IAP2-22-351

Oceans, ice sheets and tectonics: investigating climate evolution in the Gulf of Alaska

The record of global climate over the last 5 million years is marked by the transition from the relative warmth of the Pliocene into a colder world (the Pleistocene) dominated by the onset and intensification of major Northern Hemisphere glaciations. Recently, it has been argued that changes to moisture and heat fluxes driven by ocean circulation might allow the development of larger northern hemisphere ice sheets on long timescales (thousands/millions years), whereas on shorter timescales (centuries/millennia) ice sheet advance and retreat may impact on the oceans via meltwater input. A growing body of evidence reveals that the well-documented millennial-scale climate oscillations of the last glacial cycle (e.g. D-O events) are not unique, but may relate to some critical ice volume threshold regularly crossed during glaciations of the Early Pleistocene. This raises important questions about the background climate states under which millennial-scale and abrupt climate changes might be possible.

Our understanding of these processes is, however, largely dominated by investigation of the large Laurentide ice-sheet in North America, and its interaction with ocean circulation in the North Atlantic. Thanks to ocean drilling in the Gulf of Alaska (during Integrated Ocean Drilling Program, IODP, Expedition 341) this project will test hypotheses of ocean-ice sheet interaction over the Pliocene and Pleistocene. This will be achieved through reconstructions of NE Pacific sea-surface temperatures (SSTs), ocean productivity, and inputs of ice-rafted debris (IRD) to explore when the NW American Cordilleran Ice Sheet (NCIS) advanced and retreat. Full training will be given in all of the proposed techniques.

The key research questions for this project:
1. What was the magnitude and timing of changes in sea surface temperatures in the Gulf of Alaska over Pleistocene glacial cycles?
2. Did changes in ocean circulation evolve before, after, or in synchrony with NCIS advance and retreat?
3. Can we detect millennial-scale climate variability during both cold (glacial) and warm (interglacial) climate states?

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Image Captions

Drilling during IODP Expedition 341, with the Bering Glacier in the background (Photo credit: Erin McClymont)

Methodology

This project will analyse high resolution marine sediment sequences recovered during IODP Expedition 341 in the Gulf of Alaska. The extensive sediment sequences which were recovered present unrivalled opportunities to examine oceanography and glaciology changes over the Pleistocene at a range of timescales.

The primary methodology employed will be the application of established organic geochemistry (biomarker) proxies using the organic geochemistry facilities at Durham Geography. We regularly train PhD students in these techniques:

• Sea surface temperatures (UK37 index)
• Sea ice (IP25)
• Biological productivity (sterols, diols, alkenones)
• Terrestrial inputs from ice/dust/rivers

The student will also learn sediment stratigraphy and measurement of ice-rafted debris, to build a detailed picture of ocean temperature change and ice sheet advance/retreat.

Project Timeline

Year 1

Literature review and refinement of research questions; receive training in laboratory techniques; sample preparation for biomarker analyses.

Year 2

Reconstruct surface ocean conditions during the last few glacial-interglacial cycles at orbital and sub-orbital timescales, with a focus on the time window across which the Northwest Cordilleran ice sheet expanded. The student will also visit Newcastle University to receive training in sediment description and ice-rafted debris analysis, and will develop these data sets. Development of first research paper.

Year 3

Complete data sets by fully characterising evidence for inputs from land and the impacts on ocean productivity, to investigate the interaction between ocean circulation changes, ice sheet growth, ice-rafting and productivity. Presentation of emerging data at an international conference. Development of second research paper, and thesis writing.

Year 3.5

Completion and submission of thesis, finalisation of remaining research papers.

Training
& Skills

The student will receive specialist training and support in the following techniques, which are regularly used outside of academia in the analysis of environmental samples:
• Microwave assisted solvent extraction of lipids
• Liquid and gas chromatography (LC, GC)
• Mass spectrometry
• Foraminifera stable isotope mass spectrometry
• Sediment stratigraphy
• Time series analysis and other appropriate statistical techniques to ensure the resulting data sets can be explored to their full extent

The student will be enrolled in a graduate training programme (Durham University) to gain a range of study skills and transferable skills. They will attend and contribute to the regular departmental seminars and discussion groups. They will attend national and international conferences, networking events and outreach activities, developing an important network for feedback and future employment.

References & further reading

Lang, D. C., et al. (2014) The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site. Quaternary Science Reviews 93, 125-141.

Sánchez-Montes, M. L., McClymont, E. L., Lloyd, J. M., et al., (2020) Late Pliocene Cordilleran Ice Sheet development with warm Northeast Pacific sea surface temperatures, Climate of the Past, https://cp.copernicus.org/articles/16/299/2020/

Sánchez Montes, M. L., Lloyd, J. M., McClymont, E. L. et al., (2022). Plio-Pleistocene ocean circulation changes in the Gulf of Alaska and its impacts on the carbon and nitrogen cycles and the Cordilleran Ice Sheet development. Paleoceanography and Paleoclimatology, 37, e2021PA004341. http://doi.org/10.1029/2021PA004341

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