| Abstrakt: |
The oceanic biological carbon pump modulates atmospheric CO2 concentrations by transporting carbon from the sunlit surface to greater depths. The efficiency of the biological pump and its response to warming temperatures are of great importance to future projections of global change. Here, we investigate a time series of organic carbon fluxes from a monthly resolved sediment trap mooring in the Gulf of Aqaba (GOA), northern Red Sea, between 2014 and 2016. We evaluate the attenuation of sinking organic carbon in the context of the seasonally changing euphotic zone and provide the first estimates of biological pump efficiency in this region. The base of the euphotic zone changed seasonally as the system transitioned from oligotrophic and stratified conditions in summer to mesotrophic conditions during the winter mixing period. Carbon attenuation assessed using a power law fit yields an average coefficient of b = 0.80 ± 0.37, lower than expected based on the warm temperatures in the GOA. Estimates of export efficiency decreased from 40% in summer to 20% in winter, and show the opposite seasonal pattern as transfer efficiencies, which increased from 50% in summer to ∼95% in winter. Overall, the efficiency of the carbon pump was close to ∼20% in both seasons. These observations challenge the notion of a globally uniform positive correlation between increasing temperature and increasing carbon attenuation in the ocean and imply that warm subtropical ecosystems can support moderately enhanced carbon pump efficiencies, possibly also related to increased, dust‐driven, mineral ballasting in low latitude regions such as the GOA. Plain Language Summary: Phytoplankton growth in the upper sunlit ocean drives the oceans' biological carbon pump, a collection of processes that sequester atmospheric CO2 into the deeper ocean where it is stored for centuries to millennia. However, a large fraction of carbon does not reach greater depths but is respired by bacteria and other microorganisms as it sinks. Earlier field work found that, for water temperatures between 2 and 17°C, warmer water is associated with more carbon respiration. However, we observe that carbon respiration in the Gulf of Aqaba, a deep warm water body in the northern Red Sea, is much less intense than expected based on water temperature (≥20°C). Moreover, the local ecosystem exports a considerable fraction of carbon to intermediate depths (∼300–570 m). These results question the universal role of temperature in regulating carbon export in the ocean. They also suggest that ecosystems dominated by small phytoplankton can support considerable carbon export despite warm temperatures, especially when mineral dust is available to enhance the sinking of marine particles. Key Points: Particulate organic carbon fluxes in the Gulf of Aqaba (GOA) are studied from a moored array of sediment traps between 2014 and 2016We report GOA seasonal patterns of the power law coefficient b, export efficiency, and transfer efficiencyAttenuation is lower than expected based on temperature, challenging its universal control on carbon remineralization in the ocean [ABSTRACT FROM AUTHOR] |
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