publications

2025

1. Cold Seeps and Coral Reefs in Northern Norway: Carbon Cycling in Marine Ecosystems With Coexisting Features

   Muhammed Fatih Sert, Hans C Bernstein, Knut Ola Dølven, and 5 more authors

   Journal of Geophysical Research, 2025

   Abs

   Cold seeps and cold‐water corals (CWCs) coexist on Northern Norway’s continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet none reaches the sea surface. Instead, the methane dissolves and disperses in the ocean where it is ultimately consumed by methane‐oxidizing microorganisms. These microorganisms metabolize methane and release carbon dioxide and dissolved organic matter (DOM), which may impact the biogeochemical habitat of CWCs in close vicinity of cold seeps. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, DOM compositions, and microbial diversity in the water column. Our results indicated that dissolved inorganic carbon concentrations were 29% higher near cold seeps with modified carbon’s isotopic compositions. The hydrophysical parameters and surface‐to‐bottom control of sinking particles mainly govern water column productivity and nutrient cycle. DOM compositions implied that the seep‐associated microbiomes modify DOM’s chemical diversity and isotopic composition at CWCs and the entire water column near cold seeps. Cold seeps and CWCs coexist in Northern Norway’s continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may modify the carbon cycling in the area, which could mitigate the ecological role and functioning of CWC reefs in the future.

2024

1. Contrasting Methane Seepage Dynamics in the Hola Trough Offshore Norway: Insights From Two Different Summers

   Bénédicte Ferré, Thibaut Barreyre, Stefan Bünz, and 10 more authors

   Journal of Geophysical Research: Oceans, 2024

   _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2024JC020949

   Abs DOI

   This study investigates the temporal variations in methane concentration and flare activity in the Hola trough (offshore Norway) during May 2018 and June 2022. Between these time periods, methane seep activity exhibits 3.5 times increase, as evidenced by hydroacoustic measurements. As the seep area in the Hola trough is constantly within the hydrate stability zone, the observed increase cannot be attributed to migration of its shallow boundary due to temperature increase. However, a combination of low tide conditions resulting in a lower sediment pore pressure and a bottom water temperature increase resulting in a lower methane solubility is likely to explain the increase in the number of seeps observed in June 2022. The hypothesis of tide influence is supported by data collected from a piezometer deployed and recovered during the cruise showing that the tidal effect was observed 3 m below the seafloor. Despite the numerous methane seeps detected, methane concentration and gas flow rates near the seafloor were low (\textless19 nM and \textless70 mL min−1, respectively) compared to other areas with methane seep activity. This is likely due to strong currents rapidly dispersing methane in the water column. Sub-seafloor investigations identified pathways for gas migration in methane seep areas, influenced by topography. This study provides valuable insights into the temporal dynamics of methane concentrations, flare activity, and gas distribution in the Hola trough, contributing to our understanding of offshore methane dynamics in the region.

2. Carbon cycling in coexisting marine ecosystems: Cold seeps and coral reefs in Northern Norway

   Muhammed Fatih Sert, Knut Ola Dølven, Sebastian Petters, and 4 more authors

   In , 2024
3. Replication data for: Cold Seeps and Coral Reefs in Northern Norway: carbon cycling in marine ecosystems with coexisting features

   Muhammed Fatih Sert, Hans C. Bernstein, Timo Kekäläinen, and 1 more author

   2024

   Abs DOI

   This dataset contains water column measurements, dissolved organic matter compositions, hydrographical profiles and 16S rRNA data collected from th...

