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Rise and Fall of Roman Empire Exposed in Greenland Ice Samples

posted by martyb on Tuesday May 15 2018, @01:54PM   Printer-friendly
from the leading-theory dept.

An Anonymous Coward writes:

Modern people aren't the only ones who've polluted the atmosphere. Two thousand years ago, the Romans smelted precious ores in clay furnaces, extracting silver and belching lead into the sky. Some of that lead settled on Greenland's icecap and mixed in with ever-accumulating layers of ice. Now, scientists studying annual deposits of those ice layers have found that spikes and dips in lead pollution during the Roman era mirror the timing of many historical events, including wars fought by Julius Caesar.

=> https://www.sciencemag.org/news/2018/05/rise-and-fall-roman-empire-exposed-greenland-ice-samples

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  • (Score: 5, Informative) by The Shire on Tuesday May 15 2018, @02:41PM (6 children)

    by The Shire (5824) on Tuesday May 15 2018, @02:41PM (#680053)

    >Not all the lead came from pollution related to ore smelting; some came from naturally occurring dust and volcanic emissions, which researchers estimated and subtracted from the total lead count. The result: an incredibly detailed 1900-year timeline of Roman lead pollution,

    Right away this struck me as odd. If you're introducing estimates of lead from naturally occuring sources and volcanic emissions then your data cannot be "extremely detailed". Statistics is very specific about this - your result is only as accurate as the least accurate part of your dataset.

    >Based on air circulation patterns, the team thinks that the Roman-era pollution, which peaked annually at just under a millionth of a gram of lead deposited per square meter, came mostly from the western half of the Roman empire, in western and northern Europe

    Emphasis on "the team thinks" - so this is a guess. Take this paper as a theory not a fact. Humans, which you should always remember includes scientists, are very good at seeing the patterns they want to see. If you set out to find lead levels from the Roman Empire and you're able to fudge with the numbers by applying estimates of naturally occuring sources, the results are fairly predictable.

    Sorry, I'm just tired of seeing scientific papers taken at face value by the media for clicks rather than anyone applying even a little bit of critical thinking to evaluate its level of accuracy.

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  • (Score: 3, Informative) by VLM on Tuesday May 15 2018, @03:14PM (2 children)

    by VLM (445) on Tuesday May 15 2018, @03:14PM (#680064)

    Anyone got a PNAS subscription? I don't, so I only got to read the journalist clickbait and the actual paper abstract, and neither mention lead isotope ratios with would have been a pretty conclusive fingerprint. Lead is one of the few ores that varies semi-predictably by specific mine area such that you should be able to scrape up that greenland dust and match its lead isotope ratios with archeological lead pipes in Euro cities. Well, in theory, and it probably takes a lot more sample than micrograms per sq meter, but presumably if they tried hard enough... perhaps they did, and it merely didn't make the abstract or clickbate.

    Now not matching isotope ratios exactly does not prove there's not some completely wiped out mine in France or WTF so it could have been Australian aboriginals refining that lead (not likely, LOL, but a nice made up example). But if the ratio of isotopes in both ancient lead pipes in Paris matches the dust exactly, well, I guess some silver/lead mine near-ish to Paris made both the pipes and the dust. So you can't disprove the results, but as a fingerprint you could make a positive result nearly certain, via isotopic analysis... assuming you have a large enough sample to analyze, budget to bother, etc...

    • (Score: 1, Interesting) by Anonymous Coward on Tuesday May 15 2018, @07:06PM

      by Anonymous Coward on Tuesday May 15 2018, @07:06PM (#680152)

      Some excerpts:

      Materials and Methods

      Continuous Measurements of the NGRIP2 Ice Core.

      The bedrock NGRIP2 ice core (75.1°N, 42.32°W, 2,917 m) was collected beginning in 1998 adjacent to the intermediate NGRIP core (33). For this study, longitudinal samples (∼1.0 by 0.035 by 0.035 m) from 159.56 to 582.43 m depth were cut in 2015 from the University of Copenhagen’s NGRIP2 archive and analyzed using the Desert Research Institute’s (DRI’s) continuous melter system (7, 8, 14, 34, 35).

