ALBERT

Description: A multiproxy record including benthic foraminifera, diatoms and XRF data of a marine sediment core from a SW Greenland fjord provides a detailed reconstruction of the oceanographic and climatic variations of the region during the last 4400 cal. years. The lower part of our record represents the final termination of the Holocene Thermal Maximum. After the onset of the `Neoglaciation' at approximately 3.2 ka cal. BP, the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the Labrador Sea and the North Atlantic region. Our data show that increased advection of Atlantic water (Irminger Sea Water) from the West Greenland Current into the Labrador Sea was a typical feature of Northeast Atlantic cooling episodes such as the `Little Ice Age' and the `European Dark Ages', while the advection of Irminger Sea Water decreased significantly during warm episodes such as the `Mediaeval Warm Period' and the `Roman Warm Period'. Whereas the `Mediaeval Warm Period' was characterized by relatively cool climate as suggested by low meltwater production, the preceding `Dark Ages' display higher meltwater runoff and consequently warmer climate. When compared with European climate, these regional climate anomalies indicate persisting patterns of advection of colder, respectively warmer air masses in the study region during these periods and thus a long-term seesaw climate pattern between West Greenland and Europe.

Description: Benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in Placentia Bay, SE Newfoundland, are used to construct an ~13,000-year-long record of regional oceanographic changes in the SW Labrador Sea. The area is located in the boundary zone between the cold, ice-loaded Labrador Current (LC) in the north and the warm Gulf Stream (GS) waters to the south. After the Younger Dryas termination, the influence of GS-derived water increased and was further strengthened at 10.7 cal. kyr BP through enhanced northward flow of Atlantic water via the Slopewater Current. A short-term event of increased terrestrial input and water column stratification at 8.4 cal. kyr BP was likely linked to the distal drainage of glacial Lake Agassiz. After 7.3 cal. kyr BP, a stronger LC weakened the inflow of warmer subsurface waters from the GS. This may be explained by extensive meltwater release from ice sheets in Arctic Canada and is concurrent with a general shift in oceanographic conditions in the Labrador Sea region. Around 4.0 cal. kyr BP, conditions became more stable with a slight increase in salinity, indicating a decrease in meltwater transported via the LC. The Northern Hemisphere neoglacial cooling around 2.8 cal. kyr BP was characterized off SE Newfoundland by a further stabilization of the current system, dominated by the LC with some continued influx of GS water.

Description: A marine sediment core from Vaigat in Disko Bugt, West Greenland, has been analysed in terms of lithology, dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on West Greenland glacier stability. The data show that during the past 5200 years the Atlantic foraminiferal abundance in the subsurface waters of the West Greenland Current (WGC) episodically increased, indicating periods of increases in the inflow of subsurface warm Atlantic water at 2000—1500 cal. yr BP and 1300 cal. yr BP as well as periods of less pronounced increased bottom-water temperatures around 4700—4000 cal. yr BP, 3100—2800, 2600, 1000—800, 500—400, and at 200 cal. yr. The sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of Irminger Sea-derived waters are accompanied by increased iceberg rafting, which we link to increased iceberg calving in relation to destabilization of the Jakobshavn Isbrae. The long-term trend in the data documents the end of a late-Holocene Thermal Maximum between 5200 and 4300 cal. yr BP and a final onset of the Neoglaciation at 3500 cal. yr BP. Increased responses of the iceberg rafting after 3500 cal. yr BP, reflects a westward/seaward advance of the glacier margin in relation to onset of Neoglaciation and a development of the glacier into a floating tongue after 2000 cal. yr BP. A comparison of our record with a record from the eastern North Atlantic indicates that a NAO-like anomaly pattern between subsurface waters in West Greenland and atmospheric temperature in the Eastern North Atlantic may have been operating during most of the late Holocene. However, during the past 1000 years the NAO signal may have weakened as some other mode of climate variability overprints the anti-phase climate signal in this region.

Description: Several studies indicate that changes in solar activity may have driven Holocene subtropical monsoon variability on decadal and centennial timescales, but the strength and nature of this link remains debated. In this study, we combine a recent mapping of the Holocene solar-cycle activity with four subtropical speleothem 18 O records, which allows a strong test of the link between solar activity, monsoon activity (or intensity), and the hydrological cycle. This is possible because the speleothem 18 O records mainly reflect changes in local rainfall composition, which is controlled by changes in total moisture loss along the atmospheric transport path and monsoon intensity. We find that the spectral density distributions of the speleothem records exhibit particularly significant ~210 yr cyclicities that tend to coincide in time with the three Suess solar-cycle bursts, i.e. intervals around 1850–3200 BP, 4500–5700 BP, and 7750–8850 BP when the ~210 yr solar cycle was particularly strong. The speleothems from Dongge Cave (China) and Sofular Cave (Turkey) appear to have recorded all three Suess bursts, whereas the speleothems from Heshang Cave (China) and Pink Panther Cave (southwestern USA) only recorded the first and last Suess bursts, and the middle Suess burst, respectively. The temporal relationship between the Suess solar cycle and particularly significant 210 yr oscillations in the speleothem 18 O records therefore supports the notion that solar variability played a significant role in driving centennial-scale changes in the hydrological cycle in the subtropics during the Holocene.

