Antarctic sulfur from the 1286 eruption starts rising in August 1285

Monthly sulfate from the study's own data (Greenland NS1-2011, Antarctica WAIS Divide WD2014), first month clearly above background and peak: 1229 eruption (dark eclipse Dec 1229): Antarctica rises Sep 1229, peaks Nov 1230; Greenland rises Dec 1231, peaks Jun 1232. Greenland 19 months behind. Samalas 1257: Antarctica rises Jan 1258, peaks Nov 1258; Greenland rises Mar 1258, peaks Jan 1259. 2 months behind. 1276 eruption (dark eclipse Nov 1276): Antarctica rises Jul 1276, peaks Jan 1277; Greenland peaks Jan 1278. 12 months behind. 1286 eruption: Antarctica rises Aug 1285, peaks Sep 1286; Greenland rises Aug 1286, peaks Jan 1288. 16 months behind.

What it means: the year-long lag in Greenland looks dramatic but is normal for this dataset, since it also appears after 1229 and 1276, eruptions that certainly darkened northern skies. Samalas is a tie point where the two timescales are pinned together, so it lines up; between tie points they drift. So the lag cannot tell us the volcano was southern. What survives: the better-dated Antarctic record starts climbing in August 1285, which fits an eruption in early or mid 1285, plus or minus the record's dating error of about a year. And Greenland got about as much sulfur as Antarctica relative to normal (3.9 times versus 2.8 times background), which argues against a veil that stayed in the south.