Thesis Spatial-Temporal Mapping Of Hydrothermal Fluxes And The Associated Benthic Communities At The Lucky Strike Hydrothermal Vent Field M - F H/F - Ifremer

Join Ifremer, an ally of planetary well-being, to gain a better understanding of and better protection for the ocean.

From the abyss to the surface, from the coast to the open SEA, Ifremer is the French research institute that is wholly dedicated to the Ocean. Its teams carry out research, innovate and produce expert reports to protect the ocean, exploit its resources in a responsible manner and shares marine data.

Ifremer contributes its scientific expertise to throw light on public policies and develops solutions drawn from the ocean to meet the challenges of the ecological transition. Ifremer is the operator of France's oceanographic fleet with its shipbuilding subsidiary Genavir, and imagines, designs and deploys leading edge technological means to solve the ocean's mysteries.

Join our teams, made up of 1500 scientists and research support staff, present all along the coastal areas of France and French overseas territories.

www.ifremer.fr

Deadline for applications: 20/04/2026

Who are we ?
The PhD thesis will take place within the UMR BEEP, a joint research unit affiliated with the REM department of the Institute. The founding goal of UMR BEEP is the study of the biology and ecology of deep-sea ecosystems through a multidisciplinary approach and across multiple scales, from microorganisms to macrofauna, and from communities to molecules. The aim is to describe biological diversity and understand its dynamics in relation to environmental heterogeneity at different spatial and temporal scales, regardless of the type of ecosystem considered. Over recent years, this objective has enabled the development of research projects that integrate, through a comparative approach, the various compartments (microorganisms, meiofauna, and macrofauna) of chemosynthetic or sedimentary ecosystems. This PhD is affiliated with the Deep Environment Laboratory, which is particularly dedicated to studying biodiversity from meiofauna to megafauna and benthic habitats.

The joint research unit Biology and Ecology of Deep-Sea Ecosystems (Ifremer, UBO) is one of the three units of the Deep-Sea Physical Resources and Ecosystems Department (REM).

What is the topic of the thesis?

Hydrothermal fluid circulation at mid-ocean ridges plays a fundamental role in transferring thermal and chemical energy from the Earth's interior to the oceans, with a significant impact on ocean biogeochemical cycles and the export of matter to surrounding environments. These impacts are directly linked to the magnitude and variability of energy fluxes emerging from the seafloor, which are difficult to quantify due to their inherent spatial and temporal variability. This hydrothermal circulation supports unique ecosystems whose food webs are based on microbial chemosynthesis and host complex endemic biological communities. This local production also facilitates the establishment of peripheral, non-endemic species that benefit from the input of organic matter (OM). The transfer of this OM through the food web plays a key role in shaping the functional and trophic diversity of benthic communities in both active and peripheral zones. Consequently, these assemblages are distributed in mosaics across different spatial and temporal scales, although the relative influence of the various factors and the underlying control mechanisms are still poorly understood. Early studies highlight the role of energy availability for primary production and food supply in structuring peripheral communities.

The objective of this PhD project is therefore to map hydrothermal fluid emissions and habitat distribution at the scale of the Lucky Strike hydrothermal field, in order to better constrain the role of hydrothermal circulation on ecosystem structure. A central question is how the temperature and chemical variability of diffuse vents are influenced by fluid outflow velocities in the underlying basalts and by the modifications occurring in the upper layer of porous volcanoclastic sediments. These likely control the spatial and temporal distribution of hydrothermal emissions, as well as how these fluxes are transferred to biological communities in terms of energy and carbon fluxes. Expanding the spatial coverage of biological observations, combined with concurrent studies of local fluid circulation, will improve our understanding of the role of environmental filters (i.e., fluid chemical composition) relative to site topography and geomorphology (i.e., the age and morphology of the edifice) in shaping biodiversity and habitat distribution.

What will your mission and activities be?
The specific objectives of the PhD are as follows:

- To quantify heat and mass fluxes, their partitioning between diffuse and focused flows, as well as their spatial and temporal distribution and variability.
- To assess the relative influence of hydrothermal fluxes and terrain variables (topography, roughness, slope) on the distribution of biological communities at the scale of the hydrothermal field.
- To measure changes in hydrothermal activity and associated biological communities over decadal timescales.

To achieve these objectives, the student will be required to:

- Produce orthomosaics from submersible imaging data using Metashape.
- Create maps from a wide variety of datasets using QGIS.
- Digitize and annotate orthomosaics using QGIS.
- Conduct spatial and temporal analyses to better understand the role of hydrothermal fluxes in shaping the distribution of fauna and habitats at the scale of the field.

Key Words :

Hydrothermal fluxes, peripheral fauna, carbon flux, hydrothermal vents, microbial mats

How are your activities organised ?

- The PhD will be based at LEP on the Ifremer site, with regular visits to IUEM, GéoOcéan laboratory (Plouzané).
- Image processing and annotation in a dedicated imaging facility.
- Numerical and statistical analyses carried out on computer.
Possible participation in research cruises.
- Likely visit to the National Oceanography Centre in Southampton (UK) as part of an international collaboration.

Who are you ?

- Master in Marine Ecology/Geology or equivalent

You have the following skills, knowledge and experience :

- Skills in habitat mapping
- Required: QGis, R, processing of rasters and vectors
- Skills in spatial analyses
- English

You have the following qualities :

- Work as a team
- Scientific rigour and integrity