Interannual variability of temperature at a depth of 125 meters in the north atlantic ocean

Analyses of historical ocean temperature data at a depth of 125 meters in the North Atlantic Ocean indicate that from 1950 to 1990 the subtropical and subarctic gyres exhibited linear trends that were opposite in phase. In addition, multivariate analyses of yearly mean temperature anomaly fields between 20 degrees N and 70 degrees N in the North Atlantic show a characteristic space-time temperature oscillation from 1947 to 1990. A quasidecadal oscillation, first identified at Ocean Weather Station C, is part of a basin-wide feature. Gyre and basin-scale variations such as these provide the observational basis for climate diagnostic and modeling studies.     

Deep crustal drilling in the north atlantic ocean

Oceanic crustal drilling by R. V. Glomar Challenger at 15 sites in the North Atlantic has led to a complex picture of the upper half kilometer of the crust. Elements of the picture include the absence of the source for linear magnetic anomalies, marked episodicity of volcanic activity, ubiquitous low temperature alteration and evidence for large scale tectonic disturbance. Comparison sections in the Pacific and much deeper crustal drilling are needed to attack problems arising from the North Atlantic results.     

Influence of the Atlantic subpolar gyre on the thermohaline circulation

During the past decade, record-high salinities have been observed in the Atlantic Inflow to the Nordic Seas and the Arctic Ocean, which feeds the North Atlantic thermohaline circulation (THC). This may counteract the observed long-term increase in freshwater supply to the area and tend to stabilize the North Atlantic THC. Here we show that the salinity of the Atlantic Inflow is tightly linked to the dynamics of the North Atlantic subpolar gyre circulation. Therefore, when assessing the future of the North Atlantic THC, it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account.     

Paleocirculation of the deep north atlantic: 150,000-year record of benthic foraminifera and oxygen-18

Benthic foraminiferal faunas in a piston core from 3331 meters at 44 degrees N on the Mid-Atlantic Ridge show striking variations in the relative abundance of species. Uvigerina peregrina, which is broadly distributed today in the South Atlantic and in the Pacific in water that has been long isolated from the surface, is absent in the North and Equatorial Atlantic at depths occupied by highly oxygenated North Atlantic deep water. This species dominated the fauna at this site for much of the past 150,000 years. It is suggested that North Atlantic deepwater production was much reduced or eliminated at times of Uvigerina peregrina abundance, as a result of cooling and stratification of the Norwegian Sea surface, coincident with the times of the southward migration of the polar front in the North Atlantic.     

Magnetic boundaries in the north atlantic ocean

Magnetic boundaries parallel the continental slope and separate undisturbed from disturbed magnetic regions on both sides of the North Atlantic. The boundaries lie 2000 to 2500 kilometers from the axis of the mid-Atlantic ridge and roughly equidistant from it. The undisturbed zone, lying on the continental side of the boundaries, may reflect the long period of no reversals in magnetic polarity that occurred during the late Paleozoic.     

Interannual variability in the North Atlantic Ocean carbon sink

The North Atlantic is believed to represent the largest ocean sink for atmospheric carbon dioxide in the Northern Hemisphere, yet little is known about its temporal variability. We report an 18-year time series of upper-ocean inorganic carbon observations from the northwestern subtropical North Atlantic near Bermuda that indicates substantial variability in this sink. We deduce that the carbon variability at this site is largely driven by variations in winter mixed-layer depths and by sea surface temperature anomalies. Because these variations tend to occur in a basinwide coordinated pattern associated with the North Atlantic Oscillation, it is plausible that the entire North Atlantic Ocean may vary in concert, resulting in a variability of the strength of the North Atlantic carbon sink of about +/-0.3 petagrams of carbon per year (1 petagram = 10(15) grams) or nearly +/-50%. This extrapolation is supported by basin-wide estimates from atmospheric carbon dioxide inversions.     

Asynchronous climate changes in the North Atlantic and Japan during the last termination

Pollen records from the annually laminated sediment sequence in Lake Suigetsu, Japan, suggest a sequence of climate changes during the Last Termination that resembles that of the North Atlantic region but with noticeable differences in timing. An interstadial interval commenced a few centuries earlier [approximately 15,000 years before the present (yr B.P.)] than the North Atlantic GI-1 (B?lling) event. Conversely, the onset of a Younger Dryas (YD)-like cold reversal (12,300 to 11,250 yr B.P.) postdated the North Atlantic GS-1 (YD) event by a few centuries. Climate in the Far East during the Last Termination reflected solar insolation changes as much as Atlantic influences.     

Tropical origins for recent North Atlantic climate change

Evidence is presented that North Atlantic climate change since 1950 is linked to a progressive warming of tropical sea surface temperatures, especially over the Indian and Pacific Oceans. The ocean changes alter the pattern and magnitude of tropical rainfall and atmospheric heating, the atmospheric response to which includes the spatial structure of the North Atlantic Oscillation (NAO). The slow, tropical ocean warming has thus forced a commensurate trend toward one extreme phase of the NAO during the past half-century.     

Trajectory shifts in the Arctic and subarctic freshwater cycle

Manifold changes in the freshwater cycle of high-latitude lands and oceans have been reported in the past few years. A synthesis of these changes in freshwater sources and in ocean freshwater storage illustrates the complementary and synoptic temporal pattern and magnitude of these changes over the past 50 years. Increasing river discharge anomalies and excess net precipitation on the ocean contributed approximately 20,000 cubic kilometers of fresh water to the Arctic and high-latitude North Atlantic oceans from lows in the 1960s to highs in the 1990s. Sea ice attrition provided another approximately 15,000 cubic kilometers, and glacial melt added approximately 2000 cubic kilometers. The sum of anomalous inputs from these freshwater sources matched the amount and rate at which fresh water accumulated in the North Atlantic during much of the period from 1965 through 1995. The changes in freshwater inputs and ocean storage occurred in conjunction with the amplifying North Atlantic Oscillation and rising air temperatures. Fresh water may now be accumulating in the Arctic Ocean and will likely be exported southward if and when the North Atlantic Oscillation enters into a new high phase.     

