Spatial and temporal variability of particle flux at the NW European continental margin

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Antia, A.N., Maaßen, J., Herman, P.M.J., Voss, M., Scholten, J.C.M., Groom, S., Miller, P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2001
• Subjects: North Atlantic
• Online Access: https://pure.knaw.nl/portal/en/publications/a7677d42-d900-4a54-9f7b-ee350795ea55; https://doi.org/10.1016/S0967-0645(01)00033-9; https://hdl.handle.net/20.500.11755/a7677d42-d900-4a54-9f7b-ee350795ea55

A synopsis of results from two sediment trap moorings deployed at the mid- and outer slope (water depths 1450 and 3660 m, respectively) of the Goban Spur (N.E. Atlantic Margin) is presented. Fluxes increase with trap deployment depth; below 1000 m resuspended and advected material contributes increasingly to bulk flux. Fluxes of dry weight, POC and diatoms in the traps 400 m above bottom (mab) are smaller than those recorded at the sediment surface due to lateral fluxes in the benthic nepheloid layer. These near-bottom fluxes are larger at shallower water depths. Pa-231/Th-230 ratios in sedimenting material suggest that boundary scavenging is not significant at the Goban Spur. Fluxes of Pb-210 in the intermediate and deep traps are comparable to the Pb-210 supply rate at this site. At the outer slope, sediment Pb-210 fluxes are similar to those measured in the traps 400 mab; at the mid- slope they are a factor of 2 higher, once again indicating large near-bottom lateral particle input. Based on POC- normalised biomarkers in sedimenting material, we followed changes in the quality of sedimenting material with differing trap depth and on seasonal and event-related time scales. In spring fresh, diatom-dominated sedimentation occurs, with progressive degradation of POC with time (to winter) and depth (from 600 to 3220 m). Deeper traps are distinguished on the basis of opal and aluminium fluxes that are dominant in lateral input. A storm event during late September 1993 was clearly reflected in the delta N-15 isotope ratio of sedimenting material, with a time lag of 2-3 weeks. Diatom and opal fluxes were elevated in this storm-related signal, and its biomarker composition in the 600-m trap was similar to that during spring. An estimate made of upward nitrate flux (new production) at the shelf break and at the outer slope indicated a 2-fold higher new (export) production at the shelf break. Particulate organic carbon export from the shelf break to below the depth of maximal seasonal mixing ranges between 3 and 9% of primary production. [KEYWORDS: Isotopic composition; north-atlantic; goban spur; organic-matter; open-ocean; sediments; nitrogen; carbon; phytoplankton; 20-degrees-w] A synopsis of results from two sediment trap moorings deployed at the mid- and outer slope (water depths 1450 and 3660 m, respectively) of the Goban Spur (N.E. Atlantic Margin) is presented. Fluxes increase with trap deployment depth; below 1000 m resuspended and advected material contributes increasingly to bulk flux. Fluxes of dry weight, POC and diatoms in the traps 400 m above bottom (mab) are smaller than those recorded at the sediment surface due to lateral fluxes in the benthic nepheloid layer. These near-bottom fluxes are larger at shallower water depths. Pa-231/Th-230 ratios in sedimenting material suggest that boundary scavenging is not significant at the Goban Spur. Fluxes of Pb-210 in the intermediate and deep traps are comparable to the Pb-210 supply rate at this site. At the outer slope, sediment Pb-210 fluxes are similar to those measured in the traps 400 mab; at the mid- slope they are a factor of 2 higher, once again indicating large near-bottom lateral particle input. Based on POC- normalised biomarkers in sedimenting material, we followed changes in the quality of sedimenting material with differing trap depth and on seasonal and event-related time scales. In spring fresh, diatom-dominated sedimentation occurs, with progressive degradation of POC with time (to winter) and depth (from 600 to 3220 m). Deeper traps are distinguished on the basis of opal and aluminium fluxes that are dominant in lateral input. A storm event during late September 1993 was clearly reflected in the delta N-15 isotope ratio of sedimenting material, with a time lag of 2-3 weeks. Diatom and opal fluxes were elevated in this storm-related signal, and its biomarker composition in the 600-m trap was similar to that during spring. An estimate made of upward nitrate flux (new production) at the shelf break and at the outer slope indicated a 2-fold higher new (export) production at the shelf break. Particulate organic carbon export from the shelf break to below the depth of maximal seasonal mixing ranges between 3 and 9% of primary production. [KEYWORDS: Isotopic composition; north-atlantic; goban spur; organic-matter; open-ocean; sediments; nitrogen; carbon; phytoplankton; 20-degrees-w]