L. David Meeker

Volcanic Aerosol Records and Tephrochronology of the Summit, Greenland, Ice Cores

The recently collected Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project ice cores from Summit, Greenland, provide lengthy and highly resolved records of the deposition of both the aerosol (H2SO4) and silicate (tephra) components of past volcanism. Both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism-climate system. The continuous time series of volcanic SO42− for the last 110,000 years show a strong relationship between periods of increased volcanism and periods of climatic change. The greatest number of volcanic SO42− signals, many of very high magnitude, occur during and after the final stages of deglaciation (6000–17,000 years ago), possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins (sea level change). The increase in the number of volcanic SO42− signals at 27,000–36,000 and 79,000–85,000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation, respectively. A comparison of the electrical conductivity of the GISP2 core with that of the volcanic SO42− record for the Holocene indicates that only about half of the larger volcanic signals are coincident in the two records. Other volcanic acids besides H2SO4 and other SO42− sources can complicate the comparisons, although the threshold level picked to make such comparisons is especially critical. Tephra has been found in both cores with a composition similar to that originating from the Vatnaoldur eruption that produced the Settlement Layer in Iceland (mid-A.D. 870s), from the Icelandic eruption that produced the Saksunarvatn ash (∼10,300 years ago), and from the Icelandic eruption(s) that produced the Z2 ash zone in North Atlantic marine cores (∼52,700 years ago). The presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras. The presence of both rhyolitic and basaltic shards in the Z2 ash in theGISP2 core and the composition of the basaltic grains lend support to multiple Icelandic sources (Torfajokull area and Katla) for the Z2 layer. Deposition of the Z2 layer occurs at the beginning of a stadial event, further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions.

A 10,000-year high-resolution diatom record from Pilkington Bay, Lake Victoria, East Africa

A new diatom record from Lake Victoria’s Pilkington Bay, subsampled at 21- to 25-year intervals and supported by 20 AMS dates, reveals a ∼10,000 calendar year environmental history that is supported by published diatom and pollen data from two nearby sites. With their chronologies adjusted here to account for newly documented ancient carbon effects in the lake, these three records provide a coherent, finely resolved reconstruction of Holocene climate change in equatorial East Africa. After an insolation-induced rainfall maximum ca. 8800–8300 cal yr B.P., precipitation became more seasonal and decreased abruptly ca. 8200 and 5700 yr B.P. in apparent association with northern deglaciation events. Century-scale rainfall increases occurred ca. 8500, 7000, 5800, and 4000 yr B.P. Conditions after 2700 yr B.P. were generally similar to those of today, but major droughts occurred ca. 1200–600 yr B.P. during Europe’s Medieval Warm Period.

Cooling cycles, Heinrich event 1, and the desiccation of Lake Victoria

Abstract East Africa’s enormous Lake Victoria dried out at the close of the last glacial, but the precise timing and origin of that drying event have not been clarified, largely because of uncertainty regarding core stratigraphy and ancient carbon effects on 14 C dates from the lake. New dates and re-examination of evidence from widely distributed cores shows that desiccation occurred some time between 15 900 and 14 200 calendar years BP, and perhaps also ca. 18–17 kyr BP. These lake level minima were briefer than has been previously suggested and were synchronous with pronounced global climate disruptions including North Atlantic ice-rafting Heinrich event 1. Less severe declines occurred during the Older and Younger Dryas intervals. Dansgaard–Oeschger type cooling cycles registered in the GISP2 ice core record tracked major lake level regressions in East Africa and weakenings of Afro-Asian monsoons during the late Quaternary, possibly linking the desiccation of Lake Victoria to century-scale reductions in solar radiation output.

The polar expression of ENSO and sea-ice variability as recorded in a South Pole ice core

Abstract An annually dated ice core recovered from South Pole (2850 m a.s.l.) in 1995, that covers the period 1487–1992, was analyzed for the marine biogenic sulfur species methanesulfonate (MS). Empirical orthogonal function analysis is used to calibrate the high-resolution MS series with associated environmental series for the period of overlap (1973–92). Utilizing this calibration we present a ~500 year long proxy record of the polar expression of the El Niño–Southern Oscillation (ENSO) and southeastern Pacific sea-ice extent variations. These records reveal short-term periods of increased (1800–50, 1900–40) and decreased sea-ice extent (1550–1610, 1660–1710, 1760–1800). In general, increased (decreased) sea-ice extent is associated with a higher (lower) frequency of El Niño events.

Effect of energy intake on the promotion of mammary carcinogenesis by dietary fat.

