Double diffusion; Permanent stratification; Diffusive-regime; Convective instabilities; Methane; Subaquatic springs; meromixis; unstable boundary-layers
(2015), Minimal model for double diffusion and its application to Kivu, Nyos, and Powell Lake, in Journal of Geophysical Research - Oceans
, 120(9), 6202-6224.
(2014), Double diffusion in saline Powell Lake, British Columbia, in Journal of Physcial Oceanography
, 44(11), 2893-2908.
(2014), Double-diffusive interfaces in Lake Kivu reproduced by direct numerical simulations, in Geophysical Research Letters
, 41(14), 5114-5121.
(2013), Interface structure and flux laws in a natural double-diffusive layering, in JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
, 118(11), 6092-6106.
(2013), Revisiting Microstructure Sensor Responses with Implications for Double-Diffusive Fluxes, in JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY
, 30(8), 1907-1923.
(2012), Diffusive-type of double diffusion in lakes-a review, 271-284.
(2012), Simulations of a double-diusive interface in the diusive convection regime, in J of Fluid Mechanics
, 711, 411-436.
(2012), Stability of a Double-Diffusive Interface in the Diffusive Convection Regime, in JOURNAL OF PHYSICAL OCEANOGRAPHY
, 42(May 2012), 840-854.
(2012), Stratification, mixing and transport processes in Lake Kivu, 13-29.
(2012), Temperature steps in salty seas, in PHYSICS TODAY
, 65(3), 66-67.
A two year prolongation (“Verlängerung”) on the project “Lake Kivu - turbulence and double diffusion in permanent stratification” (NF-Grant 200021 - 122183) is proposed for the period of 1 March 2012 to 28 February 2014. In the first year the focus is on finishing the PhD thesis of Tobias Sommer and for the second year, we seek for post-doc salary and finances to (i) complete the data base in Lake Kivu and (ii) exploit the findings in an integrative and comparative analysis. The project aims at explaining the build-up and maintenance of the unusual density strati¬fication, and its role in the unique accumulation of methane (CH4) in Lake Kivu. The water column is density stratified due to subaquatic inputs of salty and carbondioxide-rich (CO2) water. This strati¬fication is unique insofar, as the lake water contains four relevant components: Salt and CO2 increa¬se stratification while temperature and CH4 reduce stratification. This competition leads to a so-called double-diffusive layering regime, which causes an unprecedented staircase of more than 250 well-mixed layers, separated by thin but extremely stable interfaces. To understand how such a stable structuring can establish and evolve is the primary goal of this project.As a result of the permanent stratification, the continuous supply of CO2 and decomposition of organic matter (plankton), led to the accumulation of astounding volumes of CH4 (~60 km3) and CO2 (~300 km3). The lake is therefore (i) of great economic interest (>20 billion $ in value for CH4) and (ii) a potential risk for a catastrophic out-gassing. Hence, the two riparian governments decided to use the CH4 for power production and thereby reduce the risk. It is of great interest to quantify the CH4 production and related vertical fluxes of bio-geochemical constituents (such as nut¬rients). The secondary goal of this proposal is the integration of our field observations on turbulent and double-diffusive mixing to the parallel SNF/SDC project “Lake Kivu: Learning from the past for managing its future” (Grant IZ70Z0_123923) in order to constrain the carbon/CH4cycling in Lake Kivu and contribute to a sustainable harvesting plan. So far we have acquired an unprecedented data set of more than 55 km of sub-mm scale Temperature-Salinity profiles, containing more than 10,000 layers (~250 per full profile) and interfaces, by using the micro¬structure profiler VMP-500 and by collecting several months of thermistor data in various layers at 5 seconds reso¬lution. This prolongation will build on this data and its preliminary analysis. We define five objectives for continuing the current project to be completed after two years: (1) Estimate the baroclinic energy content (internal waves) in the permanent stratification(2) Quantify rates of merging of layers and interface spitting from thermistor records (3) Linking turbulence, heat fluxes and temporal evolution within zones of the staircase(4) Complete the microstructure data set on the Congolese part of Lake Kivu(5) Complete and publish the following manuscripts in peer-reviewed journals: - Comparison between Direct Numerical Simulations and in-situ observations - Homogeneity and coherency of the double-diffusive staircase - Baroclinic energy and staircase dynamics - Comparative analysis between Lake Kivu and Lake Nyos - Synthesis: relation between overall vertical structure, lateral gradients and staircase dynamics. The project will make a significant contribution to research into double-diffusive regimes on the scales of real natural systems. In addition, the results of this project will be made available for the benefit of optimized planning of the CH4 extraction.