Oceanography projects

Laboratory and field work

Antarctic fish larvae, their distribution, feeding and growth in a highly productive polynia near Amundsen Sea (master)
Antarctic polynias are areas surrounded by drift ice and glaciers which remain open for much of the year due distinct hydrographic features. These have a very high primary production which supports a wide array of organisms including fish. One Antarctic area of outstanding productivity is located in the Amundsen Sea, however, only few studies have been carried out in this area. Further information on this polynia (open water) is now available from the 2010-2011 cruise by US Icebreaker Nathaniel B. Palmer which investigated the hydrographic features, and phytoplankton, zooplankton and fish larvae distributions and community compositions of the area. 

The aim of the proposed project is to outline the distribution and investigate possible retainment of fish in relation to the hydrographic features of the polynia. In this context also the diet and growth history of different larval species will be related to the hydrography and secondary productivity at the specific location where they were sampled. Methods include identification of preserved fish larvae, and microscopic investigation of their gut content and the growth information from the microstructure of their otoliths. 

In a future warmer climate the Antarctic polynias will probably expand. Thus, further information on the linkage between the planktonic ecosystem and the specific physics of these areas would be of great value in the evaluation of potential future changes in the spawning and early life of fish at the Antarctic continental shelf.
Contact: Peter Munk, pm@aqua.dtu.dk   

Linking UV-visible spectroscopic properties of dissolved organic matter to chemical structures (bachelor or master)
Dissolved organic matter (DOM) is present in all natural waters (rivers, lakes, oceans, glacial melt-water, sea ice). It essentially consists of a very complex mixture of organic compounds, which represent the remains of living organisms and subsequent degradation products.  UV-Visible spectroscopic measurements (absorption and fluorescence) are increasingly used as a rapid and sensitive approach to characterize and trace DOM. However, the chemical structures responsible for these signatures remain elusive. Within this research theme there is the possibility to carry out several Master and Bachelor projects documenting the UV-visible spectroscopic properties of known compounds, linking these signatures to those measured in natural waters and coupling these to detailed molecular characterization of DOM.
Contact: Colin A. Stedmon, cost@aqua.dtu.dk   

Quantifying the importance of photochemistry and microbes in carbon and nutrient mineralization (bachelor or master)
Over 97% of the organic carbon in the ocean exists as dissolved organic matter (DOM). The remaining 3 % accounts for all living organisms from bacteria to whales and includes detrital particles. This reservoir of organic carbon is similar in size to that present as CO2 in the atmosphere and on land as terrestrial biomass. Small changes in the mineralization rates of this large reservoir of organic carbon therefore have the potential to considerably change atmospheric CO2 levels and thereby our climate. In addition to carbon, essential nutrients such as nitrogen and phosphorus are also bound in DOM. Together photochemistry and microbial degradation control the recycling of carbon, nitrogen and phosphorous back to inorganic forms which can taken up by phytoplankton. Within this broad theme several Masters or Bachelor projects can be designed to study specific aspects and link to current research projects in the section to Oceanography and Climate.
Contact: Colin A. Stedmon, cost@aqua.dtu.dk 

Post bloom plankton dynamic in the Disko bay (bachelor or master)
Most of our understanding of Arctic pelagic ecosystems is based on the phenology of the large fat calanoid copepods (Calanus sp.) in the food web. This group of zooplankton is responsible for the transfer of energy from the spring phytoplankton bloom to the higher tropic levels. After the spring bloom the majority of the Calanus biomass leaves the surface layer and migrates to the near-bottom water where they stay until the next spring. After the spring bloom when the surface layer is stratified and strongly nutrient limited plankton community dominated by small species establishes. Knowledge about the impact of food and temperature on this late summer plankton community is limited. The aim of the present project is to investigate the later summer plankton dynamics in the Disko bay- in particular the importance of changes in food and temperature conditions for the development and succession of the later summer plankton community.
Contact: Torkel Gissel Nielsen, tgin@aqua.dtu.dk 

Chemical communication in the plankton (bachelor or master)
Small pelagic zooplankton may find food by the odor it produces, females produce pheromones that attract males, and zooplankton produce substances that allow their phytoplankton prey to change behavior to avoid being eaten. Chemical communication is widespread in the blind world of the plankton but is very poorly understood. The project may take many different directions, from focus on chemistry (what are the substances?) or genomics (what genes are up-regulated in response to chemical signals?) to more behaviorally oriented studies (how do organisms respond to signal chemicals?). Examples of specific projects include experimental testing of chemo-attractants to various species of zooplankton (what substances attract copepods, for example?) or experiments to describe how phytoplankton respond in swimming behavior or chain-formation to grazer odors.
Contact: Thomas Kiørboe, tk@aqua.dtu.dk

