A north atlantic climate pacemaker for the centuries

Although El Ni?o and La Ni?a are the largest single sources of global interannual climate variability, climate shifts on longer time scales than El Ni?o's 2 to 7 years are also drawing the attention of researchers. On multidecadal time scales of 40 to 80 years, a restless North Atlantic seems to be at work, alternately countering and enhancing humankind's alterations of climate. The evidence for this is turning up in such records as tree rings, ice cores, and corals.     

Synchronous climate changes in antarctica and the north atlantic

Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events-the rapid warming that marks the end of the last glacial period and the Bolling/Allerod-Younger Dryas oscillation-are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres.     

Abrupt climate events 500,000 to 340,000 years ago: evidence from subpolar north atlantic sediments

Subpolar North Atlantic proxy records document millennial-scale climate variations 500,000 to 340,000 years ago. The cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle. These findings suggest that such climate variations are inherent to the late Pleistocene, regardless of glacial state. Sea surface temperature during the warm peak of Marine Isotope Stage 11 (MIS 11) varied by 0.5 degrees to 1 degrees C, less than the 4 degrees to 4.5 degrees C estimated during times of ice growth and the 3 degrees C estimated for glacial maxima. Coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature.     

A 0.5-million-year record of millennial-scale climate variability in the north atlantic

Long, continuous, marine sediment records from the subpolar North Atlantic document the glacial modulation of regional climate instability throughout the past 0.5 million years. Whenever ice sheet size surpasses a critical threshold indicated by the benthic oxygen isotope (delta18O) value of 3.5 per mil during each of the past five glaciation cycles, indicators of iceberg discharge and sea-surface temperature display dramatically larger amplitudes of millennial-scale variability than when ice sheets are small. Sea-surface temperature oscillations of 1 degrees to 2 degreesC increase in size to approximately 4 degrees to 6 degreesC, and catastrophic iceberg discharges begin alternating repeatedly with brief quiescent intervals. The glacial growth associated with this amplification threshold represents a relatively small departure from the modern ice sheet configuration and sea level. Instability characterizes nearly all observed climate states, with the exception of a limited range of baseline conditions that includes the current Holocene interglacial.     

North atlantic deep-sea fertility

Observations have been made on two cruises in the North Atlantic in which large numbers of microscopic, unicellular flagellates have been found throughout the aphotic zone below 1000 meters. Preliminary measurements also indicate the uptake of dissolved organic substances, suggestive of an apparently viable, actively metabolizing community at these depths.     

Species diversity: benthonic foraminifera in Western north atlantic

Maximum species diversity occurs at abyssal depths of greater than 2500 meters. Other diversity peaks occur at depths of 35 to 45 meters and 100 to 200 meters. The peak at 35 to 45 meters is due to species equitability, whereas the other two peaks correspond to an increase in the number of species.     

North atlantic ocean: preliminary description of normal modes

The three lowest gravitational modes of free oscillation of the North Atlantic Ocean are estimated by numerical integration of Laplace's tidal equations. These modes have periods of approximately 21, 14, and 11 hours, and structures, respectively, of one, two, and three positive amphidromic systems. The phase distribution of the first mode resembles cotidal charts of the diurnal tide, and the period of the second mode is consistent with that inferred by Wunsch from tidal data in Bermuda and the Azores.     

Carbonate sediments: oriented lithified samples from the north atlantic

Indurated carbonate samples, obtained from the North Atlantic sea floor with a deep-sea drill coring apparatus, suggest that the phenomenon of deep-sea carbonate lithification is more complex than had been thought previously. Lithified-nonlithified couplets can now be related in age and orientation. Age determinations based on the method of carbon-14 dating show that adjacent nonlithified-lithified layers may differ in age by more than 30,000 years.     

Case studies on smallholder farmer voice: an introduction to a special symposium

In the spring of 2013, project leaders who received funding from the John Templeton Foundation’s program “Can GM Crops Help to Feed the World?” met in England to discuss progress on funded projects and to identify common objectives and research interests. The collection of essays in this special symposium is one outcome of that meeting. This introduction provides background on the symposium’s theme of understanding the challenges to smallholder farmers having a voice. Farmer voice is important not only in debates about genetically modified crops but also for policies, technologies and other efforts designed by interests seeking ostensibly to improve the livelihoods of smallholder farmers.     

Crustal plates in the central atlantic

Various people have proposed that North and South America are a part of a gigantic crustal plate within which little differential movement is taking place. Considerations of the size of this postulated plate and the pattern of seismicity around the Caribbean indicate that it is in fact two plates, separated in the region between the Lesser Antilles and the Mid-Atlantic Ridge. Many of the offsets of the Mid-Atlantic Ridge opposite the Caribbean are the result of differential spreading rates and the westward continuations of the fracture zones extending from these offsets are active left-lateral faults.     

Monoplacophora in the South atlantic ocean

Occurrence of Neopilina off the southeastern tip of South America may indicate rather widespread distribution of this abyssal group, under favorable conditions, throughout the seas of the world.     

Foraminifera: distribution of provinces in the Western north atlantic

All published distributional data on recent benthic foraminifera of the North American Atlantic continental margin were archived into computerized catalogs. Cluster analysis of these data delimited seven large, marginally overlapping provinces exhibiting a congruous relationship with western North Atlantic water masses. The single major latitudinal faunal change occurs at Cape Hatteras.     

Jurassic sandstone from the tropical atlantic

The oldest sediment yet sampled from the abyssal margins of South America, late Jurassic (or possibly very early Cretaceous) shallow-water, coarse-grained, calcareous sandstone containing palynomorphs and mollusk prisms, was recovered from a depth of 4400 meters on the seaward scarp of the Demerara Plateau. The sandstone was deposited in a shallow, late Jurassic epicontinental sea after the initial stages of rifting when the newly created Atlantic began to founder.