Where significant, the relationship between mean temperatures of successive months in the United States, based on 60–80 years of data, was found to be generally of a persistent nature. Maximum persistence occurs in mid-nation in summer with secondary maxima found in the West from April to May and in the East from December to January. The geographical distribution of persistence allows tentative identification of large-scale components of the atmospheric circulation associated with persistence throughout the year. Persistence distribution, further-more, is found to be generally compatible with current theories suggesting that persistence is of local origin arising from the anomalous thermal state of the earth's surface. It is found that month-to-month temperature persistence is essentially independent of long-term temperature trends and of relationships between the temperatures of a given month in adjacent years. However, regions of month-to-month persistence are found to correspond broadly to are...

As the world warms, the expectation is that the freshwater outflows from the Arctic Ocean to the North Atlantic will strengthen and may act to suppress the rate of the climatically-important Atlantic meridional overturning circulation. Hitherto, however, we have lacked the system of measurements required to estimate the totality of the freshwater flux through subarctic seas. Though observations remain patchy and rudimentary in places, we piece-together the results from recent large-scale observational programmes together with associated modelling, to establish preliminary maps of the rates and pathways of freshwater flux through subarctic seas. These fluxes are calculated according to two reference salinities, S=34.8 to conform with the majority of estimates reported in the literature, and S=35.2, the salinity of the inflowing Atlantic water, to calculate the freshwater balance of the ‘Arctic Mediterranean’. We find that 148mSv of freshwater enters the Nordic Seas across its northern boundary. There it is supplemented by around 54mSv of freshwater from Baltic runoff, Norwegian runoff, P−E and Greenland ice melt, so that the total freshwater contribution to the Nordic Seas from all sources is 202mSv. Of this, around 51mSv of freshwater is estimated to pass south to the deep Atlantic in the dense water overflows leaving an assumed balance of 151mSv to leave the Nordic Seas in the upper water export through Denmark Strait. The corresponding estimate for the freshwater outflow west of Greenland is 103mSv relative to 35.2 so that the total freshwater flux reaching the North Atlantic through subarctic seas is around 300mSv.

Three interrelated climate phenomena are at the center of the Climate Variability and Predictability (CLIVAR) Atlantic research: tropical Atlantic variability (TAV), the North Atlantic Oscillation (NAO), and the Atlantic meridional overturning circulation (MOC). These phenomena produce a myriad of impacts on society and the environment on seasonal, interannual, and longer time scales through variability manifest as coherent fluctuations in ocean and land temperature, rainfall, and extreme events. Improved understanding of this variability is essential for assessing the likely range of future climate fluctuations and the extent to which they may be predictable, as well as understanding the potential impact of human-induced climate change. CLIVAR is addressing these issues through prioritized and integrated plans for short-term and sustained observations, basin-scale reanalysis, and modeling and theoretical investigations of the coupled Atlantic climate system and its links to remote regions. In this paper, a brief review of the state of understanding of Atlantic climate variability and achievements to date is provided. Considerable discussion is given to future challenges related to building and sustaining observing systems, developing synthesis strategies to support understanding and attribution of observed change, understanding sources of predictability, and developing prediction systems in order to meet the scientific objectives of the CLIVAR Atlantic program.

Abstract This chapter provides a broad review of the North Atlantic Oscillation (NAO) and its forcing of the North Atlantic Ocean. Of particular interest is the long, irregular amplification of the oscillation towards one extreme phase during winter over recent decades. This climatic event, which is unprecedented in the modern instrumental record of NAO behaviour, has produced a wide range of effects on North Atlantic ecosystems. Some attention will also be given to the climatic impacts of periods of atypical NAO behaviour, such as the spatial displacement of the main centres of action in some winters, or to periods when other patterns of large-scale Atlantic climate variability are more pronounced.

The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton.The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research. (C) 2003 Elsevier Ltd. All rights reserved.

