Ballast minerals and the sinking carbon flux in the ocean: carbon-specific respiration rates and sinking velocity of marine snow aggregates

摘要

Recent observations have shown that fluxes of ballast minerals (calciumcarbonate, opal, and lithogenic material) and organic carbon fluxes areclosely correlated in the bathypelagic zones of the ocean. Hence it has beenhypothesized that incorporation of biogenic minerals within marineaggregates could either protect the organic matter from decomposition and/orincrease the sinking velocity via ballasting of the aggregates. Here wepresent the first combined data on size, sinking velocity, carbon-specificrespiration rate, and composition measured directly in three aggregatetypes; Emiliania huxleyi aggregates (carbonate ballasted), Skeletonema costatum aggregates (opal ballasted), andaggregates made from a mix of both E. huxleyi and S. costatum (carbonate and opal ballasted).Overall average carbon-specific respiration rate was ~0.13 d?1and did not vary with aggregate type and size. Ballasting from carbonateresulted in 2- to 2.5-fold higher sinking velocities than those of aggregatesballasted by opal. We compiled literature data on carbon-specificrespiration rate and sinking velocity measured in aggregates of differentcomposition and sources. Compiled carbon-specific respiration rates(including this study) vary between 0.08 d?1 and 0.20 d?1. Sinkingvelocity increases with increasing aggregate size within homogeneous sourcesof aggregates. When compared across different particle and aggregatesources, however, sinking velocity appeared to be independent of particle oraggregate size. The carbon-specific respiration rate per meter settled varied between0.0002 m?1 and 0.0030 m?1, and decreased with increasing aggregate size.It was lower for calcite ballasted aggregates as compared to that of similar sized opal ballasted aggregates.