In Pursuit of Palaeodust on Chatham Island

Atmospheric dust from Australia and New Zealand is a significant source of nutrients for the vast and remote region where the South Pacific and Southern Ocean meet. Here
primary producers such as phytoplankton rely on dust to deliver iron, cobalt, and other nutrients.

Dust flux over the past few thousand years is unknown, but a record of dust inputs can be found in geoarchives. Island peat bogs can be particularly useful as palaeodust archives. Peat bogs create a record of mineral inputs because water-saturated conditions slow plant decomposition, causing peat to accumulate. As a peat bog develops over years and centuries, it preserves a geochemical signal of mineral inputs, including atmospheric dust.

In March, I traveled with a team from the University of Wollongong to Chatham Island, 800 km east of New Zealand, in search of rain-fed peat bogs. A 1976 pollen study reported well-developed peatlands on the island’s south side. However, access to this area is challenging due to the lack of roads, the presence of dangerous wild cattle, and the need to first secure permission from private landowners.

Luckily for us, this area is owned by a truly kind and accommodating family. We came to know each other through phone conversations about every six months through the COVID-19 pandemic. Even though the trip was delayed for three years due to border lockdowns, they remained interested and supportive. Finally, the day came when we were on the island and met each other in person. Many lovely cups of tea later, we were aboard the quad bikes and ready to head out!

In the case of this fieldwork, persistence paid off. Our field sites were spectacularly gorgeous and productive. We collected a 9.5 m peat core from the southern tablelands and another 9.5 m core from a coastal site. These are unusually deep peat cores, and the coastal core has a 10 cm section of tephra that is likely from an eruption that happened over 26,000 years ago. The prospect of finding dust signals over that many centuries is genuinely exciting.

With geochemical analysis, we hope to identify long-travelled dust signals in the cores and trace the origins of the dust, likely to be New Zealand and Australia. This will help us understand the contribution of Australia and New Zealand to nutrient cycling on the island and in the neighbouring ocean basins. Additionally, reconstructing the dust transport pathways will shed light on air transport patterns and give insights into the behaviour and position of the Southern Hemisphere mid-latitude westerly winds over this period of time.

We’d like to thank the Seymour family of Chatham Island and the peat corers (Sam Marx, Pascal Saker, Chris, and Richard Seymour). We also gratefully acknowledge financial assistance provided by AINSE, The Antarctic Science Foundation, and a UOW Research Training scholarship.

About the author

Andrea Johansen is a PhD Candidate at the University of Wollongong