Enhanced open ocean storage of CO2 from shelf sea pumping

Seasonal field observations show that the North Sea, a Northern European shelf sea, is highly efficient in pumping carbon dioxide from the atmosphere to the North Atlantic Ocean. The bottom topography-controlled stratification separates production and respiration processes in the North Sea, causing a carbon dioxide increase in the subsurface layer that is ultimately exported to the North Atlantic Ocean. Globally extrapolated, the net uptake of carbon dioxide by coastal and marginal seas is about 20% of the world ocean's uptake of anthropogenic carbon dioxide, thus enhancing substantially the open ocean carbon dioxide storage.     

Deep Circulation of the North Atlantic over the Last 200,000 Years: Geochemical Evidence

Variations in the cadmium/calcium ratio of North Atlantic Deep Water are recorded in the fossil shells of benthic foraminifera. The oceanic distribution of cadmium is similar to that of the nutrients, hence the cadmium/calcium ratio in shells records temporal variations in nutrient distributions. Data from a North Atlantic sediment core show that over the past 200,000 years there has been a continuous supply of nutrient-depleted waters into the deep North Atlantic. The intensity of this source relative to nutrient-enriched southern waters diminished by about a factor of 2 during severe glaciations. This evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested.     

The last glacial-Holocene transition in southern Chile

Warming at the last glacial termination in the North Atlantic region was interrupted by a period of renewed glacial activity during the Younger Dryas chronozone (YDC). The underlying mechanism of this cooling remains elusive, but hypotheses turn on whether it was a global or a North Atlantic phenomenon. Chronological, sedimentological, and palaeoecological records from sediments of small lakes in oceanic southern Chile demonstrate that there was no YDC cooling in southern Chile. It is therefore likely that there was little or no cooling in southern Pacific surface waters and hence that YDC cooling in the North Atlantic was a regional, rather than global, phenomenon.     

Central North Atlantic Plate Motions over the Last 40 Million Years

The relative motion vector for the North American and African plates has been determined from detailed charting of the trend of the Atlantis fracture zone for over 1000 kilometers in the central North Atlantic near 30 degrees N and from identification of marine magnetic anomalies and deep-sea drilling results. The vector (pole) is located at 52.5 degrees N, 34 degrees W and has a magnitude (opening rate) of 5.7 x 10(-7) degree per year. Major changes in either the pole location or the opening rate are not evident for the last 40 million years.     

The deglacial evolution of North Atlantic deep convection

Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon ((14)C)-depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation.     

A cyanobacterium capable of swimming motility

A novel cyanobacterium capable of swimming motility was isolated in pure culture from several locations in the Atlantic Ocean. It is a small unicellular form, assignable to the genus Synechococcus, that is capable of swimming through liquids at speeds of 25 micrometers per second. Light microscopy revealed that the motile cells display many features characteristic of bacterial flagellar motility. However, electron microscopy failed to reveal flagella and shearing did not arrest motility, indicating that the cyanobacterium may be propelled by a novel mechanism.     

黄河中游流域外来龟、鳖类对原有种类的生态威胁

在我国黄河中游流域自然水域中已发现了鳄龟、佛罗里达鳖,这是一个危险且值得高度警惕的信号。针对鳄龟、佛罗里达鳖、乌龟和中华鳖的有关生物学习性进行对比,指出当鳄鱼、佛罗里达鳖达到一定数量时,流域内原生的乌龟和中华鳖的生态位将会受到严重威胁,建议相关领域学者重视对两栖爬行动物等外来物种在中国的入侵状况与控制策略的研究。     

A possible younger dryas record in southeastern alaska

A stratigraphic record of climatic cooling equal in timing and severity to the Younger Dryas event of the North Atlantic region has been obtained from lacustrine sediments in the Glacier Bay area of southeastern Alaska. Fossil pollen show that a late Wisconsin pine parkland was replaced about 10,800 years ago by shrub- and herb-dominated tundra, which lasted until about 9,800 years ago. This vegetational change is matched by geochemical evidence for loss of organic matter from catchment soils and increased mineral erosion. If this event represents the Younger Dryas, then an explanation for a hemisphere-wide propagation of a North Atlantic climatic perturbation must be sought.     

Decadal trends in the north atlantic oscillation: regional temperatures and precipitation

Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.     

The arctic mirage and the early north atlantic

The arctic mirage is a phenomenon that is common in higher latitudes. It occurs under conditions of pronounced temperature inversion, which impart to the air a refractive capability that may equal or exceed the curvature of the earth. Manifestations of the arctic mirage, though largely forgotten in modern times, are described in the earliest accounts of North Atlantic discovery. This interdisciplinary investigation, combining historical induction with scientific observation and analysis, has suggested a new interpretation of historical events. We believe that information gleaned from these mirages was vital to Norse navigation and exploration in the North Atlantic. We further contend that the mirage may furnish a logical basis for the pervasive ancient and medieval concept of the flat or saucer-shaped world.     

Surface and deep ocean interactions during the cold climate event 8200 years ago

Evidence from a North Atlantic deep-sea sediment core reveals that the largest climatic perturbation in our present interglacial, the 8200-year event, is marked by two distinct cooling events in the subpolar North Atlantic at 8490 and 8290 years ago. An associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the Atlantic meridional overturning circulation. The existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying Laurentide Ice Sheet margin.