Fieldwork in the Atacama Desert, Chile

Friday, 20 November 2015

Trace element paper finally published!

My paper based on the third chapter of my thesis is finally published: 'Environmental and diagenetic records from trace elements in the Mediterranean coral Cladocora caespitosa'. This one looks at the analysis of coral skeleton trace element content to attempt to extract palaeoclimate information.

This was the part of the thesis which caused the most problems: the most time spent in method development, the most time swearing at broken machinery and the most time confused and frustrated by meaningless data – over a year of the PhD all in all.

Turning the chapter into a paper proved just as difficult, we originally submitted the paper in February and I got back to thinking about isotopes (and working at Go Outdoors) for a few months. It took until July for the reviewers to get back to us…they’d been busy, very busy ripping apart the paper – major revisions needed. I received the list of required revisions while on holiday, read it, swore and wrote off the paper as impossible to fix, ignoring it for the next month. Luckily (?) my supervisor was less pessimistic and reckoned it was doable – even if neither of us knew what half the corrections meant. So we begged an extension and got to it. The reviewers’ main issue was the total lack of the statistical analysis (I’m not a stats person at all). The addition of regression analysis, correlation coefficients and frequency analysis turned the study from a thrown together piece of work into something resembling a legitimate scientific study, which was accepted at the start of October. Taking almost 9 months from the initial submission to the final version being available online.

The full paper can be read here (without a subscription until the 8th of January thanks to Elsevier’s sharing policy), but here’s a summary of the main points:

I fired lasers at coral (Cladocora caespitosa) skeletons: modern ones from Croatia and fossil ones from Greece. The fossil ones date from the last two interglacials: MIS 5e (108-133 thousand years ago) and MIS 7a or 7c (186-195 thousand years ago). This allowed us to measure the trace element content of the coral’s skeleton at a very high resolution (every 200 μm – about a fortnight’s growth) to look at how it changed throughout the year. This is important as trace element uptake by corals is linked to water temperature and therefore could be a good palaeoclimate indicator.

We found that individual modern corals do indeed record seasonal variation of sea surface temperature in both their strontium and magnesium contents. However, every coral analysed demonstrated a different relationship between temperature and trace element content. This is because each growing coral is putting an individual, strong and unpredictable biological control (a vital effect) on the elemental uptake. This means that a universal calibration equation to link trace element content in this species of coral to temperature is impossible to produce. This means that we were unable to calculate growth temperatures for the fossil corals – which is what we were really trying to do.

What we did find which was interesting was that one of the modern corals contained a massive spike in trace element contents which coincided with the 2007 wildfires which engulfed a large area of Croatia. This showed that these corals can be used to inform on any events that cause increased sediment discharge into the coastal zone – such as fires and floods – which could allow fossil samples of these corals to be used to discover whether these events happened more or less frequently during the past interglacials and thereby giving some indication into the past climate.

In other good news this week the final hardbound copy of my thesis is now handed in and I’m due to graduate next month – so I finally get to change everything to say Dr on it.

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