During HERMES cruises in spring 2006 and 2007 to a cold-water coral (CWC) reef at the border between Norway and Sweden, we studied effects of the reef on the quality (C/N ratio) of suspended particles. The Tisler reef is situated on top of a southeast-northwest-oriented sill forming the connection between the Kosterfjord and the open Skagerrak. In spring 2006, two benthic landers equipped with sediment traps, current meters, and turbidity sensors were deployed at the northwest and southeast edges of Tisler reef. The unidirectional northwest currents during the deployment enabled comparison of the quality of particles before and after crossing the reef. Before the onset of the 2006 spring bloom, particles trapped at the northwest reef edge had a more degraded character than those at the southeast edge. When the spring bloom swamped the study area with fresh phytoplankton, cross-reef distinctions in particle quality disappeared. In spring 2007, near-bottom suspended particles were collected with submersible pumps during one part of a tidal cycle. Analysis revealed a difference in composition of suspended particulate matter along the reef, with highest quality at the northwest edge where particles were delivered, and lower quality at the middle and southeast edge of the reef. Results from both cruises show that particles passing over Tisler reef are subject to preferential removal of nitrogen, indicating that even a relatively small reef such as Tisler has an impact on the biochemistry of its environment. This evidence suggests that, globally, CWC reefs are hotspots of mineralization activity in the ocean.

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