Jökull - 01.01.2015, Síða 73

Reviewed research article
Marine climate variability from Arnarfjörður, NW Iceland
during the Medieval Warm period and early/middle Little Ice Age
Ingibjörg Rósa Jónsdóttir1, Sædís Ólafsdóttir2, Áslaug Geirsdóttir1
1Institute of Earth Sciences – Science Institute, University of Iceland, Sturlugata 7, 101 Reykjavík
2Department of Earth Science and Bjerknes Centre for Climate Research,
University of Bergen, Allégaten 41, 5007 Bergen, Norway
Corresponding author: irj2@hi.is
Abstract — A high-resolution sedimentary record from the subarctic fjord Arnarfjörður in northwestern Ice-
land provides information on local changes in sea ice cover and a regional oceanographic climatic signal
reflecting changes in the position of the Polar Front that separates the North Atlantic Current and the East
Greenland Current. The 520 cm long sediment core spans approximately 2000 years and thus offers a multi-
decadal time resolution during the Medieval Warm Period (MWP) and the early to middle part of the Little Ice
Age (LIA). Approximately 150 years from the top of the core were lost during coring. The marine climate recon-
struction is based on multi-proxy study with focus on benthic foraminiferal fauna allowing down-core bottom
water temperature (BWTTF ) estimations based on the statistical transfer function approach. This first of the
kind study from Arnarfjörður demonstrates significant variability in the benthic foraminiferal fauna dominated
by Cibicides lobatulus, Cassidulina reniforme and Elphidium excavatum, BWTTF variations of ∼3◦C, fluctuat-
ing from ca. 1.5±1.1◦C to 4.5±0.6◦C. The data is in harmony with previously reported LIA characteristics from
the region, which has been described as a period of high amplitude fluctuations, with non-stable conditions and
cold bottom waters.
INTRODUCTION
The oceanographic system around Iceland, the largest
landmass in the northern North Atlantic Ocean, is
dominated by the Irminger Current transporting warm
(3–8◦C) and salty (∼35‰) water from the south (Stef-
ánsson, 1999) and the East Greenland Current, which
brings cold and fresh polar water from the north (Fig-
ure 1a). These two main water masses are sepa-
rated by the Polar Front (Valdimarsson and Malm-
berg, 1999). The position of the front varies over
time and shapes the climate of Iceland. The Vestfirð-
ir peninsula, NW-Iceland, is in close proximity to the
Polar Front and thus ideal for reconstructing marine
climate variability.
The North Atlantic climate is influenced by the
North Atlantic Oscillation (NAO), which consists of
two opposed pressure centers, one around Iceland and
the other around the Azores. An NAO index, based
on the difference of normalized sea level pressure
(SLP) readings from these two locations, was defined
by Hurrell (1995, 1996). Fluctuations in the strength
of these features strongly influence the speed and
orientation of westerly winds (Hurrell et al., 2003),
ultimately affecting temperature and precipitation in
the N-Atlantic area. During negative winter NAO the
westerly winds are weaker than normal and the pres-
sure difference smaller, resulting in reduced Atlantic
Water advection and cold/dry conditions over NW-
Europe (Hurrell, 1995). Conversely, during positive
winter NAO the increased pressure difference results
in stronger winter storms crossing the Atlantic Ocean
on a more northerly track, generating warm and wet
winters in North Europe.
JÖKULL No. 65, 2015 73