The 8200 year B.P. event in the slope water system, western subpolar North Atlantic

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA2003, doi:10.1029/2004PA001074.Stable isotope, trace metal, alkenone paleothermometry, and radiocarbon methods have been applied to sediment cores in the western subpolar North Atlantic between Hudson Strait and Cape Hatteras to reveal the history of climate in that region over the past ∼11 kyr. We focus on cores from the Laurentian Fan, which is known to have rapid and continuous accumulation of hemipelagic sediment. Although results among our various proxy data are not always in agreement, the weight of the evidence (alkenone sea surface temperature (SST), δ18O and abundance of Globigerinoides ruber) indicates a continual cooling of surface waters over Laurentian Fan, from about 18°C in the early Holocene to about 8°C today. Alternatively, Mg/Ca data on planktonic foraminifera indicate no systematic change in Holocene SST. The inferred long-term decrease in SST was probably driven by decreasing seasonality of Northern Hemisphere insolation. Two series of proxy data show the gradual cooling was interrupted by a two-step cold pulse that began 8500 years ago, and lasted about 700 years. Although this event is associated with the final deglaciation of Hudson Bay, there is no δ18O minimum anywhere in the Labrador Sea, yet there is some evidence for it as far south as Cape Hatteras. Finally, although the 8200 year B.P. event has been implicated in decreasing North Atlantic ventilation, and hence widespread temperature depression on land and at sea, we find inconsistent evidence for a change at that time in deep ocean nutrient content at ∼4 km water depth.Funding for JPS was from the NOAA Climate and Global Change Program (NA 16GP2679), NSF-Earth System History (0116940), the Jeptha H. and Emily V. Wade Award for Research, and a Henry L. and Grace Doherty Professorship. LDK and YR were funded by NSF grant OCE-0117149

Causes and Consequences of Past and Projected Scandinavian Summer Temperatures, 500–2100 AD

Tree rings dominate millennium-long temperature reconstructions and many records originate from Scandinavia, an area for which the relative roles of external forcing and internal variation on climatic changes are, however, not yet fully understood. Here we compile 1,179 series of maximum latewood density measurements from 25 conifer sites in northern Scandinavia, establish a suite of 36 subset chronologies, and analyse their climate signal. A new reconstruction for the 1483–2006 period correlates at 0.80 with June–August temperatures back to 1860. Summer cooling during the early 17th century and peak warming in the 1930s translate into a decadal amplitude of 2.9°C, which agrees with existing Scandinavian tree-ring proxies. Climate model simulations reveal similar amounts of mid to low frequency variability, suggesting that internal ocean-atmosphere feedbacks likely influenced Scandinavian temperatures more than external forcing. Projected 21st century warming under the SRES A2 scenario would, however, exceed the reconstructed temperature envelope of the past 1,500 years

The constitutional dilemma of European integration

The paper analyzes European integration from a constitutional economics perspective. It is argued that the use of the Prisoners' Dilemma as a description of the advantages of European integration is fallacious. If the situation is a PD, the solution is impossible; if it is not, it is unnecessary

Eight-hundred-year temperature variability from the Norwegian continental margin and the North Atlantic thermohaline circulation

Four cores raised from the eastern Norwegian Sea and adjacent Norwegian fjords at sites influenced by Atlantic water have been investigated. Oxygen isotope analyses in benthic and planktonic foraminifera are used as a proxy for the paleotemperature development spanning the last 800 years. The cores have been dated using a combination of 210Pb and radiocarbon dates yielding time resolutions of 2–5 years for the last century and 9–25 years beyond this. The proxy records have been compared with instrumental time series covering the last 100 years in order to validate the oxygen isotope measurements as a proxy for paleotemperature. The comparison shows that the paleotemperature variability derived from the oxygen isotope analyses is generally similar to the amplitudes and trends seen in the instrumental time series. In particular, a cooling around 1905–1925 followed by a warming until 1955 is evident in all proxy records as well as in the instrumental time series. Beyond the last century the proxy records show two periods from ~1225–1450 and ~1650–1905(25) when temperatures were 1.3–1.6°C lower than present separated by a period of temperatures periodically comparable to present. The last 80 years represent the modern warming and appear to be the warmest period of the last 800 years. We find that that the ocean temperature variability is comparable to terrestrial reconstructions from the region implying a strong link in the ocean-atmosphere climate system. This suggests that the climate variability in this region beyond the period covered by instrumental time series was also associated with changes in the thermohaline circulation

Large ancient organic matter contributions to Arctic marine sediments (Svalbard)

Soils, fine-grained ice-rafted detritus (IRD), coals, and marine surface sediments in the Arctic realm (Svalbard)were collected in 2007 and 2008 to characterize organic matter (OM) sources in Arctic marine sediments. Bulkgeochemical (C : N ratio and stable carbon isotopic composition) parameters suggest a predominant marinecontribution to sedimentary OM. The branched and isoprenoid tetraether index (a proxy of soil OM input)indicates that soil OM contribution to the marine sediments is minor. However, the presence of retene (used as anindicator for coal-derived OM), the low carbon preference index and the average chain length of n-alkanes, andthe depleted bulk radiocarbon content (D14C value) suggest that ancient OM of both coal-derived and matureIRD-derived OM is being buried in the Kongsfjord–Krossfjord system of Svalbard in the high Arctic. Therelatively low retene concentrations in the marine surface sediments other than those in close vicinity of NyA˚lesund, previously a coal-mining town, indicated that input of IRD-derived OM was predominantly responsiblefor the generally low D14C value. We applied three-end-member models based on D14C and retene and n-alkaneconcentration data to disentangle relative coal-derived, IRD-derived, and marine OM proportions to sedimentaryOM. Sediments were comprised on average 2% 6 4% of coal-derived OM, 37% 6 17% of IRD-derived OM, and61% 6 18% of marine OM with higher IRD-derived OM deposit in the Kongsvegen glacier front. Our resultshighlight the important role of ancient OM on carbon dynamics in Arctic environments, in particular for benthicfood webs