2023

1. Elevated methane alters dissolved organic matter composition in the Arctic Ocean cold seeps

   Muhammed Fatih Sert, Hannah D. Schweitzer, Tim R. Groot, and 7 more authors

   Frontiers in Earth Science, 2023

   Abs

   Cold seeps release methane (CH4) from the seafloor to the water column, which fuels microbially mediated aerobic methane oxidation (MOx). Methane-oxidising bacteria (MOB) utilise excess methane, and the MOB biomass serves as a carbon source in the food web. Yet, it remains unclear if and how MOx modifies the composition of dissolved organic matter (DOM) in cold seeps. We investigated MOx rates, DOM compositions and the microbial community during ex-situ incubations of seawater collected from a cold seep site at Norskebanken (north of the Svalbard archipelago) in the Arctic Ocean. Samples were incubated with and without methane amendments. Samples amended with methane (∼1 µM final concentration) showed elevated rates of MOx in both seep and non-seep incubations. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses showed that the number of DOM formulas (i.e., molecular diversity) increased by up to 39% in these incubations. In contrast, the number of formulas decreased by 20% in samples not amended with methane, both from non-seep and seep locations. DOM composition was thus altered towards a more diverse and heterogeneous composition along with elevated methanotrophic activity in methane-amended conditions. In addition to microbial DOM production, abating microbial diversity indicates that elevated DOM diversity was potentially related to grazing pressure on bacteria. The diversity of DOM constituents, therefore, likely increased with the variety of decaying cells contributing to DOM production. Furthermore, based on a principal coordinate analysis, we show that the final DOM composition of non-seep samples amended with methane became more resemblant to that of seep samples. This suggests that methane intrusions will affect water column DOM dynamics similarly, irrespective of the water column’s methane history.

2. Replication Data for: Elevated methane alters dissolved organic matter composition in the Arctic Ocean cold seeps

   Muhammed Fatih Sert, Timo Kekäläinen, Bénédicte Ferré, and 1 more author

   Sep 2023

   Abs DOI

   This dataset contains water column measurements, dissolved organic matter compositions, and hydrographical profiles collected from the Norskebanken seep site at Northern Svalbard, Arctic Ocean. Data are presented along with the R codes for the replication of analyses, and figures that were added in our submitted paper. We recommend using R (v4.3.1) and R Studio (2023.06.1) to run R project file (.Rproj) which can access all codes and data. Running codes in the given order will create corresponding data tables and all the figures that were used in the article. Cold seeps release methane (CH4) from the seafloor to the water column, which fuels microbially mediated aerobic methane oxidation (MOx). Methane oxidising bacteria (MOB) utilise excess methane, and the MOB biomass serves as a carbon source in the food web. Yet, it remains unclear if and how MOx modifies the composition of dissolved organic matter (DOM) in cold seeps. We investigated MOx rates, DOM compositions and the microbial community during ex-situ incubations of seawater collected from an active cold seep site at Norskebanken (north of the Svalbard archipelago) in the Arctic Ocean. For comparison, we used seawater collected from a control site (a non-seep environment). Samples were incubated with and without methane amendments. Samples amended with methane (~1 µM final concentration) showed elevated rates of MOx in both seep and non-seep incubations. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses showed that the number of DOM formulas (i.e., molecular diversity) increased by up to 39 % in these incubations. In contrast, the number of formulas decreased by 20 % in samples not amended with methane, both from non-seep and seep locations. DOM composition was thus altered towards a more diverse and heterogeneous composition along with elevated methanotrophic activity in methane-amended conditions. In addition to microbial DOM production, abating microbial diversity indicates that elevated DOM diversity was potentially related to grazing pressure on bacteria. The diversity of DOM constituents, therefore, likely increased with the variety of decaying cells contributing to DOM production. Furthermore, based on a principal coordinate analysis, we show that the final DOM composition of non-seep samples amended with methane became more resemblant to that of seep samples. This suggests that methane intrusions will affect water column DOM dynamics similarly, irrespective of the water column’s methane history.

2022

1. Compositions of dissolved organic matter in the ice-covered waters above the Aurora hydrothermal vent system, Gakkel Ridge, Arctic Ocean

