High-amplitude Changes Research Articles

Earth rotation, ocean circulation and paleoclimate

During the 20 Ka glaciation maximum Earth's rate of rotation was significantly faster. The subsequent glacial eustatic rise in sea level meant an increase of the equatorial radius and hence led to a general deceleration in the Earth's rate of rotation. At about 6000 BP the glacial eustatic rise in sea level finished and a new situation began which was characterized by feedback interchanges of angular momentum between the solid Earth and the hydrosphere. There is a strong linkage between Earth's rate of rotation — total as well as differential — and the changes in ocean surface circulation. The ocean circulation changes are, in their turn, strongly linked to the paleoclimatic evolution of the boardering land masses. This is due to the high heat-storing capacity of the oceans, the ocean/ atmosphere heat flux, and the ocean/land interaction via heat transport by the winds. Consequently, we see a causal connection between Earth's rotation, oceanic circulation, ocean/atmosphere heating, atmospheric (wind) heat transport and continental paleoclimatic changes. We propose that the paleoclimatic changes on the decadal to millennial time scale are primarily driven by this mechanism. Observational data of changes in ocean water masses and paleoclimate are presented for the 20 Ka situation, for the high-amplitude changes 13-10 Ka ago, for the decadal-to-century changes during the Holocene, for the last centuries' instrumental data and for the ENSO-events. This implies that the oceanic system (the ocean surface circulation system) has a much more important role than previously appreciated.

Temporal (circadian) and functional relationship between atrial natriuretic peptides and blood pressure.

Long-acting natriuretic peptide, vessel dilator, and atrial natriuretic factor consisting of amino acids (a.a.) 1 to 30, 31 to 67, and 99 to 126 of the 126-a.a. atrial natriuretic factor (ANF) prohormone, respectively, circulate in humans and have potent vasodilatory properties. To determine if these atrial natriuretic peptides are directly related to blood pressure in clinically healthy normotensive humans, we obtained 24-h profiles of vessel dilator, long-acting natriuretic peptide, ANF, and blood pressure in 10 men in 1988 and 11 men in 1993 (seven men were studied twice) to compare circulating concentrations of atrial natriuretic peptides with naturally occurring changes in blood pressure. Overall, vessel dilator, long-acting natriuretic peptide, and ANF each had significant (p<0.001) circadian rhythms, with peak concentrations late during sleep (at 04:00 h) being nearly twice their concentrations in the afternoon and evening. This high-amplitude circadian change allowed for the refinement of normal limits for ANF peptides by computing 3-hourly tolerance intervals (chronodesms) against which to compare time-specified single samples for normality. Systolic, diastolic, and mean arterial blood pressure also had significant circadian rhythms (p<0.001) with peaks and troughs that were exactly opposite those of the ANF peptides. In addition to this inverse temporal relationship, there was a significant inverse correlation between absolute values for blood pressure and each ANF peptide (p<0.001), implying a functional relationship. These data suggest that in addition to other well-established neurochemical factors, the ANF peptides (vessel dilator, long-acting natriuretic peptide, and ANF) are important for the maintenance of blood pressure and modulation of its circadian rhythm.

Global change: the high-amplitude changes 13-10 ka ago—novel aspects

Within the period 13-10 ka, the Earth experienced high-amplitude fluctuations in climate and to a lesser degree, also in sea level. These high-amplitude changes occurred within the period of superposition of two exponential curves in the eustatic rise in sea level. This intermediate period seems to represent the Earth's geodynamic response to the general deceleration due to the sea level rise. The deceleration caused water-masses to move polewards. At a critical point, the symmetry axes of the Earth's core and mantle were displaced with respect to each other along a meridional path recorded in a trans-polar shift of the axis of the geomagnetic dipole field. At about the same time, the Earth came into a new mode with large-scale interchanges of angular momentum between the “solid” Earth and the hydrosphere. These speeding-ups and slowing-downs of the hydrosphere caused increases and decreases in the ocean current system. The Gulf Stream affecting climate and sea level in Europe, the Labrador Current controlling climate and ice marginal changes in the Hudson Strait region. The Humboldt Current controlling climate and precipitation in South America, the coastal upwelling and the marine productivity and in that way also affecting the atmospheric CO 2 content. These ocean current changes are the main controlling factors of the high-amplitude changes within the intermediate period from about 13.5 to 9.5 ka.

Younger Dryas in southernmost south America — An update

High resolution pollen data from a peat section in southern Tierra del Fuego documents high paleoenvironmental variability between 11 ka and 9 ka. Detailed analysis of plant macro remains in the same section showed that the repeated high-amplitude changes in pollen taxa were related to repeated fire disturbance burning at least once even the surface of the mire. In many peat sections from southernmost Patagonia and Tierra del Fuego charcoal particles have been found intermittently since about 13 ka and in great abundance especially after 11 ka. This suggests that the environmental changes previously interpreted to imply a return to colder climates comparable to the North Atlantic Younger Dryas event instead are in response to local and regional disturbances by fires.

