def inferred_wfo(s_orig, s_new, volume):
    """Calculate the inferred cumulative global total wfo for a given change in soga.
    
    wfo = net water flux into sea water
    soga = global mean sea water salinity
    v = volume of ocean (m3)
    
    """
    
    p = 1027  # kg/m3; average density of global ocean - could calculate from rhopoto data
    m_globe = volume * p
    
    delta_m = -1 * m_globe * (1 - (s_orig / s_new))    
    
    return delta_m