The effect of low-fat and high-fat diets on the induction of mammary carcinomas by 1-methyl-1-nitrosourea (MNU) was studied in female Sprague-Dawley rats. All rats were given MNU (25 mg/kg body wt) at 50 days of age. For the first 17 weeks after carcinogen administration, they were fed a purified diet containing either 5 or 20% fat incorporated into agar gel. Food intake was restricted, so that the amounts fed provided the same amount of net utilizable energy each day for both groups, regardless of the fat content of the diets. From 17 to 32 weeks, the diets were fed ad libitum. During the restricted feeding period, there was no significant difference in tumor incidence or in the number of tumors detected between the groups. During the weeks in which animals were fed ad libitum, significantly more tumors appeared in the high-fat group than in the low-fat group. The data provide support for the hypothesis that consumption of a high-fat diet can lead to an enhancement of mammary carcinogenesis. It appears, however, that diets must be consumed ad libitum for the stimulatory effect on tumor occurrence to be exhibited.

Ocean color and river data reveal fluvial influence in coastal waters

A critical yet poorly quantified aspect of the Earth system is the influence of river-borne constituents on coastal biogeochemical dynamics. Coastal waters contain some of the most productive ecosystems on Earth and are sites of intense downward particle fluxes and organic accumulation. Also, in many parts of the world, coastal ecosystems are experiencing unfavorable changes in water quality some of which can be linked directly to the transport of waterborne constituents from land. These include the well-publicized, increasing frequency of hypoxia events in the Gulf of Mexico [Goolsby, 2000], harmful algal blooms [Smayda, 1992], diminished water quality and changes in marine biodiversity [Radach et al., 1990].

Constraints on the age and dilution of Pacific Exploratory Mission‐Tropics biomass burning plumes from the natural radionuclide tracer 210Pb

During the NASA Global Troposphere Experiment Pacific Exploratory Mission-Tropics (PEM-Tropics) airborne sampling campaign we found unexpectedly high concentrations of aerosol-associated 210Pb throughout the free troposphere over the South Pacific. Because of the remoteness of the study region, we expected specific activities to be generally less than 35 μBq m−3 but found an average in the free troposphere of 107 μBq m−3. This average was elevated by a large number of very active (up to 405 μBq m−3) samples that were associated with biomass burning plumes encountered on nearly every PEM-Tropics flight in the southern hemisphere. We use a simple aging and dilution model, which assumes that 222Rn and primary combustion products are pumped into the free troposphere in wet convective systems over fire regions (most likely in Africa), to explain the elevated 210Pb activities. This model reproduces the observed 210Pb activities very well, and predicts the ratios of four hydrocarbon species (emitted by combustion) to CO to better than 20% in most cases. Plume ages calculated by the model depend strongly on the assumed 222Rn activities in the initial plume, but using values plausible for continental boundary layer air yields ages that are consistent with travel times from Africa to the South Pacific calculated with a back trajectory model. The model also shows that despite being easily recognized through the large enhancements of biomass burning tracers, these plumes must have entrained large fractions of the surrounding ambient air during transport.

OPEN SYSTEMS AND MULTI-LEVEL PROCESSES: IMPLICATIONS FOR SOCIAL RESEARCH†

Abstract Much of contemporary social science methodology is predicted on the assumption of closed, morphostatic (structure maintaining) systems for which “general principles”, “ laws”, and “functional relationships”, are fixed. We argue that multi-variate, non-dynamic techniques as well as single-level, dynamic models and methods, although suitable for stable, basically closed or context insensitive systems, are inadequate, at best partial tools for the general scientific task of representation and explanation of social phenomena. Because human systems are typically open (adaptive, self-transforming systems as opposed to mechanical systems) with morphogenic or structure changing tendencies or potentialities, we stress the need to investigate structural change as well as maintenance and to develop multi-level models and methods appropriate for describing and analysing such phenomena.

The description and analysis of system stability and change: Multi-level concepts and methodology

The Description and Analysis of System Stability and Transformation : Multi-level Concepts and Methodology

Conflict and Structure in Multi-Level Multiple Objective Decision-Making Systems

Over the past several years, we have attempted to model from an open systems perspective human evaluation and decision-making, both individual and collective (Burns and Meeker, 1973, 1974, 1975, 1976; Baumgartner et al, 1975a). Our work has entailed the specification and elaboration of a number of premises which are seen as being basic to any attempt at model building and which stand in opposition to many of the questionable psychological and sociological assumptions underlying game theory as well as most theories of decision-making. Firstly, it is taken as axiomatic that human actions lead to complex interaction effects and to unintended consequences as a result of the complex interrelatedness or structure of most action situations, particularly social situations. At the same time, human action involves multiple objective evaluation and decision-making, since humans act in settings where effective action or survival itself requires controlling or coping with multiple features or dimensions of the environment. As a result of this property, evaluation and decision processes often manifest properties of conflict and inconsistency and related characteristics such as ambivalence, intransitivity, and indecidability. Secondly, human decision and action processes entail problem-solving and creative activities and manifest a pattern of learning and development as theory (guiding action) interacts with practice.