Projects on marine systems

Ecological interactions between phytoplankton and bacteria arguably represent the most crucial and complex inter-organism association in marine environments. For decades, researchers have investigated the association between bacteria and phytoplankton through the assimilation and remineralization of phytoplankton-derived organic matter into inorganic nutrients by heterotrophic bacteria. Notwithstanding, there are a variety of phytoplankton-bacteria interactions, spanning from beneficial (mutualism and commensalism) to negative (parasitism, predation or competition) relationships. Many of these interactions are mediated by the production and exchange of volatile organic components (VOCs). VOCs are a diverse bioactive molecules of low molecular weight and high vapor pressures. These VOCs are also very important in atmospheric chemistry as are main biogenic precursors of ozone, which is a greenhouse gas and a toxic air pollutant. Even though, the interactions between phytoplankton-bacteria and VOCs strongly influence in biochemical cycles, regulate the productivity of aquatic food webs, and affect ocean-atmosphere fluxes of climatically relevant chemical. There is still a lack of information about the role of phytoplankton and bacteria interactions in the production and composition of VOCs in marine environments.

Key-reseacher: Cecilia Costas Selas

Funded by DNRF

Volatile organic compounds (VOCs) are widespread in the oceans. However, limited research has been conducted to identify which organisms are involved in the cycling of marine VOCs, under what conditions, and to what extent. Generally, there is a lack of baseline information on organism-specific blend profiles from marine environments, leaving a significant gap for fundamental research on the biological production of VOCs. Factors such as species interactions, population dynamics, environmental forces, and nutrient cycling likely influence the production of marine VOCs, yet few studies have explored these factors in a marine biogeochemical context. Additionally, there are few studies that have directly measured the consumption of marine VOCs by marine organisms. Novel findings on the production, consumption, and cycling of VOCs in the marine environment could profoundly impact our foundational knowledge of marine element cycles and food web dynamics.The goal of my PhD is to contribute fundamental knowledge on VOC emission profiles for various marine plankton, such as bacterioplankton and phytoplankton, provide novel evidence of VOC consumption by marine microorganisms, investigate the potential influence of biotic and abiotic factors on the production and consumption of VOCs, and link these findings to mechanistic understandings of the marine carbon cycle.

Key-reseacher: Eve Isobel Galen

Funded by DNRF

Recent studies highlight the vital roles of VOCs in atmospheric processes, including the formation of tropospheric ozone and secondary organic aerosols, as well as their influence on greenhouse gas lifetimes and ecological interactions. Although extensively researched in terrestrial environments, our understanding of VOCs in aquatic ecosystems remains limited. This project focuses particularly on the exchange of these organic compounds between the sea and the atmosphere. Previous oceanic flux measurements have primarily concentrated on selected sulfur compounds (mainly DMS), oxygenated VOCs, and isoprene. These studies have been restricted to a few compounds, often lacking comprehensive temporal coverage, leaving many VOCs unexplored. By utilizing high-frequency VOC measurements, specifically PTR-TOF-MS, this study aims to conduct direct flux measurements at a coastal site to investigate the temporal variability of exchanges across a range of VOCs and their relationship to changes in environmental forces and ecological variations.

Key-researcher: Mehrshad Foroughan

Funded by DNRF

Since primary production in the Arctic Ocean (AO) is limited by nitrogen (N) availability, knowledge about sources and sinks of N is of critical importance. Surprisingly, a few recent studies have presented sporadic data suggesting N2 fixation in the AO. This import of bioavailable N could be of fundamental importance for N and carbon biogeochemistry in the AO, but data are scarce. This cross-disciplinary and international project aims to quantify pelagic N₂ fixation in the AO – a biological process hitherto unaccounted for. In situ measurements, experiments, and use of cutting-edge methodology will provide unprecedented data on fixation rates, identity of the active organisms, and insights into controlling factors in a cross-Arctic Ocean survey. This information is essential for prediction of primary production in the future AO, particularly in the face of climate change.

Key-researcher: Stine Zander

Collaborators: Colin Stedmon (DTUAqua), Takuhei Shiozaki (UTokyo)

PI: Lasse RIemann 

Funded by Independent Research Fund Denmark