James D. Hays

Age dating and the orbital theory of the ice ages: Development of a high-resolution 0 to 300,000-year chronostratigraphy

Using the concept of “orbital tuning”, a continuous, high-resolution deep-sea chronostratigraphy has been developed spanning the last 300,000 yr. The chronology is developed using a stacked oxygen-isotope stratigraphy and four different orbital tuning approaches, each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data. Each approach yields a separate chronology. The error measured by the standard deviation about the average of these four results (which represents the “best” chronology) has an average magnitude of only 2500 yr. This small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used. Excellent convergence between chronologies developed using each of five different paleoclimatological indicators (from a single core) is also obtained. The resultant chronology is also insensitive to the specific indicator used. The error associated with each tuning approach is estimated independently and propagated through to the average result. The resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr, in excellent agreement with the 2500-yr estimate. Transfer of the final chronology to the stacked record leads to an estimated error of ±1500 yr. Thus the final chronology has an average error of ±5000 yr.

Variations in the Earth's Orbit: Pacemaker of the Ice Ages

1) Three indices of global climate have been monitored in the record of the past 450,000 years in Southern Hemisphere ocean-floor sediments. 2) Over the frequency range 10–4 to 10–5 cycle per year, climatic variance of these records is concentrated in three discrete spectral peaks at periods of 23,000, 42,000, and approximately 100,000 years. These peaks correspond to the dominant periods of the earths solar orbit, and contain respectively about 10, 25, and 50 percent of the climatic variance. 3) The 42,000-year climatic component has the same period as variations in the obliquity of the earths axis and retains a constant phase relationship with it. 4) The 23,000-year portion of the variance displays the same periods (about 23,000 and 19,000 years) as the quasi-periodic precession index. 5) The dominant, 100,000-year climatic [See table in the PDF file] component has an average period close to, and is in phase with, orbital eccentricity. Unlike the correlations between climate and the higher-frequency orbital variations (which can be explained on the assumption that the climate system responds linearly to orbital forcing), an explanation of the correlation between climate and eccentricity probably requires an assumption of nonlinearity. 6) It is concluded that changes in the earths orbital geometry are the fundamental cause of the succession of Quaternary ice ages. 7) A model of future climate based on the observed orbital-climate relationships, but ignoring anthropogenic effects, predicts that the long-term trend over the next sevem thousand years is toward extensive Northern Hemisphere glaciation.

Pliocene-Pleistocene Sediments of the Equatorial Pacific: Their Paleomagnetic, Biostratigraphic, and Climatic Record

Magnetic stratigraphy of 15 oriented cores from the equatorial Pacific was determined as far back as the Gilbert reversed-polarity epoch. Ranges of selected species of four major microfossil groups (diatoms, silicoflagellates, foraminifers and Radiolaria) are compared with the record of geomagnetic reversals during the last 4.5 m. y. in eastern equatorial Pacific deep-sea cores. Characteristics of the fossil assemblages are used as criteria for recognition of most of the paleomagnetic reversals that occurred during this interval. Two zones of major paleontological change occur characterized by extinctions of several species and coiling direction changes in some foraminifers. The first change comes in the middle of the Gauss normal magnetic series (about 3 m.y. B.P.) and the second near the Olduvai magnetic event (about 2.0 m.y. B.P.). Seven equatorial foraminiferal species, two radiolarian species, and two diatom species become extinct near reversals. The establishment of the true chronostratigraphic relationships of these selected microfossil species allows us to date zonations of previous authors and provides absolute dates that can be used in worldwide correlation of marine sediments. The percentage of calcium carbonate was determined throughout the lengths of four cores. Eight distinct carbonate cycles are present in the Brunhes series, having periodicities of about 75,000 years in the upper Brunhes to over 100,000 years in the lower Brunhes. It is possible to correlate these carbonate cycles among our cores and also to correlate them with the previous work of Arrhenius who equated the carbonate peaks with glacial stages and the troughs with interglacial stages. This interpretation is supported by paleomagnetic and C14 dating of the last carbonate high which is synchronous with the Wisconsin glaciation (80,000 to 11,500 years B.P.). It, therefore, is probable that there were eight major glacial fluctuations during the last 700,000 years. During the last 400,000 years there is good correlation between the carbonate cycles of the Pacific and evidence of climatic fluctuations in the Atlantic established by Ericson and Wollin (1968) and Emiliani (1966) based on fossil abundances and oxygen isotope ratios, respectively. The rates of sedimentation during the Brunhes series range between 3.5 mm/1000 years for siliceous ooze to 17.5 mm/1000 years for highly calcareous sediment.

