Understanding the internal ocean variability and its influence on climate is imperative for society. A key aspect concerns the enigmatic Atlantic Multidecadal Oscillation (AMO), a feature defined by a 60- to 90-year variability in North Atlantic sea-surface temperatures. The nature and origin of the AMO is uncertain, and it remains unknown whether it represents a persistent periodic driver in the climate system, or merely a transient feature. Here, we show that distinct, ∼55- to 70-year oscillations characterized the North Atlantic ocean-atmosphere variability over the past 8,000 years. We test and reject the hypothesis that this climate oscillation was directly forced by periodic changes in solar activity. We therefore conjecture that a quasi-persistent ∼55- to 70-year AMO, linked to internal ocean-atmosphere variability, existed during large parts of the Holocene. Our analyses further suggest that the coupling from the AMO to regional climate conditions was modulated by orbitally induced shifts in large-scale ocean-atmosphere circulation.

No abstract

The forcings behind the rapid increase in mass loss from the Greenland Ice Sheet in the early 2000s (ref. 1) are still debated. It is unclear whether the mass loss will continue in the near future and, if so, at what rate. These uncertainties are a consequence of our limited understanding of mechanisms regulating ice-sheet variability and the response of fast-flowing outlet glaciers to climate variability. In southeast Greenland, Helheim Glacier, one of the regions largest glaciers, thinned, accelerated and retreated during the period 2003-2005 (ref. 4) and although it has since slowed down and readvanced 9 , it has still not returned to its pre-acceleration flow rates. It has been suggested that warming 8,10 and/or inflow variability 11,12 of the nearby subsurface ocean currents triggered the acceleration, but to establish a causal relationship between glacier and climate variability, long-term records are needed. Here we present three high-resolution (1-3 years per sample) sedimentary records from Sermilik Fjord ( Fig. 1 and Supplementary Information) that capture the 2001-2005 episode of mass loss, and use them to reconstruct the calving variability of Helheim Glacier over the past 120 years. Next, this record is compared with records of climate indices.

No abstract

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.