More than 20 years of zooplankton data from the deep Southern Ocean

Svenja Halfter
Zooplankton Ecologist
National Institute of Water and Atmospheric Research LTD (NIWA)

Despite playing an important role in the food web and carbon cycle of the Southern Ocean, zooplankton biodiversity and dynamics in subsurface waters remain largely understudied. Our understanding of temporal variability in the zooplankton community is hampered by logistical constraints that come with working in this remote oceanic region of the planet. Here, we present a long-term time-series of zooplankton swimmers intercepted by sediment traps; tools that are usually used to measure time-series in downward carbon flux. Swimmers are organisms that enter the traps and are subsequently preserved. At the Southern Ocean Time Series (SOTS) site (47°S, 140°E) in the subantarctic zone, sediment traps have been deployed in the meso- and bathypelagic zone since 1997, resulting in one of the longest time-series for deep-sea zooplankton. Analysis of the archive from 1997-2020 indicates that the zooplankton community was dominated by copepods, amphipods, and pteropods, and abundance and diversity decreased with depth. For most taxa, no significant seasonal increase in abundance during summer was found. Moreover, large influxes of swimmer biomass were caused by amphipod swarms entering the traps, with a potential negative impact on particulate organic carbon flux that requires further investigation. Finally, we present biases and opportunities for using sediment traps to collect deep-sea zooplankton community data, as well as potential community shifts caused by climate change in the Southern Ocean.