This project aims to understand the interaction between sea ice cover, export of particulate organic carbon and its mineralization at the seafloor, and how benthopelagic fluxes of oxygen, carbon, and inorganic nutrients on the Antarctic shelf are influenced by climate change.

The Antarctic continental shelf represents roughly 11% of the world’s continental-shelf area and is considered the most productive part of the Antarctic. On the shelf, primary production strongly varies depending on light conditions, sea ice cover, mixing depth and nutrient availability. In regions impacted by global warming, such as the Antarctic Peninsula, these conditions are changing, leading to the retreat of sea ice and ice shelves and to the exposure of previously covered areas to marine primary production, with important repercussions on nutrient and carbon fluxes. Further, increased calving of icebergs and increased iceberg scours are expected to affect carbon turnover near the seabed.

Marwa BALOZA

The aim of the PhD project is to advance our understanding of the distribution and ecological role of glass sponges (Porifera, Hexactinellida) in the shelf areas of the southeastern Weddell Sea.

Sponges are important components of the seafloor communities in many regions of the Antarctic shelf. They often dominate the benthic biomass and can form extensive sponge grounds in some areas. The most conspicuous species belong to the class Hexactinellida, or glass sponges, which form skeletal needles of silicon dioxide and can grow up to 2 m in height. They are of ecological importance, because the sponge grounds provide a complex, three-dimensional habitat for a variety of other animals and may play a significant role in the cycling of silicon and carbon. However, many questions about their ecology and mode of life remain unresolved. The objectives of my PhD project are

1. to determine biomass ratios and size-biomass relationships for different glass sponge morphotypes, which can then be used to calculate glass sponge biomass from images,
2. to estimate glass sponge metabolism and their impact on carbon cycling from measured pump rates and respiration, and
3. to identify parameters governing their distribution, biodiversity, abundance and biomass on the southeastern Weddell Sea shelf.

This knowledge will help us to assess how these important ecosystem engineers will be affected by environmental changes. 

Luisa FEDERWISCH

To describe the present situation of the benthic fauna in the Weddell Sea by using new and old samples, describe community changes form past descriptions and asses how will benthic communities be affected by the ongoing climate change.

This project uses quantitative data of multi-box corer stations and seabed images taken during several cruises with RV Polarstern. As a first step the data will be used to fill gaps in current knowledge of benthic communities to the compare the "present" state with its "past" description. Additionally, environmental data (e.g. hydrography, sediment chemistry) is included in the analysis to asses which environmental factors regulate benthic distribution. The analysis of the past and present of benthic fauna and how the environment regulates benthos will be incorporated in a model to evaluate the effect of climate change over benthic faunal communities.

Dr. Santiago PINEDA-METZ

Prof. Dr. Claudio RICHTER

We investigate the growth of cold-water corals (CWC) in a naturally acidified Patagonian fjord (Comau Fjord / Chile) and the role of zooplankton in sustaining their nutritional supply.

Calcification and growth of CWC depends on seawater chemistry, particularly the saturation state of aragonite, the mineral composing the skeleton. The rising CO₂ levels in the atmosphere are predicted to change seawater chemistry and lower the aragonite saturation state, with negative consequences particularly for the deep biota. Because many CWC live at or near aragonite saturation, already slight changes in saturation state may have dire consequences for the calcification and survival of these corals. Comau Fjord (Chile) offers a unique window into the future, where the stratified fjord allows to time-travel from aragonite-supersaturated waters near the surface to undersaturated waters at depth. Recent research has shown that the CWC Desmophyllum dianthus abounds below the aragonite saturation horizon, suggesting adaptation to ocean acidification. Because coral calcification is energetically costly, we postulate that a high supply of zooplankton food provides the metabolic energy for the coral to maintain calcification in acidified waters. The project involves observational and experimental studies on the ecology of the corals and their regulation of internal pH, their ability to cope with global CO₂ and temperature rise, and the ecology of the plankton, its distribution in space and time, vertical migrations and seasonality.

Prof. Dr. Claudio RICHTER

Understanding the trophic interactions of ecosystem engineering cold-water corals through the current era of environmental degradation and climate change, is among the most pressing challenges that biologist face.

Cold-water corals play an important role as ecosystem engineers by providing the three-dimensional structural basis and habitat for a rich associated fauna. Despite its importance, these species are among the most threatened by climate change through ocean acidification. In southern Chile, the cold-water scleractinian Desmophyllum dianthus populates the steep walls of Comau Fjord. Here its principal energy source, zooplankton, is less abundant in winter. This coral species is often associated with filter-feeders, but the nature and possible trophic significance of this relationship remains enigmatic. Dense belts of the mussel Aulacomya atra and the brachiopod Magellania venosa thrive in the productive waters above and between D. dianthus, and both, visual observation and diver-operated push net samples revealed a rain of biodeposits from these filter-feeders to the corals. This study aims to determine if microscopic plankton, which is inaccessible to corals may be accessible to the corals’ tentacles through the conversion by filter-feeders to macroscopic strings of faeces and pseudofaeces. If so, this may represent a new and so far overlooked trophic link channeling surface production to the corals. 

Thomas HERAN ARCE

This project will help to understand the fluxes of particulate organic carbon within the North Sea and how anthropogenic activities might alter the potential for carbon sequestration in marine sediments.

Mitigation of the negative effects of CO₂ release from anthropogenic activities is one of the most important task of our generation. CO₂ can be taken up from the atmosphere by marine phytoplankton and from there transported towards deeper waters where it can be sequestered in oceanic sediments. This sequestration depends on the hydrodynamics of the water column, whereas processes within the North Sea are so far poorly understood. Additionally, anthropogenic activities can alter this mechanism. Bottom fishing activities for example are expected to resuspend and thereby release the deposited carbon again to the water column, where it can be remineralized. Therefore, we will measure the particulate carbon transport within the German North Sea and conduct in-situ resuspension experiments in combination with short term deployments of a benthic observatory to quantify carbon fluxes in relation to hydrodynamics and disturbances.

Dr. Ulrike HANZ