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he twilight zone contains the largest and least exploited fish stocks of the world's oceans. Spanning from just below 200 metres to 1,000 metres deep, it is an interface between the well-studied marine life in the sunlit zone above and the ecosystems of the abyss below. It has a major role in removing carbon dioxide from the atmosphere and storing it for centuries or longer. The twilight zone is also privy to the largest migration on Earth. Huge numbers of fishes and zooplankton move hundreds of metres towards the surface each night to feed, before retreating back down at dawn. Yet the zone is poorly understood-physically, biogeochemically and ecologically. Exploitation and degradation of the mysterious layer between the sunlit ocean surface and the abyss jeopardize fish stocks and the climate. The elongated bristlemouth (Sigmops elongatus) is abundant in the oceans' twilight zone.

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[1] The role of biominerals in driving carbon export from the surface ocean is unclear. We compiled surface particulate organic carbon (POC), and mineral ballast export fluxes from 55 different locations in the Atlantic and Southern Oceans. Substantial surface POC export accompanied by negligible mineral export was recorded implying that association with mineral phases is not a precondition for organic export to occur. The proportion of non-mineral associated sinking POC ranged from 0 to 80% and was highest in areas previously shown to be dominated by diatoms. This is consistent with previous estimates showing that transfer efficiency in such regions is low. However we propose that, rather than the low transfer efficiency arising from diatom blooms being inherently characterized by poorly packaged aggregates which are efficiently exported but which disintegrate readily in mid water, it is due to such environments having very high levels of unballasted organic C export.

Particle sinking velocity is considered to be a controlling factor for carbon transport to the deep sea and thus carbon sequestration in the oceans. The velocities of the material exported to depth are considered to be high in high‐latitude productive systems and low in oligotrophic distributions. We use a recently developed method based on the measurement of the radioactive pair 210Po‐210Pb to calculate particle sinking velocities in the temperate and oligotrophic North Atlantic during different bloom stages. Our estimates of average sinking velocities (ASVs) show that slowly sinking particles (<100 m d−1) contribute significantly to carbon flux at all the locations except in the temperate regions during the bloom. ASVs appear to vary strongly with season, which we propose is caused by changes in the epipelagic community structure. Our results are the first field data to confirm the long‐standing theory that particle sinking velocities increase with depth, with increases of up to 90% between 50 and 150 m depth.