Category Archives: Blog

Blog: Late Quaternary history of Easter Island

Easter Island (or Rapa Nui) has continuously drawn the attention of the scientific community since it was first sighed by Dutch Sailors in 1722. By those early days it was already described as a mysterious and isolated islet boasting hundreds of monumental stone statue –the Moais- and as the only island of the South Pacific that was completely deforested.

Moais
The iconic Moais of Rapa Nui called the attention of the European sailors that firs visited the island during the 18th century. The stone statues contrast with the highly eroded and deforested landscape. Photo courtesy of Nicolas de Camaret.

Many of these early mysteries are still debated, and there has been an ongoing interest in understanding its environmental history; not only for the potential of developing terrestrial reconstruction in a remote and isolated island in the middle of the South Pacific – possibly providing a link between the southwest and southeast Pacific, but also because of the fascinating analogies to our own isolated and resource-limited world (1).

Easter Island map
The position of Easter Island in the South Pacific and the main atmospheric component of the region. Map from Margalef et al. (2013).

Despite the long-lasting scientific attention, the environmental history of the island is poorly understood. Available proxy reconstructions have been mainly based on pollen analyses on sediment cores retrieved from the water-filled volcanic craters that border the island, and from macroscopic plant identification coming from various surface sites. However, the records have been dogged by stratigraphic gaps, dating problems and contradictory data, allowing for a range of interpretations.

An article published this year (2) presents the oldest terrestrial record published so far. Their reconstruction is based on a complete geochemical and mineralogical analysis of two sediment cores retrieved from a small peat bog located in one of the island’s crater slopes, plus a set of 27 AMS 14C dates. Changes in the chemical composition and accumulation rates of peat facies are used to infer changes in precipitation and temperature in the island over the last 70,000 years. Relative high (low) peat accumulation (oxidation) between 70,000-42,000 cal yr BP (MIS 4 and early MIS 3) is interpreted as increased rainfall and relative warm temperatures, while the opposite trend is observed between 40,000-31,000 (late MIS 3). Low temperatures and substantial rainfall are recorded between 27,000-18,000 cal yr BP (MIS 2). The authors attribute these climate variations to the interaction of different climate components, including north/south movements of the Southern Ocean and the Westerly Winds (SWW), and east/west shifts of the South Pacific Convergence Zone and the South Pacific Anticyclone (SPA).

This new reconstruction also provides interesting details of the island ecological history. Well preserved remains of the extant Totora reed (Scirpus californicus), a popular South American species of the bullrush family, suggest that this species have been present on the Island for at least 45,000 year. Its arrival is attributed to be windblown from South America (Totora is found in the self-made floating islands where Uru people dwell in Lake Titicaca, Bolivia).

Another recent reconstruction provides clues about the environmental histories of Easter Island during the Holocene, including early Polynesian arrival (3). In this case the proxy information is based on pollen, charcoal and plant macrofossils analyses from a AMS dated lake sequence that extend back for about 7500 years. This study highlights an apparently extended dried period that ended sometime before 750 cal yr BP. Based on present-day climate controls, the authors argue for centennial-scale southward shifts of the SPA (and the SWW) as the main driver for this prehistoric drought, a similar atmospheric configuration behind present-day annual droughts in the central coast of Chile.

Overall these new records illustrate the sensitivity of Eastern Island to the large-scale climate variations that characterized the late Quaternary, and provide new evidence on the poorly understood climate history of the Southern Pacific. The ecological responses of the Rapa Nui to past climate changes, however, pales in comparison with the intensive process of deforestation, wild burning and erosion that dramatically change the landscape of the island soon after Polynesian arrival by about 750 cal yr BP, but I’ll save that for another blog entry…

References

  1. Diamond, J., 2007. Easter Island Revisited. Science 317, 1692-1694.
  2. Margalef, O., Cañellas-Boltà, N., Pla-Rabes, S., Giralt, S., Pueyo, J.J., Joosten, H., Rull, V., Buchaca, T., Hernández, A., Valero-Garcés, B.L., Moreno, A., Sáez, A., 2013. A 70,000 year multiproxy record of climatic and environmental change from Rano Aroi peatland (Easter Island). Global and Planetary Change 108, 72-84.
  3. Mann, D., Edwards, J., Chase, J., Beck, W., Reanier, R., Mass, M., Finney, B., Loret, J., 2008. Drought, vegetation change, and human history on Rapa Nui (Isla de Pascua, Easter Island). Quaternary Research 69, 16-28.

AQUA Blog

Hola, Kia ora everyone,

My name is Ignacio Jara and I am PhD student from Chile, currently studying at the School of Earth Sciences at Victoria University, Wellington, New Zealand. After one and a half years of living and studying in Wellington, New Zealand, I have been asked to write a monthly blog commenting on different topics about Quaternary research for AQUA.Ignacio
Ignacio in the microscope laboratory

This is going to be my first experience writing a blog and honestly I am quite excited about it. Undoubtedly this blog represents a huge challenge for me, especially because English is my second language. However, this blog is a good opportunity to write in a less formal type of English and also an opportunity to catch up with the current literature and ideas in Quaternary sciences.

My doctoral research is focused on reconstructing the vegetation and fire histories of New Zealand and Patagonia, South America. To do this, I am developing pollen records from lakes and peaks bogs on both sides of the Pacific Ocean. These two regions share important environmental and physiographical features such as latitudinal position, volcanically active cordilleras, glacial and tectonic activity and related floras; but there are also striking differences concerning their climate regimes and human histories. My study will take the form of an inter-regional comparison that (hopefully) will provide insights into the interactions between vegetation, climate change, and human activities across the southern Pacific. This work will contribute to the new, recently launched, Southern Hemisphere Assessment of Paleo-environments (SHAPE) initiative which aims to improve our understanding of the past climate change in the Southern Hemisphere. SHAPE continues the work of Aus-INTIMATE and aims to develop new proxy records and integrate with model simulations, in order to generate regional climate event stratigraphies that extend back to 60,000 cal years before present.

So far during my PhD I have looked at a pollen record from a lake in the northwest corner of the South Island of New Zealand, and at present I am spending many hours looking down a microscope counting pollen and charcoal from a peat bog in the Waikato Basin in central North Island, New Zealand.

Tarn
Adelaide Tarn in northwest South Island, New Zealand

I am also helping to coordinate a recently launched Paleo-climate seminar group with other PhD students at Victoria University. These seminars are article-based discussions and I am pretty sure they will provide a great source of information for this blog. I have become aware of a general lack of connectivity or communication between Quaternary science postgraduate students from the different universities of New Zealand and I am afraid there is a similar problem in Australia. I hope to use this blog to suggest different initiatives and promote student and general scientific networking.

But of course I am not here to talk exclusively about myself. Instead, the aim of this blog is to provide a brief monthly report about new articles, comments, recent or upcoming scientific events that may be of interest to AQUA members. The emphasis will be on research from the Southern Hemisphere. But I may also comment on research from other areas if it is relevant to our region. I am very keen to receive any ideas, recent papers or references and general feedback.  (e-mail)

Thanks and keep in touch. Hasta la vista!

Ignacio Jara Parra.