Glacial Modelling and Climate Change in New Zealand

On this page:

What is Glacial Modelling? Current Research Projects Who is working on this?

What is Glacial Modelling?

A model is a simplification of a complex set of natural processes (which in our case result in the glaciation of a landscape) into a system where the processes have been separated and quantified. It is created by gathering information from observation which is then used to define relationships between different variables, e.g. how does temperature vary with elevation? How do ice flow rates vary with ice thickness and surface slope?

Once the model has been created it can be tested by simulating a known situation and comparing the simulation with reality, making sure that the comparison is against data that have not been used to create the model in the first place! The more thoroughly a model is constrained by actual measurements taken from nature, the more confidence we have in the output.

Once set up, the input data and model parameters can be changed to test different outcomes. This allows the investigation of significant cause and effect relationships and can provide insight into the most important processes driving a system. A good model is therefore a very powerful tool for purposes of understanding, experimentation and prediction. For example, a glacier model could be used to identify the most important climate variables that affect ice volume and extent. Or it could be used to identify the climate conditions needed for the glacier to reach moraines that were deposited in the last ice age. The impact of present and future climate change on glaciers can also be investigated. Glacier models can be driven by climate proxy information (such as ice core, speleothem or palaeoecological reconstructions), and/or can be coupled to broader models of atmospheric and/or oceanic circulation.

Models are becoming increasingly significant for planning for the future in many areas of social and economic life such as agriculture, medicine, insurance, energy generation and transport. In the Antarctic Research Centre, our glacier modelling programme is helping with investigations into the way Southern Hemisphere glaciers respond to past, present and future climatic changes . This work, the only of its kind in New Zealand fills a knowledge gap in the understanding of Southern Hemisphere mid latitude climate processes.

Current Research Projects

A main focus of our research at present (2007 – 2008) is to reconstruct glacier coverage and climate in New Zealand and Tasmania during the last 30,000 years by numerical modelling. This project is supported by the New Zealand Marsden Fund and the Comer Science and Education Foundation.

Although this project is largely based on modelling, detailed field research on glaciers in the Southern Alps of New Zealand, along with other glaciological and geological research such as moraine mapping and annual aerial surveys of snow lines and glacier extent is being used to constrain our modelling reconstructions.

Background

Temperate alpine glaciers are sensitive indicators of changing temperature and precipitation. They have moulded the Southern Alps in New Zealand and the highlands of Tasmania, both of which are situated in the path of the “Roaring Forties” westerly winds and near the boundary between subtropical and sub-Antarctic ocean waters. During the last 10 years significant progress has been made on the age dating and mapping of glacial deposits and landforms in both areas, offering superb geological records of glacier fluctuations spanning the last 30,000 years. (http://maps.gns.cri.nz/website/csigg/ )

The Last Glacial Cycle is a period when ice sheets waxed and waned in the Northern Hemisphere and extensive ice caps and mountain glaciers developed in New Zealand, Tasmania and Patagonia. Abrupt, millennial scale climatic shifts that punctuate this period are well documented in paleoclimate records from Northern Hemisphere ice cores and marine sediments. In contrast, there is a dearth of quality terrestrial records from the ocean-dominated southern mid-latitudes and the response of this region to abrupt climate change is poorly understood. The geological signature of climatic changes is best preserved on land and New Zealand and Tasmanian moraine sequences provide detailed records of fluctuating climate during the last 30,000 years. Glaciers covered more than 1000 km2 in Tasmania, during the Last Glacial Maximum (LGM), approximately 20,000 years ago, and the moraine sequence preserves several late Quaternary events that correlate with New Zealand sequences. Despite the quality of these records, interpretation of their climatic significance remains problematic. It is not clear for example, whether past temperature or precipitation were more important as drivers of glacier extent.Our inability to identify the dominant driver of Southern Hemisphere glacier fluctuations means that we are severely limited in the ability to use moraine records as climate proxy indicators

Glacier modelling by ARC researchers is hoping to make a significant breakthrough in this area. It will provide quantitative estimates of past temperature and precipitation in Tasmania and New Zealand, and similar results from Patagonia will allow changes in climate to be identified on a hemispheric scale. For example, changes in the position and strength of the Southern Westerlies will be traceable across all three southern landmasses using data from our model runs.

