25 Jul 2022
25 Jul 2022
Status: this preprint is open for discussion.

Depth-related patterns in microbial community responses to complex organic matter in the western North Atlantic Ocean

Sarah Allison Brown1, John Paul Balmonte2,a, Adrienne Hoarfrost2,b, Sherif Ghobrial2, and Carol Arnosti2 Sarah Allison Brown et al.
  • 1Environment, Ecology, and Energy Program, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA, 27599
  • 2Department of Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA, 27599
  • acurrent address: HADAL and Nordcee, Department of Biology, University of Southern Denmark, Campusvej 55, 5230
  • bcurrent address: NASA Ames Research Center, Moffett Field, CA, USA, 94035

Abstract. Oceanic bacterial communities process a major fraction of marine organic carbon, with a substantial portion of this carbon transformation occurring in the mesopelagic zone, and a further fraction fueling bacteria in the bathypelagic zone. However, the capabilities and limitations of the diverse microbial communities at these depths to degrade high molecular weight (HMW) organic matter are not well constrained. Here, we compared the responses of distinct microbial communities from North Atlantic epipelagic, mesopelagic, and bathypelagic waters at two open ocean stations to the same input of diatom-derived HMW particulate and dissolved organic matter. Microbial community composition and functional responses – as measured by polysaccharide hydrolase, glucosidase, and peptidase activities – were very similar between the stations, which were separated by 1370 km, but showed distinct patterns with depth. Changes in microbial community composition coincided with changes in enzymatic activities. In epipelagic mesocosms, the spectrum of peptidase activities became especially broad and glucosidase activities were very high, a pattern not seen at other depths. The spectrum of polysaccharide hydrolase activities was enhanced particularly in epipelagic and mesopelagic mesocosms, with fewer enhancements in rates or spectrum in bathypelagic waters. The timing and magnitude of these distinct functional responses to the same HMW organic matter varied with depth. Our results highlight the importance of residence times at specific depths in determining the nature and quantity of organic matter reaching the deep sea.

Sarah Allison Brown et al.

Status: open (until 05 Sep 2022)

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  • RC1: 'Comment on egusphere-2022-682', Anonymous Referee #1, 17 Aug 2022 reply

Sarah Allison Brown et al.

Sarah Allison Brown et al.


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Short summary
Bacteria use extracellular enzymes to cut large organic matter to sizes small enough for uptake. We compared the enzymatic response of surface, midwater, and deep ocean bacteria to complex natural substrates. Bacteria in surface and mid-depth waters produced a much wider range of enzymes than those in the deep ocean, and may therefore consume a broader range of organic matter. The extent to which organic matter is recycled by bacteria depends in part on its residence time at different depths.