Twilight zone to deep-ocean floor. Developing an understanding of particle dynamics and trophic interactions using a molecular experimental approach

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Photosynthetic primary production is the basis of much of the oceanic food chain. The energy fixed by phytoplankton is transferred to grazers and to higher consumers. The efficiency of the energy transfer between producer and consumer reflects the state of the ecosystem, for example nutrient replete vs nutrient deficient. Through sinking, particulate organic matter (POM) from surface waters is transferred to the deep sea, where it is an important resource for deep-dwelling animals, be they living in pelagic (in the water) or benthic (at the sea floor) environments. We know that in the northern Atlantic Ocean at mid- to high latitude, the deposition of POM is seasonally driven by the surface water spring bloom. However, there is considerable variability in the composition of the POM, which is driven partly by the nature of the phytoplankton, but also by the organisms that graze on them. Much of the POM leaving surface waters is lost in the so-called twilight zone; processes occurring there also presumably modify the chemical composition of the sinking POM. We know virtually nothing about the biological processing of POM that occurs in the twilight zone. The material arriving at the sea floor which feeds the benthic animals is potentially highly altered and depleted in many chemicals, nevertheless, the deep-sea community is highly diverse. In this project, we will work with scientists at the National Oceanography Centre, Southampton and the University of Bristol to try to shed some light on how the energy locked up in organic matter fixed in surface waters is partitioned between consumers living in the deep sea. We will study in detail, the chemistry of particulate material, which includes the phytoplankton and small size organisms that feed on it (bacteria and microzooplankton), the biochemistry of the zooplankton and larger animals living in the deep sea and at the sea floor. We will also carry out incubation experiments using the remotely operated vehicle, Isis, in order to assess how micro-organisms break down organic matter in the twilight zone and how and whether large animals living at the sea floor are able to react to an influx of POM.