Exotic pollen as an indicator of variable atmospheric circulation over the Labrador Sea region during the mid to late Holocene

Abstract

Variability in the abundance of exotic (non-native) pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation, but the difficulty of gaining sufficient total exotic pollen and the incomplete understanding of atmospheric pollen transport patterns has hindered its application. In light of recent advances in the study of pollen transport, we present an exotic pollen record from two fjord sediment cores taken from the west (Placentia Bay, Newfoundland) and east (Narsaq Sund, Greenland) Labrador Sea as a basis for studying variations in regional atmospheric circulation. The two cores cover the last ca. 5500 years and indicate a shift in dominant spring/summer air masses at ca. 2000 (southern Greenland) and 3000 cal a BP (Newfoundland) transporting reduced concentrations of pollen from southerly and south-westerly vegetation zones. This may suggest a shift away from more dominantly zonal atmospheric circulation (a feature of positive North Atlantic Oscillation years) to more frequent meridional circulation. These results support sea ice/sea-surface temperature proxy reconstructions from Newfoundland, investigated as part of the same project, which also suggest increased winter atmospheric circulation during the early part of the time period studied. In this region, more positive North Atlantic Oscillation years, and therefore more zonal atmospheric circulation, are associated with increased atmospheric circulation in both the winter and the summer seasons.

Holocene cooling culminates in sea ice oscillations in Fram Strait

“…Reduced Siberian river discharge during the past 2000 years BP and vegetation changes in northeast European Russia, for example, are interpreted to reflect the development of a colder and dryer climate in the Eurasian Arctic and could be related to negative NAO-like conditions (Stein et al, 2004;Salonen et al, 2011). And also Jessen et al (2011) relate changes in Late Holocene pollen records from southern Greenland and the Labrador Sea to a distinct reduction of south-westerly air masses in favour of colder air originating from the north and thus conclude that the atmospheric circulation pattern in the subpolar North Atlantic likely shifted from a more positive to a more negative NAO. Sicre et al (2008) attribute short-term SST changes off North Iceland during the Late Holocene to low frequency NAO forcing that partly seems to be associated with fluctuations in the meridional overturning circulation (Latif et al, 2006) and thus (large-sale) alterations in the Atlantic hydrological cycle.…”

A 250-year periodicity in Southern Hemisphere westerly winds over the last 2600 years

“…pollen, charcoal) but not so close that the influx is constant over time. Whilst numerous studies have been undertaken in the Arctic (Fredskild, 1984;Jessen et al, 2011) and the high latitudes of the Indian and Pacific oceans (McGlone et al, 2000;Scott and van Zinderen Barker, 1985), few have been reported from the South Atlantic. Recent work on a lake core taken from Annekov Island, South Georgia (Strother et al, 2015) demonstrates the considerable potential of this approach but the relatively large distance from the nearest source in South America ( Fig.…”

The biogeographical status of Alnus crispa (Ait.) Pursch in sub-Arctic southern Greenland: Do pollen records indicate local populations during the past 1500 years?

“…These data therefore suggest that there was potentially an increased availability of Alnus pollen for long-distance transport to southern Greenland during this period. Indeed, a fjord sediment core from southern Greenland does record increased Alnus pollen percentages at this time (Jessen et al 2011). Although these data are far from conclusive, they do hint at the possibility of scattered populations of alder in the Vatnahverfi region.…”

“…Nevertheless, it may relate to the increased exposure of the more southerly sites to the westerly track of air masses across the North Atlantic. These air masses, arriving from eastern North America, are responsible for the majority of the precipitation experienced in southern Greenland (Chen et al 1997;Jessen et al 2011) and would have ample opportunity to become enriched in Alnus pollen (e.g. Rousseau et al 2005).…”

“…) to attribute all Alnus pollen in his diagrams from lakes around Kap Farvel and Qassiarsuk to extra-regional sources (sensu Jannsen 1973), arriving on the prevailing westerly and south-westerly winds from Labrador and adjacent parts of Canada, something which is evident in more recent data (e.g. Rousseau et al 2005Rousseau et al , 2008Jessen et al 2011).…”