Dr. Mahyar Mohtadi is a palaeooceanographer and palaeoclimatologist specializing in past climate change with an emphasis on the mid- and low-latitude climate, particularly in the following areas: Western Pacific Warm Pool hydrology, past climate of the Indonesian Archipelago and East Asian monsoon variability. He is currently a Senior Scientist at the Center of Marine Environmental Sciences (MARUM), University of Bremen, Germany. Dr. Mohtadi is author and co-author of over 40 articles in scientific journals such as Nature, Nature Geoscience, PNAS and Paleoceanography.
Climate models predict a slowdown of the zonal and meridional atmospheric overturning circulation over the tropics (the Walker and Hadley circulations) for the twenty-first century with severe consequences for tropical and global climate. However, debate exists on the appropriate interpretation of historical records and observations over the twentieth century, such as ENSO and the IOD, and necessitates longer records of past changes in tropical circulation to test the model results. Several records of continental rainfall, sea surface and thermocline temperatures extending back to the last glacial period suggest a stronger-than-today glacial zonal circulation in the tropics. Changes in the meridional circulation occurred through a number of forcings and feedbacks: while model simulations underscore the sensitivity of tropical circulation to temperature change, among other forcings, they remain equivocal and in part, inconsistent with proxy evidence. Untangling the (competing) impacts of meridional and zonal circulation changes on tropical hydroclimate, and whether and how these changes are reflected by different proxies at different sites, remains a critical task for both climate reconstructions and simulations.