Department Surface Waters - Research and Management

MACRO: Tracking the Polynesian migration


The MACRO project (Molecular traces of Anthropogenic and Climatic impact in Remote Oceania) investigates the timing and extent of human impacts on previously unoccupied islands of Remote Oceania. Lake and swamp sediment cores will be retrieved from several Islands across the Pacific Ocean (Vanuatu, New Zealand, French Polynesia). Multi-proxy analyses of the sediments will then provide combined paleoenvironmental and paleoclimatic reconstructions. The investigation will center on organic molecular fossils (lipid biomarkers).
The arrival of humans and subsequent evolution of population size will be documented by variations in coprostanol (faecal biomarker) and bile acid. New biomarkers will be developed to trace the introduction of cultivated plants. Past variations in rainfall intensity – the most prominent climate variable in this region – will be reconstructed from the hydrogen and carbon isotopic composition of aquatic and terrestrial plant lipids.
We will especially focus on the development of agriculture and the related environmental consequences triggered by land use change (e.g. soil loss, arrival of invasive species, changes in water quality).

Funding

SNF Professorship Nathalie Dubois

Publications

Palmitone as a potential species-specific biomarker for the crop plant taro (Colocasia esculenta Schott) on remote Pacific islands

The Pacific Island ecosystems of Remote Oceania were dramatically transformed following the arrival of humans within the last ∼3000 years, as the new settlers required technological innovations and environmental modifications to maintain their populations. These modifications included the introduction of numerous exotic species, including the important crop Colocasia esculenta Schott (taro) and the development of infrastructure suitable for its cultivation. Archeological reconstruction of C. esculenta use in the Pacific has been challenging because of the low-specificity of fossil starch granules and its limited pollen production during periods of intense cultivation. Here, we assess a lipid biomarker approach to trace C. esculenta cultivation in the past. We characterized the neutral lipid compositions of leaf samples from common cultivars and widespread indigenous species from the archipelago of Vanuatu by gas chromatography–mass spectrometry (GC−MS). The compound palmitone (hentriacontan-16-one) was a major leaf wax constituent in C. esculenta cultivar samples (mean concentration of 402 ± 63 µg/g dry wt) and was only detected in one other species, the ornamental tree Cananga odorata (175 µg/g dry wt). The structure of palmitone is favorable for its long-term stability and we demonstrate its preservation potential in a 55 cm sedimentary record from Lake Vesalea on Espiritu Santo, Vanuatu, where C. esculenta is grown today. Palmitone concentrations in this core fluctuated up to 4.1 µg/g dry wt. Our results indicate that in appropriate environmental contexts, sedimentary palmitone concentrations could be used to reconstruct C. esculenta cultivation and to provide insights about past horticultural innovations in Remote Oceania.
Krentscher, C.; Dubois, N.; Camperio, G.; Prebble, M.; Ladd, S. N. (2019) Palmitone as a potential species-specific biomarker for the crop plant taro (Colocasia esculenta Schott) on remote Pacific islands, Organic Geochemistry, 132, 1-10, doi:10.1016/j.orggeochem.2019.03.006, Institutional Repository