The Ocean's Response to North Atlantic Oscillation Variability Martin Visbeck, Martin Visbeck Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, U.S.A.Search for more papers by this authorEric P. Chassignet, Eric P. Chassignet RSMAS/MPO, University of Miami, Miami, Florida, U.S.A.Search for more papers by this authorRuth G. Curry, Ruth G. Curry Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, U.S.A.Search for more papers by this authorThomas L. Delworth, Thomas L. Delworth Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, New Jersey, U.S.A.Search for more papers by this authorRobert R. Dickson, Robert R. Dickson Center for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, United KingdomSearch for more papers by this authorGerd Krahmann, Gerd Krahmann Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, U.S.A.Search for more papers by this author Martin Visbeck, Martin Visbeck Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, U.S.A.Search for more papers by this authorEric P. Chassignet, Eric P. Chassignet RSMAS/MPO, University of Miami, Miami, Florida, U.S.A.Search for more papers by this authorRuth G. Curry, Ruth G. Curry Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, U.S.A.Search for more papers by this authorThomas L. Delworth, Thomas L. Delworth Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, New Jersey, U.S.A.Search for more papers by this authorRobert R. Dickson, Robert R. Dickson Center for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, United KingdomSearch for more papers by this authorGerd Krahmann, Gerd Krahmann Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, U.S.A.Search for more papers by this author Book Editor(s):James W. Hurrell, James W. HurrellSearch for more papers by this authorYochanan Kushnir, Yochanan KushnirSearch for more papers by this authorGeir Ottersen, Geir OttersenSearch for more papers by this authorMartin Visbeck, Martin VisbeckSearch for more papers by this author First published: 01 January 2003 https://doi.org/10.1029/134GM06Citations: 195Book Series:Geophysical Monograph Series AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Observed SST Response Pattern Air-Sea Flux Response of the Ocean Circulation Advection of Anomalies By Mean Ocean Currents Changes in Water Masses The Sea-Ice Response Summary and Discussion Citing Literature The North Atlantic Oscillation: Climatic Significance and Environmental Impact, Volume 134 RelatedInformation

Europe's relative warmth is maintained by the poleward surface branch of the Atlantic Ocean thermohaline circulation. There is paleoceanographic evidence for significant variability and even shifts between different modes of thermohaline circulation. Coupled ocean-atmosphere climate modelling allows first insight into the relative role of the various drivers of the Atlantic thermohaline circulation variability, i.e. the North Atlantic Oscillation, the tropical Atlantic variability, the ocean basin exchanges, small scale processes like high-latitude convection, overflows and mixing as well as effects of changes in the hydrological circle, the atmospheric CO2-content and solar radiation. The strong need for continous model improvement requires concerted efforts in ocean time series observations and relevant process studies. New instrumentation and methods, both for in situ measurements and remote satellite sensing are becoming available to help on the way forward towards as improved understanding of North Atlantic climate varibility.

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 © 2001 Royal Meteorological Society

The match-mismatch hypothesis. which relates timing of plankton production to recruitment of fish, is difficult to test for a number of reasons. not least of which is lack of adequately resolved spatial and seasonal data for matching information on fish larvae and their food. Spatial, seasonal, and interannual variability of water-column stratification. primary production. and copepod egg production can be modelled. but do such models adequately represent features of interannual variability that affect survival of fish larvae? Information on the timing and location of cod larvae in the Irish Sea and at Iceland is used to identify target areas for which long-term hindcasts of plankton production are made using a one-dimensional model of water-column stratification and production of chlorophyll and copepod eggs, driven by hourly meteorological data. Hindcast spring chlorophyll and nitrate values for Faxa Bay (Iceland) in 1966 correspond well with observations. Hindcast interannual variability in Calanus egg production appears to have a significant effect on cod recruitment in the Irish Sea and at Iceland. While the conclusions from such a limited study must be tentative, they suggest that local meteorological forcing, in areas where cod larvae occur, exerts an effect on their survival, owing to the match between plankton production and larval feeding.

