Hassler Christel

Impact of interactions between biological key players on iron and carbon recycling in the Southern Ocean: Consequences for iron limitation

Project Number: PP00P2_166197
Project Type: Research_Project
Project Duration: 01/01/2016 - 12/31/2018
Funding Source: SNF ,
Project Leader: Prof. Christel Hassler
Groupe Biogéochimie marine et lacustre
Département F.-A. Forel des sciences de l'environnement et de l'eau
Université de Genève
66 Bvd Carl-Vogt
1211 Genève 4
Phone: +41 (0) 22 379 03 09 ; +41 (0) 22 379 03 00
FAX: +41 (0) 22 379 03 29
e-Mail: christel.hassler(at)unige.ch

related to this project.

Research Areas:
High Altitude

Virus, Bacteria, Carbon, Iron, biogeochemical cycle

The Southern Ocean (SO) plays a critical role on atmospheric CO2 sink mediated by the physical, biological and microbial pumps and thus affects our climate. The SO is the largest oceanic iron-limited region, and unsurprisingly it has been extensively studied. However, how iron limitation takes places and its consequences for the efficiency of the biological carbon pump mediated by phytoplankton remain mostly unresolved. The lack of understanding of the link between iron chemistry and its bioavailability as well as the key drivers and processes at play, significantly prevents advances in this research area. Because iron is mostly associated with organic ligands and limits the growth of phytoplankton in most of the SO, the biogeochemistry of Fe and carbon are closely inter-related. Moreover, the labile dissolved organic compounds excreted by phytoplankton are rapidly consumed by heterotrophic bacteria to fuel carbon export mediated by the microbial carbon pump. It is thus evident that both carbon pumps are inter-related with the production and recycling of organic carbon and bioavailable Fe acting as critical connectors in the SO. However, the link between these pumps is mostly conceptual and controlling mechanisms remain unknown. As this connection is critical for the functioning of this ecosystem including its footprint on our climate, it is urgent to learn how these pumps are connected and controlled. This project addresses specific aspects related to this major gap of knowledge by investigating pathways involved in the production/recycling of carbon and iron in surface water. This will be achieved by combining experiments at sea and in the laboratory. For this purpose, marine dissolved organic compounds (DOC) from various origins will be isolated and characterized.  Here, we will isolate and characterize DOC from iron-limited and iron replete regions chosen to represent the biochemical variability encountered across the SO. In addition, DOC produced by key biological players from the SO will be isolated and studied, including DOC excreted by bacteria, phytoplankton and grazers. Moreover, DOC sensitivity to photo- and viral degradations – two important transformation pathways – will be quantified. An extensive and unique analytical matrix is proposed to resolve key properties and functional groups in DOC as well as its iron binding properties, likely identifying, for the first time, the “dark matter” constituting DOC compounds involved in Fe binding as well as binding mechanism. The comparison of the various DOC compositions will identify whether a unique chemical traceable signature is associated with specific origin or transformation pathways. The impact on the microbial pump will be inferred from DOC lability whereas the impact on the biological pump will be inferred from iron bioavailability (55Fe bioaccumulation), pigments, photo-physiology and POC analyses. Finally, this project explores a novel research area: the role of viruses in the degradation of marine DOC and its impact for both the biological and the microbial pumps. Marine viruses constitutively bear enzymes that are efficient in passively degrading their hosts carbohydrates in solution, whose impact has never been addressed. Given the high concentration and biodiversity of viruses in the ocean, and the facts that carbohydrate constitute up to 50 % of marine DOC and can affect iron chemistry, this study might totally revisit the role of viruses in marine biogeochemistry and result in seminal publications. Major breakthrough in the field of marine biogeochemistry is thus expected as well as solid contributions to international research programs, such as SCOR and GEOTRACES. Being related to climate, ecosystem functioning and biodiversity, this project benefits to the scientific community at large.

Last update: 4/28/17
Source of data: ProClim- Research InfoSystem (1993-2019)
Update the data of project: CH-6037

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