Description: Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south (Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador Sea region during the last 5700 years. Fresh and cold conditions, probably accompanied by seasonal sea ice, prevailed both north and south of Newfoundland from c . 5.7 to 4.0 cal. kyr BP. This may be linked to intensified Labrador Current export of cold meltwater and/or sea ice from the Arctic, presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong (north)westerly winds. After c . 4.0 cal. kyr BP, sea-surface conditions warmed up and sea ice decreased northeast of Newfoundland, but conditions were still cold south of Newfoundland. This suggests a decrease in Arctic meltwater export and westerly wind strength. After 2.9—2.5 cal. kyr BP, only minor changes in sea-surface conditions affected the study sites. Sea-surface temperatures increased and sea ice decreased at both sites, which may be related to a more meridional atmospheric circulation pattern associated with the general Northern Hemisphere neoglacial cooling. In Placentia Bay the warmest part of the record corresponds to the Roman Warm Period, while the warmest part of the records in Bonavista Bay notably corresponds to the Dark Ages.

Description: The freshwater runoff from the glaciated and snow-covered Sermilik Fjord catchment, SE Greenland, was estimated at annual resolution for the period 1900–2008 and at decadal resolution for the past four millennia. Our simulations were forced with available meteorological station data (1900–2008) and Greenland ice core estimated temperature data (1899 bc – ad 1980) from Dye3 and GISP2. Time series of estimated ice discharge (2000–2009) for the three major outlet glaciers Helheim, Fenris, and Midgård indicate that 53–74% of the ice discharge variations could be explained by variations in areally averaged glacier terminus surface (supraglacial) runoff. Based on these data and together with calculated subglacial geothermal and frictional melting as well as net precipitation for the fjord area, the Sermilik Fjord freshwater flux was deduced for the period 1900–2008. Our simulations indicated that during the last century surface freshwater runoff has equaled 13% of the Sermilik Fjord average freshwater flux of 33.0±5.7 x 10 9 m 3 /yr, covering a periodic runoff variation of 20 years. Ice discharge has accounted for 81%, with 63% of the freshwater flux originated from the Helheim glacier. This indicates that the Helheim outlet glacier plays a dominant role as a freshwater source to both Sermilik Fjord and ultimately the Irminger Sea. For the palaeorecords of the last 4000 years, simulated surface runoff has averaged 4.4±0.2 x 10 9 m 3 /yr. A very weak decreasing trend in runoff over the last 4 k years (1899 bc – ad 1980) is presumably associated with the general insolation-generated Northern Hemisphere cooling since the Holocene Thermal Maximum. Our simulations furthermore indicated centennial- to submillennial-scale variations in surface runoff concurrent with the well-known climate episodes such as the ‘Roman Warm Period’, the ‘Dark Ages Cold Period’, the ‘Medieval Climate Anomaly’, and the ‘Little Ice Age’. During the ‘Little Ice Age’, e.g., the average surface runoff was about 0.7 x 10 9 m 3 /yr lower than today, while the increase in runoff for the Modern Warming, since the late 1800s, was the second strongest and fastest for the last 4 k years.

Description: A reconstruction of oceanographic variability of the past 5800 years on the southeast Greenland shelf was obtained by analysing a combined marine sediment record based on two cores from the same site. Cores Fox04G/05R were retrieved from a side basin to a cross-shelf trough connecting the 900 m deep Sermilik Fjord with the Irminger Sea in the northwestern North Atlantic. The record was analysed in terms of grain size distribution, XRF and benthic and planktonic foraminiferal content and the chronology was obtained on the basis of 210 Pb and 14 C dating. The late-Holocene paleoceanographic variations in the record were characterised by a marked influence from the Irminger Current (IC) at the onset of the record at 5800 cal. yr BP and the regional Holocene Climatic Optimum between 5200 and 4200 cal. yr BP. After 3600 cal. yr BP Neoglacial cooling with increased influence of polar waters from the East Greenland Current (EGC) diminished the influence from the IC. Between 1500 and 700 cal. yr BP, the environment was highly dominated by cold low-salinity water masses characterised by sea ice forming locally and/or transported with an intensified EGC. At 700 cal. yr BP, concordant with the onset of the ‘Little Ice Age’, inflow of IC water masses intensified, notably during short-lived warming episodes of the North Atlantic Current most likely related to a contracted subpolar gyre. At the same time, the EGC polar water transport also intensified leading to a stratified water column on the shelf and this may have favoured entrainment of warm subsurface IC waters. Alternatively, the relatively warm rim of the eastern subpolar gyre may have promoted intense submarine melting of extended Southeast Greenland outlet glaciers at this time, producing enhanced meltwater outflow which favoured estuarine circulation processes maintaining the inflow of IC water masses.

Description: Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales.