A multi-proxy geology approach to resolving critical uncertainties in Irish cosmogenic nuclide geochronology

With Gordon Bromley (U. Galway) and Frank McDermott (UCD)

Geological Survey Ireland Short Call

Paleomonitoring - Geochemical analysis of twentieth century stalagmites to improve understanding of stalagmite proxy response

Maynooth University Department of Geography Research Incentivisation Award

Irish Research Council and Marie Skłodowska-Curie CAROLINE Fellowship

Constraining past moisture variability in sub-Saharan Africa to improve future projections and enhance resiliency under a changing climate

Irish Research Council and Marie Skłodowska-Curie CAROLINE Fellowship

Overarching Research Goals

Impact of climate change on humans

This project led by Gordon Bromley at the University of Galway aims to calibrate surface exposure dates in Ireland using high-resolution U/Th geochemistry of growth phases of stalagmites.

Proxy calibration of geochemical signatures in stalagmites is difficult because cave-monitoring time series remain short, and inter-cave variability limits spatial calibration. One way to assess proxy dependency is to compare high-resolution geochemical records with observations from nearby weather stations, reanalysis data sets, and satellite measurements. However, a lack of build-up of thorium in young stalagmite calcite prevents the precise age models needed to assess the relationships properly. One area of my current research involves combining radiocarbon bomb-pulse detection with seasonal strontium cycles in stalagmites to create high-resolution twentieth century stalagmite records.

I have already published one such record on a stalagmite in Australia, have one record from Madagascar in preparation, and am analysing a stalagmite from Ireland in the coming months.

Changes in rainfall amount, timing and the intensity of extreme droughts and floods are the least reliable quantity in projections of future climates but have an outsized impact on society through natural hazards and water resources for drinking and agriculture. My Irish Research Council and Marie Skłodowska-Curie CAROLINE Fellowship investigated the impact of climate change on sub-Saharan African rainfall, principally in Malawi and Madagascar.

I used satellite estimates of rainfall, observational data from weather stations and climate model reanalysis datasets, to learn where, when and how rainfall is changing in the region. In addition to the usual estimates of yearly or seasonal rainfall, I worked with Self Help Africa to investigate climate parameters and indices that are more agriculturally relevant. For example, changes in rainfall in the crucial first few weeks following planting. Changes in these more derived metrics have more influence over the lives and livelihoods of smallholder farmers in sub-Saharan Africa, and the NGOs that help support them. Understanding how these parts of the climate system have changed recently, and are likely to change in the future, will enhance the strategies of Self Help Africa in introducing climate smart agriculture to the region. This will ultimately increase the resiliency of thousands to climate change.

The primary focus of my research is on understanding the past behavior of tropical monsoons, working on a variety of timescales from seasonal variability to tens of thousands of years. I investigate not only how the rainfall amount has changed in one place, but the regional spatial relationships to determine which parts of the climate system interact to produce these changes.

To do this I specialize in terrestrial paleoclimate and paleoenvironment reconstructions using carbonate geochemistry. I use speleothems (calcium carbonate cave deposits such as stalagmites and flowstones) as a tool to investigate past rainfall and rainfall dynamics. Using a multi-proxy approach to combine traditional stable isotopes with trace elements from the same stalagmite allows me to assess variability of different components of the hydrological system; to uncover past changes in rainfall and the climate dynamics that caused them.

Paleoclimate records can be used to validate climate models but are typically multivariate, noisy and chronologically uncertain. Therefore, to improve rainfall projections requires not only greater spatial and temporal coverage of past climate changes using paleoclimate records, but also the quantification of paleoclimate proxies. My future research pathway uses a multi-faceted approach to tackle these issues, with the goal of developing stalagmites as quantified paleo-rain gauges. To achieve this, I combine i) multiple proxies, stable isotopes and trace elements, to isolate different components in the hydrologic system, ii) multiple locations to understand regional versus local processes, and iii) multiple timescales, comparing observed modern variability and proxy-derived past variability.

Additionally I am interested in the impacts of changing rainfall variability on environments, flora, fauna and human society. This includes human evolution, megafaunal extinctions and the growth and collapse of human societies. By understanding when, how and why rainfall variability changed in the past and the impacts of those changes, I hope to better understand how rainfall is likely to change and impact society in the future.

The context that surrounds paleoclimate records reveal the impacts and consequences of a changing climate. Paleoclimatology is often at its best not to its own ends, but when it is answering questions posed by other disciplines such as archaeologists and anthropologists, opening the way for interdisciplinary research. My collaborations with colleagues in archaeological and anthropological disciplines have uncovered climatic driving forces behind major events in human civilization, mammalian evolution, adaptation and extinction.

This has included:

1. the collapse of the Mature Harappan civilization in the Indus River Valley around the 4.2 kyr climatic event.

2. collapse and extinction of the megafauna on Madagascar

3. the frequency, timing and severity of droughts in the Murray-Darling basin, Australia’s breadbasket

4. the paleoclimatic and paleoenvironmental context surrounding the existence and extinction of the hominin Homo floresiensis on the island of Flores Indonesia