Raja Ganeshram
Raja Ganeshram holds a Personal Chair of Geochemistry at the School of GeoSciences, University of Edinburgh. Raja began his studies at the University of Madras, from which he holds BSc and MSc degree and continued to get a MS from the Indian Institute of Technology- Madras. He completed a PhD in Oceanography at the University of British Columbia, Canada in 1996 and conducted postdoctoral studies at Woods Hole Oceanographic Institution, Massachusetts, USA. Raja moved to the University of Edinburgh in Scotland in 1999. He is currently the head of the Ocean and Past Climate Research Group. His work variously deals with past, present and future changes in carbon, nutrients and oxygen, cycles in the ocean. He has published over 100 papers in major peer-reviewed journals including Science and Nature and has won many prestigious awards including distinguished scientist award by CSIR-India.
Climate forcing on ocean oxygenation
Ocean de-oxygenation is recognised as one of the key climate change stressors impacting marine biogeochemistry and ecology. Currently, there are several limitations in understanding and predicting how ocean oxygen content will change in the future. Although there is a general acknowledgment that ocean oxygen levels will decline in response to climate warming predictions vary widely. In this regard, a better understanding on climate controls on ocean de-oxygenation and the associated natural variability is important. Palaeo-records can be useful in this regard.
The intense oxygen minimum zones (OMZs) in the subtropical Pacific and the Northern Indian Ocean are recognised as hotspots of future ocean deoxygenation where time-series observations have recorded recent expansions of low-oxygen waters. Currently, how much of these changes are related to natural variability as opposed to human-induced climate warming and the mechanisms that come into play are widely debated. The talk will address this debate by presenting nitrogen isotope records reconstructed from marine sedimentary archives from these OMZ’s. These records cover all the major OMZs and range in time scales from glacial-interglacial, millennial, centennial, decadal and inter-annual. The modes of natural variability and climate forcing mechanisms in each of these time scales will be discussed. The talk will reveal that these records show a coherent response to North Hemisphere climate forcing in all time scales but the mechanisms that come into play vary both locally between OMZs and time scales. These results will be placed in the context of future warming trends to address climate forcing on ocean de-oxygenation.
