Temperature reconstructions for SW and N Iceland waters over the last 10 cal ka based on δ18O records from planktic and benthic Foraminifera

We have obtained δ18Ocarb data from planktic (N. pachyderma (s.)) and benthic foraminifera (C. lobatulus, M. barleeanus) from eight cores between 40 and 500 m water depth along the SW (core B997-347) and N Iceland margins (cores B997-321, -324, -327, -328, -329, -330, and -332) that span the last 10 cal ka. Sampling resolution varies between centuries to millennial scales. Over this time range, changes in δ18Ocarb in foraminifera are the product of changes in the global ice volume, and the temperature and salinity of the water at the level in which the foraminifera live. In order to evaluate the relative roles of these variables we investigate: (1) the salinity (S‰) and δ18Owater values for present-day waters off Iceland; and (2) the present-day relationships between δ18Ocarb (or calcite) values of foraminifera and water column temperature and salinity data. We estimate the average error in the temperature estimate to be ∼±0.3 °C based on a Monto Carlo simulation of the various error terms. We argue that around Iceland the variations in δ18Ocarb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important. Spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores, respectively. Reconstructed temperatures for sites around SW-N Iceland indicate that surface and seafloor water temperatures were warmest in the early Holocene (10-6 cal ka). Beginning at 6 cal ka, surface and seafloor temperatures began to cool in N Iceland and to become less stratified in SW Iceland. Over the last 5000 yrs, sea surface temperature variations have been ⩽1 °C for 50% of the observations with a maximum range of ∼2.5 °C. A profound decrease in temperature of ∼1.5 °C is recorded in our fjord site (B997-328) during the Little Ice Age. An abrupt, earlier cold event is well expressed in at least three N Iceland cores around 5 cal ka.