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.
Figure 1: Underwater sampling of a fossil microatoll
Figure 2: Living microatoll on Pulau TambakuluFigure
Figure 3: Sediment cores were drilled with a ram corer
Figure 4: Beachrock
Figure 5: Fossil microatolls on Pulau Sanrobengi
Figure 6: Pulau Sanrobengi, one last mangrove sourrounded by fossil microatolls
My first destination was Jakarta to receive my research permit. 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.
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 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 found four or five individuals around an island but here, they crowded this study side. It was amazing.
In summary, it can be concluded that preparing and conducting fieldwork in Indonesia requires a lot of time and personal commitment. However, this fieldtrip has also been very successful. In the next months I 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.