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 loa index phase in the 1960s to its most persistent and extreme high index phase in the late 1980s/early 1990s. This long-period 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 hom the Fram Strait.

A mass mortality of `warm‐water' tilefish in the Middle Atlantic Bight between April and August of 1882 suggests an episode of extreme cold in the shelf waters off the north‐eastern United States. This cooling is hypothesized to be a consequence of enhanced equatorwards transport of cold water in the Labrador Current, coincident with a minimum in the North Atlantic Oscillation (NAO) index during the early 1880s.Although there is little direct evidence for this historical event, an analogue for the 1880s cooling is found in the 1960s, at the most recent NAO‐index minimum. Post‐1945 observations in the Middle Atlantic Bight / Gulf of Maine region reveal changes in winter baroclinic circulation between cool and warm decades, with greater equatorward penetration of south‐westwards flow along the shelf‐edge during the cool 1960s. Over the period 1934–77, the NAO is found to account for 17% of the interannual variance in Labrador Current transport around the Grand Banks.Proxy evidence for the cold episode of the early 1880s is sought. Records of bottom temperature in the Middle Atlantic Bight region are reconstructed using stable oxygen isotopic analysis on the annual bands of shells of a bivalve mollusc (Arctica islandica) and an empirical model of covariability with local air temperature. The result is confirmation of the presence of anomalously cold water during the early 1880s.

Hydrographic, current meter and ADCP data collected during two recent cruises in the South Indian Ocean (RRS Discovery cruise 200 in February 1993 and RRS Discovery cruise 207 in February 1994) are used to investigate the current structure within the Princess Elizabeth Trough (PET), near the Antarctic continent at 85°E, 63–66°S. This gap in topography between the Kerguelen Plateau and the Antarctic continent, with sill depth 3750m, provides a route for the exchange of Antarctic Bottom Water between the Australian–Antarctic Basin and the Weddell–Enderby Basin. Shears derived from ADCP and hydrographic data are used to deduce the barotropic component of the velocity field, and thus the volume transports of the water masses. Both the Southern Antarctic Circumpolar Current Front (SACCF) and the Southern Boundary of the Antarctic Circumpolar Current (SB) pass through the northern PET (latitudes 63 to 64.5°S) associated with eastward transports. These are deep-reaching fronts with associated bottom velocities of several cm s-1. Antarctic Bottom water (AABW) from the Weddell–Enderby Basin is transported eastwards in the jets associated with these fronts. The transport of water with potential temperatures less than 0°C is 3 (±1) Sv. The SB is shown to meander in the PET, caused by the cyclonic gyre immediately west of the PET in Prydz Bay. The AABW therefore also meanders before continuing eastwards. In the southern PET (latitudes 64.5 to 66°S) a bottom intensified flow of AABW is observed flowing west. This AABW has most likely formed not far from the PET, along the Antarctic continental shelf and slope to the east. Current meters show that speeds in this flow have an annual scalar mean of 10cms-1. The transport of water with potential temperatures less than 0°C is 20 (±3) Sv. The southern PET features westward flow throughout the water column, since the shallower depths are dominated by the flow associated with the Antarctic Slope Front. Including the westward flow of bottom water, the total westward transport of the whole water column in the southern PET is 45 (±6) Sv.

Observations of chlorofluorocarbons (CFCs), carbon tetrachloride, temperature, and salinity from five sections following the outflow path of Antarctic Bottom Water (AABW) into the southwest Indian Ocean are reported. The transient tracer data clearly show the plume of recently ventilated water whose hydrographic properties are progressively altered by mixing with the overlying waters. We use the CFC measurements to estimate the mean speeds (or transit times) and mixing rates (or dilutions) of the abyssal flow at each section using simple kinematic circulation models. Given our assumptions, the CFC ventilation age equals the transit time. The results suggest a transit time of 23 +/- 5 years (outflow speed of 1.2 +/- 0.3 cm s(-1)) to the Crozet-Kerguelen Gap with a dilution of 8-15 from the surface waters of the Weddell Sea. The estimated horizontal diffusivity is 30-70 m(2) s(-1), and the vertical diffusivity is 3-7 x 10(-4) m(2) s(-1). Combined with the estimate of R. R. Dickson (unpublished data, 1998) for the AABW transport at this point, we conclude that a volume flux of 0.8-1.6 Sv (10(6) m(3) s(-1)) is leaving the continental shelves of the Weddell Sea to eventually enter the abyssal Indian Ocean past Crozet Island.

