Dr. Rick Hennekam

Paleoceanographer Rick Hennekam studies past changes in Earth’s climate and environment. “This kind of research may go back 2,5 billion years, through samples from ancient sea floors, that are now piled up on land in South Africa or Australia. I generally look at samples that are slightly younger of age and use ocean sediments as climatological and environmental archives. The cores we take by ship are often shorter than 20 metres, which limits the time interval within these archives to about a million year or so.”

Focused view on geological archives

“One of the aspects that I am interested in is the variability of dissolved oxygen concentrations over time. Large algal blooms result in oxygen loss. When these organisms die and decay within the water column it consumes oxygen and may cause anoxic (oxygen-free) conditions, especially in water bodies that have a layered structure. This so-called stratification happens when relatively warm and/or freshwater lies on top of relatively cold and/or saltwater. The different densities of these water masses cause stratification and hamper oxygen exchange between the top and lower water layers. The transition from oxygenated to oxygen-free conditions can be rather quick and, hence, it is important to know how, why, and where anoxic conditions occur. You’d even like to predict upcoming anoxic events.”

“Such research benefits from new technological advances that allow reconstructions of past oxygen conditions with unprecedented sampling resolutions. Only with enough “focus” on our geological records, you will be able to extract information that may help predict upcoming anoxic events. We recently discovered that dissolved oxygen levels start to sway slower and wider over time as an anoxic event approaches. Back in the day, a big volume of sediment sample allowed to reconstruct past oxygen levels with only a resolution of hundreds to even thousands of years. Now, with new analysis methods, we can take a much closer look and make reconstructions on much shorter time scales. We literally look at layers of millimetres thick, or even less, and reconstruct past oxygen levels from year to year.”

Human time scales

“With our novel analytical techniques, we introduced a more 'human time scale' in our research. We reconstruct the climate and environment on time intervals that we as humans can relate to, such as years to decades.  I also reconstruct conditions on short time scales in our more recent past. Not only the climate of thousands or millions of years ago but also the climate during our great, great, great grandfathers’ lives is worth reconstructing. These relatively recent climate and environmental archives often overlap with real instrumental data, allowing to produce reconstructions with unmatched fidelity. For example, I also look at the layers of corals that, like tree rings, tell us from season to season what the environmental conditions at a particular reef were. By trying to understand this recent past, we hope to better predict and understand the future.”