R09: Ocean Controls

Quantifying the release of greenhouse gases during sill intrusion in sedimentary basins using numerical flow models
Dr. Karthik Iyer,  read more The major aim of this proposal is to constrain the amount of CH4 and CO2 released during sill intrusion events using the Vøring basin off western Norway and the PETM as a case study. The biggest advantage of the new modeling approach will be that it will not only predict the total amount of greenhouse gases released but also the rates and time-scales over which this release would take place. These estimates could then be used as input in paleoclimate models to, for example, explore predicted warming and consistency with proxy data on the PETM.

Detecting the fingerprint of the Atlantic meridional overturning circulation on decadal to millennial time scales
Dr. Uta Krebs-Kanzow,  read more The Atlantic meridional overturning circulation (AMOC) exerts a strong influence on global climate by providing up to one quarter of the maximum meridional heat transport of the coupled climate system (Wunsch, 2005, Trenberth and Caron, 2001). Climate models consistently predict a slow-down of the AMOC in response to rising atmospheric CO2 concentrations for the coming decades (Schneider et al, 2007). The rate of the slow-down is however poorly constrained and adds considerable uncertainties to model projections of the future climate. Moreover, the natural variability of the AMOC beyond inter annual time scales is not known as direct continuous measurements only exist for the past 6 years (Kanzow et al, 2010). Paleo reconstructions reveal that the AMOC was subject to strong variation during both the last glacial period and the transition to the present Holocene warm period. The deglaciation is of particular interest as it represents the most recent period of global warming associated with significantly increasing atmospheric CO2 concentration. Since paleo data do not allow to quantify the amplitude of past AMOC variations and since the climate response might depend on the background climate, it is a major problem to separate past AMOC induced climate variations from superimposing climate signals related to changes in ice-volume, greenhouse gas concentrations or orbital parameters. However, during the last glacial period events of extremely weakened AMOC exhibit common characteristics such as low northern hemispheric temperatures and shifts in low latitudinal precipitation (as review see Hemming, 2004 and references therein) which might represent a fingerprint of AMOC variations. The proposed work will focus on the identification of fingerprints of the AMOC which are valid over an as wide as possible range of climate-controlling parameters using a suite of climate model experiments which differ in continental ice caps, greenhouse gas concentration, orbital parameters and geometry of major ocean passages. Ultimately, this shall be used to decipher the role of AMOC variation during the deglaciation and to define and evaluate proxies, which potentially reconstruct AMOC variations indirectly from observed climate patterns on centennial to millennial time scales.

Investigation of large-scale methane releases induced by increasing temperatures from global warming and break-up magmatism
Ines Dumke,  read more The consequences of warming oceans are manifold and not yet fully understood. One aspect associated with ocean warming is the release of methane gas into the water column, particularly where large amounts of methane are stored in sedimentary gas hydrates. Increased bottom water temperatures affect the sediments and eventually cause hydrate destabilisation and release of free gas into the water column. A high amount of methane may also escape into the atmosphere where, being a stronger greenhouse gas than CO2, it will accelerate global warming. Consequently, it is important to understand the processes involved in gas hydrate destabilisation in areas like the Arctic. To assess the likelihood of triggered hydrate dissociation and large-scale methane release, it is necessary to study other events during which large amounts of methane may have been released. This includes sub-sea magmatism commonly occurring during rifting events. The high temperatures associated with magmatic intrusions alter overlying sediments and may lead to thermogenic methane production. Hydrothermal systems are formed from which large amounts of methane may emanate into the water column and possibly into the atmosphere. Understanding of these hydrothermal systems in terms of fluid migration and their relationship to magmatic intrusions, will give insights into the effects these systems had on oceans and atmosphere, and help to constrain the factors involved in the current global warming period.

Role of intermediate water variability in the Caribbean and Gulf of Mexico in deglacial climate change
read more To better constrain future climate predictions we need to understand how tropical Western Hemisphere Warm Pool (WHWP) dynamics and changes in the thermohaline circulation including re-organisations in intermediate water masses (e.g., AAIW) operate and interact on short time scales. The overall goal of the planned project is to reconstruct the subtropical W-Atlantic / Caribbean / Gulf of Mexico intermediate water variability on the millenial scale climate changes of the last ~40 ka, and determine the role of intermediate water variability in deglacial climate change for interhemispheric heat exchange, thermocline variability, ocean surface properties, and intermediate ocean ventilation. The study intends to test current hypotheses, which suggest the short-term presence of Antarctic Intermediate Water (AAIW) in the subtropical Atlantic (RÜHLEMANN et al., 2004 PAHNKE et al., 2008), and N-Atlantic sourced intermediate water masses in Florida Strait (CAME et al., 2008) during deglacial cool periods when the Atlantic Meridional Overturning Circulation (AMOC) was supposedly weak or collapsed.

