Variable DSO modes linked to short-term changes in surface water
composition
On centennial timescales, the immense shift from peak glacial DSO modes
1 and 2 to deglacial mode 3 was directly paired with the distinct onset
of a δ18O depletion of (sub-) surface waters at
PS2644. It started right at the base of deglacial time segment III, 18.4
cal. ka, subsequent to a long-term constant LGM δ18O
maximum near ~4.5 ‰ that had prevailed since
~22.0 cal. ka (Fig. 4). The start of a gradual decrease
in planktic δ18O by up to 1.5 ‰ displays the onset of
both warmer and meltwater-diluted surface waters advected through the
Denmark Strait, a precursor of the North Iceland branch of the Irminger
Current. After 17.2 cal. ka, the shift resulted in an SST rise by
2°–4°C during time segment IV (based on census counts of planktic
foraminifera of Voelker, 1999; Pflaumann in Sarnthein et al., 2001;
Hagen and Hald, 2002). The rise was paired with a meltwater-induced
salinity reduction that necessarily led to continued sea ice cover (You
et al., 2023; Sadatzki et al., 2020). Thus, any local
CO2 and 14C exchange between
atmosphere and surface waters off East Greenland was continuously
suppressed until ~15.1 cal. ka (Fig. 2a).