▁, ▁detected ▁in ▁Ant ar ctic ▁ice ▁cores , ▁has ▁also ▁been ▁associated ▁with ▁the ▁ 7 7 4 – 7 7 5 ▁event . ▁ ▁The ▁event ▁appears ▁to ▁have ▁been ▁global , ▁with ▁the ▁same ▁carbon - 1 4 ▁signal ▁found ▁in ▁tree ▁rings ▁from ▁Germany , ▁Russia , ▁the ▁United ▁States , ▁and ▁New ▁Zealand . ▁ ▁The ▁signal ▁exhib its ▁a ▁sharp ▁increase ▁of ▁ ≈ 1 . 2 % ▁followed ▁by ▁a ▁slow ▁decl ine ▁( see ▁Figure ▁ 1 ), ▁which ▁is ▁typical ▁for ▁an ▁instant ▁production ▁of ▁carbon - 1 4 ▁in ▁the ▁atmosphere , ▁indicating ▁that ▁the ▁event ▁was ▁short ▁in ▁duration . ▁The ▁glob ally ▁aver aged ▁production ▁of ▁carbon - 1 4 ▁for ▁this ▁event ▁is ▁calculated ▁as ▁. ▁ ▁Hyp oth eses ▁Several ▁possible ▁causes ▁of ▁the ▁event ▁have ▁been ▁considered . ▁ ▁The ▁" red ▁cru c if ix " ▁recorded ▁by ▁the ▁Ang lo - S ax on ▁Chron icle ▁was ▁thought ▁to ▁have ▁been ▁a ▁super n ova . ▁However , ▁since ▁no ▁super n ova ▁rem nant ▁has ▁been ▁found ▁for ▁this ▁year , ▁it ▁is ▁interpreted ▁as ▁an ▁aur ora ▁bore alis . ▁ ▁In ▁China , ▁there ▁is ▁only ▁one ▁clear ▁reference ▁to ▁an ▁aur ora ▁in ▁the ▁mid - 7 7 0 s , ▁namely ▁the ▁one ▁on ▁ 1 2 ▁January ▁ 7 7 6 . ▁Instead , ▁an ▁anom alous ▁" th under st orm " ▁was ▁recorded ▁for ▁ 7 7 5