Understanding the role of the tropical Indian Ocean on regional and global climate over the last 2000 years

Overview

The warm and salty waters off the coast of Madagascar are a key component of the Aghulas current. This surface ocean current flows around eastern Africa into the South Atlantic. The leakage of these waters into the Atlantic is crucial for providing the salt and hence promoting deepwater formation in the North Atlantic (Biastoch et al., 2008). Future climate projections predict an increase in this flow of these warm and salty waters into the Atlantic through changes in the southern hemisphere westerly winds (Biastoch et al., 2009). However, limited data exists on how the tropical Indian Ocean varied naturally on centennial time-scales and its impacts on the global and regional climate over the recent past. This is largely because ocean measurements are relatively short (~150 years) and are therefore not sufficient to study natural climate variability on the scale of decades to centuries or to distinguish between natural versus human induced climate changes. This project will use a suite of novel geochemical proxies in order to reconstruct for the first time the centennial scale changes experienced in the tropical Indian Ocean across the last two millennia. This project will use a unique high-resolution (~30 year) marine sediment core located off Madagascar. Foraminiferal oxygen isotopes and Mg/Ca will be used to quantitatively reconstruct temperatures and salinities at different ocean depths. Independent temperature reconstructions will be produced by analysing the organic compounds in the sediments. This project will fill in a geographical gap in our knowledge of the climate of the Common Era (McGregor et al., 2015) and determine the role that the Indian Ocean played on well-known climate events recorded in the North Atlantic such as the Little Ice Age (Moffa-Sanchez et al., 2014, Moffa-Sanchez et al., 2017).

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Image Captions

Photo taken from the Mozambique Channel (I. Hall)

Methodology

This project aims to extend ocean observations (temperature and salinity) back 2000 years from the Tropical Indian Ocean. This will be done by using organic and foraminiferal geochemistry on a unique high-resolution marine sediment core located off Madagascar (in the Mozambique Channel) recovered during the Meteor Expedition M75 in 2008. The methodologies will include:
• Identification and selection of different foraminiferal species (benthic and planktic) for high-resolution chemical and isotopic analysis.
• Preparing and processing samples for radiocarbon dating including hands-on training at the NERC Radiocarbon Analytical Facility (East Killbridge).
• Organic geochemical separation of individual chemical compounds, for identification and characterisation by GC-MS.
• Sample preparation and analysis of stable isotope (oxygen and carbon) ratios and Mg/Ca in foraminiferal calcite.

Project Timeline

Year 1

Production of a literature review on the topic and design of specific hypothesis. Initial laboratory work will include processing sediment samples and foraminiferal identification and selection. Introduction to the organic and inorganic geochemical laboratory procedures and techniques. A week-long training at the NERC Radiocarbon Facility will be provided to the student and the samples will be analysed for their dating.

Year 2

Geochemical analysis including organic chemistry and foraminiferal Mg/Ca and oxygen isotopes. Potential seagoing experience and attendance to national meeting/conference to present preliminary results. Review and preparation of thesis content and structure.

Year 3

Completion of laboratory/analytical work and processing and interpretation of the data. Reconstruction of the ocean conditions in the Mozambique Channel. Presentation of results at an international conference. Write thesis and corresponding articles.

Year 3.5

Completion of thesis and submission of articles to peer review journals.

Training
& Skills

Training and supervision will be given in:
• Experimental design, sedimentary core processing and analysis, including microfossil identification (Durham)
• Organic geochemistry, including compound-specific GC-MS, and foraminiferal Mg/Ca analysis (Durham, with visits to facilities at the Department of Earth and Ocean Sciences at Cardiff University )
• Specialist radiocarbon analysis and construction of chronologies, from sample pre-treatment to measurement (Durham/ SUERC).
• Data interpretation, scientific writing and communication of results to the international scientific community and international partners on this project.
During this project opportunities may arise for the student to gain seagoing experience by sailing in an oceanographic research expedition. The student will be a member of the Ice Sheets and Sea Level Research Cluster in the Department of Geography. A full and progressive range of transferable skill training is accessible to the student through IAPETUS specific provision and the University of Durham. This project is a collaboration with Cardiff University (Prof. Ian R. Hall) and Kiel University (GEOMAR) (Prof. Ralph Schneider) and as such, the student will be involved and encouraged to visit and discuss their results with the different partners and national and international experts in the field.

References & further reading

Biastoch, A., C. W. Boning, and J. R. E. Lutjeharms (2008), Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation, Nature, 456(7221), 489-492.
Biastoch, A., C. W. Boning, F. U. Schwarzkopf, and J. R. E. Lutjeharms (2009), Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies, Nature, 462(7272), 495-498.
McGregor, H. V., et al. (2015), Robust global ocean cooling trend for the pre-industrial Common Era, Nature Geosci, 8(9), 671-677.
Moffa-Sanchez, P., A. Born, I. R. Hall, D. J. R. Thornalley, and S. Barker (2014), Solar forcing of North Atlantic surface temperature and salinity over the past millennium, Nature Geosci, 7(4), 275-278.
Moffa-Sánchez, P., and I. R. Hall (2017), North Atlantic variability and its links to European climate over the last 3000 years, Nature Communications, 8(1), 1726.
Rouault, M., P. Penven, and B. Pohl (2009), Warming in the Agulhas Current system since the 1980’s, Geophysical Research Letters, 36(12).

Further Information

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