1) Perturbing phytoplankton under Ocean acidification

How will marine calcifiers respond to increasing levels of carbon dioxide and environmental acidity? We have used various techniques from the sedimentary record to culture manipulations to probe whether the coccolithophores, which calcify intracellularly, but also photosynthesise using the inefficient Rubisco enzyme, will be detrimentally affected in the future ocean.

  • Winter A., J. Henderiks, L. Beaufort, R. E. M. Rickaby, C. W. Brown, Poleward expansion of the coccolithophore Emiliania huxleyi, Journal of Plankton Research, 36, 316-325, 2014
  • Young, J. N., Bruggeman, J., Rickaby, R. E. M., J. Erez, M. H. Conte, Evidence for changes in carbon isotopic fractionation by phytoplankton between 1960 and 2010, Global Biogeochemical Cycles, 27, 505-515, 2013
  • Johnson VR, Brownlee, C, Rickaby REM, Graziano M, Milazzo M & Hall-Spencer, JM Responses of marine benthic microalgae to elevated CO2. Marine Biology, 160, 1813-1824, 2013
  • Moolna, A., and Rickaby, R. E. M., Changing the interaction of the coccolithophore Gephyrocapsa oceanicawith its carbon environment: responses to a recreated high CO2 geological past. GeoBiology, 10, 72-81, 2012
  • Beaufort L., de Garidel-Thoron T., Ruiz-Pino D., Metzl N., Goyet C., Buchet, N. Coupel, P., Grelaud, M., Rost, B., Probert, I., Rickaby, R. E. M., and de Vargas, C.: Sensitivity of coccolithophore calcification to carbonate chemistry and ocean acidification, Nature, 476, 80-83, 2011.
  • Rickaby, R. E. M., J. Henderiks, and J. N. Young, Perturbing phytoplankton: response and isotopic fractionation with changing carbonate chemistry in two coccolithophore species, Clim. Past, 6, 771-785, 2010
  • Iglesias-Rodriguez, M. D., P. R. Halloran, R. E. M. Rickaby, I. R. Hall, E. Colmenero-Hidalgo, J. R.Gittins, D. R.H. Green, T. Tyrrell, S. J. Gibbs, P. von Dassow, E. Rehm, E. V. Armbrust and K.P. Boessenkool, Phytoplankton calcification in a high CO2 world, Science, 320, 336-340, 2008
  • Halloran P. R., I. R. Hall, E. Colmenero-Hidalgo, and R. E. M. Rickaby Evidence for a multi-species coccolith volume change over the past two centuries: understanding a potential ocean acidification response, Biogeosciences, 5, 1651-1655, 2008

2) Novel methods to reconstruct and understand past atmospheric pCO2

Two key variables, temperature and atmospheric carbon dioxide (pCO2), define the sensitivity of the Earth’s climate system, the crucial parameter for the prediction of how the Earth will respond to anthropogenic inputs of CO2 to the atmosphere. The geological record provides our only evidence of the past climate sensitivity of the Earth system, but there is no direct quantitative measure of pCO2 or temperature beyond the 650 kyr extent of the Antarctic ice cores. The reconstruction of past climate, on timescales of millions of years, relies on the analysis of chemical or isotopic proxies in preserved shells or organic matter. Such indirect approaches depend upon empirical calibration in modern species, without understanding the biological mechanisms that underpin the incorporation of the climate signal. We have explored both isotopic signals in the hard parts of the fine fractions, as well as enzymatic adaptation to changes in atmospheric composition as a means of probing both past CO2 concentrations and mechanisms driving the change. The ultimate goal is to find a proxy within biology that is understood quantitatively:

  • Heureux, A. M., and Rickaby, R. E. M. Refining our estimate of atmospheric CO2 across the Eocene-Oligocene climatic transition, EPSL, 2015
  • Egan, K., R. E. M. Rickaby, K. R. Hendry, A. N. Halliday, Opening the gateways for diatoms primes Earth for Antarctic glaciation, Earth and Planet. Sci. Letts., 375, 34-43, 2013
  • Egan, K., Rickaby, R. E. M., M. J. Leng, K. R. Hendry, M. Hermoso, H. J. Sloane, H. Bostock, and A. N. Halliday, Diatom Silicon Isotopes as a Proxy for Silicic Acid Utilisation: Southern Ocean Core Top Calibration, Geochim., Cosmochim. Acta, doi.org/10.1016/j.gca.2012.08.002, 2012
  • Hermoso, M., F. Minoletti, Rickaby, R. E. M., S. P. Hesselbo, F. Baudin, H. C. Jenkyns, Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change, Earth and Planetary Science Letters, 319, 45-54, 2012.
  • Young, J. N., Rickaby, R. E. M., Kapralov, M., and Filatov, D., Adaptive Signals in Algal Rubisco Reveal a History of Ancient Atmospheric CO2, Philosophical Transactions of the Royal Society, 367, 483-492, 2012.
  • Hendry, K. R., B. Georg, R. E. M. Rickaby, L. F Robinson and A. Halliday, Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions, Earth Planet. Sci Letts., 292, 290-300, 2010

