New multibeam mapping of the unique Ikaite columns in Ikka Fjord, SW Greenland

Ikka Fjord in SW Greenland is world famous for its submarine, cold-water craving ikaite (CaCO3·6H2O) tufa columns. Due to the uniqueness of the columns, Ikka Fjord is declared a protected area by the Greenlandic authorities. In the summers of 2018–19, multibeam sonar bathymetry and aerial drone photogrammetric surveys were made in Ikka Fjord mapping and counting the columns and comparing the results to data from geophysical surveys of the fjord in 1995–96. The new surveys provide highly detailed maps of the fjord bathymetry and its columns, their height and position, and several hitherto unknown pockmarks in the seabed. A total of 938 individual columns and structures ranging 0.5–20 m in height from the sea floor were identified: a number surpassing the 678 taller columns (> 1 m) known from previous mapping. Our results support previous observations that the columns are restricted to the spatial extents of the Grønnedal-Íka igneous complex. The new survey data show that column distribution exhibits lineations and variable density over the fjord floor, notably that the innermost central deep part is free of columns. The tallest columns are observed to grow up to the halocline at approximately 2–4 m water depth. The majority of columns have reached only 15–50% of their growth potential. The ~60 columns of maximum growth stand in clusters, interpreted as representing exceptionally favourable growth settings. New seawater data collected in 2019 shows a worrying increase in temperature since the previous measurements in 1995 and 2007–2009, which could potentially affect the stability of the delicate columns of Ikka Fjord.