Oceanographic changes through the last millennium off North Iceland: temperature and salinity reconstructions based on foraminifera and stable isotopes

Temperature and salinity reconstructions for two 1000-year high-resolution sedimentary records, located at the boundary between Atlantic and Arctic surface waters on the North Icelandic shelf, are based on transfer functions and oxygen isotopes for planktonic and benthic foraminifera. There is a general increase of Arctic Water indicator species at the transition from the Medieval Warm Period into the Little Ice Age (LIA) and a subsequent return of Atlantic Water indicator species towards the end of the LIA and in the 20th century. The timing of the reconstructed temperature changes, both at the beginning and at the end of the LIA, appears to be slightly different for the different water masses. The earliest temperature change is seen in the bottom and subsurface waters, where a cooling is reconstructed as early as AD 1150-1200 at both locations, whereas previously published diatom-based and alkenone-based sea-surface temperature reconstructions show a change at AD 1300, coinciding with the air temperature shift in the area. Our results show the need of a thorough understanding of the oceanography in the study area, as well as the different living habitat for the biological proxies used for the temperature estimates.