Yesterday's Science magazine had an article about seasonal CO2 cycle 10.1126/science.aac4971 I think this is a much better approach than what I tried. Their basic message (which qualifies as good news) is that photosynthetic C uptake is increasing faster than decomposition C release.
Reference below teaches when and when ocean carbon sink could be detected as changing: Timescales for detection of trends in the ocean carbon sink Galen A. McKinley et al. Nature 530: 469-472. doi:10.1038/nature16958 Changes in CO2 over oceans are poorly known, and OCO-2 satellite reveals them better. One hopes that those authors’ ‘long times to know’ can be reduced. The 100s millions $ for satellites is a big part of few billions $ spent on climate change research.