Stable carbon isotope record of planktonic foraminifera and organic matter from sediment cores in the Gulf of Aqaba

The stable carbon isotopic composition of the planktonic foraminifera Globigerinoides sacculifer and G. ruber (white) and sedimentary organic matter from the northern Gulf of Aqaba have been investigated to estimate changes in delta13CDIC in surface waters during the last 1,000 years. The high sedimentation rates at the core sites (about 54 cm/Kyear) provide high temporal resolution (~10 years). Recent sediments at the top of the cores reflect conditions younger than 1950. The delta13C records of the planktonic foraminifera from three multicores display similar trends, showing a uniform and consistent pattern before the 1750s, and a gradual decrease of approximately 0.63 per mil over the last two centuries. This decrease seems to track the decrease of delta13CDIC in surface waters, which is mainly caused by the increase of anthropogenic input of 13C-depleted CO2 into the atmosphere. Similarly, a trend towards lighter values of the carbon isotopic composition of sedimentary organic matter (delta13Corg) during the last 200 years supports the interpretation obtained from the planktonic foraminiferal delta13C. Furthermore, direct measurements of seawater show that delta13C of the dissolved inorganic carbon (DIC) in the northern Gulf of Aqaba has decreased by about 0.44 per mil during the period 1979-2000. The average annual decrease is 0.021 per mil, which is similar to that observed globally. The delta13C values of planktonic foraminifera combined with organic matter delta13C from marine sediments are good indicators for reconstructing past changes in atmospheric CO2 concentrations from the northern Gulf of Aqaba.