|Title||Coral reefs will transition to net dissolving before end of century|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Eyre B.D, Cyronak T., Drupp P., De Carlo E.H, Sachs J.P, Andersson AJ|
|Type of Article||Article|
|Keywords||calcification; calcium-carbonate; chemistry; climate-change; dissolution; future; ocean acidification; Science & Technology - Other Topics; seawater; sediments; state|
Ocean acidification refers to the lowering of the ocean's pH due to the uptake of anthropogenic CO2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calciumcarbonate (CaCO3) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (War) of overlying seawater and that CaCO3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater War reaches 2.92 +/- 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution.
Under present-day average tropical ocean Ωar (3.3), coral reef sediments are net precipitating and coral calcification and NEC are positive . However, the model shows there has already been on average a reduction in coral reef sediment precipitation from 18.1 to 4.3 mmol m−2 day−1, a reduction in NEC from 210.7 to 78.5 mmol m−2 day−1, and a reduction in coral calcification of 111.4 to 92.8 mmol m−2 day−1 since pre-industrial time when the average tropical ocean Ωar was ~4.5. When the average tropical ocean Ωar reaches ~2.92 in ~2048, coral reef sediments will become net dissolving. By 2082, global average coral reef NEC will become negative (i.e., net dissolving). By 2078 (Ωar = 2.62), sediment dissolution will exceed the global average coral reef NEC. For coral reefs with 5% coral cover and 95% sediment cover, probably a common future scenario with increasing coral cover loss, this transition to net dissolution will also occur in 2085 (Ωar = 2.55).