Good news and bad news of blue carbon

Traditionally, ocean acidification researchers have focused on how secular changes in carbon dioxide (CO2) or pH will impact organisms. Global mean pH is estimated to have decreased by 0.1 pH units (representing a 28% increase in acidity) since the preindustrial age and may drop another 0.3 pH units by the end of this century (1). Several recent papers, however, have highlighted the importance of understanding changes in the short-term variability in carbon parameters in addition to the secular trends (2⇓–4). An article in PNAS by Pacella et al. (5) examines how net community metabolism (NCM) in a coastal seagrass bed can help slow the long-term secular change in ocean acidification but exacerbates the short-term variations in carbon system parameters. These short-term variations can drive the pH or the saturation state of the waters with respect to aragonite below a threshold for certain organisms that may prevent them from ever benefitting from the long-term relief.

Of course, the driver of the secular ocean acidification trend is the accumulation of anthropogenic (human-derived) carbon in the surface ocean. This accumulation occurs everywhere (coastal and open ocean) as atmospheric CO2 increases, even in areas where seawater CO2 values are higher than atmospheric values. Whether it is low CO2 waters absorbing more CO2 from the atmosphere over time or high CO2 waters releasing less CO2 back into the atmosphere over time, the net effect of carbon accumulation and acidification of the waters is the same.

The seasonal cycle of CO2 has been appreciated for its impact on our ability to detect when …

Sabine C. L., in press. Good news and bad news of blue carbon. Proceedings of the National Academy of Sciences of the United States of America. Article (subscription required).

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