Rapid oxygen-dependent changes in erythropoietin mRNA in perfused rat kidneys: Evidence against mediation by cAMP

Erythropoietin (EPO) is mainly produced in the kidneys and is regulated by blood oxygen availability. Studies with isolated perfused kidneys have established that an oxygen-sensing system exists intrarenally but the mechanisms involved are poorly understood. Using a quantitative RNase protection assay, we have demonstrated oxygen-dependent EPO mRNA production in isolated perfused rat kidneys, with EPO mRNA levels increasing 30-fold when perfusate pO2 was reduced from 474 to 25 mm Hg. To determine if the high amplitude changes in EPO mRNA levels in response to hypoxia are mediated by cyclic AMP, four agents, which activate the cyclic AMP system in different ways, were administered to isolated kidneys perfused over a range of perfusate pO2. Salbutamol and N6-ethyl carboxamidoadenosine, which activate adenylate cyclase, dibutyryl cyclic AMP (a cyclic AMP analogue) and forskolin did not augment EPO mRNA production, and no significant differences in the regression of log (EPO mRNA) on perfusate pO2, were found between experimental groups exposed to each of these compounds and controls. We conclude that the rapid increase in EPO mRNA levels in response to hypoxia is not mediated or substantially modulated by a cyclic AMP-dependent mechanism.

Forced regressions in a large wave- and storm-dominated anoxic lake, Rhaetian-Sinemurian Kap Stewart Formation, East Greenland

During Rhaetian-Sinemurian time a large wave- and storm-dominated lake was situated in the Jameson Land basin, East Greenland. Lake deposits consist of alternating black unfossiliferous mudstones and sheet sandstones. Anoxic conditions dominated at the lake bottom during deposition of the muds, and the water column was probably stratified. The sandstones were deposited by progradation of wave- and storm-dominated deltas in a water depth of less than 15 m. Sequence-stratigraphic interpretation suggests that the mudstones were deposited in periods of rising and very high stands of lake level, whereas progradation of the deltaic sheet sandstones took place during forced regressions caused by significant falls. The lake thus underwent a large number of fairly high amplitude changes in level, probably caused by climatic fluctuations. The high-order cycles can be grouped into several long-period cycles that show the same number of major fluctuations as published eustatic sea-level curves. This similarity suggests a causal link between eustasy and long-period variations in the lake. The Kap Stewart Formation represents one of the few ancient examples of a large wave- and storm-dominated lake, and it is probably the first documented case of abundant well-developed lacustrine forced regressions.

Hunter-gatherer economic complexity and “population pressure”: A cross-cultural analysis

This paper examines the relaionship between “population pressure” and socioeconomic complexity among hunter-gatherers. Population pressure is defined as the ratio between population density and the density of available resources. Socioeconomic complexity is measured by means of several correlated variables: storage-dependence, sedentism, social inequality, and use of a medium of exchange. Correlations between these variables are calculated from an ethnographic sample of 94 hunter-gatherer groups. The correlations between population pressure and socioeconomic complexity are found to be extremely high. Two major types of hunter-gatherers exist which are distinguished by a number of variables and may be termed “simple” and “complex.” Transitional groups between these two types are quite rare. It is also noted that population pressure does not arise in continental climates where famine mortality is common because of high-amplitude changes in productivity from year to year. It is argued that population pressure is a necessary and sufficient condition for and the efficient cause of socioeconomic complexity. The widespread disavowal by archaeologists of population pressure as a possible explanation for the prehistoric development of complex hunter-gatherers has no basis in ethnographic fact.

The Nature and Magnitude of in vivo 5-Hydroxyindoleacetic Acid Output from 5-Hydroxytryptamine Terminals Is Related to Specific Regions of the Suprachiasmatic Nucleus

Eight cycling female rats were implanted with push-pull cannulae over the region of the suprachiasmatic nuclei (SCN) and allowed 7-10 days for recovery. Perfusion of the SCN continued in these freely behaving rats for 5-6 h of the light period and the subjective scotophase. The release of 5-hydroxyindoleacetic acid (5-HIAA) ranged from 10 to 350 pg 5-HIAA/min. Significantly, the amplitude and characteristics of the output of 5-HIAA were highly location dependent in that rostral cannulae placements revealed high amplitude changes with initial mean values of 40 pg 5-HIAA/min, which increased toward the dark phase to mean peak values of 195 pg 5-HIAA/min. Caudal cannulae placements revealed a low amplitude, high frequency, basal type of 5-HIAA release which did not increase toward the dark period (approximately 5 pg/min). 5-Hydroxytryptophan infusion resulted in a significant marked increase in the basal release of 5-HIAA confirming the biochemical viability of the area undergoing perfusion. These results suggest that the in vivo measurement of 5-HIAA from 5-hydroxytryptamine (5-HT) terminals in the region of the SCN could reflect discrete functional activity of serotonergic terminals within specific regions of the SCN in a freely behaving rat. Furthermore, the biochemical viability of these 5-HT terminals and the ability of the rat's SCN to exhibit marked differential changes in 5-HT activity emphasizes the physiological relevance of this model system to study neuroendocrine events in freely behaving animals.