Biological pump processes in the cryopelagic and hemipelagic Arctic Ocean: Canada Basin and Chukchi Rise

Abstract

The object of this study was to clarify the characteristics of the biological pump system operating in permanently or seasonally ice-covered ocean (cryopelagic) conditions by examining the export of particulate organic carbon (POC) and other components of oceanic particles in the Canada Basin at 120, 200, and 3067 m and in hemipelagic Chukchi Rise waters at 120 m. The first time-series sediment trap (TS-trap), B96-200m, was tethered to an Ice Ocean Environmental Buoy (IOEB) and deployed at 79.1°N, 132.2°E in March 1996; it was recovered in July 1997 at 76.7°N, 131.8°E, having drifted exclusively in the cryopelagic environment. The second TS-trap, S97-120m, also tethered to an IOEB, was launched at 75.2°N, 142.5°E in October 1997 and recovered at 80.0°N 155.9°E, having first traversed the cryopelagic Canada Basin to the west and then the hemipelagic Chukchi Rise. The third TS-trap, CD04-3067m, was deployed in August 2004 beneath the cryopelagic drift route of S97-120m at a water depth of 3067 m on a mooring in the interior of the 3824-m-deep Canada Abyssal Plain. All three TS-traps intercepted marine particles in 21 time-series sets of 17-day intervals for a total of 357 days each. The TMF (annual dried mass flux) intercepted by TS-trap B96-200m was only 0.4 g m −2 yr −1, and the FC org (mole annual export flux of POC) was 7.0 mmol C m −2 yr −1. The export of FSi bio (mole Si in diatom frustules) and lithogenic particles (in mole Al) were both extremely small. Ballast particle flux was three orders of magnitude smaller than in global epipelagic areas where the biological pump represents an important vehicle for carbon export to depth. The FC org and ballast particles were rather small in the second drifting TS-trap, S97-120m. We conclude that the biological pump is currently ineffective in the cryopelagic Canada Basin so that, instead of removal to deep waters, carbon from primary production (2–4 mmol C m −2 yr −1) is remineralized or converted to dissolved organic carbon (DOC) within the surface layer. At 4.3 gm −2 yr −1, the TMF sampled by moored TS-trap CD04-3067m was an order of magnitude larger than the mass flux to the traps drifting at 120 and 200 m. The lithogenic particle flux was about 18 times larger than that in S97-120m. FC org sampled by the moored trap was 14.2 mmol C m −2 yr −1, 1.4–2 times larger than the POC fluxes encountered by the 120-m and 200-m drifting TS-traps. The Δ 14C values in the POC collected at 120 m indicated that the POC was mostly autochthonous. In contrast, the POC exported to 3067 m had an apparent 14C age of 1900 years, indicating it was predominantly derived from aged, allochthonous carbon. The particle composition was largely invariant throughout the annual cycle, suggesting that the upper ocean ecosystem plays a minimal role in transporting POC and other marine particles. Instead, the majority of POC and other particulate matter is transported laterally to deep ocean layers from the shelf/slope reservoir. On the Chukchi Rise, we found a mosaic of environmental regimes, ranging from the intermittent development of a polynya in some locations where an efficient biological pump operates, to an area characterized by re-suspended allochthonous POC with an exceptionally high FAl. Such spatial heterogeneity, and associated sensitivity to the various physical and biogeochemical forcing factors, are distinctive characteristics of hemipelagic Arctic environments.