9,400 yr B.P. The mortality of mollusk shell (Mya truncata) at high Arctic is associated with a sudden cooling event

An 118-cm-long, well-preserved sediment profile was collected from a paleo-notch formed by ocean wave action before rising to the terrace on Ny-Ålesund, Svalbard, Norway. A large number of mollusk shell fragments, predominantly Mya truncata, were found in the sediment profile. AMS ¹⁴C dating and stable oxygen and carbon isotope analyses were performed on the shell fragments samples. The reservoir-corrected radiocarbon ages averaged ~9,400 yr B. P., which accurately dates the raised terrace and the upper marine limit after Kongsfjorden was completely deglaciated. The calibrated aragonite isotopic temperature equation was established for Ny-Ålesund by comparing the δ¹⁸O profiles of modern mollusks as follows: T (°C) = 16.26 - 3.68(δ¹⁸O_{aragonite-PDB} - δ¹⁸O_water-VSMOW). The reconstructed paleotemperature range was -0.52 to +4.78°C, warmer than today by about 1°C, which was further confirmed by reconstructed sea surface temperature (SST) in west Svalbard. Moreover, the mortality of mollusks was very likely caused by an abrupt cooling event at about 9,400 yr B. P., which was triggered by reduced insolation, weakened thermohaline circulation, and abruptly decreased SST. More evidences for this distinct but short cooling event centered at about 9,400 yr B. P. were found in Northern Siberia, North Atlantic, Alps, and Eastern Europe.