Interactions of the Atlantic Meridional Overturning circulation and the atmospheric hydrological cycle during the Last Glacial Termination
Dr. Uta Krebs-Kanzow,  read more Today the Earth's climate is rapidly warming. There is ample evidence for other, dramatic transitions to warmer climates in the Earth's history. Understanding climate transitions of the past is key to provide better predictions for the coming centuries. Compared to equilibrium simulations, however, the transient simulation of past climates is still in its infancy. The aim of this project is to provide a transient climate simulation of the Last Glacial Termination with a state-of the-art coupled atmosphere ocean general circulation model (AOGCM) to investigate changes in the Atlantic meridional overturning circulation (AMOC) and the atmospheric hydrological cycle in a globally warming climate. The simulation will cover the period between the end of the Last Glacial Maximum (LGM, 19 kyr B.P1) and the onset of the warm Bølling-Allerød (about 15 kyr B.P.) and will be forced by changes in atmospheric CO2 and methane concentrations, insolation, and deglacial meltwater discharge. Together with idealized climate simulations and vegetation model experiments this simulation will be used to • quantify the individual contributions of the simultaneously changing forcings to the observed climate evolution • analyze the relationship between Atlantic meridional heat transport and the atmospheric hydrological cycle • develop techniques to constrain reconstructions of precipitation and AMOC strength

Emerging marine diesease: why to shift from friendly to nasty
Prof. Hinrich Schulenburg,  read more Pathogens exert extreme selective pressure on their hosts and are highly prevalent in the marine realm and thus of central importance for marine ecosystem dynamics. Yet, to date, we still lack precise understanding on the complexity of environmental changes that determine shifts in pathogen virulence and thus influence the dynamics of host-pathogen interactions in the oceans. We here aim at developing a “virulence-atlas” for the most abundant marine pathogens from the genus Vibrio. We will take a multidisciplinary approach by integrating several virulence parameters in over 200 isolated Vibrio strains, infection experiments in two established host systems, and candidate virulence gene analysis, in each case under alternative environmental conditions. This project will yield a comprehensive baseline data set essential for an in-depth understanding of the consequences of emerging marine diseases under future scenarios of global change.

Surrogate-based Optimization for Marine Biochemical Models
Dr. Iris Kriest,  read more Marine biogeochemical models are of great importance for a quantitative understanding of the ocean’s role in the global carbon cycle and are essential for projections of the oceanic CO2 uptake and the marine ecosystem’s responses to climate change. The applicability of a marine biogeochemical model for prognostic simulations crucially depends on its ability to adequately describe the relevant physical, chemical, and biological processes. This is typically assessed by a calibration of the often poorly known model parameters. For three-dimensional coupled biogeochemistry-circulation models, a calibration using conventional optimization algorithms is still very time-consuming or even infeasible even on high performance computers. Such a computationally demanding calibration can now be achieved by novel time-efficient Surrogate-based Optimization (SBO) techniques. Extending and advancing our previously developed modular and flexible optimization framework, we propose to perform a calibration of two three-dimensional biogeochemical models of different structural complexity against real data of global distributions of phosphate and oxygen. The proposed interdisciplinary research at the interface of numerical optimization and marine biogeochemistry is expected to provide significant contributions to seek powerful and versatile tools for model-based investigations of marine ecosystems.

Double trouble: Tracing the effect of Ocean Acidification and Ocean Warming in the shells of pteropods and the potential proxy implications
Dr. Nina Keul,  read more Global climate change is one of the most pressing challenges our society is facing at the moment. In combination with temperature reconstructions, accurate atmospheric paleo-CO2 estimates are necessary to validate models that aim at predicting global temperature rise related to CO2 -forcing mechanisms (e.g. Lüthi et al., 2008), while reconstruction of atmospheric pCO2 going further back in time relies on sedimentary archives (e.g. Hönisch et al., 2012). Although work to date has led to important advances in the use of proxies for CO2 reconstructions, existing uncertainties in the measurement of these proxies results in the need for the establishment of new CO2-proxies. I propose to analyze the proxy potential of pteropods, a group of marine calcifiers that are abundant in all major oceans (Lalli and Gilmer, 1989).

Life in a toxic environment: How do extreme redox conditions affect oceanic N2 fixation?
Dr. Hermann Bange,  read more Nitrogen (N) is a limiting element of life in the ocean. Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium, is quantitatively the most important external source of new nitrogen to the ocean and mostly depends on the availability of a phosphorous (P) and iron (Fe) source. While oxygen (O2) depletion favors N2 fixation, the presence of hydrogen sulfide (H2S) under conditions of extreme anoxia may hinder that process by (i) a direct toxic effect on the diazotrophic community and (ii) immobilization of Fe through precipitation of Fe sulfide minerals. In order to explore the sensitivity of N2 fixation to changes in O2 and H2S, we propose an interdisciplinary field study at the time series station Boknis Eck, located in the Eckernförde Bay (www.bokniseck.de), serving as a natural laboratory. This allows an incomparably detailed monitoring of the diazotrophic response to naturally occurring extreme changes in redox conditions. We further aim to explore the potential of the responsible microbial community to adapt to rapidly changing redox conditions in a chemostat. The results are crucial to understand basic controls of N2 fixation and primary productivity over various geological timescales and to further predict them in a changing ocean.

The role of hybridization and microbial associations for invasion success in a comb jelly
Dr. Cornelia Jaspers,  read more Marine invasive species have globally increasing biological and economic impacts. However, the role of hybridization and subsequent changes in microbiota structure, favoring range expansion and invasiveness remain poorly understood. In controlled experiments, recently formed hybrid populations along with ancestral control lines will be exposed to stress. We will investigate fitness effects of hybridization as well as microbiota changes using tagged amplicon sequencing in one of the most notorious marine invasive species, the comb jelly Mnemiopsis leidyi. Results will reveal whether or not hybridization leads to outbreeding depression or increased hybrid vigor and to what degree the microbiota differs among native, invasive and hybrid populations. This will help to understand fitness consequences due to hybridization and its possible contribution to acceleration of invasion success.