OceanBUG: the Biogeochemistry research group

Dr Ros Rickaby...OceanBUG logo

The research focus of the OceanBUG group is to understand the interaction between marine phytoplankton and pCO2. I have funded research projects examining trace metal signatures in algae from sea-ice brines (AFI), and the natural glacial-interglacial cycles of pCO2 (QUEST). A recently funded NERC project aims to investigate the role of diatoms in long and short-term climate change using silicon isotopes preserved in diatom opal (δ30Si), and to establish the role of diatoms in mitigating the rise of atmospheric pCO2 on a centennial timescale. A new ERC study provides a perfect complement to these projects. It aims to develop a detailed understanding of the influence of species-specific photosynthetic partitioning of pCO2 between the ocean and the atmosphere on timescales of ~100 ka to 100 Ma from the novel viewpoint of genetic encoding and specificity of carbon fixation mechanisms, and allows the scope to establish a new interdisciplinary approach.

Some recent research highlights:

  • A novel development has been the ability to reconstruct past oceanic carbonate ion concentration and pH using foraminiferal trace metal proxies. We used N. pachyderma (s.) harvested off the West Antarctic Peninsula to construct a time series for the calibration of calcite proxies in a high latitude seasonal sea-ice environment which allows a unique insight into shell chemistry controls since temperature and carbonate ion concentration are decoupled throughout the year (Hendry et al., submitted). Using these calibrations, we constructed down-core records of carbonate ion from the Weddell Sea which demonstrate that the bottom waters had a carbonate ion concentration elevated by 20 µmol/kg. This glacially enhanced carbonate ion could account for a large portion of the glacial pCO2 draw-down (Rickaby et al., in prep).
  • Coccolith fraction Sr/Ca and Mg/Ca: a measure of bloom species abundance with a 400 kyr cyclicity and resonance, with Pleistocene eccentricity. There is an intricate link between the production of bloom species in the ocean, burial of organic carbon, and the Earth’s orbital eccentricity. A highly eccentric orbit results in an inverse correlation between growing season length and growing season insolation. I suggest that blooming coccolithophores are best adapted today to low eccentricity orbits, due to optimisation of growing season length and insolation.
  • Whether the recent transition from glacial advance to retreat across the Antarctic peninsula is an unprecedented response to global warming remains unresolved. Accelerated glacial retreat may have a significant impact on the freshwater and nutrient supply to the phytoplankton communities of the highly productive coastal regions. We have developed records of trace element-to-silicon ratios of diatom opal from two rapidly accumulating nearshore sites off the West Antarctic Peninsula, which show an increase in seawater micronutrients as a result of recent retreat of the Sheldon glacier and a corresponding increase in productivity. We show that recent melting in this region is unprecedented for over 300 years.
  • We used the temperature history recorded by deep and shallow dwelling planktonic foraminifera from the west and east equatorial Pacific to investigate the equilibrium state of the Pacific thermocline during the most recent period of global warmth (the Pliocene).