Paleomagnetic Study of Antarctic Deep-Sea Cores

The magnetic inclinations and inten sities of about 650 samples from seven deepsea cores taken in the Antarctic were measured on a spinner magnetometer. This series of measurements provided a magnetic stratigraphy, based on zones of normally or reversally polar ized specimens for each core, which was then correlated with the magnetic stra tigraphy of Cox et al. (1). One core (V16-134) gave a continuous record of the paleomagnetic field back to about 3.5 million years. When selected samples were subject ed to alternatingfield demagnetization, most were found to have an unstable component that was removed by fields of 150 oersteds; all samples from two cores were partially demagnetized in a field of 150 oersteds. The average inclination in these two cores was then in good agreement with the average inclination of the ambient field for the latitude of the core site. It was also found that the intensities of the samples decreased at the points of reversal; this finding is to be expected if, as has been postulated by the dynamo theory, the intensity of the dipole field decreases to zero and builds again with opposite polarity. We believe that the magnetiza tion of the cores results from the pres ence of detrital magnetite, although other magnetic minerals also may be present. Four faunal zones (, X, , and ) have been recognized in these Antarctic cores on the basis of upward sequential disappearance of Radiolaria. The faunal boundaries and reversals consistently have the same relations to one another, indicating that they are both timedependent phenomena. Using previously determined times of reversal, one may date the following events in the cores: 1) Radiolarian faunal boundaries:-X, 2 million years; X-, 0.7 million years; -, 0.4 to 0.5 million years. These dates are in good agreement with ages previously extrapolated from radio metric dates. 2) Initiation of Antarctic diatom ooze deposition, approximately 2.0 mil-lion years ago. 3) First occurrence of ice- rafted detritus, approximately 2.5 million years ago. One can also calculate rates of sedi mentation, which vary in the cores studied from 1.1 to about 8.0 millimeters per 1000 years. Sedimentation rates for the Indian Ocean cores are higher than for the Bellingshausen Sea cores. The near coincidence of faunal changes and reversals in the cores suggests but does not prove a causal relation. We conclude from this study that paleomagnetic stratigraphy is a unique method for correlating and dating deep sea cores, and that future work with such cores may provide a complete or nearly complete record of the history of the earths magnetic field beyond 4 million years.

Mediterranean island arcs and origin of high potash volcanoes

Abstract Active volcanoes of the Mediterranean Sea are distributed along two arc structures: the Hellenic arc in the Aegean Sea and the Calabrian arc in the Tyrrhenian Sea. The active volcanoes in both arcs lie above earthquakes with focal depth greater than 100 km. The depth of these earthquakes increases generally northward reaching a maximum depth of about 200 km in the Aegean Sea and more than 300 km in the Tyrrhenian Sea. The K 2 O versus SiO 2 value in volcanic rocks of the active volcanoes of the Hellenic and Calabrin arcs increases with increasing depth of underlying earthquakes which is similar to the pattern found in Pacific and Indonesian volcanic arcs. The high potash rocks of the Mediterranean suite are the culmination of this trend toward increasing potash as earthquake depth increases. The ratio of the trace element rubidium to silica also increases with increasing depth of earthquakes. Both the intermediate earthquakes and volcanic activity in the Mediterranean, as in Indo-Pacific volcanic arcs, are considered to have originated in dehydration of oceanic crust underthrusting the Aegean and Tyrrhenian Seas as a consequence of a counterclockwise rotation of Africa relative to Eurasia. The released water, we believe, works its way toward the surface in a hydrous melt scavenging potash and other alkali on the way. The ultimate ratio of K 2 O versus SiO 2 and Rb versus SiO 2 will be determined by the temperature of the hydrous melt and the distance traveled through the asthenosphere.

