High Arctic Lake sediments show that Heinrich Event 2 was preceded by summer warming

Abstract

Throughout the Last Glacial period, episodic deposition of Ice Rafted Debris marks phases of circum-North Atlantic ice sheet instability. The causes of these Heinrich Events remain contested; while initially attributed to internal ice sheet dynamics, there is a growing consensus that favors external climate forcing. But based on the timing and expression of change, it remains unclear whether this trigger was oceanic or atmospheric. We present data from a High Arctic Lake sediment sequence, whose geochronology was previously published, that suggests Heinrich Event 2 was preceded by atmospheric warming. Alkenone-inferred temperatures, geochemical indicators of stratification and provenance, and leaf wax-based information about moisture availability, all indicate summers warmed from 27.5 to 23.5 thousand years before present. This evidence supports the view that Heinrich Stadials were marked by extreme seasonality rather than year-round cold conditions. Our findings also show that a High Arctic Lake ecosystem existed during the Last Glacial Maximum.