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the one project that actually measures oceanic currents directly (and continuously) is the RAPID MOC project. To my knowledge, there is not a similar project for the Labrador current.

The article describes a coral growth ring study, meaning a proxy study, which may imply that not a single current measurement was taken. Perhaps a few were taken (snapshots over the years). As I tried to explain in Frank's diary, taking snapshot measurements from ocean currents is a method riddled with statistical uncertainties and wouldn't give a proper picture.

by Nomad on Wed Jan 5th, 2011 at 05:26:32 PM EST
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Wouldn't nutrient levels as revealed in coral growth rings be exactly the cumulative evidence needed to coalesce the snapshots?

It seems that dismissing snapshots and also cumulative but "secondhand" or "derivative" evidence is really just a way to dismiss all evidence.

Align culture with our nature. Ot else!

by ormondotvos (ormond.otvosnospamgmialcon) on Sat Jan 8th, 2011 at 09:33:18 PM EST
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is not really an issue at this point.

A proxy study is able to show a certain side (1) of scientific "truth". There are caveats with proxy-studies.

Measuring oceanic currents show another side (2) of scientific "truth". There are caveats there too (see below).

Finally, one also could measure an oceanic current for a period of time and combine that data with a proxy study to see if the one study actually makes sense to the other (3). But particularly combining data from different sources has some serious caveats.

However. The question raised above by askod was whether the Labrador current can be measured directly. My answer: It can, but recent studies show one should tread carefully how to do that.

A snapshot study of measuring oceanic currents (that is, run a transect with a boat every x years and take a measurement every y meters) should now be considered a highly unreliable method to say something about the actual truth (whatever that may be). That is the core take-away lesson from the RAPID study and hullabaloo about the MOC shutdown: oceanic currents are fickle and their dynamics are unreliably mapped by a few years of snapshot measurements.

Secondly, no one here, myself included, seems to know at this point if the study actually included oceanic current measurements - snapshot or otherwise - or combined data sets. I will give it a look if it has.

Yet if we know that a certain methodology (snapshot measurements) is insufficient to properly capture a side of scientific truth, coalescing the data would not be of any help to learn us something extra.

None of this invalidates the proxy-data (1) in any way.

by Nomad on Sun Jan 9th, 2011 at 09:58:35 AM EST
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is here. Abstract reads:

Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes (δ15N) preserved in sediments and other bioarchives. Traditional bulk δ15N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids (δ15N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the δ15N variability of bulk organic matter. Here, we demonstrate the first use of δ15N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral δ15N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new δ15N-AA approach to control for variable trophic processing, we are able to interpret coral bulk δ15N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of δ15N-AA for paleoceanographic studies of the marine N cycle.

by Nomad on Sun Jan 9th, 2011 at 10:52:36 AM EST
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