Sulfite radicals in banded coral

We compare records of stable oxygen ratio (σ¹⁸O) and SO₃⁻/CO₂⁻ ratio in an 8 yr long modern coral skeleton from a small volcanic island in the Banda Islands, eastern Indonesia. The SO₃⁻/CO₂⁻ ratio in ESR signal intensity reflects the skeletal SO₃²⁻/CO₃²⁻ ratio, which is the degree of sulfite incorporation. The resulting σ¹⁸O and SO₃⁻/CO₂⁻ records correlate well for the most recent years of growth. We speculate that water mass effect and possibly sea surface temperature (SST) control the sulfite incorporation in the coral. The rainfall in Banda Islands and the SO₃⁻/CO₂⁻ record correlate negatively. This indicates that the source of sulfites in this coral is seawater and rainfall dilutes this sulfite loading to an inverse relationship between the SO₃⁻/CO₂⁻ and rainfall. A weaker negative correlation with SST exists which may represent an additional factor affecting SO₃⁻/CO₂⁻ ratios. We also analyzed ESR of a coral from Manado, Sulawesi Island which was affected by river discharge. The SO₃⁻/CO₂⁻ ratio of the coral is about twice as large as that of the Banda Islands in average, indicating there is additional sulfite source from terrestrial waters. The SO₃⁻/CO₂⁻ record also correlates negatively with rainfall. rainfall seems to dilute both the oceanic sulfite and the sulfite being delivered by Manado River.