Guest post from Harriet Moore – Burning Questions

As you are all here to ‘Explore Our Oceans’ I am pretty sure fire has yet to cross your minds during this course, until now……stick with me on this one, I am not going mad! If I was to ask you to think about fire, one of the very last things you would think about is the oceans. Did you know though that is it actually possible to reconstruct fire history by using the oceans (or more precisely marine sediment cores) and that the oceans can provide us with a really good record of changes in continental hydroclimate. Reconstructing the fire history of North Africa is the focus of Harriet’s research and it has important implications for our understanding of the recent and future evolution of North African climate. Charcoal is the key to all this and so here is Harriet to tell you more…… 

Hi, my name is Harriet and I am a third year Palaeoclimate PhD student at the University of Southampton. I research changes in fire activity in North Africa during the last glacial cycle (0-150,000yrs), by examining the charcoal preserved in ocean sediments cores collected from off the North West African coast.  By understanding how fire activity has behaved in the past, I am able to help make better predictions about how fire activity will behave in the future in North Africa.

Figure 1: Microscopic charcoal recovered from ocean sediments.

I use charcoal (Figure 1) as an indicator of fire activity, because more fires on land results in more charcoal in ocean sediments. By measuring the amount of charcoal in different sedimentary layers I can identify time periods of high and low fire activity.  The level of fire activity across North Africa is dependent on the vegetation abundance.  High abundances of vegetation results in higher fires activity, smaller abundances of vegetation result in lower fire activity.  As a result charcoal can also be used to indicate variations in vegetation coverage across North Africa.

I compare my fire activity record with a record of dust production on North Africa, in order to understand the climate factors driving the changes in fire activity occurring on land.  Changing dust volumes in the ocean sediment cores can indicate periods of arid and wet conditions on land, arid conditions are indicated by high dust levels whereas, less dust is suggestive of wetter conditions.

My research reveals three main phases of fire activity across North Africa during the last glacial cycle: low fire and low dust (Figure 2); low fire and high dust (Figure 3); and high fire and low dust (Figure 4).  In periods of low fire activity and low dust (Figure 2) I can infer that conditions on land were very wet, in order to support the growth of large amounts of vegetation but that the persistent wet conditions suppressed fire activity.

Figure 2: Schematic illustrating the conditions on North Africa to produce indicators of low fire and low dust conditions in the ocean sediments

In periods of low fire activity and high dust (Figure 3) I can infer that conditions on land were very dry and North Africa was only sparsely vegetated.  Lack of plant material to burn resulted in low fire activity during these time intervals.

Figure 3: Schematic illustrating the conditions on North Africa to produce indicators of low fire and high dust conditions in the ocean sediments.

In periods of high fire activity and low dust (Figure 4), I can infer there was sufficient moisture to support the growth of lots of burnable vegetation, but conditions weren’t sufficiently wet to prevent fire activity (Figure 2).

Figure 4: Schematic illustrating the conditions on North Africa to produce indicators of high fire and low dust conditions in the ocean sediments.

I hope this glimpse at my research has ignited your interest in understanding past fire activity and provided an insight into what secrets the oceans hide, and the surprising nature of what they can help us learn.

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