Malleable jobs can adapt to varying degrees of available parallelism. This is an interesting approach to more flexible usage of parallel resources. For example, malleable jobs can be scheduled optimally and efficiently where more restricted forms of parallel jobs are NP-hard to handle. However, little work has been done on how to make fundamental computations malleable. We study how this can be done for sorting. Our algorithm is an adaptive version of Multiway Merge Sort and outperforms a state-of-the art implementation in the multi core STL when the number of available cores fluctuates.