Coordinator: Prof. Dr. Arne Körtzinger
(Deputy: Prof. Dr. Christa Marandino)

Mission:

This WP investigates biological, chemical and physical processes in the surface ocean and at the air-sea interface, their control on matter exchange across the interface and their role in biogeochemical cycles in view of the impacts of and feedbacks to global change. 

Scientific Questions

Global climate change will first and foremost affect the surface ocean, which is why WP1 focuses on its impact on chemical processes in the surface ocean and at the air-sea interface. Important questions that will be addressed include:

• How do oceanic sources or sinks of atmospheric trace gases influence radiative and chemical properties of the atmosphere?
• What is the influence of chemical and physical properties of the air-sea interface on key processes such as gas exchange and aerosol formation?
• How do key biogeochemical processes of the ocean-atmosphere interaction respond to and influence climate change?

Contents and Goals

A major challenge in this WP is to unravel the multiple facets of ocean-atmosphere coupling from a chemical perspective on the basis of field observations and experiments. To achieve a more encompassing assessment of future chemical responses to ocean change and their feedback to the atmosphere, this WP will:

• Develop and apply advanced analytical instrumentation to measure chemical trace species [link with WP2],
• Improve observational capabilities in time and space through novel techniques [link with Topic 1], including both novel autonomous platforms and sensors or analytical systems,
• Mount field campaigns to study distributions of biogeochemical trace substances and their source/sink dynamics,
• Link information on air-sea fluxes with interior ocean processes and storage [link with WP2], and
• Improve and expand the scientific scope of the Cape Verde Ocean Observatory (CVOO).

Key processes and tasks to be addressed in this WP:

Cycling of marine carbon: The oceans’ CO₂ sink shows both strong inter-annual variability and signs of weakening in key ocean regions. The reason for this is most likely the effect of physical and biological processes on the natural carbon cycle. Combined observation of surface ocean CO₂ and O₂ dynamics can help to elucidate the driving mechanisms. Research in this area is based on observations from a ‘Voluntary Observing Ship’ line across the sub-polar North Atlantic and a regional focus in the tropical Atlantic where upwelling off West Africa and at the equator constitutes a major and climate-susceptible driver of ocean carbon dynamics. This research area also has a strong methodological component, involving innovative sensors and state-of-the-art autonomous observation platforms [link to Topic 2-WP2].

Tracing oceanographic circulation: Large-scale circulation and mixing govern transport and distribution of biogeochemically important substances and transient tracers. Anthropogenic tracers (such as CFC, SF₆ or PFC) can thus be used for quantification of anthropogenic carbon storage. In addition, deliberately released tracers (e.g., CF₃SF₅) provide a powerful tool for studying interior-ocean mixing and advection. Research with transient, as well as deliberately-released, tracers focuses on vertical mixing processes, diffusivity in the interior ocean and the application of this knowledge to the cycling of biogeochemical parameters. [link to Topic 1-WP2]

Surface ocean cycling of halogenated volatile organic compounds (HVOC): Chlorinated, brominated and iodinated volatiles are ubiquitously distributed in the open and coastal oceans. They have both natural biological and chemical sources and exchange across the air-sea interface. HVOC have a variety of impacts in the atmosphere (e.g., aerosol formation, destruction of tropospheric and stratospheric ozone, oxidative capacity of the atmosphere). Since measurements of this compound class are rare, we initiated the HalOcAt database, which brings together global oceanic and atmospheric HVOC data. In close collaboration with atmospheric scientists, fieldwork is carried out in various oceanic regions with a particular focus on the tropics, where important source regions are found, and with special emphasis on various types of anthropogenic forcing [link with Topic 1].

Surface ocean cycling of oxygenated volatile organic compounds (OVOC): OVOCS such as acetone and methanol play an important role in the chemistry of the troposphere (e.g. global radiative budget, oxidative capacity of the atmosphere). It has been shown that these compounds may be of special importance in remote marine regions, especially those with high convective activity. However, it is still unclear whether the ocean is a source or a sink of these compounds and how they are cycled in the surface ocean. Detailed studies investigating the air-sea gradient, direct flux measurements and surface ocean sources and sinks are carried out using state-of-the-art instrumentation (APCI-MS) in order to constrain the role of the ocean in the atmospheric budget of these compounds.

