NOAA/WDS Paleoclimatology - Mafia Archipelago, Tanzania 17th and 20th Century Diploastrea Coral d18O

The slowly growing coral Diploastrea heliopora affords a novel opportunity to obtain multicentury records of paleoclimate, including details of the interannual rhythms associated with the El Nino-Southern Oscillation (ENSO) system. We examine climate variability in an ENSO-teleconnected region using new oxygen isotope records from D. heliopora, spanning most of the twentieth (1896-1998) and seventeenth (1622-1722) centuries, from the Mafia archipelago, Tanzania. The modern record demonstrates coherency with relevant instrumental and proxy time series, documents twentieth century warming, and displays significant power at ENSO periodicities. The seventeenth century record lacks any trend, exhibits interannual variance comparable to the modern record, and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records. We find no clear evidence of solar irradiance influence on interannual variability in the western Indian Ocean during these intervals, although the mean sea surface temperature appears to vary inversely with insolation. This dataset includes d18O values and anomalies from a coral that grew in the tropical western Indian Ocean, in Tanzania's Mafia archipelago. Data span the 20th century at monthly resolution and the interval of 1622-1721 at bimonthly resolution. Anomalies were calculated by subtracting the mean value for the 1 or 2 month period as appropriate for dataset resolution. These data originate from a single colony of Diploastrea heliopora cored in July 2000 at Fungu Mrima Reef in the Mafia Archipelago of Tanzania. We slabbed and X-rayed the core and characterized the growth geometry using SEM. We sampled the columella portion of the skeleton at 0.25 mm (for the 20th-century) and 0.5 mm (for the 17th century) depth intervals using a diamond-encrusted drill bit. We assigned ages to the samples based on density banding and isotopic seasonality, assuming d18O maxima fell in August (the coldest month). We estimate the age uncertainty for the 20th century interval as ~±1yr and for the older interval at ~±5yr. Fungu Mrima Reef, Mafia Archipelago, Tanzania: 8°1'S, 39°30'E, water depth 6m.