Multidisciplinary research in the space sciences

Research activities were carried out in the following areas during this reporting period: (1) astrophysics; (2) climate and atmospheric modeling; and (3) climate applications of earth observations & geological studies. An ultra-low-noise 115 GHz receiver based upon a superconducting tunnel diode mixer has been designed and constructed. The first laboratory tests have yielded spectacular results: a single-sideband noise temperature of 75 K considerably more sensitive than any other receiver at this frequency. The receiver will replace that currently in use on the Columbia-GISS CO Sky Survey telescope. The 1.2 meter millimeter-wave telescope at Columbia University has been used to complete two large-scale surveys of molecular matter in the part of the inner galaxy which is visible from the Northern hemisphere (the first galactic quadrant); one of the distant galaxy and one of the solar neighborhood. The research conducted during the past year in the climate and atmospheric modeling programs has been focused on the development of appropriate atmospheric and upper ocean models, and preliminary applications of these models. Principal models are a one-dimensional radiative-convective model, a three-dimensional global climate model, and an upper ocean model. During the past year this project has focused on development of 2-channel satellite analysis methods and radiative transfer studies in support of multichannel analysis techniques

Atmospheric, climatic and environmental research

Research conducted during the past year in the climate and atmospheric modeling programs was focused on the development of appropriate atmospheric and upper ocean models, and preliminary applications of these models. Prinicpal models are a one-dimensional radiative-convection model, a three-dimensional global climate model, and an upper ocean model. Principal application is the study of the impact of CO2, aerosols and the solar constant on climate. Also the performance of the International Satellite Cloud Climatology Project cloud detection algorithm was evaluated, concentrating initially on its application to geosynchronous data, with an eventual switch of the developed methodologies to data from polar orbiting satellites. In the process, a number of improvements were made, in particular: an improved technique for tracking small scale day to day variability in clear sky continental temperatures; a number of techniques for the statistical assessment of cloud detection uncertainties due to cloud types which are spatially and temporally invariant; and a method used to detect those cloudy regions which have long term spatial and temporal stability

Plötzliche Klimawechsel: In der Vergangenheit haben sich die Durchschnittstemperaturen auf der Erde wiederholt in wenigen Jahrzehnten um mehrere Grad verändert. Droht uns ein ähnlich jäher Klimasprung?

Die letzten zehn Jahrtausende, in denen sich die menschliche Zivilisation entwickelte, sind eine Ausnahmeerscheinung in der jüngeren Klimageschichte unseres Planeten: Nie zuvor in den vergangenen 100000 Jahren herrschten über so lange Zeit derart konstante und ausgeglichene Witterungsbedingungen, sondern es kam immer wieder zu Kälteeinbrüchen und Wärmeperioden, die jeweils mindestens 1000 Jahre andauerten. Wie Bohrkerne von verschiedenen Stellen auf dem grönländischen Eisschild zeigen, fielen oder stiegen die mittleren Wintertemperaturen in Nordeuropa innerhalb von nur einem Jahrzehnt um bis zu zehn Celsiusgrade. Zeugen dieser plötzlichen Änderungen sind der atmosphärische Staub, die Methanmenge und das Verhältnis der Sauerstoff-Isotope mit den Atommassen 18 und 16, die in den jährlichen Eisschichten konserviert sind. Die letzte tausendjährige Kälteperiode wird nach dem lateinischen Namen der Tundrapflanze Silberwurz, deren Lebensraum sich damals stark ausweitete, als jüngere Dryaszeit bezeichnet. Sie endete vor etwa 11000 Jahren und hat ihre Spuren in den Sedimenten auf dem Meeresboden des Nordatlantik, in den skandinavischen und isländischen Gletschermoränen sowie in den nordeuropäischen und großen kanadischen Seen und Mooren hinterlassen. Auch Neuengland kühlte sich damals deutlich ab. Wahrscheinlich war der Kälteeinbruch der jüngeren Dryaszeit sogar von globalem Ausmaß. Jedenfalls gibt es dafür immer mehr Hinweise. So wurde die nacheiszeitliche Erwärmung des antarktischen Festlandsockels für 1000 Jahre unterbrochen; die neuseeländischen Gletscher dehnten sich erheblich aus, und das Artenspektrum der Planktonpopulation im Südchinesischen Meer änderte sich markant. Der Methangehalt der Atmosphäre nahm um 30 Prozent ab. Nur die Pollenuntersuchungen in einigen Teilen der USA zeigen keine Spuren dieser Kaltzeit

Will Our Ride into the Greenhouse Future be a Smooth One?

