The great salinity anomaly in the northern North Atlantic 1968-1982
TL;DR: In this paper, the authors describe the Great Salinity Anomaly as an advective event, traceable around the Atlantic subpolar gyre for over 14 years from its origins north of Iceland in the mid-to-late 1960s until its return to the Greenland Sea in 1981-1982.
About: This article is published in Progress in Oceanography.The article was published on 1988-01-01. It has received 1182 citations till now. The article focuses on the topics: North Atlantic Deep Water & Thermohaline circulation.
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TL;DR: The match/mismatch hypothesis is given in this chapter to cover the subsequent development through larval life up to metamorphosis, and possibly just beyond and the limited conclusion drawn is that, investigations of fish larvae should continue to be a part of the study of population dynamics of fishes.
Abstract: Publisher Summary The degree of match and mismatch in the time of larval production and production of their food has been put forward as an explanation of part of the variability in recruitment to a stock of fish. The magnitude of recruitment is not completely determined until the year-class finally joins the adult stock, and the processes involved probably begin early in the life-history of the fish when both their growth and mortality rates are high. The match/mismatch hypothesis is given in this chapter to cover the subsequent development through larval life up to metamorphosis, and possibly just beyond. The match/mismatch hypothesis has now been extended to the upwelling areas and oceanic divergences equatorward of 40° latitude on the basis that fish in these regions release batches of eggs more frequently when they are well fed and, more generally, that pelagic fish may modify their reproductive strategies such that they can feed and spawn at the same time. A delay in predation is of great importance, particularly when production peaks in early development. This model illustrates the difficulties that occur when growth and mortality are allowed to interact. On the other hand, there are three consequences of the match/mismatch hypothesis that are presented in this chapter. However, the limited conclusion drawn in this chapter is that, investigations of fish larvae should continue to be a part of the study of population dynamics of fishes.
1,858 citations
TL;DR: The North Atlantic Oscillation (NAO) is one of the most prominent and recurrent patterns of atmospheric circulation variability as discussed by the authors, and it dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during boreal winter.
Abstract: The North Atlantic Oscillation (NAO) is one of the most prominent and recurrent patterns of atmospheric circulation variability. It dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during boreal winter, so variations in the NAO are important to society and for the environment. Understanding the processes that govern this variability is, therefore, of high priority, especially in the context of global climate change. This review, aimed at a scientifically diverse audience, provides general background material for the other chapters in the monograph, and it synthesizes some of their central points. It begins with a description of the spatial structure of climate and climate variability, including how the NAO relates to other prominent patterns of atmospheric circulation variability. There is no unique way to define the spatial structure of the NAO, or thus its temporal evolution, but several common approaches are illustrated. The relationship between the NAO and variations in surface temperature, storms and precipitation, and thus the economy, as well as the ocean and ecosystem responses to NAO variability, are described. Although the NAO is a mode of variability internal to the atmosphere, indices of it exhibit decadal variability and trends. That not all of its variability can be attributed to intraseasonal stochastic atmospheric processes points to a role for external forcings and, perhaps, a small but useful amount of predictability. The surface, stratospheric and anthropogenic processes that may influence the phase and amplitude of the NAO are reviewed.
1,712 citations
TL;DR: In this article, the authors examine the control of the vertical circulation in the northern seas, and the potential for altering it, by considering the budgets and storage of fresh water in the Arctic Ocean and in the convective regions to the south.
Abstract: Salinity stratification is critical to the vertical circulation of the high-latitude ocean. We here examine the control of the vertical circulation in the northern seas, and the potential for altering it, by considering the budgets and storage of fresh water in the Arctic Ocean and in the convective regions to the south. We find that the present-day Greenland and Iceland seas, and probably also the Labrador Sea, are rather delicately poised with respect to their ability to sustain convection. Small variations in the fresh water supplied to the convective gyres from the Arctic Ocean via the East Greenland Current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past. The North Atlantic salinity anomaly of the 1960s and 1970s is a recent example; it must have had its origin in an increased fresh water discharge from the Arctic Ocean. Similarly, the freshening and cooling of the deep North Atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the Arctic Ocean into the convective gyres. Finally, we note that because of the temperature dependence of compressibility, a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean.
1,627 citations
TL;DR: In this paper, the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems.
Abstract: We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance The initiation of fishing in an unfished system leads to dramatic changes in fish community structure As fishing intensity increases the additional effects are more difficult to detect Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator–prey coupling between invertebrate feeding fishes and sea urchins Fishing has reduced, and locally extirpated, populations of predatory fishes These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem
1,546 citations
TL;DR: Variability of the North Atlantic Oscillation and the Tropical Atlantic dominate the climate of North Atlantic sector, the underlying ocean and surrounding continents on interannual to decadal time scales as mentioned in this paper.
Abstract: 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.
971 citations
References
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01 Jan 1983TL;DR: In this paper, a color-coded map of the Antarctic and the southern oceans is presented, showing brightness temperatures and concentrations of pack ice averaged for each month, 4-year monthly averages, and month-to-month changes.
Abstract: Data from the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite are used to determine the extent and distribution of Antarctic sea ice. The characteristics of the southern ocean, the mathematical formulas used to obtain quantitative sea ice concentrations, the general characteristics of the seasonal sea ice growth/decay cycle and regional differences, and the observed seasonal growth/decay cycle for individual years and interannual variations of the ice cover are discussed. The sea ice data from the ESMR are presented in the form of color-coded maps of the Antarctic and the southern oceans. The maps show brightness temperatures and concentrations of pack ice averaged for each month, 4-year monthly averages, and month-to-month changes. Graphs summarizing the results, such as areas of sea ice as a function of time in the various sectors of the southern ocean are included. The images demonstrate that satellite microwave data provide unique information on large-scale sea ice conditions for determining climatic conditions in polar regions and possible global climatic changes.
