def bottom_remineralization(vs, source, sink, scale):
    """Exported material falling through the ocean floor is converted to nutrients

    Note
    ----
    There can be no source, because that is handled by the sinking code

    Parameters
    ----------
    scale
        Factor to convert remineralized material to nutrient. Typically Redfield ratio.
    """
    return {sink: vs.npzd_export[source] * vs.bottom_mask * scale}