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

Overview

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 recent ocean drilling in the Gulf of Alaska (during Integrated Ocean Drilling Program, IODP, Expedition 341) this project will test for the first time hypotheses of ocean-ice sheet interaction over the Pliocene and Pleistocene. This will be achieved through reconstructions of NE Pacific palaeoceanography and comparing these reconstructions with evidence for expansions of the NW American Cordilleran Ice Sheet (NCIS).

Previous investigations of the NW Pacific have advocated an important role for ocean circulation in driving North American glaciation. Yet, evidence for ice-sheet-ocean interactions proximal to the NCIS, in the NE Pacific, is currently largely based on records of ice-rafted debris inputs to this region. The Gulf of Alaska is bounded to the north by the St Elias mountain range, on which the NCIS nucleated. NCIS history is nevertheless poorly understood, despite the sensitivity of the regional climate in the modern day to ocean and atmospheric circulation in the North Pacific. Understanding the timing of NCIS advance and retreat is important for assessing whether glacial cycles had globally synchronous expressions (and drivers), and for testing existing hypotheses of how oceans and ice-sheets interact across a range of timescales.

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. Is the magnitude of millennial-scale climate variability connected to a climate or ice volume threshold?

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Image Captions

View to the St Elias Mountains from the JOIDES Resolution, during IODP Expedition 341 in June/July 2013 (Photo: 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.

The primary methodology employed will be the application of established organic geochemistry (biomarker) proxies using the organic geochemistry facilities at Durham Geography:
• Sea surface temperatures (UK37 index)
• Sea ice (IP25)
• Biological productivity (sterols, diols, alkenones)
• Terrestrial inputs from ice/dust/rivers

In the St Andrews isotope Geochemistry (STAiG) laboratories the student will explore evidence for changing ocean circulation via stable isotope and trace element geochemistry analyses. At Exeter, the student will identify and characterise inputs of ice-rafted debris, using sedimentology and geochemical analyses.

Project Timeline

Year 1

Literature review and generation of project research questions. First year Progression Paper to detail project overview, research questions, and planned methodology. Training in, and application of, and initial laboratory analysis at Durham (details below).

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 St Andrews and Exeter to receive training in the stable isotope and geochemistry measurements, and will develop these data sets. Development of first research paper.

Year 3

Complete data sets by fully characterising evidence for marine/terrestrial organic matter inputs and investigating the interaction between ocean circulation changes, ice-rafting and productivity. Presentation of emerging data at an international conference (target: International Conference on Paleoceanography, Bergen, 2022). Development of second research paper, and thesis writing.

Year 3.5

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

Training
& Skills

The supervisory team will provide the student with training in laboratory analytical techniques such as organic and inorganic geochemistry, microscope analysis, and isotope analysis. Additional knowledge in palaeoceanography, northern hemisphere ice sheet histories and Alaska tectonic evolution will be developed, especially through the formulation of the literature review and development of research papers. The student will receive training in stable isotope analysis and trace metal analysis through an extended visit to St Andrews. Training in analysis of ice-rafted debris will be undertaken at the University of Exeter.

The student will receive regular supervisory meetings and support at Durham. Through their enrolment in the graduate training programme at Durham University and through IAPETUS2-specific training, the student will gain a range of transferable skills relevant to completion of the PhD and developing a career path, including writing research proposals and giving oral presentations. The student will attend and contribute to the programme of regular departmental seminars and discussion groups, to support the development of a well-rounded scientist. S/he will attend national and international conferences, networking events and outreach activities, developing networks for feedback and future employment.

References & further reading

Lang, D. C., Bailey, I. 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.

Rae, J. W. B., et al. (2014) Deep water formation in the North Pacific and deglacial CO2 rise. Paleoceanography, doi: 10.1002/2013PA002570.

Sánchez-Montes, M. L., McClymont, E. L., Lloyd, J. M., Müller, J., Cowan, E. A., and Zorzi, C.: Late Pliocene Cordilleran Ice Sheet development with warm Northeast Pacific sea surface temperatures, Clim. Past Discuss., https://doi.org/10.5194/cp-2019-29, in review, 2019.

Further Information

Professor Erin McClymont, Durham University, 00 44 191 334 3498, erin.mcclymont@durham.ac.uk.

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