Supplemental Data

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Persistent Solar Influence on North Atlantic Climate During the Holocene
Gerard Bond, Bernd Kromer, Juerg Beer, Raimund Muscheler, Michael N. Evans, William Showers, Sharon Hoffmann, Rusty Lotti-Bond, Irka Hajdas, Georges Bonani

Supplementary Material

Notes and References

1). In Denmark Strait at VM28-14, we doubled the sample resolution relative to the earlier work (text, 1) to about 100 yrs (1 sample/cm). At the eastern North Atlantic site, VM29-191, we increased the sample resolution in (text, 1) to about 30 yrs (1 sample/0.5 cm), and in addition, we extended the record to the present using data from nearby multicore KN158-4 MC52. The multicore has a modern top (> 100% modern radiocarbon; text, Table 1) and also has a sample resolution of about 30 yrs (1sample/cm). It was patched into VM29-191 at 1000 yrs BP (text, Fig. 2). At our site off Newfoundland, we extended a previously published late Holocene record (text, 2) from multicore KN158-4 MC21, which also has a modern top, to the early Holocene with new data from a longer core at the same site, KN158-4 GGC22. The multicore and gravity core records were joined at 2,000 yrs BP, and the combined records have a sample resolution of 50 years (1 sample/cm). Petrologic counting methods, isotopic methods and errors given in (text, 1).

2). The observational record demonstrates that North Atlantic drift ice is highly sensitive to subtle inter-annual and decadal changes in winds and in ocean surface temperatures (1-4). Even in the warm modern climate, between about 1880 and the mid-1960's, there were numerous iceberg sightings in the eastern North Atlantic between 45° and 60°N, and those are only part of a much wider distribution of observed open ocean drift ice extending as far south as Bermuda (5). The number of icebergs passing the Grand Banks annually peaked at times of reduced air and ocean surface temperatures and stronger zonal winds during the 1970's, 1980's and 1990's, and during the 1970's the high pressure anomaly over Greenland strengthened and the East Iceland Current became a polar-like current, transporting drift ice southeastward (6, 7) toward the coring site in the eastern North Atlantic. Similarly, during the cold years of the LIA sea ice extent was substantially larger than at present around Iceland (8-10), and in the Barents and Nordic Seas (11). In the Nordic Seas, a 33% reduction in the LIA sea ice extent occurred before 1900, reflecting a natural trend of recovery from the colder period (11). As increased amounts of sea ice also enhance the survival of drifting icebergs (e.g. 12), the petrologic tracers are sensitive indices regardless of which kind of ice transported them. They can be regarded as a record of iceberg and/or sea ice anomalies relative to a mean Holocene trend, that, by analogy with modern drift ice fluctuations, were highly responsive to changes in surface winds and air/ocean surface temperatures. Because the contrast in tracers carried by ice in the cooler versus warmer waters is relatively large (text, Fig. 1), even subtle southward and eastward advections of the tracer-rich drift ice would leave a robust signal in our records.

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Supplemental Figure 1. Comparison of detrended and smoothed 10Be flux and 10C production rate as in Figure 3 (text) with adjustment to the marine time series to improve the correlations. Adjustment to time series was done using the pointer method in Analyseries (1) and the linear rescaling option. Dots indicate where adjustment was made and the number of years the marine time series was shifted. All adjustments are within the 2name errors of the calibrated ages as given in Table 1 (supplementary data). The adjustments were made assuming that the grouped patterns of the centennial-scale variations, which are common to all of the records, are of the same age.

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Supplemental Figure 2. A) Power spectrum of the unadjusted time series of hematite-stained grains (HSG) in MC52-VM29-191 (Fig. 2) computed using the multi-taper method (1). Time bandwidth product = 3; number of windows = 5. Raw time series was linearly detrended. The mean red noise spectrum (heavy dashed line) is for 1000 random time series with variance and lag-1 autocorrelation structure of the petrologic data. Upper chi-squared confidence interval at 90 percent level (light dashed line) is on power spectrum estimates. Arrows mark frequencies of spectral peaks estimated from time series of the residual name10C tree ring data set (3-5). 1) unnamed (~512 years); 2) deVries cycle (206 years). A third cycle at about 2300 years (Hallstatt cycle) has been inferred but does not appear to be statistically significant (3). B) Cross spectral coherency of marine and nuclide records using the Blackman Tuckey method (2). For HSG and 10C, 70 yr sampling interval, 95% confidence interval, 69 lags and 0.00039 bandwidth. Coherency in both the 300 to 500-year and 900 to 1100-year band is 0.84; for HSG and 10Be, 70 yr sampling interval, 95% confidence interval, 48 lags and 0.000557 cycles/yr band width. Coherency in a 300 to 500-year band is 0.75 and in a 900 to 1100-year band is 0.93.

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Supplemental Figure 3. Comparison of change in solar irradiance for the 20th century (1) with the timing of the Great Salinity Anomaly (2).

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