Zooplankton behavior and fluid dynamics (bachelor or master)
Zooplankton live in a viscous environment and their behavior is constrained in often non-intuitive ways.  At the same time it is often difficult to actually observe the behavior of these organisms as they are small and transparent, and their behaviors so fast that they cannot be perceived by the human eye. The project will use high speed video to observe the behavior of selected plankton organisms: this will allow a view into a world that has been observed by very few and where fundamental new discoveries are possible. The project may further flow visualization to help us understand the hydromechanical constraints on behavior as well as the signal that moving and feeding zooplankters produce and that may reveal their presence and position to potential predators. The key question is how zooplankters perform their fundamental missions of moving, eating, and mating in a way that minimizes their exposure to predators.
Contact: Thomas Kiørboe, tk@aqua.dtu.dk

Investigation of the lipid pump in the oceans (bachelor or master)
Many, especially cold water copepods store large amounts of lipids that they use during overwintering at great depths in the oceans.  By this, the copepods remove enormous amounts of high quality carbon from the surface layer to the deep sea and this transport is called the lipid pump.  There are several aspects of this lipid transport that are interesting to look further into.  One is basically to calculate the energy content and the impact on the trophic transfer. Other is to further look into the interesting question how can a buoyant copepod full of fat stay for many months in the deep ocean without drifting to the surface again. The project requests gathering of data from the literature on lipids in different oceanic environments, synthesis of new data and a generation of a simple model of the physical characteristics of lipids and their role in marine pelagic food webs.
Contact: Sigrún Jónasdóttir, sjo@aqua.dtu.dk   

Effect of multiple environmental stressors on food-web interactions and vertical flux (bachelor or master)
The response of zooplankton to climate change is likely to be a combination of their physiological responses to diverse environmental stressors (sometimes acting to opposite directions), and the changes in their feeding conditions through altered physiology of phytoplankton. The aim here is to quantify the effect of multiple stressors (for instance, T, CO2 salinity, nutrient ratios) and their combinations on food web interactions and the allocation of phytoplankton carbon between microzooplankton grazing, mesozooplankton grazing and the part which is not being grazed on and might eventually sink out of the productive layer. The focus can be on diatoms, prymnesiophytes or cyanobacteria, and on Baltic or marine micro-or mesozooplankton. The project(s) will investigate how stressor-induced changes in copepod or algal physiology (e.g., production of toxins, DOC or TEP) can influence grazing by micro vs. mesozooplankton, trophic transfer efficiency, and aggregate formation, sinking and degradation.
Contact: Jörg Dutz, jdu@aqua.dtu.dk, and Marja Koski, mak@aqua.dtu.dk 

Modeling and data analysis

Machine learning and artificial neural networks: applications in systems research (master)
Complexity of the world reveals itself through each of its natural or man-made networks, from weather and climate to economic and social systems. Like the entire biosphere, marine ecosystems are controlled by a dynamic network of interactions and relationships, and not static entities. In order to project future ecosystem states under a changing climate, we are challenged to design innovative approaches potentially capable of interpreting the complexity of interactions in the marine as well as other natural systems.
In this project you will have the opportunity to apply artificial intelligence tools (such as artificial neural networks) to help solve one of many puzzles of marine science, e.g.: what drives recruitment of cod in the Baltic Sea, or herring in the Atlantic Ocean, what controls the efficiency of the so-called "biological carbon pump" or how to project future spatio-temporal distribution of key zooplankton species in the North Atlantic?
Apart from working on an exciting research question, you will use of state-of-the-art analytical tools with wide applications in engineering (e.g. wireless communication), medical research (e.g. heart donor-receiver matching), economics (e.g. bankruptcy prediction), resource & business management and geophysics (e.g. earthquake prediction).
Contact: Michael St. John, mstj@aqua.dtu.dk and Artur Palacz, arpa@aqua.dtu.dk

Are the ocean deserts (actually) expanding? (master)
One of the consequences of climate change predicted by circulation models is the expansion of the sub-tropical gyres – the so-called “ocean deserts”. Several authors have presented evidence that this is already happening: however, the analyses that they base their results upon are fundamentally flawed, and may have given a “false-positive” result. In this project you will analyse satellite remote-sensing products to estimate the size of each of the sub-tropical gyres as a function time. You will then analyse this time series to ask the question, is the variation in size observed statistically meaningful?
Contact: Mark Payne (mpa@aqua.dtu.dk) 

Is the timing of the North Atlantic spring-bloom changing in response to climate change? (master)
The timing (phenology) of the North Atlantic spring phytoplankton bloom results from the dynamics of the physical, chemical and biological environment. Climate change is expected to impact all of these processes individually, and therefore it seems unlikely that the dynamics of the bloom will remain unaffected. The dynamics of the spring bloom are critical for both the ecosystems that are dependent upon it, and also for the draw-down of carbon from the atmosphere (via the biological pump). In this work you will collate data sets that can be used to draw inference about the bloom timing: particularly from the ocean weather ship archive and other fixed stations. You will then analyse this data with the aim of answering the question: has the timing of the spring-bloom changed?
Contact: Mark Payne, mpa@aqua.dtu.dk 

