Surface sediment diatom distribution and Holocene paleotemperature variations in the Greenland, Iceland and Norwegian Sea

Abstract

One hundred and four surface sediment samples and two piston cores from the Greenland, Iceland and the Norwegian (GIN) Sea (Hopkins, 1988) were analyzed. Diatoms were common to abundant in most surface sediment samples and throughout the Holocene. Q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91.7% of the total variance. Mapping of the six factors showed their close affinity to hydrographic regimes. These are the Norwegian‐Atlantic Current assemblage (Thalassionema nitzschioides, Paralia sulcata, Proboscia alata), Arctic Water assemblage (Thalassiosira gravidaspores), Sea Ice assemblage (Nitzschia grunowii, Nitzschia cylindra, Thalassiosira hyalina), Arctic‐Norwegian Waters Mixing assemblage (Rhizosolenia hebetata f. semispina, Rhizosolenia borealis), Atlantic assemblage (Thalassiosira oestrupii), and Norwegian‐Arctic Waters Mixing assemblage (Thalassiosira gravidavegetative cells). Transfer functions (GINT2) relating factor distributions to winter (February) and summer (August) surface water temperatures were generated. The transfer functions have a standard error of estimate of ±1.5°C (August) and ±1.0°C (February). Downcore studies of core 52–43 from the Norwegian Basin and core 57–5 from the Iceland Plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the Holocene. The first appearance of diatoms in cores 52–43 and 57–5 occurs within the Vedde ash layer (10,600 years B.P.) and the Saksunarvatn ash layer (9100 years B.P.), respectively. Diatom abundances increase steadily throughout the Pre‐Boreal‐Atlantic time to 25 and 35 million valves per gram dry sediment in the Norwegian Basin and Iceland Plateau cores, respectively. Application of the temperature transfer functions (GINT2) to the two Holocene records revealed higher than present sea surface temperatures during the Boreal‐Atlantic chronozones for the Iceland Plateau and during the middle Younger Dryas‐Sub Boreal chronozones for the Norwegian Basin core. Temperatures decreased steadily since then with a slight increase to the present values. Both the Iceland and the Norwegian seas experienced a strong influx of temperate Atlantic surface waters in the beginning of the Holocene. Sea surface temperatures dropped steadily in the latter part of the Holocene as the influx of the Atlantic surface waters diminished.