Position:

AINSE Research Fellow

Room:

41.G26

Phone No:

+61 2 4221 4265

Email:

mcgregor@uow.edu.au

OR

mcgregor@uni-bremen.de

1. How and why does El Niño-Southern Oscillation (ENSO) vary? Coral climate records of past ENSO changes.

2. Ocean circulation during individual El Niño events: reconstructing changes using coral radiocarbon.

3. The sea level and reef history of Kiritimati Island – the world’s largest coral atoll.

4. Interested in other aspects of past and present tropical climate change or coral paleoclimatology? Send me an email and we’ll see what we can work out.

Understanding the El Niño-Southern Oscillation (ENSO) is crucial for prediction of Australian drought and rainfall variability.

ENSO is a coupled climate system between the atmosphere and the ocean, and it oscillates irregularly on a time scale of two to seven years.

In an El Niño event, anomalously warm surface ocean temperatures are observed in the central and eastern equatorial Pacific (red area, graph above).

Rainfall follows the warmest water, so during the El Niño event above average rainfall is recorded over the central Pacific but Australia’s rainfall is generally reduced, which can result in drought (yellow area, graph above).

El Niño events have become stronger and more frequent since the mid-1970s. However, there is debate about whether strengthened El Niño is a result of global warming or whether the 1970s intensification resulted from a decadal or longer-term cycle of ENSO variability.

The relatively short instrumental record does not give a complete picture of ENSO behaviour, and models are unable to simulate ENSO fully, limiting our ability to predict future ENSO scenarios.

My research uses fossil corals from islands in the tropical equatorial Pacific to reconstruct ENSO and expand our knowledge of ENSO variability.

Left: Sampling a 4,400 year old fossil coral from Kiritimati (Christmas) Island, central equatorial Pacific.

We have shown that in modern corals from Kiritimati Island the coral oxygen isotope ratio (δ¹⁸O; red trace) is a measure of ENSO-related changes in surface ocean temperature (SST; purple trace, graph above).

We are now measuring δ¹⁸O in fossil corals and have identified times of very strong El Nino’s – stronger than those of the past century.

Climatically-driven coastal upwelling zones, although representing <1% of the global ocean by area, provide ~20% of the world’s fisheries.

Coastal upwelling occurs along the eastern margins of major ocean basins, for example along the Moroccan coast, and develops when predominantly alongshore winds force offshore Ekman transport of surface waters, leading to ascending (upwelling) of cooler, nutrient-rich water.

Left: September 2004 sea surface temperature (SST) image of NW Africa, with the location of our study site marked (star symbol). The SST data show a narrow strip of cold coastal waters (purple and dark blue), 3-5°C colder than open ocean SSTs, indicating the upwelling centre.

In our 2007 Science we describes our discovery of an unambiguous and rapid increase in upwelling intensity off the coast of Morocco during the 20th Century, unprecedented over the past 2500 years (cooler SSTs; red trace). The results showed an unexpected connection between upwelling and northern hemisphere temperatures (blue, green and yellow traces); warmer northern hemisphere temperatures give rise to increased upwelling. Together, these results suggest that coastal upwelling off northwest Africa will continue to intensify as global warming and atmospheric CO₂ levels increase.

Examining other parameters in the Moroccan marine sediment cores I, and colleagues in Bremen, Germany, notice a whole raft of changes occurring in the core at around 700 AD. These changes included:

Above: Goats in an eroded landscape, and in the background a goat climbing an argan tree in search of fruit and fodder (photo courtesy of Robbie Morrison, Ottawa, Canada. See more of Robbie’s photos at http://www.flickr.com/photos/photo_art/ ).

A three-fold increase in sedimentation rate (brown, left).

A rapid increase in Fe intensity (terrestrial material) and decrease in Ca intensity (marine carbonate; orange – the Fe/Ca ratio, left).

A rapid increase in terrestrial material delivered to the core Site via rivers (blue trace, left). The sedimentation rate, Fe/Ca and fluvial input all suggest an increase in erosion.

An increase in the level of Cichorioideae pollen from 10% to 20% (pink, left). Cichorioideae pollen probably comes from the shrub species Launaea arborescens, which grow in local southern Moroccan forests and indicates degraded vegetation.

A decrease in Quercus robur/pubescens-type (deciduous oak tree; green, left) pollen. Young trees of this species do not recover after browsing by goats.

Changes in the ocean temperature record from the same core (red, left) cannot explain the results. Other Moroccan records of climate do not explain the results.

The timing of the changes coincided with the arrival of Islamic invaders in southern Morocco and an increase in population, agriculture, and pastoralism, and particulary goat herding (white boxes at the top of the graph). Goats in southern Morocco have voracious apatite’s and even climb trees in search of food. The increased development in southern Morocco most likely led to the increase in erosion and degradation of the ecosystem.

I am committed to improving understanding of climate change science. Check out the links to for accurate climate information from climate scientists:

Above: from the IPCC 2007 Report, “Solid lines are multi-model global averages of surface warming (relative to 1980-99) for the scenarios A2, A1B and B1, shown as ontinuations of the 20th century simulations. Shading denotes the plus/minus one standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The gray bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the gray bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints.”

Links

The United Nations Intergovernmental Panel on Climate Change (IPCC) 4^th Assessment Report, which is the latest consensus view on the state of the world’s climate and includes projections for the future. Of particular interest is:

The Summary for Policymakers

http://www.ipcc.ch/ipccreports/ar4-syr.htm

The Physical Science Basis (the FAQ chapter is really good)

http://www.ipcc.ch/ipccreports/ar4-wg1.htm

The other IPCC 2007 AR4 chapters can be downloaded from:

http://www.ipcc.ch/#

The Realclimate website is a great source of information on the basics of climate science, providing robust commentary on the latest climate issues and debunking the myths of the global warming sceptics’:

http://realclimate.org/

Above: the from IPCC 2007 Report, “Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. The red line is a reconstruction of global mean sea level from tide gauges and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations. Over many centuries or millennia, sea level could rise by several metres.”