Predictability of marine ecosystems (master)
It is rapidly becoming apparent that modern physical oceanographic models have a significant predictive skill in the North Atlantic region up to 10 years int advance i.e. the temperature of the North Atlantic can be predicted, somewhat reliably, well into the future. These models could therefore be used to make predictions about the future dynamics of the ecosystem, and thereby optimise the management of these resources (e.g. fisheries). However, the biological knowledge necessary to translate physical predictions into biological predictions is unfortunately widely scattered, and in most cases, simply lacking. In this work you will review the current state of knowledge in this regard, with a view to identifying the “low-hanging fruit” i.e. the systems where there is sufficient understanding to make such predictions. In some cases it may also be possible to work directly with the outputs of these models, to actually start to make predictions.
Contact: Mark Payne, mpa@aqua.dtu.dk 

Search efficiency in a patchy environment (bachelor or master)
A current topic in ecology (including marine ecology) concerns the foraging efficiency of various search geometries. Much has been written on the efficiency of Lévy walks for instance, but the underlying theory is somewhat flawed.  A more relevant model is a composite search geometry, where the forager switches between intensive searches and, if no target has been found within some “give-up time”, long runs to bring the forager to some new, unexplored area. Crucially, this behaviour can be meshed to the underlying distribution of prey, where the behavioural shift can be triggered by the time elapsed since the forager last found a target. The aim of this project is to determine the optimal relationship between give-up time and the patchiness of their prey field, and the trade-offs such search behaviour elicits in terms of foraging benefit and predation risk. This is a fundamental question with application not just for plankton ecology, but a whole host of ecological settings. The project will involve modelling and mathematical analysis.
Contact: Andy Visser, awv@aqua.dtu.dk 

Sinking of natural particles through a pycnocline (bachelor or master)
Detrital marine particles such as marine snow and faecal pellets constitute a major element of the biological pump; the process by which carbon is transported and sequestered in the deep ocean by marine biological processes. Such particles, in general, experience a momentarily reduced settling speed when they encounter a pycnocline (density gradient), due either to the “added mass” effect or the density contrast of interstitial water in porous particles. In both cases, the concentration detrital particles is increased within the pycnocline with consequences for both the marine organisms (bacteria, protists, zooplankton) that feed on them, and the by-products (dissolved organic compounds, nutrients) produced as they are remineralized. The aim of this project is to develop a hydrodynamic model to predict the settling speed of natural detrital particles as a function of their size, shape, density and porosity, and the characteristics of the pycnocline (steepness, temperature, salinity) they encounter.
Contact: Andy Visser, awv@aqua.dtu.dk 

Preferential concentration of marine particles in turbulence (bachelor or master)
The preferential concentration of plankton by turbulence is a potentially important effect, influencing the patchiness of the marine environment, the coagulation of detrital material, and the contact rate of planktonic predators and their prey. The aim of this project is to critically examine the physics that lead to differences between the trajectories of fluid elements and rigid, finite-sized inertial particles. The project will examine the theoretical background to the 2 mechanisms involved; density contrast and flow curvature. This will involve a mathematical analysis of the theoretical background, and the analysis of measured trajectories and clustering statistics of real particles entrained in a turbulent flow.
Contact: Andy Visser, awv@aqua.dtu.dk 

Vertical migration of zooplankton (bachelor or master)
The daily vertical migration of many zooplankton species such as copepods can be seen as a trade-off between feeding opportunities in the surface layers of the ocean, and a day-time refuge from visual predators in the oceans dark depths. Indeed this type of trade-off can be readily modelled as a function of day length (season), and the abundance of food and predators. The aim of this project is to develop a generic, mechanistic, trait-based model of the vertical migratory behaviour of zooplankton that can predict the key characteristics of this behaviour as a function of imposed environmental conditions. The model will be used to explore the “optimal” behaviour for different species and different life stages, how this behaviour changes with season, water clarity, the type of predator, and the investment of energy into growth, reproduction or storage for over wintering.
Contact: Andy Visser, awv@aqua.dtu.dk

Trait-based plankton ecology (bachelor or master)
A new generation of ecosystem models – trait based models – is currently being developed. Instead of describing all the species in an ecosystem, individuals are characterized by few essential traits and their associated trade-offs. We are launching a large project aimed at identifying key traits for plankton organisms, quantifying their tradeoffs (what are the costs and benefits of a particular trait, measured in the currency of Darwinian fitness), and examining (by models) the individual behaviors (fitness optimization) and ecosystem structures that emerge under different environmental conditions. Become member of a larger group of researches and do one of the many possible thesis projects – experimental, theoretical, or a model – that are possible within this large project.
Contact: Thomas Kiørboe, tk@aqua.dtu.dk