Sören Thomsen

Planetly by OneTrust

Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different system...

The influence of chlorophyll shading on ocean dynamics has been usually disregarded in eastern boundary upwelling systems modeling studies in spite of their very high primary productivity. Here, we study how this effect impacts on the Peru upwelling system using a regional mesoscale‐resolving physical biogeochemical coupled model. We show that the...

Coastal upwelling rates are classically determined by the intensity of the upper-ocean offshore Ekman transport. But (sub-)mesoscale turbulence modulates offshore transport, hence the net upwelling rate. Eddy effects generally oppose the Ekman circulation, resulting in so-called “eddy cancellation”, a process well studied in the Southern Ocean. Her...

Filaments and fronts play a crucial role for a net offshore and downward nutrient transport in Eastern Boundary Upwelling Systems (EBUSs) and thereby reduce regional primary production. Most studies on this topic are based on either observations or model simulations, but only seldom are both approaches are combined quantitatively to assess the impo...

Ce document synthétise la démarche de réflexion et d'élaboration du vote au sein du LOCEAN visant à réduire l'empreinte carbone de nos activités, de octobre 2018 à septembre 2020.

Plain Language Summary Transport and mixing of water masses driven by ocean currents influence a variety of fundamental processes, including heat redistribution, ecosystem functioning, and pollutants spreading. Therefore, understanding how fluid transport will be affected by climate change is crucial, in particular in the ocean surface, where marin...

The intraseasonal evolution of physical and biogeochemical properties during a coastal trapped wave event off central Peru is analysed using data from an extensive shipboard observational programme conducted between April and June 2017, and remote sensing data. The poleward velocities in the Peru–Chile Undercurrent were highly variable and strongly...

The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterised by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilised by microbial communities, and the degradation of POM is associated w...

Infographie réalisée en Juillet 2020 pour préparer le vote sur le réduction de l'empreinte carbone de septembre.

Abstract. Filaments and fronts play a crucial role for a net offshore and downward nutrient transport in Eastern Boundary Upwelling Regions (EBUS) and thereby reduce primary production. Often studies are either based on observations or model simulations but seldom both approaches are combined quantitatively to assess the importance of filaments for...

Abstract. The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterized by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilized by microbial communities. The degradation of POM is associ...

The Peruvian Upwelling System is characterized by high primary productivity fuelled by the supply of nutrients in a highly dynamic boundary circulation. The intraseasonal evolution of the physical and biogeochemical properties is 10 analysed based on shipboard observations and remote sensing conducted between April and June 2017 off central Peru. T...

The eastern tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZs) in the world ocean, where dissolved o...

In combination to sluggish ventilation by ocean currents, the nutrient upwelling and high surface productivity, followed by organic matter remineralization, leads to a pronounced oxygen minimum zone (OMZ) in the eastern tropical South Pacific (ETSP). There, oxygen concentrations drop below 1 µmol/kg at a water depth <80 m. The high productivity res...

Upwelling systems play a key role in the global carbon and nitrogen cycles and are also of local relevance due to their high productivity and fish resources. To capture and understand the high spatial and temporal variability in physical and biogeochemical parameters found in these regions, novel measurement techniques have to be combined in an int...

The parameterization of sub-grid scale processes is one of the key challenges towards improved numerical simulations of the atmospheric and oceanic circulation. Numerical weather prediction models as well as climate models would benefit from more sophisticated turbulence closures that allow for less spurious dissipation at the grid-scale and conseq...

Upwelling systems play a key role in the global carbon and nitrogen cycles and are also of local relevance due to their high productivity and fish resources. To capture and understand the high spatial and temporal variability of physical and biogeo-chemical parameters found in these regions novel measurement technics have to be combined in an inter...

The Eastern Tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZ) in the world ocean where dissolved oxy...

Members of the gammaproteobacterial clade SUP05 couple water column sulfide oxidation to nitrate reduction in sulfidic oxygen minimum zones (OMZs). Their abundance in offshore OMZ waters devoid of detectable sulfide has led to the suggestion that local sulfate reduction fuels SUP05-mediated sulfide oxidation in a so-called “cryptic sulfur cycle”.We...

As a major source for atmospheric CO2, the Peruvian upwelling region exhibits strong variability in surface fCO2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO2 budget. In th...

While being a major source for atmospheric CO 2 , the Peruvian upwelling region exhibits strong variability in surface f CO 2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO 2...

As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a k...

The Peruvian upwelling system encompasses the most intense and shallowest oxygen minimum zone (OMZ) in the ocean. This system shows pronounced submesoscale activity like filaments and fronts. We carried out glider-based observations off Peru during austral summer 2013 to investigate whether submesoscale frontal processes ventilate the Peruvian OMZ. W...

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs), which a...

The Peruvian upwelling region shows pronounced near-surface submesoscale variability including filaments and sharp density fronts. Submesoscale frontal processes can drive large vertical velocities and enhance vertical tracer fluxes in the upper ocean. The associated high temporal and spatial variability poses a large challenge to observational app...

Microstructure Measurements during METEOR cruise M93

The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent (PCUC) in January and February 2013 is investigated using a multi-platform four-dimensional observational approach. Research vessel, multiple glider and mooring-based measurements were conducted in the Peruvian upwelling regime near 12°30'S. The dataset consists of > 100...

The role of meso- and submesoscale processes for the near-coastal circulation, physical and biogeochemical tracer distributions and oxygen minimum zone ventilation in the Peruvian upwelling regime is investigated in this thesis. A multi-platform four-dimensional observational experiment was carried out off Peru in early 2013 and is the basis for th...

The interaction between near-inertial wave propagation and geostrophic flow was already investigated by Kunze (1985). Anticyclones can trap and enhance downward propagation of near-inertial wave energy. A critical-layer can be formed below these eddies where the associated vorticity anomaly vanishes. Several recent model studies point out the impor...

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There ar...

The formation of an anticyclonic mode water eddy in Jan/Feb 2013 within the Peru-Chile Undercurrent is pre- sented based on a multi-platform observational study. Two consecutive research cruises, a glider swarm experiment and moored measurements were conducted as part of the interdisciplinary "SFB 754 Climate-Biogeochemistry Interactions in the Tro...

In meso- and submesoscale regimes a strong physical-biogeochemical coupling is thought to exist. A swarm experiment with seven gliders equipped with sensors measuring pressure, temperature, salinity, oxygen and chlorophyll fluorescence was conducted in early 2013 within the upwelling region off Peru. The goal was to study near-coastal pathways for...

Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 and 5 days and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in...

Gliders based microstructure measurements using a MicroRider turbulence package from different locations in the tropical Atlantic are used to investigate the diurnal variability of turbulence and stratification in the mixed layer. The autonomous platform enables us to collect time series of turbulent dissipation rates along with stratification over...

An extensive measurement program within the Atlantic Cold Tongue (ACT) region was carried out during the ACT onset in boreal summer 2011. During two consecutive cruises shipboard microstructure profiles, conductivity-temperature-depth-O2 (CTD-O2) profiles and shipboard velocity profiles were collected between mid-May and mid-July. The shipboard mea...

Mixing processes in the upper equatorial Atlantic at 23°W on the basis of direct microstructure measurements from June 2006, March 2008, and November 2009 have been studied. These measurements indicate large differences in mixing intensities below the mixed layer. In March 2008 vertical shear and mixing levels were comparatively low. At similar str...