Palaeoclimate reconstructions from Tierra Del Fuego to detect Land-Ocean-Atmosphere Interactions

Lead Research Organisation: University of Aberdeen
Department Name: School of Geosciences

Abstract

The nature of future human induced climate change is highly uncertain with projected global temperature increases in 2100 spanning 0.3-6.4 Celsius (IPCC 2007, AR4). Part of this large uncertainty is due to the paucity of climate & proxy-climate data to validate climate models & constrain Earth System sensitivity to simulated forcing, particularly in the Southern Hemisphere (SH). A key component of variability of the SH atmosphere is the Southern Annular Mode (SAM), which is an oscillation of atmospheric mass that results in changes in the westerly winds over the Southern Ocean. The SH westerly winds modify the upwelling of carbon-rich deep water & therefore influence the global balance of carbon dioxide between the ocean and the atmosphere. It is uncertain whether the recently observed intensification of the southern westerlies will cause the Southern Ocean to be a net source or sink of atmospheric carbon dioxide. Little is known about the long-term past variability of the southern westerlies & atmospheric carbon dioxide, making it difficult to separate internally & externally-forced fluctuations. It is imperative to rectify this deficiency in order to generate & test hypotheses to explain the processes of change in the strength of the southern westerlies & how these are related to (inter-)hemispheric climate change during known periods of contrasting climate change, for example the Medieval Climatic Anomaly & the Little Ice Age.
This project will investigate four new sites located in southern South America (SSA). This region is located in the core of the southern westerlies and is ideally located to capture changes in their intensity. SSA terrestrial peatland-based palaeoclimate archives are capable of recording long-term changes in the westerlies, given that wind intensity affects precipitation mainly produced in winter by fronts & low-pressure systems embedded in the prevailing westerly circulation. The selected sites are all rain-fed peat bogs, which provide excellent climate archives. Plant & protozoan (testate amoebae) fossils preserved in well-dated cores extracted from these bogs will be used to reconstruct past changes in Bog Surface Wetness (BSW, an index of surface water balance) over the last ~2000 years, at a time resolution of 10-100 years. The same core samples will be analysed for stable isotopes of oxygen & hydrogen. The spatial & temporal distribution of the heavy isotopes of these elements in precipitation is related to air temperature, & hence to atmospheric circulation. The isotope signal captured in the cellulose fraction of Sphagnum moss closely tracks that of the precipitation used by the plant for cellulose synthesis. Hence, fossil Sphagnum from raised peat preserves a clear signal of past changes in climate & atmospheric circulation. The stable isotope data will be compared with isotope measurements from moss banks & ice cores from the maritime Antarctic and Antarctic Peninsula, in addition to stable water isotope data & BSW reconstructions from eastern North America. Analyses of fossils & stable isotopes from the same core levels will allow us to reconstruct the timing, magnitude & spatial pattern of the regional terrestrial response, as well as exploring the impact of different causal factors such as changes in atmospheric & ocean circulation & solar variability on the climate of the study area. In this way, insight will be gained into the mechanisms that have driven climate change over the last ~2000 years.
Hypotheses to be tested:
1 Climate changes during the last ~2000 years in SSA are in phase with climate changes identified in eastern North America & NW Europe, & represent inter-hemispheric teleconnections.
2 Climate changes in SSA during the last ~2000 years are in antiphase with Northern Hemisphere climate changes & represent a bipolar seesaw.
3 Climate changes in SSA during the last ~2000 years are uncorrelated with Northern Hemisphere climate changes.

Planned Impact

Who will benefit from this research?
1. Palaeoclimate scientists and Earth System modellers interested in the nature and causes of long-term climate change. 2. Peatland scientists and conservation agencies interested in the long-term record of peat forming plants, in terms of stability and response to former periods of climate change. 3. Peatland scientists and Earth System modellers interested in the interplay between long-term climate change and carbon sequestration in peatlands, given that these ecosystems represent a significant component of the global terrestrial carbon cycle. 4. The media and the wider public, students and school-level audiences. 5. Training and development of project PDRA staff with specialist, media, presentation and oral communication skills.

How will they benefit from this research?
1. Better understanding of the rate and nature of climate change in southern South America and how this is related to changes in the Northern Hemisphere. 2. The creation of quantitative reconstructions of climate change and stable water isotope reconstructions in a data poor region will have an impact upon Earth System modellers. Rigorous AOGCM development is dependent upon the availability of high quality palaeodata to ensure meaningfull data/model comparisons.