3) Trace Metal “Nutrients”

Many trace metals masquerade as nutrients in the ocean which is fantastic for using them as proxies for past efficiency of the biological pump but why they look like nutrients remains elusive. Aside from better documenting the distribution of trace metals and their relationship with key environmental variables, we have started to question whether these signals of uptake can necessarily be taken to equate to use:

  • Horner, T. J., R. B. Y. Lee, G. M. Henderson, R. E. M. Rickaby, Reply to Morel, 2013
  • Horner, T. J., R. B. Y. Lee, G. M. Henderson, R. E. M. Rickaby, Unavoidable uptake and homeostasis drives the oceanic cadmium cycle, PNAS, 110, 2500-2505, 2013
  • Hendry, K. R., M. Meredith, C. I. Measures, D. S. Carson, R. E. M. Rickaby, The role of sea ice formation in the cycling of aluminium in northern Marguerite Bay, Estuarine, Coastal and Shelf Science, 87, 103-112, 2010.
  • Hendry, K. R., Rickaby, R. E. M., C-J. M. de Hoog, M. J. Meredith, Cadmium and phosphate in coastal Antarctic seawater: Implications for Southern Ocean nutrient cycling, Mar. Chem., 112, 149-157, 2008.
  • Elderfield, H., & R. E. M. Rickaby, Oceanic Cd/P ratio and nutrient utilisation in the glacial Southern Ocean, Nature, 405, 305-310, 2000

4) Reconstructing paleo-ENSO

Deciphering a decadal scale variability of the El Nino Southern Oscillation from the sedimentary record is challenging and yet key to understanding how ENSO responds and drives climatic change. We have grappled with sediments from the Pliocene Pacific as a way of reconstructing mean water column conditions as well as variability during this key period, thought to be the best analogue for global warming in the tropics.

  • Scroxton, N., Rickaby, R. E. M., Bonham S., Lawrence, S., Hermoso, M., and A. M. Haywood, Persistent El Niño-Southern Oscillation variation during the Pliocene Epoch, Paleoceanography, 26, PA2215, 2011.
  • Rickaby, R. E. M. and P. Halloran, Cool La Niña during the warmth of the Pliocene? Science 307, 1948-1952, 2005

5) Ikaite: a palaeoenvironmental proxy

In order to predict the consequences of global warming, it is essential to understand the quantitative response of the climate system in terms of temperature and ice volume (hence sea level) to atmospheric carbon dioxide. The geological record of past climatic fluctuations has the power to reveal the natural interplay between these three Earth system parameters. But reconstruction of independent and continuous records of ocean temperature, and ice volume as reflected in the stable oxygen isotopic composition of seawater (δ18Osw), remains a challenge, because the traditional proxy, δ18O of carbonate, integrates both temperature and δ18Osw. Lack of constraint on seawater δ18O prevents complete and quantitative interpretation of any marine carbonate δ18O record. We have hypothesised that ikaite (CaCO3.6H2O), a metastable hydrated form of calcium carbonate which precipitates in organic rich sediments, captures the isotopic composition of ambient waters trapped as hydration waters within the crystal (Rickaby et al., 20061), and offers a promising method of probing directly the δ18Osw for periods other than the Last Glacial Maximum (LGM). We propose a multi-disciplinary approach to integrate mineralogical and biogeochemical laboratory experiments with field observations to characterise and understand the presence and climatic significance of ikaite and its isotopes within the natural environment. Our primary aims are to lay the foundations for, and apply this novel ikaite proxy to the reconstruction of δ18Osw, hence ice volume, and extending application of the proxy to different timeslices and water masses.

  • Zhou, X.,, Z. Lu, R. E. M. Rickaby, E. W. Domack, J. S. Wellner, H. A. Kennedy, Ikaite abundance controlled by porewater phosphorus level: potential links to dusk and productivity, Journal of Geology, 123 269-281. 2015
  • Lu Z., H. Kennedy, R. E. M. Rickaby, B. Georg, S. Shaw, A. Lennie, R. D. Pancost, J. B. Anderson and J. S. Wellner, An ikaite record of late Holocene climate at the Antarctic Peninsula, Earth and Planetary Science Letters, 325-326, 108-115, 2012.
  • Lu., Z., R. E. M. Rickaby, J. Wellner, B. Georg, N. Charnley, J. B. Anderson, and C. Hensen, Pore fluid modelling approach to identify recent meltwater signals (MWS) on the west Antarctic Peninsula, G-Cubed, 11, Q06017, doi:10.1029/2009GC002949, 2010.
  • Rickaby, R. E. M., S. Shaw, G. Bennitt, H. A. Kennedy, M. Zabel and A. Lennie, The potential of ikaite to record the oceanic evolution of d18O, Geology, 34, 497-500 2006.