Sediment cores were retrieved at low tide using an open-face stainless steel tube corer. Within each 10 m x 10 m sampling plot sediment cores were taken. Core samples were obtained to a depth of 30 cm and each core was divided into depth intervals of 0-5 cm, 5-10 cm and 10-30 cm. A 2 cm subsample was cut out of the middle of each layer i.e. 0-5 cm, 5-10 cm and 10-30 cm, stored in a labeled plastic bag and dried at 40 °C for approximately 72 hours. The samples were then transported to the Analytical laboratory at Leibniz Center for Marine Tropical Research (ZMT) for further processing and analysis. Any large items, such as twigs, roots and stones were removed from the dried sample and large clumps were separated with a spatula. The samples were homogenized using a Fritsch Pulverisette 7 milling device. The milling device was set to 500 rpm at two minutes. Between each soil sample the device was cleaned to avoid cross-contamination. For each dried and homogenized sample we used a Mettler Toledo microscale model MX5 to weigh two sub-samples between 10 and 20 mg. One sample for sediment total carbon (samples were put into tin cups) and sediment organic carbon (samples were placed into silver cups). Organic carbon samples were acidified with 0.2 ml HCl to remove all inorganic carbon compounds and then again dried for 48 hours at 40 °C. To measure total and organic carbon content of the samples a Euro EA Elemental Analyzer (HEKAtechGmbH) was applied measuring OAS 5 standards between each five samples. To determine sediment inorganic carbon (SIC) the sediment organic carbon was subtracted from sediment total carbon.
