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Variability of the North Atlantic Oscillation and the Tropical Atlantic dominate the climate of the North Atlantic sector, the underlying ocean and surrounding continents on interannual to decadal time scales. Here we review these phenomena, their climatic impacts and our present state of understanding of their underlying cause. Copyright

Updating an earlier account by Dickson et al., (1990), this paper reviews the initial development phase of North Atlantic Deep Water (NADW) production from the points where the dense inflows from Nordic seas cross the Greenland-Scotland Ridge to the point off south Greenland where the buildup of new production appears almost complete. In particular, three long-term current meter arrays totaling 91 instruments and set at • 160 km intervals south from the Denmark Strait sill are used to validate earlier short-term arrays by others and, in combination with these earlier arrays, to describe the downstream evolution of mean speed, depth and entrainment, the variability of the overflow current in space and time, and the likely contribution of the other three main constituents of NADW production at densities greater than tr0 = 27.8. From the points of overflow (5.6 Sv) the transport within this range increases by entrainment and confluence with other contributory streams to around 13.3 Sv at Cape Farewell. While recirculating elements prevent us from determining the net southgoing transport, a NADW transport of this order appears consistent with recent estimates of net abyssal flow passing south through the North and South Atlantic. Antarctica during austral winter [Warren, 1981] but principally formed (-80%) in the Weddell Sea [Foldvik and Gammelsrod, 1988]. On the millennial timescales which describe the glacial/ postglacial signal the teaC13 record in benthic forams from Southern Ocean sediments is interpreted as showing radical and rapid change in the production and flux of NADW in the abyssal circulation [Charles and Fairbanks, 1992]. Our knowledge of its present-day production, however, remains poor. This paper is intended to update an earlier report by Dickson et al. [1990] by describing the renewal, variability (where known), and pathways of the four main constituents of NADW through the northern North Atlantic. The primary aim, however, is to provide a more detailed description than currently exists for the Denmark Strait Overflow component using a large body of new and direct observational evidence. As Broecker and Peng [1982, p. 317] point out, a more realistic quantitative representation of the ventilation of the deep sea "remains one of the major unsolved problems in oceanography." The most famous papers of a series describing schemes for deep ventilation and exchange in the northern gyre are those by Worthington [1970, 1976] and McCartney and Talley [1984]. Although these schemes (Figures la-lc) derive more or less the same value for the transport of the Deep Western Boundary Current (DWBC) where it passes south through 50øN (10 Sv in both of Worthington's [1970, 1976] schemes and 11.1 Sv in one case described by McCartney and Talley [1984]; 1 Sv = 106 m 3 s-l), these numbers are in fact based on completely different sets of assumptions, suggesting that the available range of conjecture is too wide to be useful. For example, although Worthington's [1970, 1976] schemes both imply a 10 Sv DWBC passing throug...

The climatically sensitive zone of the Arctic Ocean lies squarely within the domain of the North Atlantic oscillation (NAO), one of the most robust recurrent modes of atmospheric behavior. However, the specific response of the Arctic to annual and longer-period changes in the NAO is not well understood. Here that response is investigated using a wide range of datasets, but concentrating on the winter season when the forcing is maximal and on the postwar period, which includes the most comprehensive instrumental record. This period also contains the largest recorded low-frequency change in NAO activity-from its most persistent and extreme low index phase in the 1960s to its most persistent and extreme high index phase in the late 1980s/early 1990s. This longperiod shift between contrasting NAO extrema was accompanied, among other changes, by an intensifying storm track through the Nordic Seas, a radical increase in the atmospheric moisture flux convergence and winter precipitation in this sector, an increase in the amount and temperature of the Atlantic water inflow to the Arctic Ocean via both inflow branches (Barents Sea Throughflow and West Spitsbergen Current), a decrease in the late-winter extent of sea ice throughout the European subarctic, and (temporarily at least) an increase in the annual volume flux of ice from the Fram Strait.

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