Temperature effects on carbon-specific respiration rate and sinking velocity of diatom aggregates - potential implications for deep ocean export processes

摘要

Most deep ocean carbon flux profiles show low and almost constant fluxes of particulate organic carbon (POC) in the deep ocean. However, the reason for the nonchanging POC fluxes at depths is unknown. This study presents direct measurements of formation, degradation, and sinking velocity of diatom aggregates from laboratory studies performed at 15 °C and 4 °C during a three-week experiment. The average carbon-specific respiration rate during the experiment was 0.12±0.03 at 15 °C, and decreased 3.5- fold when the temperature was lowered to 4 °C. No direct influence of temperature on aggregate sinking speed was observed. Using the remineralisation rate measured at 4 °C and an average particle sinking speed of 150md~(-1), calculated carbon fluxes were similar to those collected in deep ocean sediment traps from a global data set, indicating that temperature plays a major role for deep ocean fluxes of POC. 2003). This is termed "the biological pump" (Volk and Hoffert, 1985), which is characterised by continuous consumption and remineralisation of the settling aggregates, resulting in high attenuation of carbon fluxes with increasing depth in the euphotic and upper mesopelagic zone (e.g. Martin et al., 1987). The efficiency of the biological pump is mainly determined by aggregate sinking velocities and degradation rates of the organic material within settling aggregates, with high export when sinking velocities are high and/or degradation rates are low.