Initial modelling work has indicated that the glaciers of the Southern Alps appear to be the most sensitive on Earth to climatic changes, a consequence of high precipitation rates. In the context of future global climatic changes, it is important to understand how New Zealand’s glaciers might change, as special parts of our landscape, and as valuable resources for tourism, hydro-electric power generation and irrigation.

Research Objectives

The overall aim of our research is to translate well-dated moraine records of former glacier extent into quantitative information about past temperature and precipitation, using a modelling methodology. We have three specific objectives:

1. To develop an Energy Balance Model for the Southern Alps of New Zealand, validated by empirical mass balance data.



This will achieve an important preliminary step in developing a process-based Energy Balance Model for the Southern Alps of New Zealand. The combination of relief and high precipitation results in over 3000 glaciers occupying an area of 1159 km2 and volume of 53 km3. Present-day understanding of the interaction between glaciers and climate mostly comes from an annual over flight survey of end of summer snowlines, carried out since 1977. Our Energy Balance Model, which will be validated against glacier mass balance data gained the field, will have wide applications. For example, it can be used to understand the hydrology of major hydropower catchments in New Zealand and how glacier extent and the water balance may change in response to climate warming during the 21st Century.

By using an Energy Balance Model (EBM) to simulate glacier mass balance, strong local climatic and topographic gradients in the Southern Alps can be considered explicitly. The first stage of our model development is the application of a distributed EBM to the Brewster Glacier where suitable data are available to construct and tune the model. The EBM will be forced with data from two weather stations on and adjacent to the glacier, and tuned against ablation stake data, snow accumulation data and continuous measurements of mass balance. Stream discharge data from the Brewster Glacier outlet stream is used as an independent test of model performance. This work is largely complete. Please contact Brian.Anderson (link to website) if you would like a preprint.

The second stage is to then construct an EBM for the Southern Alps based on a high-resolution Digital Elevation Model (DEM) .This model is being be tuned with mass balance data from two glaciers which represent a diversity of topographic and climatic environments in the Southern Alps, from the extremely maritime Franz Josef Glacier on the West Coast where annual precipitation exceeds 10 m/yr, to the Tasman Glacier, New Zealand’s largest located to the east of the main divide where the climate is sunnier and drier. The latitudinal and altitudinal distribution of End of Summer Snowlines for the entire Southern Alps will provide an independent test.

When the EBM model is applied to Tasmania, it cannot be tested in a similar manner, as the island presently lacks glaciers. However the optimised parameters from New Zealand make it suitable for Tasmania because of its similar mid latitude climatic setting in the zone of the Southern Westerlies.


2. To simulate ice extent with glacier flow models in the South Island of New Zealand and the mountains of Tasmania for the last 30,000 years.



This involves the coupling of the Energy Balance Model (Objective 1) to the GLIMMER ice sheet model and its application to New Zealand and Tasmania. The GLIMMER model allows for the assimilation of a diverse range of palaeoclimate and geological data and has reached a high level of sophistication and standardisation. It will be used to simulate ice extent for each glacial advance during the last 30,000 years in New Zealand and Tasmania and modelled ice extent will be constrained by geological evidence in key locations where well-dated landscape records exist. These simulations of past ice extent will provide insight into the age and significance of geological evidence that has been debated for over a century.

Simulation of Southern Alps and Tasmanian glaciers will be based on the application of the GLIMMER model. (GLIMMER is a state of the art ice sheet model being developed and contributed to by an increasing number of universities and other science research organisations. It is used to simulate ice sheet evolution.)

