Are multi-decadal sea-level oscillations augmenting modern sea-level rates?

Sea-level change over the instrumental era (~1850 to present-day) is accelerating, with a departure from Holocene linear rates in the late 19^th century, and nearly a doubling of the rate over the last 25 years (Fox-Kemper et al. 2021). Whilst the anthropogenic impact on sea-level change is without question, the impact of natural variability on damping or enhancing rates of change remains an important area of continued research, particularly at ocean-climate response timescales (e.g., > 30 years). For example, Chambers et al. (2012) identify a 60-year sea-level oscillation in a global set of tide gauge records that they suggest may enhance recent rates of sea-level change across multiple ocean basins, yet their conclusions remain untested nor is a firm mechanism attributed to the signal (one suggestion is a product of a sparse tide gauge distribution).

Exploration of such oscillations either takes frequentist (e.g., harmonic analysis) or empirical approaches (e.g., wavelet analysis). The method of Empirical Mode Decomposition (EMD) is novel, efficient and allows identification of quasi-period signals in datasets, thus making a useful tool to explore natural systems with quasi-resonant behaviour (e.g., Jackson & Mound, 2010). This project will use EMD to study the dominant modes of multi-decadal sea-level variability in tide gauge and ocean model reanalyses. The results and an assessment of possible ocean-climate drivers will highlight the role of long-timescale internal variability on historical, modern, and by extension future sea-level rates.

Lead supervisor(s):

Dr Luke Jackson: luke.p.jackson@durham.ac.uk

Key references:

Chambers, D.P., Merrifield, M.A. and Nerem, R.S., 2012. Is there a 60‐year oscillation in global mean sea level?. Geophysical Research Letters, 39(18).

Fox-Kemper, B., et al., 2021: Ocean, Cryosphere and Sea Level Change. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362, doi:10.1017/9781009157896.011.

Jackson, L.P. and Mound, J.E., 2010. Geomagnetic variation on decadal time scales: what can we learn from empirical mode decomposition?. Geophysical research letters, 37(14).