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Greenland ice cores show natural swings are large and warming means less storms

Posted By Joanne Nova On February 22, 2014 @ 6:26 pm In Global Warming | Comments Disabled

A new high resolution ice core in Greenland surprises even me with the wild swings and detail. The authors are discussing wind direction and storms that occurred in specific years 12,000 years ago, which is extraordinary information if accurate. They use elements like sodium (from sea salt) to figure out how many storms have dumped salt on the ice and take bands so thin they identify each summer so long ago*. The slices are so thin, they claim to have hundreds of samples per year.

The message here is that the cold younger dryas period ended abruptly (within one year) and so did the storms. Naturally, they warn that the abrupt changes mean the climate is unstable, “be afraid” type stuff. My take on this is that if natural factors cause abrupt climate change, we need to know what those natural factors are. The obsession with CO2 is hindering that. Also if warming brings less storms, that’s probably not such a bad thing. The caveats being that this is only one site, and less storms over the GISP site doesn’t tell us if less storms occurred elsewhere. It could be that jet streams shifted and moved the storms to another spot. But still, I like the level of detail. I wish we could get more cores from other places…

Look at the transformation in these graphs from jagged noise (storms) to periods of calm. The Younger Dryas (YD) was the cold period that lasted from 15,000 years ago til about 11,000 years ago in Greenland. It looks like a phase change, it’s so sharp.

Figure 1. The GISP2 ice core record. (a) Original calcium (p.p.b.) and sodium (p.p.b.) data plotted as age (years ago with AD 2000 as 0). (b) Dots mark original 10-cm resolution sample midpoint. Rectangle marks the location of the ice section discussed in this paper (1677.575–1678.580m depth (11 643–11 675 GISP2 a BP)) bridging the Younger Drays (YD)/Holocene transition. This figure is available in colour online at wileyonlinelibrary.com.

From the introduction

In this study (2–20-mm resolution) changes in calcium and sodium atmospheric circulation proxies preceded changes in snow accumulation, followed by a change in temperature using stable water isotopes. A second example of the advantage gained by high-resolution sampling is the demonstration, based on continuous melt sampling techniques (2.5–5.0-cm resolution), that the onset of Holocene climate occurred over 1–3 years and that the abrupt shift in atmospheric circulation at this transition preceded a change in temperature (Steffensen et al., 2008). Here, we use previously developed ice core climate proxies, expand upon the concept of finer scale sampling of calcium and sodium with the addition of iron, and focus on the abrupt climate change precursor – a change in atmospheric circulation.

I think I find this study most interesting because of the sheer detail, and the transformation that appears to take place so quickly. Can we really tell what direction the winds over Greenland came from in the summer of 9,651 BC (or whatever year close to that it turns out to be?) But I also find myself wondering what life would have been like if ice ages were also full of ghastly storms. How did people cope?Here’s some more of that detail — the numbers on the graph are in meters of depth, not years, but this apparently translates to  11,643–11,675 years BP.

Figure 3. Detailed examination using the smoothed laser sampled record from Fig. 2. Detailed 5-cm-long sections for calcium, sodium and iron (all in p.p.b.) in red, blue and green, respectively, plotted as smoothed data (10-point running median). (a) Holocene (1677.75–1677.80m depth) and (b) YD and YD/Holocene transition (1678.17–1678.23m depth). Gray rectangles mark the location of chemistry peaks used to identify annual layers. Black vertical lines (1678.18–1678.19m depth) mark the YD/Holocene abrupt climate transition year. This figure is available in colour online at wileyonlinelibrary.com.

Lower levels of salt and calcium mean there were less storms:

Previous work demonstrates that peaks in calcium and sodium occur during winter/spring, consistent with increased atmospheric storminess and increased transport of terrestrial dusts and seasalt to Greenland at this time (Whitlow et al., 1992). Therefore, lower background concentrations of calcium and sodium over Greenland indicate less stormy periods, as expected during summer. Annual layering (gray rectangles Figs 2 and 3) is well preserved and defined by inphase seasonal maxima in calcium, sodium and iron. Figure 3 (only smoothed data are shown) details two 5-cm core sections noted in Fig. 2.

It all occurred in just one year?

Closer examination of Fig. 3(b) shows that the YD/ Holocene transition is defined at the depth over which levels of calcium, sodium and iron decline markedly (1678.18– 1678.19 m). This depth range spans approximately 1 year and includes a significantly reduced winter/spring peak in westerly winds (calcium) compared with the previous 3 years (1678.19–1678.22 m). During the 3 years leading up to the transition, westerly wind peak values rise progressively. Westerly winds then weaken to Holocene (Fig. 3a) values at the transition. Marine storm intrusions (sodium) are variable in the 3 years before the YD/Holocene transition as westerly winds strengthen, potentially blocking transport of marine air onto Greenland. However, marine air mass intrusion is greatest during the transition year, suggesting intensified circulation over marine areas and closer proximity of marine air to Greenland as sea ice extent is reduced and westerly wind strength declines. Marine air mass incursions are less intense following the transition into the Holocene, as evidenced by lesser concentration peaks in sodium and longer periods of less intense transport (near flat sodium concentrations) during the longer summer seasons characterizing the onset of the Holocene. Iron  concentrations drop at the beginning of the transition year and early Holocene (1678.18m and shallower depth) iron transport to Greenland is characterized by longer periods of weak transport from continental sources. Reduction in continental source calcium and iron and marine source sodium is consistent with northward migration and  weakening of the westerlies and coupled easterlies associated with warming into the Holocene as the north–south thermal gradient weakened.

 

ABSTRACT:

The abrupt climate shifts identified in Greenland ice cores transformed understanding of the climate system. Although primarily studied in the paleoclimate record, abrupt climate change induced by greenhouse gas rise poses a serious threat to modern humans and ecosystems. We present the first ultra-high-resolution view (hundreds of samples per year) of the abrupt onset (within 1 year) of the current interglacial (warm) climate retrieved from the Greenland Ice Sheet Project Two (GISP2) ice core archive. This abrupt onset is manifested by a marked reduction in storm event frequency and increase in the length of the summer season around Greenland. We apply this metric to the current rapid climatic amelioration in the Arctic as a precursor for future abrupt climate change events. Copyright # 2013 John Wiley & Sons, Ltd.

Basically, I don’t know that this tells us a lot about today, except that natural climate change is an ominous force, and there is much we don’t know  about what drives it.

Until our models could explain these dramatic natural shifts, why would we pretend they can predict the climate now, or pick apart natural or unnatural changes in a climate that is always changing.

REFERENCE

Mayewski, PA,  Sneed, S. D., Birkel,  Kurbatov, A.V., and K. A. Maasch  (2014) Holocene warming marked by abrupt onset of longer summers and reduced storm frequency around Greenland, Journal of Quaternary Science, 29(1) 99–104 ISSN 0267-8179. DOI: 10.1002/jqs.2684

*”minerals” corrected to “element”. Thanks to John for spotting that.

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