Sea Shells on the Sea Bed... by Henrieka Detlef

Henrieka Detlef
Henrieka Detlef is using shells which are over a million years old to reconstruct the different climatic components of the Bering Sea. She's a 1st year PhD student at Cardiff University and a BUFI CASE student at the British Geological Survey studying Paleoclimatology and Marine Geology. Find out from Henrieka why she's so interested in investigating climate systems of the past and how marine sediment cores will unlock the answers...

My PhD project focuses on reconstructing continental ice volume and deep sea hydrography changes, such as oxygen concentrations and temperatures, in the Bering Sea. I am working on the Integrated Ocean Drilling Program (IODP) core U1343 from the eastern Bering Sea, which is a unique area with extremely high primary productivity in the surface ocean and an oxygen minimum zone along the continental slope. The Bering Sea today is the gateway between the Pacific and Atlantic Ocean via outflow of Pacific waters through the Bering Strait. During cold stages of at least the past 2 million years continental ice volume increased significantly, causing sea level to fall by up to 130 m. During such events the Bering Strait was exposed and the Pacific Atlantic throughflow was cut-off. Together with other hydrographical and atmospherical changes this caused major shifts of sea ice extent, primary productivity, and ocean circulation in the Bering Sea during glacial intervals.

My research mainly focuses on the Mid-Pleistocene Climate Transition, 1.25 to 0.7 million years ago. During this time the frequency of cold stages changed from 41,000 years to 100,000 years and continental ice volume grew larger during glacial intervals. I plan to unravel the timing of continental ice volume change in the northern hemisphere in combination with deep sea temperature and sea ice shifts to investigate leads and lags of climatic signals and to investigate the influence of sea ice in high northern latitudes on ice sheet build up. Further I plan to look at oxygenation changes of mid-depth waters along the eastern Bering slope and their causes in combination with changes in the ocean’s carbon cycle.

Location map of sediment cores retrieved during IODP cruise 323 in the Bering Sea (red dots). U1343 is located in the eastern Bering slope. (

I plan to mainly use the shell chemistry of benthic foraminifera (little calcareous microfossils living on/in the seafloor) and assemblage changes of dinoflagellate cysts (organic walled cysts of marine protists living in the surface ocean) to reconstruct all the different climatic components.

To begin with I have to make sure that the foraminifera recovered from sediment core U1343 actually record the primary climatic signal and are not influenced by post-depositional carbonate precipitation on the shell or diagenetic recrystallization of the calcium carbonate. Therefore I plan to use a combination of imaging and chemical mapping techniques such as Scanning Electron Microscopy, Laser Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS) and solution ICP-MS.
This is where I am at the moment…

I hope you now know a little bit more about me and what I am doing during my PhD project. I will keep you updated on any exciting results 


Hennie is being supervised by Dr Sindia Sosdian, Dr Carrie Leah, Prof Ian Hall (University of Cardiff) and Dr Sev Kender, Prof Melanie Leng (BGS).