Cruise participant: Christof Pearce

I am a Ph.D. student at the Centre for Past Climate Studies of the Department of Geosciences at Aarhus University in Denmark. My research is on the reconstruction of past sea-surface conditions (temperature and sea-ice variability) in the North Atlantic Subpolar gyre region. For this I am using sedimentological, geochemical and micropalaeontological data with the main focus on diatom analysis.

Diatoms are unicellular algae and are generally the main constituents of the phytoplankton. As primary producers in the upper layers of the ocean, they play a vital role in the marine food web. The cell walls of diatoms have characteristic shapes and ornamentations depending on the species and are made up of silica, resulting usually in excellent preservation in the sediments. Because of the wide variety in species, all with their own ecological preferences (e.g. temperature, salinity, nutrient availability), diatom remains in sediments are ideal indicators of past sea-surface condition.  

At the moment I am studying a gravity core from offshore Newfoundland, that encompasses the Late Glacial to Early Holocene time period (from 12500 to 9500 years ago). In the core, the transition from glacial times to the current Holocene epoch is not smooth and is associated with numerous big climatic fluctuations such as the Younger Dryas, a cold interval when temperatures dropped almost back to glacial levels.

The diatom assemblages clearly reflect these changes as variations in sea-surface temperatures and sea ice presence.The results will be combined with analysis of benthic foraminifera and geochemical parameters to achieve a more comprehensive record. The study of these fluctuations is important to improve our understanding of past and present natural climate variability and will contribute to better future predictions.

Sampling the cores

After the cores arrived to the CORESTORE laboratory we split them longwise. Then we packed, labeled and deposited them in the cold room.

All the working halves* were taken to the GEOLOGICAL WELL SAMPLE LABORATORY. Here, with the help of Sebastian a Geology and Geography undergrad student working in the lab, we sliced each half section every 1 cm.

Dark gray layer: volcanic ashes?

The sediment composing the cores is high in carbonate content, hence the light color, however on the cores’ surface it was possible to distinguish some darker layers that we think are volcanic ashes. Some of these layers appear gray while others look greenish. The analysis of the elemental composition of the sediments will tell us why the difference in color and will confirm if those are, in fact,  pyroclastic particles.

Sebastian showing a slice of the core sediment

We use a CD to slice the cores. The physical and chemical characteristics of the polymer plastic use to produce CDs prevents the sticking of the sediment to   the CD surface, making the slicing process (that is already time consuming and a little tedious) much easier than when using aluminium or regular plastic cutters.

Each of the sample-slices was divided in 3, and each of these subsamples will be used for something different:

1. Elemental analysis (composition of the sediment) and magnetic susceptibility

2. Planktic and benthic foraminifera (assemblage changes, stable isotopes, etc)

3. Sediment characteristics (granulometric analysis)

At the end, the linning is empty and we have 265 x 3 little bags full of mud.

The end of the core, finally!!!

*The half of the core that is used for all the analyses is commonly referred as the Working half. The half that is keep intact and preserved in the cold room is the Archive.