Oceanographic conditions associated with high abundances of the radiolarian Cycladophora davisiana

Abstract The cosmopolitan radiolarian Cycladophora davisiana usually comprises less than 5% of the radiolarian fauna in Holocene sediments. In recent sediments from the Sea of Okhotsk, however, this species frequently represents more than 20% of the radiolarian assemblage. At times during the late Pleistocene, abundances of this species in excess of 40% are recorded in marine sediments from high-latitude oceans (> 40°) of both hemispheres. The Sea of Okhotsk apparently represents a modern analogue of climatic and oceanographic conditions that existed throughout large portions of high-latitude oceans at times during the late Pleistocene. The near-surface water structure of the Sea of Okhotsk is characterized by a low-salinity surface layer with a strong temperature minimum near its base. The low surface salinities are responsible for maintaining near-freezing subsurface temperatures as well as establishing relatively stable temperatures and salinities at depths below the temperature minimum. This water structure is produced, at least in part, by intense freezing of sea ice in winter with subsequent summer melting. The physical characteristics of the upper water column affect the abundance and activity of shallow-dwelling flora and fauna, while providing a stable subsurface environment for deeper-dwelling fauna.

Towards a high-resolution, global, deep-sea chronology for the last 750,000 years

Abstract Variations in the ratio of 18 O/ 16 O as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume; hence these variations provide a set of global time lines in deep-sea sediments. It is likely that the timing of major changes in oxygen isotope values is strongly influenced, if not controlled, by variations in the geometry of the Earths orbit. Since the variation of orbital parameters can be accurately calculated, the opportunity exists for transforming this orbital chronology into a geological chronology. Through careful correlation of oxygen isotope records in a set of deep-sea cores from the sub-Antarctic, South Atlantic and equatorial Pacific, we have assembled a composite isotopic section spanning the last 750,000 years with an average sedimentation rate of 2.3 cm/1000 years. A new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300,000 years to the entire 750,000-year record. Previously identified difficulties in phase locking precession with the filtered isotopic signal between 365,000 and 465,000 years B.P. have been resolved with the recognition that precessional variations have an average period of 19,000 years and not 23,000 years during this interval. Since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record, we believe that it presents the most accurate chronology yet developed for deep-sea sediments. With this new age model providing the time control, power spectral analyses of South Atlantic and sub-Antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of ∼ 100,000, 41,000 and 23,000 years.

Comparison of glacial and interglacial oceanographic conditions in the South Atlantic from variations in calcium carbonate and radiolarian distributions

Temperature estimates produced by a radiolarian-based transfer function, factor distributions of radiolarian assemblages, and variations in calcium carbonate were used to reconstruct the oceanographic conditions in the South Atlantic during the last glacial maximum (18,000 yr B.P.). This study suggests that while the position of the Subtropical Convergence at 18,000 yr B.P. was very similar to its present position, the Antarctic Polar Front shifted northward 1° to 3° of latitude in the eastern South Atlantic and 3° to 5° of latitude in the western South Atlantic. The largest temperature changes occurred in the subantarctic region and along the eastern portion of the Subtropical Gyre.

Cycladophora davisiana: a stratigraphic tool for Pleistocene North Atlantic and interhemispheric correlation

Abstract A study of three North Atlantic cores, containing Radiolaria throughout their length and two correlative volcanic ash layers, shows that the radiolarian speciesCycladophora davisiana goes through important relative abundance changes that appear to be synchronous over an area of more than 300,000 square miles during the late Pleistocene (⋍300,000 years). A comparison of theC. davisiana abundance changes with the oxygen isotope records in a North Atlantic and a subantarctic core strongly suggests that theC. davisiana fluctuations in the North Atlantic and Antarctic are also synchronous. Although the reason for the changes in the abundance ofC. davisiana is not yet understood, the apparent synchroneity of these changes between the subantarctic and North Atlantic suggests a similarity of some related environmental factors.

Globally synchronous extinction of the radiolarian Stylatractus universus

Through comparison of the extinction level of Stylatractus universus with the δO 18 record in widespread high- and low-latitude deep-sea cores, we show that this level is globally synchronous. It occurs in the lower one-third of the isotopic transition between isotope Stages 12 and 11. Several independent estimates of the date of this extinction converge on 410,000 ± 5,000 yr ago. This biostratigraphic datum is now well dated and is globally synchronous.