Radiocarbon ages and diatom abundance in cores GA306-BC4 and GA306-GC4 obtained during Galathea 3 cruise, West Greenland

Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at AD 750-1330, although with some oceanographic variability after AD 1000. A pronounced oceanographic shift occurred at AD 1330, corresponding in time to the transition from the so-called 'Medieval Warm Period' (MWP) to the 'Little Ice Age' (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at AD 1330-1350, AD 1400-1575 and AD 1660-1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations.

Diatom abundance in sediments of ODP Holes 186-1150A and 186-1151C

The diatom flora from two sediment cores recovered from the upper 27 meters below seafloor (mbsf) in the oceanic frontal area off Sanriku, northeast Japan, during Ocean Drilling Program Leg 186 were analyzed. Diatom abundance seems to be in interglacial stages and suggests a south-north shifting of the frontal area. Diatom temperature values are less reliable because frequency of the warm-water species is smaller. Site 1151 was in a warm climate at ~50 ka, as were Deep Sea Drilling Project Sites 579 and 580 in the western North Pacific Ocean. A mixed diatom assemblage in the upper 3 mbsf at Site 1150 is evidence that the Tsugaru Warm Current flowed into the studied area through the Tsugaru Strait.

Pollen abundance in ODP Site 123-765 (Table 1)

Middle Miocene to Holocene pollen assemblages reveal a history of environmental change in northern Australia. Grass pollen appeared, but was rare, in the late Miocene and was consistently present throughout the Pliocene, but did not become abundant until the Pleistocene. Myrtaceae pollen, characteristic of late Cenozoic assemblages in eastern Australia, is poorly represented, and no unequivocal evidence of rain forest was found.

Soil characteristics and Collembola and Acari abundance in control and warming plots at Abisco Research Station

Extreme weather events can have negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (2-10 °C for 2-14 days), but returning to cold winter climate exposes the ecosystem to lower temperatures by the loss of insulating snow. Soil animals, which play an integral part in soil processes, may be very susceptible to such events depending on the intensity of soil warming and low temperatures following these events. We simulated week-long extreme winter warming events - using infrared heating lamps, alone or with soil warming cables - for two consecutive years in a sub-Arctic dwarf shrub heathland. Minimum temperatures were lower and freeze-thaw cycles were 2-11 times more frequent in treatment plots compared with control plots. Following the second event, Acari populations decreased by 39%; primarily driven by declines of Prostigmata (69%) and the Mesostigmatic nymphs (74%). A community-weighted vertical stratification shift occurred from smaller soil dwelling (eu-edaphic) Collembola species dominance to larger litter dwelling (hemi-edaphic) species dominance in the canopy-with-soil warming plots compared with controls. The most susceptible groups to these winter warming events were the smallest individuals (Prostigmata and eu-edaphic Collembola). This was not apparent from abundance data at the Collembola taxon level, indicating that life forms and species traits play a major role in community assembly following extreme events. The observed shift in soil community can cascade down to the micro-flora affecting plant productivity and mineralization rates. Short-term extreme weather events have the potential to shift community composition through trait composition with potentially large consequences for ecosystem development.