The first step is to simulate the present-day geographic distribution of glaciers in New Zealand. Measurements of ice velocity on our three mass-balance glaciers (Brewster, Franz Josef and Tasman) are being used to tune the model. Reconstructions of past glacier extent in New Zealand and Tasmania can then be achieved by perturbing modern day temperature and precipitation fields in a stepwise manner until a good match is achieved between simulated ice limits and geological evidence from key locations where high quality information exists. In New Zealand, we use Lake Pukaki and West Coast moraine sequences to constrain the reconstruction and In Tasmania, we will use field evidence from the West Coast Range, Lake St. Clair and Mt. Field, where a large number of cosmogenic exposure ages are available to constrain the timing of ice advance.

The final stage of this work is involving a comparison of modelled glacier extent to wider geological and geomorphological evidence. This will identify the major seeding areas for ice growth, zones of glacial erosion, transport and deposition, regions of fast ice flow and the location of ice free areas (including possible vegetation refugia). The modelling may also enable correlation of geological sequences in valleys where chronology is lacking, and identify areas where new moraine records may be found. In the case where ice extent is controversial, for example, the extent of glaciers in New Zealand during the Late Glacial period ~13,000 years ago, our work may resolve this issue. In Tasmania, we will provide insight into the extent of the ice cap that covered the Central Plateau, and in many inaccessible mountain regions where glacial extent is poorly known Many other outputs are possible in the future including local sea level reconstructions by calculating the residual of the modelled isostatic history and global eustatic sea level history at any specific locale, and sediment transfer modelling and visualization which will allow for corroboration with marine records.



3. To provide the first quantified estimate of past temperature and precipitation levels in New Zealand and Tasmania based on glacial evidence.



Our results will be compared to climate proxy evidence from other research projects (ice cores, marine sediments, snowline reconstructions, pollen records, speleothems). Our fundamental aim of identifying the major driver of glacier fluctuations (temperature or precipitation) will help to understand the overall global climate dynamics responsible for changes in the southern mid latitudes.

Objective 3 will produce a palaeoclimate record for the Southern Alps and Tasmania at various times during the last 30,000 years. Specifically, when combined with new moraine ages our reconstruction will result in a dated, quantified, record of temperature and/or precipitation changes.

Our model will be tested against an independent data set of climate reconstructions arising from the work of Dr. Trevor Chinn of NIWA and others (The Central South Island Glacial Geomorphology or CSIGG Project insert website). This is a database of Late Quaternary snowlines estimated from geomorphic landforms and reconstructions of past glacier geometry.

Our quantified climate reconstructions will be compared to all available climate proxy evidence from the Australasian INTIMATE (INTegration of Ice-core, Marine And TErrestrial records) project including palaeo-biological indicators (pollen, chironomids, beetles), speleothems and marine sediments. By coupling our climatic reconstructions from the Southern Alps and Tasmania to those of South America we aim to identify the fundamental drivers of glacier fluctuations (temperature or precipitation change) in the Southern Hemisphere and thus test different hypotheses concerning these. The temperature and precipitation reconstructions will greatly improve our understanding of the configuration of the climate system during the last 30,000 years, especially, the location, movement and strength of the westerlies in the Southern Hemisphere during the late Quaternary.

Who is Working on this?

Andrew Mackintosh
Brian Anderson
Heather Purdie
Tom Paulin

International Research Collaborations

University of Maine
George Denton (moraine chronology & paleoclimate)
Aaron Putnam (moraine chronology)
Alice Doughty (moraine chronology)

University of Chicago
Raymond Pierrehumbert (climate dynamics & modelling)

Lamont Doherty Earth Observatory of Columbia University
Joerg Schaefer (moraine chronology)
Mike Kaplan (geochronology)

Harvard University
Peter Huybers (glacial cycles & orbital forcing)

University of Wales, Aberystwyth
Alun Hubbard (high resolution ice sheet modelling)

New Zealand Research Collaborations

GNS Science
Central South Island Glacial Geology Project

University of Otago
Sean Fitzsimons, Dorothea Stumm, Laurel George (Brewster Glacier mass balance)

University of Canterbury
Wendy Lawson, Ian Owens (Franz Josef Glacier mass balance)
Tim Kerr (Southern Alps precipitation)

NIWA
Trevor Chin
(glaciology & paleosnowlines)

Also see the New Zealand Snow and Ice Research Group