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Author Topic: Temperatures during Greenland deglaciation  (Read 4372 times)

Pmt111500

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Temperatures during Greenland deglaciation
« on: September 05, 2014, 05:11:23 AM »
"the Younger Dryas period was 4.5° ± 2°C warmer than the Oldest Dryas, due to increased carbon dioxide forcing and summer insolation. "  http://www.sciencemag.org/content/345/6201/1177

Huh, nice to know some of the earlier estimates are likely wrong and there's a larger gap between full blown ice age and the current climate, however the researchers state the temperature swings were quite abrupt, so what the future holds for us, looking decadal swings in T's, still isn't too easily predicted .

http://www.sciencedaily.com/releases/2014/09/140904141953.htm
Cooling the outside by heat pump.

A-Team

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Re: Temperatures during Greenland deglaciation
« Reply #1 on: September 08, 2014, 06:32:03 AM »
Indeed, this article describes a world-class, multi-decadal screw-up in the interpretation of a crucial parameter measured along all the Greenland ice cores -- the delta O18 used as temperature proxy. It depended way too much on the origin of the water in precip -- the source and season changed and with them the proportion of the more massive O18 -- yet the proxy interpretation put this aside, even though the outcome never made sense in the larger climate change context.

The authors here used delta N15 of trapped air instead (along with many other considerations). The scope of the temperature discrepancy under discussion is huge.

Quite right to open a whole forum topic on this, Pmt, the ramifications are far-reaching. I have read the supplemental but  still await main full text and a second substantial commentary piece by LC Sime on it, also paywalled. Despite advertising itself as an educational non-profit dedicated to the advancement of science, the journal has even blocked access to readable versions of the figures.

http://www.sciencemag.org/content/345/6201/1116.summary
http://www.sciencemag.org/content/suppl/2014/09/03/345.6201.1177.DC1/Buizert.SM.pdf
« Last Edit: September 08, 2014, 02:46:28 PM by A-Team »

sidd

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Re: Temperatures during Greenland deglaciation
« Reply #2 on: September 08, 2014, 09:29:58 PM »
Buizert(2014) fig 1 frames g-i attached, T reconstructed from delta-15N + model which is briefly described in the supplementary.

reconstruction has gravitational and thermal diffusion, firn densification and a bunch else. In principle this should be possible, but as the supplementary shows, it is not straightforward. I wonder if the analysis can be applied to other isotopes (they did so some on 18O)

Seasonality results make sense, but lean heavily on ocean+atmos models forced with meltwater efflux into N. Atlantic to shut down AMOC.

sidd

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Re: Temperatures during Greenland deglaciation
« Reply #3 on: September 09, 2014, 10:58:27 PM »
I wasn't thrilled with the three different scalings they used for the same temperature range on the three Greenland ice cores; it is re-done below. I've also appended a revised version of the post-Eemian timeline or at least the latter part corresponding to the time frame considered in the paper. Note a big committee has redone the whole timeline more carefully but it is not yet out. Let's just hope they didn't use the O18.

Sune O. Rasmussen and the INTIMATE Protocol Team
Geophysical Research Abstracts
Vol. 16, EGU2014-9481, 2014

A stratigraphic framework for naming and robust correlation of abrupt climatic changes during the last glacial period based on three synchronized Greenland ice core records


EventacronymStartEndNEEMNGRIPGRIPGISP2NEEMNGRIPGRIP
Little Ice AgeLIA450150122107------122.12107.14---cool
Medieval Warm PeriodMWP1050750245217------245.02216.84---warm
BondB115451385341304------340.87304.15---cooling
Vesuvius ash layerVes1921na410368------410.2367.84---radar horizon
BondB229742784592539------591.91539.41---cooling
BondB343294155796742------796.38742.33---cooling
BondB458025612981940------981.2940.26---cooling
BondB582078032122812191325---1227.791219.471325.11cooling
ash inside Bond 8.2B5 ash82368237123012291334---1229.911228.671334.04radar horizon
Holocene Climactic OptimumHCO9000600012871302------1286.631301.53---warm
BondB692719096130413231432---1304.051322.881432.43cooling
Saksunarvatn tholeiitic ashSaks10347na13641410------13641410---radar horizon
BondB7104131025313671414------1366.831414.33---cooling
BondB8111801102013991463------1399.291463.18---cooling
Holocene startD011703na141914921624---1418.81492.451624.27warming
Vedde alkali ashNAAZ I12171na14291506------14291506---radar horizon
Younger DryasGS-1 or H0128001150014421524------1442.321523.55---cooling
stadial 1GS-112896---144415271662---1444.471526.521662.41cold
interstadial laGI-la13099---145015351672---1449.531534.51671.7warming
interstadial 1bGI-1b13311---145415421681---1454.371542.11680.5warming
interstadial lcGI-lc13954---147115711714---1470.841570.51713.7warming
Older DryasOD140001350014721572------1471.811572.2---cooling
alkali ashash14035na14721573------14721573---radar horizon
interstadial IdGI-Id14075---147315751719---1473.191574.81718.5warming
Bølling–AllerødBA141001290014741576------1473.731575.91---
Dansgaard-OeschgerGI-le DO114680---148916051753---1488.971604.641753.39rapid  warming
HeinrichH1181461553515331682------1533.291681.57---ice rafted debris
stadial 2bGS-2b20900---156817451900---1567.671745.311899.7cold
« Last Edit: September 10, 2014, 12:34:32 AM by A-Team »

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Re: Temperatures during Greenland deglaciation
« Reply #4 on: September 10, 2014, 05:41:21 PM »
The supplemental data includes a four layer excel spreadsheet. To my great surprise, that was not some immense raw data dump but instead cleanly organized and quite useful compilations. I was curious as to how the core temperatures varied with depth and latitude so made this small animation showing how NGRIP differs from NEEM and GISP2 over the years 10,050 - 20,050 B2K (abscissa below)

http://www.sciencemag.org/content/suppl/2014/09/03/345.6201.1177.DC1/1254961-Buizert_Database_S1.xlsx

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Re: Temperatures during Greenland deglaciation
« Reply #5 on: September 11, 2014, 03:07:15 PM »
That supplemental also provides a convenient scale needed to connect radar horizons between bore holes, at least for the time interval considered in the paper. In effect, this measures differences in layer thickness which in turn measures differences in snowfall accumulation.

The vertical axis of the graph is posted at 100 year increments; the horizontal scale is depth differences in meters. Thus NGRIP ice layers are thicker than NEEM but thinner than at GISP2 over this time interval.