The North Atlantic is a peculiarly convective ocean. The convective renewal of intermediate and deep waters in the Labrador Sea and Greenland/Iceland Sea both contribute significantly to the production and export of North Atlantic Deep Water, thus helping to drive the global thermohaline circulation, while the formation and spreading of 18-Degree Water at shallow-to-intermediate depths off the US eastern seaboard is a major element in the circulation and hydrographic character of the west Atlantic. For as long as time-series of adequate precision have been available to us, it has been apparent that the intensity of convection at each of these sites, and the hydrographic character of their products have been subject to major interannual change, as shown by Aagaard (1968), Clarke, Swift, Reid and Koltermann (1990), and Meincke, Jonsson and Swift (1992) for the Greenland Sea, in the OWS BRAVO record from the Labrador Sea, (egLazier, 1980 et seq.), and at the Panulirus / Hydrostation "S" site in the Northern Sargasso off Bermuda (eg Jenkins, 1982, Talley and Raymer, 1982). This paper reviews the recent history of these changes showing that the major convective centres of the Greenland and Labrador Seas are currently at opposite convective extrema in our postwar record, with vertical exchange at the former site limited to 1000 m or so, but with Labrador Sea convection reaching deeper than previously observed, to over 2300 m. As a result, the deep water of the Greenland Sea has become progressively warmer and more saline since the early '70s as a result of increased horizontal exchange with the Arctic Ocean through Fram Strait, while the Labrador Sea Water has become progressively colder and fresher over the same period through increased vertical exchange; most recently, convection has become deep enough there to reach into the more saline NADW which underlies it, so that cooler, but now saltier and denser LSW has resulted. The horizontal spreading of these changing watermasses in the northern gyre is described from the hydrographic record. The theory is advanced that the scales of atmospheric forcing have imposed a degree of synchrony on convective behaviour at all three sites over the present century, with ventilation at the Sargasso and Greenland Sea sites undergoing a parallel multi-decadal evolution to reach a long term maximum in the 1960s, driven by the twin cells of the North Atlantic Oscillation (NAO). During the NAO minimum of the 1960s, with an extreme Greenland ridge feeding record amounts of fresh water into the northern gyre in the form of the Great Salinity Anomaly, and its partner cell over the Southeast USA causing a southwestward retraction of storm activity (Dickson and Namias, 1976), the surface freshening and postwar minimum in storm activity in the intervening area of the Labrador Sea also brought a progressive reduction, and ultimately a cessation, of wintertime convection there during the 1960s. In other words, the evolution of winter convective activity during the century was in phase but of different sign at the three sites. In these events, we see strong evidence of a direct impact of the shifting atmospheric circulation on the ocean; while this certainly does not rule out either feedbacks from anomalous ice and SST conditions on the atmosphere, or autonomous oscillations of the ocean's overturning circulation, it does tend to minimise them.

ABSTRACTThis paper reviews the impacts of climatic change on six North Atlantic cod stocks during the present century – at Iceland, Greenland, Labrador, Faroes, the Barents Sea and the Baltic. Though the relevant changes in each region can all be set in the context of the same slow shifts in the large–scale Atlantic windfield, the mechanism and scale of the response is varied, operating through changes in the interstock exchange of larvae by ocean currents, direct effects of windiness on stratification, direct and indirect effects on environmental temperature and, in the special case of the Baltic, via the effects of westerly wind events on the inflow/ stagnation cycle of the Baltic Deeps. In certain places and times, these climatic influences have constituted the dominant control on the success of a stock.