Revisiting Carbon Flux Through the Ocean's Twilight Zone

The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the "twilight zone" (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. By using neutrally buoyant sediment traps to sample this chronically understudied realm, we measured a transfer efficiency of sinking particulate organic carbon between 150 and 500 meters of 20 and 50% at two contrasting sites. This large variability in transfer efficiency is poorly represented in biogeochemical models. If applied globally, this is equivalent to a difference in carbon sequestration of more than 3 petagrams of carbon per year.

¹ Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
² National Institute of Water and Atmospheric Research Centre for Physical and Chemical Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand.
³ Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania and Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Hobart, 7001, Australia.
⁴ Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA.
⁵ Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
⁶ Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.
⁷ Analytical and Environmental Chemistry, Free University of Brussels, B-1050 Brussels, Belgium.
⁸ Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Mutsu Institute for Oceanography, Yokosuka, Kanagawa 237-0061, Japan.
⁹ Institute for Computational Earth System Science, University of California, Santa Barbara, CA 93106, USA.
¹⁰ Ocean Sciences Department, University of California, Santa Cruz, CA 95064, USA.
¹¹ Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062, USA.
¹² Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.

^* To whom correspondence should be addressed. E-mail: kbuesseler{at}whoi.edu

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