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section why

The Twilight Zone, located between the depths of ~ 200 m and 1000 m, is one of the least known environments on Earth: we mandatorily need to explore it as it provides essential services for our society and is pivotal to the ocean carbon cycle.

The Twilight Zone, which is out of reach of sunlight, is critically undersampled and understudied during most oceanographic ship-based cruises while its depths elude satellite remote sensing. Yet, the Twilight Zone has an essential role in regulating the sequestration of carbon dioxide from the atmosphere for centuries or longer; additionally, the Twilight Zone hosts unique ecosystems and huge fish populations, which could contribute to mitigate food insecurity4; finally, the Twilight Zone is the place of global ocean deoxygenation.

The ocean’s carbon-sequestration capacity is largely controlled by the Biological Carbon Pump. The Biological Carbon Pump is driven by processes that drive the downward export (pump strength) of biogenic carbon photosynthesized in the well-lit Euphotic Zone (between surface and ~100m), and the remineralisation (pump efficiency) of part of this sinking carbon in the underlying Twilight Zone.

According to a recently formulated paradigm, the Biological Carbon Pump is controlled by the cumulative and combined action of six different, biologically- or physically- mediated Biological Carbon Pumps. These are known as the Biological Gravitational Pump, the Mixed Layer Pump, the Eddy Subduction Pump, the Ekman Pump (or large-scale subduction), diel vertical migrations of zooplankton, and ontogenetic (seasonal) vertical migrations of zooplankton.

REFINE proposes a framework for an integrated observational approach of most of these Biological Carbon Pumps in the World Ocean.

section when
section how

REFINE ambitions to implement breakthrough in situ robotic process studies based on a new generation of highly instrumented jumboized profiling floats.

The successful BCG-Argo float technology provides a proven means for developing the new, more sophisticated robots required for conducting REFINE process studies. REFINE will rely on float developments initially conducted as part of the remOcean project to develop an improved, cutting-edge multi-process robot designed to address the various carbon pumps and associated carbon transformation within the Twilight Zone. This robot will integrate the latest technological developments combined with artificial intelligence algorithms to measure and derive a wide suite of variables, proxies and fluxes.

The REFINE float will be a jumboized BGC-Argo float with enhanced capabilities: more available energy, onboard data processing, ice-avoidance capability, improved on-board data storage, increased flexibility for adaptive sampling. Basically, its scientific payload will rely on two complementary packages:

  • The standard BGC-Argo package includes, beside iridium communication : a Conductivity Temperature Depth (CTD) sensor, a fluorescence sensor, a backscattering sensor a radiometer, an oxygen optode sensor, an optical nitrate sensor, a Deep-Sea DuraFET-based pH sensor.
  • The REFINE-specific sensor package will include: A transmissiometer and a miniaturized underwater vision profiler (UVP)

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section where

The breakthrough robotic process studies will be first implemented in five key regions representative of the diversity of global oceanic biogeochemical conditions and their responses to climate change.

The REFINE’s approach is to distribute the robotic process studies over a large latitudinal gradient to cover a broad scope of stratification, mixing, irradiance and nutrient conditions. As these environmental conditions are the main drivers of phytoplankton dynamics and composition, it is expected a wide range of Twilight Zone biogeochemical responses. For REFINE, the five oceanic regions are located in three main latitudinal areas.

Polar areas schema

Polar areas

The Arctic Ocean is characterized by an extreme range of surface irradiance, which forces a distinctive response in phytoplankton, hence affecting energy transfer to higher trophic levels, and carbon sequestration in deep waters. The productive period is tightly linked to the seasonal dynamic of sea ice (coverage and thickness), with early summer phytoplankton blooms generally driven by increased diatom abundance at the edge of retreating sea ice, fostered by salinity stratification. REFINE site 1 is Baffin Bay.

Temperate and sub-polar areas schema

Temperate and sub-polar areas

Temperate and sub-polar areas are characterized by distinctive seasonal signals in phytoplankton dynamics, highly dependent on the seasonal cycle of the mixed layer. Following the winter “resetting” of nutrient concentrations in the upper layer, a spring bloom will develop, generally dominated by diatoms. Next will come a summer period characterized by low to moderate production conditions. This phenological sequence is accompanied by marked regional nutrient-driven differences. REFINE site 2 is the Labrador Sea, representing the North Atlantic subpolar gyre where the global ocean’s largest spring/summer blooms are found. REFINE site 5 is upstream of the Kerguelen Plateau, representing iron-limited areas associated with low phytoplankton biomass and a low-intensity spring bloom.

Low-latitude areas schema

Low-latitude areas

Low-latitude areas are generally characterized by permanently stratified conditions matched with fairly weak seasonality and the presence of deep chlorophyll maxima (DCM) largely associated with small phytoplankton. REFINE site 3 is the Guinea Dome, the quasi-permanent cyclonic doming structures in eastern subequatorial waters. These are high production hotspots thanks to sustained nutrient supply in sub-surface waters trapped by productive DCMs. REFINE site 4 is the South Atlantic Subtropical Gyre, representative of subtropical gyres that compose 60 % of the global ocean's surface. Here, in contrast to subequatorial waters, DCMs are less productive while the main contributors to export are very small particles.

section who

We are a team of experienced scientists and engineers hosting outstanding PhD students and post-docs. Since more than 15 years, we are deeply involved in the development of autonomous platforms and of innovative ways to conduct remote observations of oceanic biogeochemical processes. We are additionally very active in using these new approaches for scrutinizing the ocean to develop and promote outreach in support of Ocean Literacy.

The REFINE objectives (science and outreach) will be tightly linked and developed in phase with the United Nations Decade of Ocean Science for a sustained development. Moreover, REFINE will be implemented in strong concertation and interaction with JETZON (Joint Exploration of the Twilight Zone Ocean Network) which is an international coordinator and focal point for Twilight Zone studies.

REFINE an EU research project carried out by a synergistical multidisciplinary team

section what's on

++ After remOcean, Hervé Claustre was awarded a 2nd ERC Research Advanced Grant. His new project REFINE (erc-refine.eu) focuses on the Ocean Carbon Pump with a particular emphasis on the Ocean Twilight Zone. ++