      The DRI ice-core analytical system includes two Element2, high-resolution inductively coupled plasma mass spectrometers (HR-ICP-MS) operating in parallel, along with a host of other instruments for continuous, near real-time, simultaneous measurements of ∼30 elements, isotopes, and chemical species (34, 36, 37). All measurements were exactly coregistered in depth. Different configurations of the DRI analytical system have been used to target specific research objectives (7, 8, 36, 38, 39). For this study, one HR-ICP-MS was used in low-slit resolution and electronic scan mode to measure a narrow range of elements that included only thallium, lead, and bismuth, with 60 individual 205Tl to 209Bi mass scans combined to yield one sample. The second HR-ICP-MS was used in medium-slit resolution to measure 14 elements, including indicators of sea salts (sodium, magnesium, chlorine), marine biogenic emissions, and volcanic fallout (sulfur), and continental dust (calcium, cerium), as well as lead, with one 23Na to 208Pb mass scan comprising a single sample. The full record between 159.56 and 582.43 m included >21,000 low (average of ∼9 samples/a) and >48,000 medium (average of ∼19 samples/a) slit resolution measurements of lead, respectively. Mixing within the continuous flow system resulted in smoothing between the individual HR-ICP-MS measurements, leading to an effective depth resolution for the HR-ICP-MS measurements of ∼0.015 m, equivalent to ∼12 samples/a during the Roman era.

      Lead concentration detection limits (defined as three times the SD of the blank) using these configurations for the low- and medium-slit resolution instruments were ∼0.01 and ∼0.18 pg/g, respectively, well below the average NGRIP2 lead concentrations of ∼1.4 and ∼3.0 pg/g during background (1100–1000 BCE) and Roman periods, respectively. Concentrations ranged from 0.40 pg/g to more than 20 pg/g during these periods. The much more precise, low-slit resolution measurements of lead were used throughout this study.

      Pollution lead was derived from the total lead concentrations measured in the NGRIP2 core by assuming that total lead was comprised of three components: crustal lead from windblown dust, volcanic lead largely from quiescent emissions (40), and pollution lead (7). To derive crustal lead, we multiplied the annual average cerium concentrations by a published “mean sediment” value for the lead to cerium ratio of 0.23 (41). Assessment of measurement recovery during continuous measurements of NGRIP2 with the DRI analytical system indicated that recovery was ∼100% and ∼60% for lead and cerium, respectively (Fig. S8). Therefore, measured cerium concentrations were scaled by a factor of 1.7 to correct for underrecovery (36, 42, 43); no correction for lead was necessary.

      Crustal lead was subtracted from measured total lead to yield noncrustal lead that included both the volcanic and pollution components. Lacking any independent indicator of fallout from quiescent volcanic emissions in our measurements, we assumed that the volcanic lead component was constant throughout the record. To estimate the maximum constant volcanic lead component consistent with our measurements, we averaged those years with the lowest noncrustal lead concentrations on the assumption that pollution lead was negligible during those specific years. We chose to average the lowest 5% of the >2,000-y record which, while somewhat arbitrary, yielded a constant volcanic lead component of 0.33 pg/g. For perspective, the average measured total lead and derived crustal lead concentrations were 2.44 and 0.93 pg/g, respectively, so the constant volcanic component represented ∼27% of the background (crustal + volcanic) lead concentration consistent with global estimates (44, 45) and only ∼13% of the total lead measured in the NGRIP2 core.

      Nonbackground or pollution lead was derived by subtracting the background lead from the total measured lead. Implicit in using the average of the 5% of years with the lowest noncrustal lead concentrations to derive the constant volcanic component was that some of the annual pollution lead values were negative.

      Following standard procedures (36), the depositional flux of nonbackground lead (Fig. S1) was calculated as the product of the nonbackground lead concentration and the annual water equivalent snow accumulation determined from the annual-layer thicknesses in the core corrected for flow thinning (46).

