To better quantify the ocean's biological carbon pump, we resolved the diversity of sinking particles that transport carbon into the ocean's interior, their contribution to carbon export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity of particles was used to model their contribution to particulate organic carbon (POC) flux. Measured POC fluxes were reasonably predicted by particle images. Nine particle types were identified, and most of the compositional variability was driven by the relative contribution of aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition varied across locations and seasons, the entire range of compositions was measured at a single well‐observed location in the subarctic North Pacific over one month, across 500 m of depth. The magnitude of POC flux was not consistently associated with a dominant particle class, but particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with depth whereas certain other classes attenuated little or not at all with depth. Small particles (<100 μm) consistently contributed ∼5% to total POC flux in samples with higher magnitude fluxes. The relative importance of these small particle classes (spherical mini pellets, short oval fecal pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux). Imaging approaches that resolve large variations in particle composition across ocean basins, depth, and time will help to better parameterize biological carbon pump models.
Plankton‐derived, microscopic, and macroscopic sinking aggregates constitute most of the particulate organic carbon (POC) flux in the oceans. While the flux of particulate organic matter and associated elements has been quantified at the Bermuda Atlantic Time‐series Study (BATS) station for several decades, we lack an understanding of the source and composition of sinking particles, as well as the fate of predominant phytoplankton taxa. We determined the composition of individual sinking particles and their microbial communities in the upper 300 m depth at the BATS station in fall 2017 and spring 2018 by image analysis and V4 amplicon sequencing of the 16S and 18S rRNA genes. The sinking particles were primarily composed of phytodetrital aggregates, fecal aggregates, and fecal pellets. In the fall, phytodetrital aggregates were numerically dominant and drove the majority of the POC flux; however, in the spring, particle flux of all particle categories declined below 150 m, and the POC flux at 200 m shifted to one driven by fecal aggregates. The relative composition of the microbial communities associated with phytodetrital and fecal aggregates were statistically indistinguishable in both seasons, and prokaryotic taxa known to be associated with the gut microbiomes of zooplankton were indicators of the sinking particles. Our results point to the utilization and modification of sinking particles by resident midwater zooplankton populations, and to fecal pellets as the predominant mechanism transporting picophytoplankton to depth.
more » « less- NSF-PAR ID:
- 10366351
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 66
- Issue:
- 10
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 3697-3713
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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