Jökull

Issue

Jökull - 01.01.2015, Page 76

Jökull - 01.01.2015, Page 76
Jónsdóttir et al. Distance (km) 0 1 2 3 4 5 34.6 34.55 34.5 34.45 34.4 34.35 34.65 8 7 6 5 4 3 20 40 60 80 D e p th ( m ) 20 40 60 80 D e p th ( m ) Temperature (°C) Salinity (psu) Distance (km) 0 1 2 3 4 5 Temperature (°C) Salinity (psu) 9 8 7 6 5 34.6 34.4 34.2 34 33.8 Figure 2. Temperature and salinity profiles in Arnarfjörður, taken in June 2005 (left) and October 2006 (right) (www.hafro.is). – Hita- og seltumælingar frá Arnarfirði, teknar í júní 2005 (t.v.) og október 2006 (t.h.). Radiocarbon dating Radiocarbon dating was performed on four marine bi- valve shells (Table 1) with an accelerator mass spec- trometer at INSTAAR, Laboratory for AMS Radio- carbon Preparation and Research in Boulder, Col- orado. The global average reservoir correction of about 400 years was applied to the 14C dates for the core (Reimer et al., 2013) (∆R = 0). Foraminifera Samples for the foraminifera analysis were taken at ca. every 10 cm, in total 66 samples. The sam- ples were wet sieved with 63, 106 and 1000µm sieves and then dried. Foraminifera were picked from the size fraction 106–1000µm. Although it is of- ten recommended to count and identify at least 300 foraminifera individuals from each sample, statistical test on foraminiferal counts, counting in total 200 ver- sus 300 individuals, on a core from a nearby fjord in- dicated no significant difference in species % or fau- nal diversity (Ólafsdóttir, 2004). As the Arnarfjörður faunal assemblages are also of low diversity >200 benthic foraminifera specimens were picked and iden- tified to species from each sample. Statistical analysis Cluster Analyses (CA) was used to subdivide the fau- nal record into assemblage zones using the software Past with squared euclidian, paired group (UPGM) and constrained clustering. A Principal Component Analysis (PCA) method was used to better under- stand the association between foraminiferal assem- blages and hydrographic and environmental factors. The PCA was performed on the foraminiferal data set, with the XLSTAT software. The data set con- tained only species with an abundance of ≥2% in at least one sample. The BWT reconstruction, in Arn- arfjörður, was performed with transfer function ap- plied to a down-core data set using the C2 program (Juggings, 2010). The transfer function is based on a calibration set by Sejrup et al. (2004). The statistical routine, weighted averaging partial least squares (WA- PLS) was applied on the training set. In an Arctic fjord environment E. excavatum f. clavata is a fairly common species due to its tolerance of high sediment accumulation rates and fluctuating salinity (Hald et al., 1994). To avoid the issue of too low temperature estimates, a square root was applied on the training set to diminish the weighing of E. excavatum on the 76 JÖKULL No. 65, 2015
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