      Lead enrichment (Fig. S1) is an indicator of relative abundance and was calculated following standard procedures (8, 36), as the ratio of lead to cerium measured in the ice core divided by the ratio for mean sediment. Here we used a mean sediment ratio of 19/83 (41). Enrichment of 1.0 indicated that all lead measured in the ice could be attributed to continental dust.

      Provenance of Greenland Lead Pollution During Antiquity.

      Lead isotopic ratios in the few previously reported discrete samples of GRIP ice were consistent with Roman-era mining and smelting operations in Spain, as well as northwestern and central Europe, as the primary sources of pollution lead during classical antiquity (2). To better understand and quantify potential sources of pollution lead deposited in north central Greenland, we evaluated published lead depositional fluxes in three western European peat bog records: Myrarnar, Faroe Islands (11); Flanders Moss, Scotland (10); and Penido Vello, Spain (9, 50). Although discontinuously sampled and with uncertainties in the 14C-based ages ranging from decades to centuries, all three peat bog records showed similar temporal variability to the NGRIP2 lead record (Fig. S3), suggesting common primary emission sources during classical antiquity. Note that Roman-era mining and smelting previously have been inferred to be the dominant sources of lead pollution in all three bogs (9⇓–11, 50), sometimes supported by lead isotopic evidence (9⇓–11).

      Deposition rates decline approximately exponentially with distance from the source. If the common emission sources during antiquity were European, then lead pollution fluxes would be substantially (one-to-three orders-of-magnitude) higher in proximal records (e.g., western European peat bogs) compared with distal records (e.g., the NGRIP2 ice core in Greenland) that would not be the case for distant emissions sources, such as in Asia. Fluxes of noncrustal lead in the European peat bog records during the first-century CE were on the order of 100–1,000 µg/m2/a, or 300–3,000 times the ∼0.33 µg/m2/a measured in the NGRIP2 core. Fluxes to the peat bogs during the Roman era generally declined exponentially with distance from southern Spain, consistent with primary sources in the Rio Tinto region. While ice cores record wet and dry deposition directly and so closely reflect atmospheric concentrations, deposition and postdeposition processes in peat bogs are more complex (51), so fluxes recorded in peat bogs often are not as directly linked to atmospheric concentrations. Moreover, local sources of lead emissions—such as those reported for Flanders Moss, Scotland (10) and Penido Vello, Spain (9)—probably enhanced fluxes during some periods at those sites.

      Other sections go into the transport models used that would carry the lead to Greenland, and how they used well-known volcanic eruptions as markers, etc. There's always a lot more meat on the bone in these papers than can be put across in those summaries. Though Science summaries are usually pretty good. Those phys.org summaries are horrendous.

    • (Score: 2) by driverless on Wednesday May 16 2018, @04:28AM

      by driverless (4770) on Wednesday May 16 2018, @04:28AM (#680283)

      We still have a ton of lead pollution today, only it's quantized, some in 7.62mm packets, others in 5.56mm ones.

  • (Score: 3, Informative) by Gaaark on Tuesday May 15 2018, @04:04PM (2 children)

    by Gaaark (41) on Tuesday May 15 2018, @04:04PM (#680077) Journal

    The wind in Canada goes mainly from West to east, so I'm assuming the same for Roman times: would that not put Greenland very far away for lead to travel even as a gas?
    My 'assumption' is that much of it would have already been grounded by then.

    I've been wrong before, but it would put another blip into the so called 'statistics'.

    --
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    • (Score: 3, Informative) by frojack on Tuesday May 15 2018, @04:47PM (1 child)

      by frojack (1554) on Tuesday May 15 2018, @04:47PM (#680090) Journal

      Not the best view angle, but this gif:

      https://plus.google.com/photos/photo/101423092138897438495/5959149048350749202 [google.com]

      Shows weather patterns scraped from current era reported winds.

      The animation suggests the only significant wind flow in Greenland are from the south east and originate from Europe. North American winds take a more southerly course.

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      • (Score: 2) by Gaaark on Tuesday May 15 2018, @05:04PM

        by Gaaark (41) on Tuesday May 15 2018, @05:04PM (#680096) Journal

        Huh! I am mistaken.

        You've always had that Sig!

        ;)

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