ALBERT

Description: Centennial and millennial scale variability of Southern Ocean temperature is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variability instead coming mainly from ice core records. Here we present a high-resolution (~ 60 year) record of diatom abundance from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka BP (calibrated kiloyears before present). The results show the dominant species are Fragilariopsis kerguelensis and Thalassiosira lentiginosa, with accompanying species typical of the Polar Front Zone and Permanent Open Ocean Zone. Species associated with warmer temperatures were most abundant in the period 12-9.5 ka BP, while species associated with lower temperatures were abundant at 14.2-9.5 ka BP.

Description: Centennial and millennial scale variability of Southern Ocean temperature is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variability instead coming mainly from ice core records. Here we present a high-resolution (~ 60 year), diatom-based sea-surface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka BP (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2–12.9 ka BP and gradual warming between 12.9–11.6 ka BP in phase with atmospheric temperature evolution. This supports that the temperature of the Southern Ocean during the deglaciation was linked with a complex combination of processes and drivers associated with reorganisations of atmospheric and oceanic circulation patterns. Specifically, we suggest that Southern Ocean surface warming coincided, within the dating uncertainties, with the reconstructed slowdown of the Atlantic Meridional Overturning Circulation (AMOC), rising atmospheric CO2 levels, changes in the southern westerly winds and enhanced upwelling. During the Holocene the record shows warm and stable temperatures from 11.6–8.7 ka BP followed by a slight cooling and greater variability from 8.7 to 1 ka BP, with a quasi-periodic variability of 200–260 years as identified by spectral analysis. We suggest that the increased variability during the mid to late Holocene may reflect the establishment of centennial variability in SST connected with changes in the high latitude atmospheric circulation and Southern Ocean convection, as identified in models.

Description: Due to the shortness of available records, the longterm patterns of climate variability in the Labrador Sea and Newfoundland region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1-2°C.

Description: Here, we present datasets of diatom abundance and a diatom-based sea surface temperature reconstruction from the Iceland Basin. The 419.5 cm long marine sediment core DA12-11/2-GC01 was recovered in September 2012 by the Danish R/V Dana using a gravity corer. The core was taken from a location at the northern edge of the Gardar Drift and the eastern edge of the Björn Drift in the Iceland Basin (61.36.536 °N, 20.42.164 °W) at a water depth of 2120 m. Diatoms were analysed at 5 cm intervals over the upper 2 m of core, representing the period 6100-0 cal years BP, with chronological constraints provided by 6 radiocarbon dates. Diatoms were analysed using standard procedures, including the identification and counting of a minimum of 300 diatom per sample, which allowed calculation of the percentage abundances of different species. These abundances were converted into estimates of sea surface temperature using the weight averaging partial least squares transfer function approach.

Description: The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more high-resolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0-10.2 kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate.

Description: Holocene oceanographic conditions in Disko Bay, West Greenland were reconstructed from high-resolution diatom records derived from two marine sediment cores. A modern dataset composed of 35 dated surface sediment samples collected along the entire West Greenland coast accompanied by remote sensing data were used to develop a diatom transfer function to reconstruct April Sea Ice Concentration (SIC) supported by July Sea Surface Temperature (SST) in the area. Our quantitative reconstruction shows that oceanographic changes recorded throughout the last c. 11000 years reflect seasonal interplay between spring (April SIC) and summer (July SST) conditions. Our records show clear correlation with climate patterns identified from ice core data from GISP2 and Agassiz-Renland for the early to mid Holocene. The early Holocene deglaciation of western Greenland Ice Sheet was characterised in Disko Bay by initial strong centennial-scale fluctuations in April SIC with amplitude of over 40%, followed by high April SIC and July SST. These conditions correspond to a general warming of the climate in the Northern Hemisphere. A decrease in April SIC and July SST was recorded during the Holocene Thermal Optimum reflecting more stable spring-summer conditions in Disko Bay. During the late Holocene, high April SIC characterised the Medieval Climate Anomaly, while high July SST prevailed during the Little Ice Age, supporting previously identified anti-phase relationship between surface waters in West Greenland and climate in NW Europe. This anti-phase pattern might reflect seasonal variations in regional oceanographic conditions and large-scale fluctuations within the North Atlantic Oscillation and Atlantic Meridional Overturning Circulation.