Pliocene vegetation and climate of Arctic Norway and the variability of the Norwegian Atlantic current

Panitz, Sina (2016) Pliocene vegetation and climate of Arctic Norway and the variability of the Norwegian Atlantic current. Doctoral thesis, Northumbria University.

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Abstract

The Pliocene Epoch (5.33–2.59 Ma) is characterised by climatic conditions similar to those predicted for 2100, with enhanced warming in the (sub-)Arctic. The climate evolution at high latitudes is not well understood due to the sparsity of time-continuous palaeoenvironmental records. This study provides new records of Pliocene vegetation changes in Arctic Norway and the variability of the Norwegian Atlantic Current based on analyses of terrestrial and marine palynomorphs from ODP Site 642 (Norwegian Sea, 67°N) to assess climate variability and identify different scale forcing mechanisms.

The Piacenzian pollen record (3.60–3.14 Ma) shows vegetation changes between cool temperate and boreal forests during warmer-than-present and similar-to-present climate phases, respectively, implying shifts of the northern deciduous/mixed forest limit of 4–8° latitude. During warm phases, warmest month temperatures were 8–14°C higher than present. The development of peatlands during cooler phases may have amplified the cooling through CO2-drawdown and positive vegetation-snow feedbacks. The high regional and hemispheric-wide climate variability highlights the importance of well-dated, high-resolution records for regional to global palaeoenvironmental reconstructions and data-model comparisons.

Long-term Pliocene vegetation changes (5.03–3.14 Ma) reveal a continuous decline of thermophilic elements over successive warm phases, supporting the notion of long-term climate cooling caused by decreasing CO2 concentrations. This cooling is superimposed on shifts between cool temperate and boreal climate phases on multi-millennial timescales. Minima in eccentricity (400-ka), together with low-amplitude obliquity/precession cycles are associated with the development of boreal conditions. At 4.56 Ma, a marked decline in pollen influx suggests atmospheric circulation changes in response to the shoaling of the Central American Seaway, a hypothesis supported by model results. Subsequently, changes in northward heat transport via the North Atlantic Current strongly affected vegetation changes. The Pliocene climate evolution represents the later part of late Neogene cooling instead of a reversal of that trend.

Dinoflagellate cyst assemblage changes (3.320–3.137 Ma) indicate variations in Atlantic and Arctic water influence, corresponding to cool temperate and boreal terrestrial climatic conditions in Arctic Norway, respectively. These records emphasise a high climate variability on glacial-interglacial timescales and linkage of both marine and terrestrial environmental changes.

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