2004, 24% (spring) and 15% (summer) of primary production was exported. They also concluded that up to~20% of primary production was exported off the shelf into the Canada Basin.…”