Anna Joy Drury

Anna Joy Drury
Position: PhD Student
Office: RSM 2.57G
Telephone: ++44 (0) 207 59 47143
Email: a.j.drury10@imperial.ac.uk

Research interest

I am interested in the use of geochemical proxies to help decipher past climate changes. In the past I have worked on the trace element analysis of speleothems, a form of inorganic carbonate. My current focus makes use of benthic and planktic foraminifera, forms of biogenic carbonate. My current project aims at studying climate variability during the late Miocene, between 8.5 – 3.5 Ma, with particular focus on understanding the causes and consequences of the late Miocene carbon isotope shift and the Messinian Salinity Crisis. 

The late Miocene (11.61 – 5.33 Ma) experienced one of the more stable climates of the past 60 Myr, and is divided into the Tortonian (11.61 – 7.25 Ma) and the Messinian (7.25 – 5.33 Ma). In the late Tortonian – Messinian stages, two large climatic events occurred of which the causes and consequences have not yet been fully resolved, namely the late Miocene carbon isotope shift (~7.6 – 6.6 Ma) and the Messinian Salinity Crisis (5.95 – 5.33 Ma). The samples I use for my project were collected as part of IODP Expeditions 320/321, and come from IODP Site U1338.

Between 7.6 and 6.6 Ma, benthic and planktic foraminiferal records show a large negative shift in δ13C, referred to as the late Miocene carbon isotope shift. This shift coincides with the peak in productivity during the late Miocene biogenic bloom. This implies the shift might be a response to changes in productivity; however, much uncertainty about the exact driving forces of the shift still remains.

During the Messinian Salinity Crisis (5.95-5.33 Ma), the present-day Mediterranean basin was isolated from the Atlantic Ocean and became an enclosed and desiccated basin, where large evaporite deposits accumulated. A combination of tectonic uplift and glacio-eustatic fall drove the isolation of the Mediterranean from the Atlantic, however the relative contributions are unclear.

My PhD is divided into three main phases. Firstly, to better constrain variations in glacio-eustacy during the Messinian Salinity Crisis, to assess the role of glacial-eustatic change during the crisis. Glacio-eustatic variations will be constrained by using a novel approach, where trace element (Mg/Ca and Li/Ca) measurements and δ18O measurements on benthic foraminifera are paired to isolate the glacio-eustatic signal. A second aim is to look at the connection between the changes in productivity (the late Miocene biogenic bloom) and the late Miocene carbon isotope shift, using a multiproxy approach combining benthic, planktic and bulk δ13C and benthic foraminifera accumulation rates. Finally, attempts will be made constrain variations in sea surface temperatures between 8.5 – 3.5 Ma by using paired Mg/Ca and δ18O measurements on planktic foraminiferal calcite.