Hi Laurynas, 

I am by no stretch of the imagination an expert in 14C dating by AMS but I seem to recall 13C analysis is used in conjunction with this technique for correction purposes.  My suggestion would be for you to contact a good friend and colleague of mine who is an expert in AMS and 14C dating:  Prof. Paula Reimer at Queen's University Belfast.  Her e-mail is [email protected]

That being said, I can give you a rough idea of what kind of d13C and d15N values to expect for your equine samples.  Horse bone collagen (if declared viable by an elemental C:N ratio of >4:1) should show d13C and d15N values of about -26 and 3 to 6 permil respectively.  Human bone collagen d13C and d15N should be higher.  For a typical omnivore one would expect to see d13C and d15N values of -22 to -20 and 8 to 10 permil respectively.  Please, note, these are approximate values.

From a diet point fo view I have never fully understood as to why human protein tissue such as bone collagen should be subject to a freshwater reservoir effect since freshwater fish typically show d13C values of -28 to -24, i.e. values similar to these found in terrestrial producers (fruit and vegetables) and lean meat of primary consumers (beef, pork, chicken). Since you mention both d13C and d15N in your question I am working on the assumption you will be analysing organic material, e.g. collagen isolated from bone.

That being said, in regions where freshwater is rich in dissolved calcite and magnesite I should imagine this additional source of carbon (carbonate) might have an effect on 14C in bone mineral (bio-apatite).  However, a high level of dissolved calcite should not impact on the 13C composition of bone collagen since even de-novo synthesis of non-essential amino acids does use carbonate or bicarbonate as precursor pool for organic carbon.  All essential amino acids are recruited straight from the diet anyhow and even most non-essential amino acids will be recruited from the diet unless there is a serious shortfall.  However, even non-essential amino acids synthesised by the human body are based on recycled organic products of metabolism.

Hope this helps.

Wolfram

Hello,

a specialist in diet reconstruction and radiocarbon is Ricardo Fernandez who is also here on researchgate. He can also show you how to calculate the influence and correct the radiocarbon age.

You need both isotopes, C13 and N15, to correct as each one answers a different question. But N15 should show you marine/freshwater influences.

Hope this helps a bit?

Best wishes

Susanne

Hi Laurynas,

Ideally to determine if you have a freshwater reservoir, you need to measure radiocarbon in a terrestrial herbivore and a freshwater fish to see what the offset is in 14C years. These should be from the same context so you can be pretty certain they are from the same period (or very close in time given the possibility for reworking of midden deposits). If a freshwater reservoir is detected then you can run more measurements on samples to calculate the offset.

For your people, you will need to use the data you have just created to determine the amount of freshwater fish protein in their diet. This is where the δ15N and δ13C are necessary. Once you have a percentage freshwater protein calculated, you can apply your correction to the radiocarbon age and then calibrate normally.

If marine resources are also being exploited then the issue is further complicated as you will want to calculate the percentage input of marine protein in the diet as well. This is not applied to the radiocarbon age (uncalibrated number) but in mixing the terrestrial (IntCal13) and marine (Marine13) calibration curves when calibrating the result.

It is with all of the dietary modelling that Ricardo's FRUITS program is especially useful.

The first though though is to independently determine what the freshwater reservoir might be.

My colleagues and I from SUERC have a number of publications about marine and freshwater reservoirs, with one in review that actually applies both a freshwater and marine correction to a series of radiocarbon dates of Viking burials in Iceland.

I hope this helps as well,

Derek

Dear colleagues,

Thank you very much for your answers. This seems to be much more complicated than I thought, on one hand, but not impossible, on the other hand. It seems that I will have to change the strategy and to try to find some fish bones. The fish/herbivore/and human assemblage in one archaeological context is a difficult thing to find. But maybe  fish/ herbivore and herbivore/human assemblages are available.

Thank you once again,

Laurynas