Evidence: There are no nitrate spikes in multiple high resolution ice cores in Antarctica.

1. Recently published in GRL: The Carrington event not observed in most ice core nitrate records, E.W. Wolff, M. Bigler, M.A. J. Curran, J.E. Dibb, M. M. Frey, M. Legrand and J.R. McConnell, GRL, 39, L08503, doi:10.1029/2012GL051603, 2012. From the Abstract: “We conclude that an event as large as the Carrington Event did not leave an observable, widespread imprint in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs”.

2. Evidence: There are no nitrate spikes in multiple high resolution ice cores in Antarctica. In Greenland nitrate spikes are common in nearly all cores, especially around 1860. However, only the GISP H core (Zeller, McCracken) has an event dated 1859 (and another in 1865), while the 2010 Zoe core from Summit and the D4 core near Summit have similar spikes dated 1863 (and 1869). Zoe and D cores had full chemistry, allowing multi-parameter dating and including ammonium which is a tracer of biomass burning. It is suggested that the 1859 event in H core is probably the same 1863 event seen in the cores dated with more constraints. Also likely that the H core had similar enhancement of ammonium (but only conductivity and nitrate were measured).

3. Additional tracers of biomass burning (black carbon or BC and vanillic acid or VA) were measured in the Zoe and D4 cores. These tracers and ammonium increase in all nitrate spikes in the 20 years around 1860. The association between nitrate and ammonium in the 1863 spike was also seen in lower resolution records from the two deep Summit ice cores. The vast majority of nitrate spikes in snow and ice in central Greenland are related to smoke plumes from wildfires, especially in summer layers in the snowpack or ice core.

4. GLEs and Summit Ice Cores “Impulsive Nitrate Events” measured in the so-called BU core dated to occur in 1942, 1946, and 1949 were linked by Kepko et al. to specific “ground level enhancements” and suggested to be caused by SEPs. There are significant nitrate spikes in the H core, and in detailed record from the B core, but they do not line up across all three records. The B core was dated by a committee, using multiple parameters, other two primarily relied on conductivity as an indicator of volcanic events, and seasonality in nitrate. Glaciochemists do not consider nitrate a good dating tool, especially in modern era.

5. The B core is the only one of these three records to have full ion chemistry. Nearly all of the nitrate peaks are associated with ammonium (tracer of smoke) or calcium (tracer of dust). Boxes indicate the years highlighted in BU core as linked to GLEs. The nitrate peak in the B core during 1949 is modest, but is somewhat exceptional by not having clear enhancement in ammonium or calcium.

6. Dating of the H and BU cores tied to conductivity spikes related to volcanic sulfate. The Hekla spike in 1947 appears to be in all cores, and gave Kepko et al. high confidence in dates in this section of core (original dating on left). We suggest that the agreement is better if the BU dates are shifted three years to match both the 1947 and 1950 spikes in the other two cores (right).

7. Of course, if the dating of the BU core is adjusted, the nitrate spikes no longer line up with the GLEs. And, they still do not line up terribly well with the nitrate spikes in the B and H cores. We suggest caution regarding the BU record, and are conducting lab studies to assess possible artifacts.

8. Three Candidate SEP Events 1)13-15 July 00: >30 Fluence 4.2x109, GLE Pct 52 Possible nitrate spikes at Summit: 21 Aug 00 5 Sep 00 22 - 30 Nov 00 (multiple) 13 Dec 00 25 Jan 01 2) 2-15 and 18 April 01: >30 Fluence 1.9x108, GLE Pct 129 26 Jun 01 22 Oct 01 3) 4-6 Nov 01: >30 Fluence 3.6x109, GLE Pct 14 12 Jan 02 19 Feb 02 4 Jul 02 Temporal resolution nearly 365 samples/year.

9. Nitrate spikes in Aug-Sep clearly fire related, the doublet at end of Nov associated with pollution. Spikes 22-24 Nov, 13 Dec and 25 Jan not readily explained. However, they seem quite late to be from Bastille day SEP event.

10. June nitrate enhancement associated with fire and pollution tracers. October spike not readily explained by tropospheric chemistry, but is 6 months after the April SEP event.

11. Nitrate spikes in Jan and Feb associated with seasalt and pollution tracers, while the one in July can be linked to enhanced ammonium.

12. Nitrate spikes at Summit: Easy glaciochemical story 21 Aug 00 Fire related 5 Sep 00 Fire related 30 Nov 00 Pollution 26 Jun 01 Fire related/Pollution 12 Jan 02 Seasalt/Pollution 19 Feb 02 Seasalt/Pollution 4 Jul 02 Fire Related Possibly just nitric acid from pollution, or regular strat/trop exchange, or stratospheric denitrification, or maybe SEP event?? 22-24 Nov 00 13 Dec 00 25 Jan 01 22 Oct 01 If from SEP, how did the NOx signal get through strat and trop impulsively? Can WACCM explain these 4 events (w/wo SEPs)? Different, but equally critical question, will the nitrate spikes be preserved??

13. Pits sampled nominally monthly, resolution about 23 samples/year.

14. Does anyone think the 4 July spike will be preserved as a 3 cm layer with > 10,000 nmol/kg? Maybe a 5-6 cm layer with ~8,000 nmol/kg?

15. We were back at Summit the next year and sampled 4 more pits. Were you really expecting to see that July 2002 layer preserved? Go back and look at the sequence of 18 pits again.