   Muhammed Fatih Sert, Helge Niemann, Eoghan P. Reeves, and 8 more authors

   Biogeosciences, Apr 2022

   Publisher: Copernicus GmbH

   Abs DOI

   \textlessp\textgreater\textlessstrong class="journal-contentHeaderColor"\textgreaterAbstract.\textless/strong\textgreater Hydrothermal vents modify and displace subsurface dissolved organic matter (DOM) into the ocean. Once in the ocean, this DOM is transported together with elements, particles, dissolved gases and biomass along with the neutrally buoyant plume layer. Considering the number and extent of actively venting hydrothermal sites in the oceans, their contribution to the oceanic DOM pool may be substantial. Here, we investigate the dynamics of DOM in relation to hydrothermal venting and related processes at the as yet unexplored Aurora hydrothermal vent field within the ultraslow-spreading Gakkel Ridge in the Arctic Ocean at 82.9\textlessspan class="inline-formula"\textgreater^\textrm∘\textless/span\textgreater N. We examined the vertical distribution of DOM composition from sea ice to deep waters at six hydrocast stations distal to the active vent and its neutrally buoyant plume layer. In comparison to background seawater, we found that the DOM in waters directly affected by the hydrothermal plume was molecularly less diverse and 5 %–10 % lower in number of molecular formulas associated with the molecular categories related to lipid and protein-like compounds. On the other hand, samples that were not directly affected by the plume were chemically more diverse and had a higher percentage of chemical formulas associated with the carbohydrate-like category. Our results suggest that hydrothermal processes at Aurora may influence the DOM distribution in the bathypelagic ocean by spreading more thermally and/or chemically induced compositions, while DOM compositions in epipelagic and mesopelagic layers are mainly governed by the microbial carbon pump dynamics and surface-ocean–sea-ice interactions.\textless/p\textgreater

2. Metanlekkasjer i Arktis - hvordan påvirker de klima og miljø? Overvåking av metan i vannet

   Benedicte Ferré, Knut Ola Dølven, Muhammed Fatih Sert, and 1 more author

   Ottar, Apr 2022
3. Hot Vents Beneath an Icy Ocean: The Aurora Vent Field, Gakkel Ridge, Revealed

   Eva Ramirez-Llodra, Claudio Argentino, Maria Baker, and 30 more authors

   Oceanography, Apr 2022

   Abs DOI

   Evidence of hydrothermal venting on the ultra-slow spreading Gakkel Ridge in the Central Arctic Ocean has been available since 2001, with first visual evidence of black smokers on the Aurora Vent Field obtained in 2014. But it was not until 2021 that the first ever remotely operated vehicle (ROV) dives to hydrothermal vents under permanent ice cover in the Arctic were conducted, enabling the collection of vent fluids, rocks, microbes, and fauna. In this paper, we present the methods employed for deep-sea ROV operations under drifting ice. We also provide the first description of the Aurora Vent Field, which includes three actively venting black smokers and diffuse flow on the Aurora mound at ~3,888 m depth on the southern part of the Gakkel Ridge (82.5°N). The biological communities are dominated by a new species of cocculinid limpet, two small gastropods, and a melitid amphipod. The ongoing analyses of Aurora Vent Field samples will contribute to positioning the Gakkel Ridge hydrothermal vents in the global biogeographic puzzle of hydrothermal vents.

4. Biogeochemistry of dissolved organic matter in Arctic Ocean waters charged with methane

   Muhammed Fatih Sert

   Nov 2022

   Accepted: 2022-11-08T12:36:56Z ISBN: 9788282364959

   Abs

   Dissolved organic matter (DOM) is defined as organic matter that is smaller than a nominal pore size filter (e.g., 0.7 µm) that passes through during the filtration of aquatic samples. It comprises the largest reservoir of reduced carbon (700 Pg C) in the oceans. The DOM pool is in close interaction with all the elemental cycles and food chains in the ocean and is an essential component in the marine microbial loop. Methane is seeping from numerous geological sources in the Arctic Ocean associated with multiple mechanisms that elevate methane production and release. Independent of the mechanism, however, liberated methane is predominantly consumed in the water column by methanotrophic bacteria (MOB), which use methane as a source of carbon and energy during an aerobic enzymatic reaction called methane oxidation (MOx). In sedimentary fluid flow systems such as cold seeps or hydrothermal vents, the amount of methane release and subsequent MOx would be substantial and further trigger other ecosystem processes such as bacterial growth and heterotrophic consumption and consequent mechanisms that alter DOM composition in the water column. Since methane is one of the most potent greenhouse gasses in the atmosphere and due to its subsequent effect on global warming, it has been quantified extensively in the oceanic environments and its fate in the water column has been investigated in different types of geological settings. However, the effects of methane emanation and methane-driven processes on DOM dynamics in the water column have been merely constrained. The main objective of this thesis was to unravel the modifications of DOM composition in relation to methane release in the Arctic Ocean cold seeps and hydrothermal vents.

