Abstract
Abstract. The flux of materials to the deep sea is dominated by larger, organic-rich particles with sinking rates varying between a few meters and several hundred meters per day. Mineral ballast may regulate the transfer of organic matter and other components by determining the sinking rates, e.g. via particle density. We calculated particle sinking rates from mass flux patterns and alkenone measurements applying the results of sediment trap experiments from the Atlantic Ocean. We have indication for higher particle sinking rates in carbonate-dominated production systems when considering both regional and seasonal data. During a summer coccolithophorid bloom in the Cape Blanc coastal upwelling off Mauritania, particle sinking rates reached almost 570 m per day, most probably due the fast sedimentation of densely packed zooplankton fecal pellets, which transport high amounts of organic carbon associated with coccoliths to the deep ocean despite rather low production. During the recurring winter-spring blooms off NW Africa and in opal-rich production systems of the Southern Ocean, sinking rates of larger particles, most probably diatom aggregates, showed a tendency to lower values. However, there is no straightforward relationship between carbonate content and particle sinking rates. This could be due to the unknown composition of carbonate and/or the influence of particle size and shape on sinking rates. It also remains noticeable that the highest sinking rates occurred in dust-rich ocean regions off NW Africa, but this issue deserves further detailed field and laboratory investigations. We obtained increasing sinking rates with depth. By using a seven-compartment biogeochemical model, it was shown that the deep ocean organic carbon flux at a mesotrophic sediment trap site off Cape Blanc can be captured fairly well using seasonal variable particle sinking rates. Our model provides a total organic carbon flux of 0.29 Tg per year down to 3000 m off the NW African upwelling region between 5 and 35° N. Simple parameterisations of remineralisation and sinking rates in such models, however, limit their capability in reproducing the flux variation in the water column.
Highlights
The biological pump plays a critical role in the discussion about glacial-interglacial pCO2 variations measured in ice cores as well as in the evaluation of future climate scenarios
Low sinking rates were obtained in the Southern Ocean, at the Walvis Ridge and in the western Equatorial Atlantic, highest values were found in the eastern Equatorial Atlantic and off NW Africa
Considering all our regional and seasonal data as well as unpublished data from experimental studies and literature values from sediment trap studies (Berelson, 2002), we have indication for higher particle sinking rates in carbonate-dominated productions systems in the equatorial Atlantic and off NW Africa (Table 3). This might reflect a major transport mode for tiny and heavy coccoliths, being densely packed within fecal pellets which are frequently found in the material collected by sediment traps (e.g. Ploug et al, 2008b; Fischer et al, 1996b)
Summary
The biological pump plays a critical role in the discussion about glacial-interglacial pCO2 variations measured in ice cores as well as in the evaluation of future climate scenarios At highest efficiency, it may strongly draw down atmospheric pCO2, at lowest efficiency, in a biologically dead ocean, the value may significantly exceed modern atmospheric values (Broecker, 1982). The efficiency of carbon transfer to depth is influenced by three major processes (de la Rocha and Passow, 2007): a) the amount of primary production in the photic zone, b) the sinking rate of organic carbon, and c) the rate of POC decomposition All these processes impact on ocean biogeochemistry. Direct field measurements are still rare and many values originated from laboratory experiments (e.g. Ploug et al, 2008a), Published by Copernicus Publications on behalf of the European Geosciences Union
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