What will be done to ensure that they benefit from this research?
1. A regularly updated website describing the project, with both technical and general sections and a choice of three languages (English, Spanish and Welsh), in order to target the wider global community and local communities in Chile and Argentina. 2. Press releases to regional, national and international conservation organisations. 3. Attendance at local and national events to promote the public's engagement with science, particularly school level audiences. We will incorporate 'hands-on' displays of real life sub-fossil samples and a moveable display of posters. 4. Routine dissemination activities through peer-reviewed journals, congress, academic newsletters and submission to specialist databases.

Publications

10 25 50
 
Description The aim of this project was to produce long-term reconstructions of changes in the position and strength of the Southern Hemisphere Westerly winds by applying established and experimental techniques developed by the Principal and Co-Applicants to peat deposits in southern Chile and Argentina. These winds fundamentally influence the world's oceans and climate, as they drive currents which move ~140 million cubic meters of water per second around Antarctica, which is about five times the transport of the Gulf Stream. They vent carbon dioxide from the ocean to the atmosphere and redistribute energy around the globe.

Wind intensity in this region affects precipitation mainly produced by fronts and low-pressure systems embedded in the westerly atmospheric circulation. Water-tables on rain-fed peat bogs in southern Chile and Argentina are maintained exclusively by this precipitation making these ecosystems highly sensitive to changes in wind intensity.

Testate amoeba 'transfer function' models estimate the water-table depth associated with the mix of different testate amoeba species we find in our samples. We have successfully developed a transfer function, novel for Tierra del Fuego, to reconstruct regional climate dynamics from peatland records.

We reconstructed former peat bog water tables using a range of plants and microscopic organisms (testate amoebae) as these are preserved as the peat accumulates. By taking core samples down to ~5 metres through peat bogs in the region we assessed how climate (wind-driven precipitation and temperature) has changed in this data poor area on multi-decadal timescales spanning the last ~2000 years.

We identified wetter conditions between ~1400 and 900 calendar years before present (stronger Southern Westerly winds). This evidence for poleward shifted/stronger Southern Westerly winds at this time is also supported by other palaeoclimatic research undertaken in the Southern Hemisphere. A pronounced recent dry shift was reconstructed in all three of the peat profiles investigated which may be related to ozone depletion. Research is currently underway to precisely date this change, to establish whether this climatic change is related to ozone depletion or not.

We have developed a triple-isotope method to simultaneously measure isotopes of oxygen, hydrogen and oxygen in common samples. We have used this methodology to measure stable isotopes preserved in sub-fossil Sphagnum moss cellulose samples in three Tierra del Fuego peat profiles. Work is currently in progress to determine how modifications to Sphagnum oxygen and hydrogen isotopic composition result from changes in relative humidity, temperature, light and water-table depth (hydrology) as well as reflecting changes in the isotopic composition of the precipitation (source) water. We will use this information to evaluate isotope-enabled climate models and to test inferences drawn from our testate amoebae palaeoclimatic data.
Exploitation Route Other researchers investigating the long term history of the Southern Westerlies and long-term climate change in southern South America.
Sectors Education,Environment

URL http://planetearth.nerc.ac.uk/features/story.aspx?id=1516&cookieConsent=A
 
Description The testate amoebae transfer function we have produced for southern South America will be form the basis for future palaeoclimate reconstructions using fossil remains of these organisms in the study region
First Year Of Impact 2014
Sector Environment
Impact Types Cultural

 
Description Letters from Patagonia 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Short article for NERC Planet Earth online

Thomas Roland and I put together this short article for the (NERC) Planet Earth Online resource. Other research scientists and the wider public can access the article.
Year(s) Of Engagement Activity 2013
URL http://planetearth.nerc.ac.uk/features/story.aspx?id=1516
 
Description Poster on stable isotopes in peat 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Quaternary Research Association (QRA) Annual discussion meeting on "Drivers and Responders" in the study of climate forcing. Poster presented outlining peat research with stable isotopes.
Year(s) Of Engagement Activity 2016
 
Description QRA Conference on the Quaternary in Southern South America. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Lecture presented to a QRA sponsored workshop on the Quaternary of Southern South America. Stable isotopic analysis of a late-­Holocene peat sequence from Patagonia.
Year(s) Of Engagement Activity 2015