2021

1. Replication data for: Compositions of dissolved organic matter in the ice-covered waters above the Aurora hydrothermal vent system, Gakkel Ridge, Arctic Ocean

   Muhammed Fatih Sert, Eoghan P. Reeves, Kevin P. Hand, and 1 more author

   Nov 2021

   Abs DOI

   This dataset contains water column measurements, dissolved organic matter compositions, and hydrographical profiles collected from Aurora Hydrother...

2020

1. Replication Data for: Arctic cold seeps alter dissolved organic matter composition at the Svalbard continental margin and the Barents Sea

   Muhammed Fatih Sert, Juliana D’Andrilli, Friederike Gründger, and 5 more authors

   Nov 2020

   Abs DOI

   Abstract: Dissociating gas hydrates, submerged permafrost, and gas bearing sediments release methane to the water column from a multitude of seeps ...

2. Compositional Differences in Dissolved Organic Matter Between Arctic Cold Seeps Versus Non-Seep Sites at the Svalbard Continental Margin and the Barents Sea

   Muhammed Fatih Sert, Juliana D’Andrilli, Friederike Gründger, and 5 more authors

   Frontiers in Earth Science, Nov 2020

   Publisher: Frontiers

   Abs DOI

   Dissociating gas hydrates, submerged permafrost, and gas bearing sediments release methane to the water column from a multitude of seeps in the Arctic Ocean. The seeping methane dissolves and supports the growth of aerobic methane oxidizing bacteria (MOB), but the effect of seepage and seep related biogeochemical processes on water column dissolved organic matter (DOM) dynamics is not well constrained. We compared dissolved methane, nutrients, chlorophyll, and particulate matter concentrations and methane oxidation (MOx) rates from previously characterized seep and non-seep areas at the continental margin of Svalbard and the Barents Sea in May and June 2017. DOM molecular composition was determined by Electrospray Ionization Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We found that the chemical diversity of DOM was 3 to 5 % higher and constituted more protein- and lipid-like composition near methane seeps when compared to non-seep areas. Distributions of nutrients, chlorophyll, and particulate matter however, were essentially governed by the water column hydrography and primary production. We surmise that the organic intermediates directly derived from seepage or indirectly from seep-related biogeochemical processes, e.g. MOx, modifies the composition of DOM leading to distinct DOM molecular-level signatures in the water column at cold seeps.

2018

1. New Insights into Methane Driven Dissolved Organic Matter Dynamics in the Arctic Ocean

   Muhammed Fatih Sert, Anna Silyakova, Friederike Gründger, and 6 more authors

   In , Feb 2018

2014

1. Assessing the occurence and removal of steroid hormones in animal wastes

   Muhammed Fatih Sert

   Feb 2014
2. Assessment of maturation in animal waste composts

   M Fatih Sert, Serap Karaca, and Işıl Balcıoğlu

   In , Dec 2014

   Abs

   Due to the mentioned factors, maturation phase of the composting operations has to be considered to evaluate compost quality. To be able to adopt this perspective, producers should view animal manure as an economic resource that can only be substituted by high quality fertilizer. Therefore in addition to rapid and effective processing of animal manure by appropriate techniques and machinery, required controls must be implemented in big scale animal farming operations based on the reference criteria for the organic fertilizers that allowed to be used in plant nutrition.

2010

1. Determination of total nitrogen and phosphorus in the northeastern Mediterranean water column

   Muhammed Fatih Sert

   Middle East Technical University, Jul 2010
2. Spatial distributions of nutrients in the northeastern Mediterranean during 2008-2009

   Fatih Sert, and Süleyman Tugrul

   In Rapp. Comm. int. Mer Médit, Jul 2010

   Abs

   North Eastern Mediterranen waters has been surveyed as two distinct basin in Turkish coasts in 2008 – 2009 period. Including Mersin Bay, Cilician Basin were examined with several cruises between March 2008 and October 2009. Moreover, we visited 10 stations (20 miles apart) on a south-north transect in Levantine Sea in March and September 2008. These studies aimed to assess spatial distributions of principal hydro-chemical properties (nutrients, DO, Chl-a) of these two basin with surface distribution and depth profiles.