“Sinking dead”—How zooplankton carcasses contribute to particulate organic carbon flux in the subantarctic Southern Ocean

Abstract

Zooplankton carcasses are an important, yet understudied, pathway of the biological gravitational pump. To understand their contribution to the downward carbon flux in the subantarctic, carcasses of the copepod Neocalanus tonsus were analyzed for carbon content, microbial remineralization rates, and sinking velocities. In addition, the sensitivity of carcass flux to varying mortality, microbial turnover, and sinking velocity rates was analyzed and compared to carbon flux measurements from sediment traps. Microbial decomposition rates (between 0.02 and 0.16 d−1) were comparable to those of marine snow, highlighting the importance of carcasses as microbial hotspots. High sinking velocities (730 ± 182 m d−1) suggest that particulate organic carbon flux to the deep ocean is substantial. Carcass flux is sensitive to a change in sinking velocity but appears less sensitive to fluctuations in microbial decomposition rate. More research on zooplankton mortality and the factors that influence carcass sinking through the water column is needed to quantify the carcass‐mediated carbon export and enable their inclusion in marine ecosystem and biogeochemical models.

Mass falls of crustacean carcasses link surface waters and the deep seafloor

“…These include the “langostilla”, Munida gregaria , in the western South Pacific (Zeldis & Jillett, 1982 ), the portunid crab, Charybdis smithii , in the Arabian Sea (Christiansen & Boetius, 2000 ), or krill, Euphausia superba in the Southern Ocean (Atkinson et al, 2008 ) and Meganyctiphanes norvegica in the North Atlantic. The latter species are also known to provide food subsidies to deep seabed communities (Christiansen & Boetius, 2000 ; Hirai & Jones, 2012 ; Schmidt et al, 2011 ), and our observations suggest a globally relevant role of crustacean carcasses in deep‐water benthic systems (Halfter et al, 2021 ). This may not just have ecological implications.…”

Carbon sequestration by multiple biological pump pathways in a coastal upwelling biome

“…Mortality at depth, in particular, may be responsible for approximately half of the total active transport in the region 37 . Mortality at depth is also likely to lead to deeper remineralization due to the sinking of carcasses and/or fecal pellets of predators that feed on vertical migrants 38 . However, mortality rates in the mesopelagic are highly uncertain due to a paucity of direct measurements, and hence we cannot robustly include this process in our carbon budget.…”

Whales in the carbon cycle: can recovery remove carbon dioxide?

“…DVM by whale prey (e.g., krill) and other nekton provides a particle injection pump that increases export efficiency relative to gravitational flux of particles alone [27]. In locations of high productivity and whale abundance, zooplankton fecal material, exuviae, and carcasses provide considerable pulses of carbon to the deep sea, thereby demonstrating the importance of whale prey to deep carbon export [50,[59][60][61].…”