Climate variability and long-term expansion of peat lands in Arctic Norway during the late Pliocene (ODP Site 642, Norwegian Sea)

Abstract

Abstract. Little is known about the terrestrial response of high latitude Scandinavian vegetation to the warmer-than-present climate of the Late Pliocene (Piacenzian, 3.60–2.58 Ma). In order to assess Piacenzian terrestrial climate variability we present the first high resolution reconstruction of vegetation and climate change in northern Norway between 3.6–3.14 Ma. The reconstructions are derived from pollen assemblages in the marine sediments of ODP Hole 642B, Norwegian Sea (67° N). The palynological assemblages provide a unique record of latitudinal and altitudinal shifting of the forest boundaries, with vegetation alternating between cool temperate forest during warmer-than-present intervals, and boreal forest similar to today during cooler intervals. The northern boundary of the nemoral to boreonemoral forest zone was displaced at least 4–8° further north and warmest month temperatures were 6–14.5 °C higher than present during warm phases. Warm climatic conditions persisted during the earliest Piacenzian (ca. 3.6–3.47 Ma) with diverse cool temperate nemoral to boreonemoral forests growing in the lowlands of the Scandinavian mountains. A distinct cooling event at ca. 3.47 Ma resulted in a southward shift of vegetation boundaries, leading to the predominance of boreal forest and the development of open, low alpine environments. The cooling culminated around 3.3 Ma, coinciding with Marine Oxygen Isotope Stage (MIS) M2. Warmer climate conditions returned after ca. 3.29 Ma with higher climate variability indicated by the repeated expansion of forests and peat lands during warmer and cooler periods, respectively. Climate progressively cooled after 3.18 Ma, resembling climatic conditions during MIS M2. A high variability of Norwegian vegetation and climate changes during the Piacenzian is superimposed on a long-term cooling trend. This cooling was accompanied by an expansion of Sphagnum peat lands that potentially contributed to the decline in atmospheric CO2-concentrations at the end of the Piacenzian warm period and facilitated ice growth through positive vegetation-snow albedo feedbacks. Correlations with other Northern Hemisphere vegetation records suggest hemisphere-wide effects of climate cooling.

Mid‐Piacenzian Variability of Nordic Seas Surface Circulation Linked to Terrestrial Climatic Change in Norway

“…The warming in the Norwegian Sea coincides with a distinct increase in the proportions of thermophilous conifer taxa, such as Sciadopitys and Tsuga, from 12 to 42% between 3.283 and 3.281 Ma (Figure 3). This is indicative of the establishment of diverse, cool temperate mixed forests, and warmer-than-present climatic conditions in northern Norway (Panitz et al, 2016). With the warming being most pronounced in the SST record from Hole 642B and vegetation changes in northern Norway (Bachem et al, 2017;Panitz et al, 2016), it is likely a response to increased obliquity forcing, which strengthened the seasonal contrast and led to warm summers (e.g., Haug et al, 2001).…”

“…Marine [this study] and terrestrial (Panitz et al, 2016) palynomorphs were studied in the same samples, with both records having a temporal resolution of 1,000 to 14,000 years. Alkenone-derived SSTs from Hole 642B have been estimated in 87 samples between 3.138 and 3.330 Ma (Bachem et al, 2016(Bachem et al, , 2017.…”

“…A proto-AF was present between Sites 642 and 907 as indicated by a gradient of~6-10°C (Figure 3). The predominance of Pinus pollen and Sphagnum spores in the pollen assemblages of Hole 642B suggests the prevalence of boreal forests and an extensive distribution of peatlands under subarctic, near-modern climatic conditions in northern Norway (Figure 3) (Panitz et al, 2016). Terrestrial climatic conditions might have been cold enough for the establishment of mountain glaciers despite the lower-than-present height of the Scandinavian mountains (Anell et al, 2009;Knies, Mattingsdal, et al, 2014;Panitz et al, 2016).…”

“…Paleoceanography 10.1002/2017PA003166 reestablishment of an active, modern-like NAC corresponds to the onset of mid-Piacenzian warm conditions (De Schepper et al, 2013). In northern Norway, the continuous presence of cool temperate and boreal forests on land indicates that mid-Piacenzian climate was too warm for the persistence of sea-terminating glaciers, even during MIS M2 (Panitz et al, 2016). It remains unclear whether the Scandinavian terrestrial realm and Nordic Seas SST changes are linked to variations in the inflow of Atlantic water into the Norwegian Sea or can merely be explained by orbitally forced insolation changes.…”

“…Here we integrate a new high-resolution dinoflagellate cyst record from ODP Hole 642B in the Norwegian Sea with pollen (Panitz et al, 2016), alkenone-derived SSTs, and ice rafted debris (IRD) records from the same site (Bachem et al, 2017) over a~180 kyrs time interval (3.320-3.137 Ma). This multiproxy approach allows us to document surface water mass changes in the Norwegian Sea throughout the mid-Piacenzian and investigate land-ocean interactions, as well as oceanographic and atmospheric forcings.…”