The influence of the sea surface micro layer (SML) on organic compounds: The SML is the boundary layer between the ocean and the atmosphere, and mediates gas fluxes from and into the ocean, as well as the emission of primary organic aerosols (POA) that were recently recognized as important nuclei for cloud condensation. Our investigations aim to unravel the relationship between plankton productivity and the enrichment of organic compounds in the SML and in POA. We study the dynamics of SML and POA at different coastal sites (BETS, upwelling off Peru) and in remote oceanic regions, such as the Arctic Ocean. Our research also includes studies with experimentally perturbed systems, such as mesocosms [link with WP2 and AWI]. 

Ocean cycling of trace metals: Trace metal biogeochemistry plays a pivotal role for open ocean productivity and hence the carbon cycle. We aim to elucidate the interrelations of trace metal input, organic complexation and trace metal redox-cycling on metal bioavailability in the context of climate change, particularly ocean acidification. Further, metal cycling in the upper water column and exchange with deep water will be addressed with special emphasis of the role and variability of oxygen minimum zones. Seawater pH plays a crucial role in trace metal solubility and cycling, potentially resulting in profound changes of nutrient and trace metal cycling in tropical oceans [link with WP2]. 

Surface ocean cycling and air-sea exchange of climate active gases (N₂O/CH₄/DMS/isoprene): Gases that can be produced in the surface ocean, such as nitrous oxide (N₂O) and methane (CH₄), have large global warming potentials, while others, such as dimethylsulfide (DMS) and isoprene, can be important precursors for aerosol formation. Our knowledge about the oceanic emissions of these gases and their prevailing biological pathways is far from complete, especially in the case of isoprene. In particular shelf regions, as well as coastal and equatorial upwelling regimes, have been identified as hot-spots for N₂O, CH₄ and DMS production and hence emissions. Therefore, we carry out focussed studies in coastal upwelling systems and at a coastal station (BETS – Boknis Eck Time Series Station). In addition, air-sea fluxes and surface-ocean cycling of DMS and isoprene will be investigated in order to understand the biogeochemical cycles of these gases. 

Key observation systems used in this WP:

Integrated Carbon Observation System (ICOS): GEOMAR operates two major components of the European ICOS project: the North Atlantic “Voluntary Observing Ship” line and the CVOO time-series. These are operated to demonstrate the feasibility of long-term autonomous measurements of CO₂ fluxes. Both components serve central long-term functions in the German and international ICOS project [collaboration with AWI].

Boknis Eck Time-Series Station (BETS): Sampling started in 1957 and BETS thus represents one of the oldest continuously sampled marine time-series sites worldwide. The location of BETS makes it an ideal site to study (i) a coastal ecosystem under the influence of pronounced changes of salinity and (ii) biogeochemical processes sensitive to pronounced changes of oxygen (i.e., hypoxia/anoxia). High-quality long time series observations at BETS are invaluable to decipher long-term trends in a representative coastal environment, which is under local and global anthropogenic pressures.

WP1 research highlight: The international ocean time-series site at Cape Verde Ocean Observatory (CVOO) was established in 2006 by the European project TENATSO and is operated by GEOMAR in cooperation with a Cape Verdean partner “Instituto Nacional de Desenvolvimento das Pescas (INDP).” The continuous observational programme currently features a multidisciplinary mooring, a monthly ship-based sampling programme with the local Cape Verdean R/V Islandia, as well as occasional intensive field campaigns with large research ships and autonomous instruments (floats, gliders). GEOMAR has ambitious goals to enhance the CVOO research portfolio through major improvements of the local infrastructure, most importantly through construction of a research station with modern laboratories, workshops, offices and meeting facilities (involving Topics 1-4), which will be available not only for GEOMAR scientists but also to the entire national and international scientific community. Research in the region involves all programme topics and addresses chemical, biological, physical and geological aspects of marine sciences research. The local research infrastructure in Mindelo has facilitated – and in some cases made possible – research projects of highly interdisciplinary nature and with innovative state-of-the-art technology.

Three examples highlight the research being carried out at the CVOO: (i) Deployment of the first ever profiling floats for autonomous measurement of CO₂ and O₂ in the surface ocean providing a Lagrangian look at combined air-sea fluxes of CO₂ and O₂ (SOPRAN); (ii) Biological project on the loggerhead sea turtle that has an ambitious biologging component which not only provides information on migration patterns and diving behaviour but also on temperature and oxygen distributions; and (iii) Two-month glider swarm experiment around CVOO providing unprecedented insight into mesoscale variability, which allowed the first observation of mesoscale dead zone features totally devoid of oxygen.