SEASchange project's Fieldwork in Indonesia

Fig. 1: Underwater sampling of a fossil microatoll.

Fig. 2: Living microatoll on Pulau Tambakulu.

Fig. 4: Beach rock.

Fig. 5: Fossil microatolls on Pulau Sanrobengi.

Fig. 6: Pulau Sanrobengi, one last mangrove surrounded by fossil microatolls.

Maren Bender (MARUM/University of Bremen), PhD student within the "Holocene Sea-Level changes in Southeast Asia (SEASchange)" project, just came back from Indonesia and she reported us her first research fieldwork.

"My first fieldwork for the SPP project 'Holocene Sea-Level changes in Southeast Asia', sponsored by DFG, brought me to Makassar, the capital of Sulawesi, Indonesia. There, we [locals and helpers, Thomas Mann from ZMT and me] aimed to find and sample fossil microatolls (Fig.1) on as many Islands of the Spermonde Archipelago as possible."

Microatolls grow upwards until they reach the waterline during low tide, thus they track this level during their lifetime. Based on this mode of life, these fossil organisms are known to be precise sea-level indicators and can be used to reconstruct the Holocene sea-level variations.

"My first destination was Jakarta to receive my research permit", says Maren. "Afterwards, I continued my travel to Makassar and at October 6th we started with the fieldwork. For the first four days, we lived on a houseboat to investigate the Islands further away from the mainland, quasi at the edge of the Archipelago. Two Indonesian students, one local and two helpers from Germany joined us on the boat. One of the German helpers lives in Bali and speaks Bahasa, which is useful to get things organized in Indonesia."

"On those first islands, we found nine fossil microatolls to sample and living analogues (Fig 2) to compare the elevations to each other. Further, we also drilled ten sediment cores (Fig.3) each one meter in length for additional sediment analyses. Related to the living and fossil microatolls, we needed to know the tidal range in the Spermonde Archipelago and how it changes. Thus, we have installed tidal loggers on different Islands, where microatolls were found. These sensors were left there until the end of the fieldwork ten days later."

Fig. 3: Sediment cores were drilled with a ram corer.

"After we have finished this working part on the outer islands, we went back to Makassar to prepare the next daily trips to closer islands. From day five to day ten, we went by boat or by car to different islands and areas along the coast to find more sea-level indicators and especially living and fossil microatolls. We ended up with 26 microatoll and beach rock samples (Fig. 4) and one slab, which was cut from a well-preserved fossil microatoll. It was a very successful fieldtrip."

"One special area that we found particularly promising was the island of Sanrobengi (Fig. 5 and 6). When the reef flat fell dry through low tide, we found a large field of emergent fossil microatolls. Normally, we would find four or five individuals around an island but here, they crowded this study side. It was amazing."

Maren acknowledges the fact that preparing and conducting fieldwork in Indonesia requires a lot of time and personal commitment, but it pays back since it was a very successful fieldtrip. In the next months, she will be busy with the evaluation of the collected data.

"As soon as the radiocarbon dates of the individual fossil microatolls are available, I will hopefully be able to tell a bit more about the Holocene sea-level history in Indonesia.", Maren concludes. 

 Maren Bender (MARUM/University of Bremen) and Thomas Mann (ZMT) work in the SEASchange project.