567 citations
TL;DR: In this paper, the authors present the results of analyses of worldwide mean sea-surface temperatures and night near-surface marine air temperature for the period 1856-1981 with the aim of estimating the magnitudes of recent climatic fluctuations of temperature at the ocean surface, taking account of changes in observing procedures.
Abstract: Paltridge and Woodruff1 found a warming of global mean sea-surface temperatures (SSTs) of ∼1°C in the first half of the present century, but there are doubts about its reality because spurious temperature fluctuations can arise from changes in measuring instruments2,3 and because inter-annual fluctuations may contain sufficient variance to allow the observed inter-decadal variations to fall within the limits of sampling error of a stationary series3. We present here the results of analyses of worldwide SSTs and night near-surface marine air temperature (MAT) for the period 1856–1981 with the aim of estimating the magnitudes of recent climatic fluctuations of temperature at the ocean surface, taking account of changes in observing procedures. Our results show a worldwide temperature fluctuation of range ≃0.6 °C (in broad agreement with a preliminary analysis of global SST2), with the coldest period being centred around 1905–10 and the warmest occurring in the 1940s. The fluctuation has a similar magnitude to, and is nearly in phase with, climatic warmings and coolings near the surface of the Northern Hemisphere land masses for the period after 1900. Before 1900 the trends are sharply different.
288 citations
TL;DR: One hundred ten satellite-tracked freely drifting buoys measured velocities and trajectories of the near-surface currents in the North Atlantic as discussed by the authors, and a horizontal map of eddy kinetic energy was prepared on a 2°×2° grid between latitudes 20° and 55°N.
Abstract: One hundred ten satellite-tracked freely drifting buoys measured velocities and trajectories of the near-surface currents in the North Atlantic. Mean velocity values and the velocity variance about the mean were calculated for different regions. A horizontal map of eddy kinetic energy was prepared on a 2°×2° grid between latitudes 20° and 55°N. Maximum eddy energy (∼3000 cm2 s−2) coincides with the high speed Gulf Stream jet where it begins large amplitude meanders near 37°N 67°W. A tongue of high eddy energy coincides with the Stream's path eastward and around the Grand Banks into the Newfoundland Basin where values of 1000 cm2 s−2 are found. A weaker tongue extends eastward across the mid-Atlantic Ridge near 45°N. A second weak extension reaches southeastward from the Stream and crosses the mid-Atlantic Ridge between 30° and 35°N. North and south of the Stream, eddy energy diminishes rapidly reaching an e folding at 300 km from the axis. Values of 200 cm2 s−2 were observed in the mid-gyre region and 100 cm2 s−2 in the Eastern North Atlantic and North Equatorial Current. Although the gross distribution of eddy energy is similar to that determined from ship drift measurements, there are significant differences. Eddy energy from drifters amounts to about twice the value measured by ship drift in the Gulf Stream and one half the ship drift values in the mid-gyre. It is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation, both of which are problems with the ship drift technique.
281 citations
01 Dec 1974
TL;DR: The Arctic Ocean (Fig. 1) is a large basin (9.5 × 106 km2) in area about four times larger than the Mediterranean Sea, connected primarily with the Atlantic Ocean via the major water bodies of the Greenland and Norwegian Seas and Baffin Bay as discussed by the authors.
Abstract: The Arctic Ocean (Fig. 1) surrounds the North Pole and is bordered by Europe, Siberia, Alaska, Canada, and Greenland. It is a large basin (9.5 × 106 km2), in area about four times larger than the Mediterranean Sea, connected primarily with the Atlantic Ocean via the major water bodies of the Greenland and Norwegian Seas and Baffin Bay, which also lie in the Arctic. Technically, the Arctic Ocean is probably not an ocean but rather a mediterranean sea of the Atlantic, as recognized by the oceanographic pioneers from Norway (in Norwegian: Nordpolarhavet = North Polar Sea). The various Arctic basins do, however, attain depths similar to those of the oceans (~4000 m), and time and convention have dictated our present nomenclature.
258 citations
TL;DR: In this article, the authors present monthly averages of water temperature, salinity, and density anomaly at 11 depths between 10 and 1500 m, at Ocean Weather Ship Bravo (56°30'N, 51°00'W), between 1964 and 1974, at the same time period.
Abstract: Monthly averages of water temperature, salinity, and density anomaly at 11 depths between 10 and 1500 m, at Ocean Weather Ship Bravo (56°30'N, 51°00'W), between 1964 and 1974 are presented. Near‐surface salinity values between 1967 and 1971 were significantly lower than those between 1964–1967. Coincident with the lower salinity values, the winter‐time heat losses were less than normal. The combination of increased stratification with the low heat losses tended to limit the convectively mixed upper layer in winter to unusually shallow depths. It is suggested that the low salinity condition was indirectly due to an anomalously high atmospheric pressure cell over Greenland. This cell increased the anticylonic air flow around Greenland causing an increase in the proportion of low‐salinity polar water in the east Greenland and Labrador Currents and subsequently in the interior of the Labrador Sea.
256 citations