There have been a couple of recent mentions of Besonen et al 2008 (including Ray Bradley) which discusses varve sediment thickness in Lower Mystic Lake, New England as a hurricane proxy, reported as a “1,000-year, annually-resolved record of hurricane activity from Boston, Massachusetts”.
When I or my students have generated data sets they are generally sent to the WDC-A (World Data Center for Paleoclimatology) once the results have been published. This is the normal procedure followed in my field.
Unfortunately, a search under Besonen did not show any contributions. In fact, a search under Bradley likewise showed no contributions other than ones where he was joint author with Mann (or in one case Jones). I guess WDC-A forgot to include Bradley’s contributions in its index. (See CA discussion from 2005 here.)
The article refers to SI to be located at ftp://ftp.agu.org/apend/gl/2008GL033950; however there is no such directory and ftp://ftp.agu.org/apend/gl/ showed no relevant candidates. The Supplementary Information linked in the HTM version of the article consisted only of radiocarbon dates, useful, but hardly complete.
The graph of sediment thickness shown in the article noticeably resembles our favorite shape as shown below. However, as observed in the article, there is (unsurprisingly) substantial non-climatic disturbance of sedimentation patterns in the Boston area and post-1870 data is removed from the analysis. Accordingly the authors say:
We confined our analysis to the period prior to 1870 given the significant anthropogenic interference and altered sedimentation dynamics as discussed above.
Figure 2 (a) LML varve thickness time series plot and identified extreme events. In the plot, actual varve thicknesses (mm) are plotted by the lower black line. The thickened gray line shows a robust estimate of the time dependent background thickness based on median smoothing with a 17 year window. The upper black line represents the med +3.5 rstd threshold, and varves with thicknesses which fall above this TDV are considered extremes (total of 47 observed). Of the 47 identified extreme events, the 36 which contain a graded bed are marked by filled black circles and listed in the inset table, and the 11 which do not contain a graded bed are marked by open black circles. The dashed vertical line at 1630 indicates the prehistoric/historic boundary for the region.
Besonen et al report that certain centuries had a “significantly” higher hurricane frequency:
Hurricane frequency, as recorded at LML, has not been constant over the last millennium (Figure 2b); the 12th–16th centuries had a significantly higher level of hurricane activity (up to 8 extreme events occurring per century) compared to the 11th and 17th–19th centuries when only 2–3 per century was the norm.
On the other hand, they note that a nearby study had also observed “significant” changes, but apparently in a different direction:
We note that conclusions about frequency changes reached from the LML record differ from those reached by studies based on lower resolution records from nearby areas. For example, a study from Long Island [Scileppi and Donnelly, 2007] concluded that activity had significantly increased over the last 300 years with reduced activity during the earlier part of the millennium.
Figure 2b, referred to in the above statement, is shown below:
Figure 2b. (b) Frequency of hurricane-related deposits in the LML record grouped by century. The darker central bars represent the number of extreme events identified using a TDV of med +3.5 rstd. The flanking light gray bars represent the number of identified extremes using TDVs of med +2.0 rstd. (left) and med +5.0 rstd. (right). Note that given our analysis range (1011–1870), the first and last columns do not span a full century.
Although the authors state that the 12th–16th centuries had a “significantly higher” level of hurricane activity, they do not describe how they carried out their significance test nor do they provide the data by which one can conduct a significance test on one’s own. Perhaps one of the readers are interested in Poisson calculations for hurricanes would be interested n writing to Bradley and Besonen and (1) inquiring what significance test was used as a basis for this claim; (2) obtaining the underlying data used to make the claim and then carry out his own significance test to see whether the variations actually show “significantly higher” levels or whether the data could be the result of a Poisson distribution. I have a pdf of the article.
Besonen, M. R., R. S. Bradley, M. Mudelsee, M. B. Abbott, and P. Francus (2008), A 1,000-year, annually-resolved record of hurricane activity from Boston, Massachusetts, Geophys. Res. Lett., 35, L14705, doi:10.1029/2008GL033950. url ftp://ftp.agu.org/apend/gl/2008GL033950