The climate record kept in ice and in sediment reveals that since the invention of agriculture some 8000 yr ago, climate has remained remarkably stable. By contrast, during the preceding 100,000 yr, climate underwent frequent, very large, and often extremely abrupt shifts. Furthermore, these shifts occurred in lockstep across the globe. They seem to be telling us that Earth's climate system has several distinct and quite different modes of operation and that it can jump from one of these modes to another in a matter of a decade or two. So far, we know of only one element of the climate system which has multiple modes of operation: the oceans' thermohaline circulation. Numerous model simulations reveal that this circulation is quite sensitive to the freshwater budget in the high-latitude regions where deep waters form. Perhaps the mode shifts revealed in the climate record were initiated in the sea. This discovery complicates predictions of the consequences of the ongoing buildup of greenhouse gases in the atmosphere. If the major climate changes of glacial time came as the result of mode shifts, can we be certain that the warming will proceed smoothly? Or is it possible that about 100 years from now, when our descendants struggle to feed the 15 or so billion Earth inhabitants, climate will jump to a less hospitable state. It is difficult to comprehend the misery that would follow on the heels of such an event

North Atlantic Deep Water Formation

Various studies concerning differing aspects of the North Atlantic are presented. The three major topics under which the works are classified include: (1) oceanography; (2) paleoclimate; and (3) ocean, ice and climate modeling

The effect of wind and currents on gas exchange in an estuarine system

The objectives were to develop a non-volatile tracer to use in gas exchange experiments in laterally unconfined systems and to study applications of deliberate tracers in limnology and oceanography. Progress was made on both fronts but work on the development of the non-volatile tracer proved to be more difficult and labor intensive that anticipated so no field experiments using non-volatile tracers was performed as yet. In the search for a suitable non-volatile tracer for an ocean scale gas exchange experiment a tracer was discovered which does not have the required sensitivity for a large scale experiment, but is very easy to analyze and will be well suited for smaller experiments such as gas exchange determinations on rivers and streams. Sulfur hexafluoride, SF6, was used successfully as a volatile tracer along with tritium as a non-volatile tracer to study gas exchange rates from a primary stream. This is the first gas exchange experiment in which gas exchange rates were determined on a head water stream where significant groundwater input occurs along the reach. In conjunction with SF6, Radon-222 measurements were performed on the groundwater and in the stream. The feasibility of using a combination of SF6 and radon is being studied to determine groundwater inputs and gas exchange of rates in streams with significant groundwater input without using a non-volatile tracer

Anomalous AMS radiocarbon ages for foraminifera from high-deposition-rate ocean sediments

Radiocarbon ages on handpicked foraminifera from deep-sea cores are revealing that areas of rapid sediment accumulation are in some cases subject to hiatuses, reworking and perhaps secondary calcite deposition. We present here an extreme example of the impacts of such disturbances. The message is that if precise chronologies or meaningful benthic planktic age differences are to be obtained, then it is essential to document the reliability of radiocarbon ages by making both comparisons between coexisting species of planktomc foraminifera and detailed down-core sequences of measurements

Upwelling rates for the equatorial Pacific Ocean derived from the bomb 14C distribution

A north-south cross section of bomb-produced radiocarbon (14C) in the upper 1000 m of the central equatorial Pacific Ocean (CEP) was measured in April, 1979 during Leg 3 of the NORPAX shuttle experiment. The 14C shows an equatorial mixed layer depletion of ∼40‰ compared to subtropical surface waters. Upwelling of deeper, 14C depleted water maintains this minimum. Two subsurface tongues of high 14C water, found north and south of the equator, are associated with high salinity water and probably result from exchange with subtropical surface water. The continued increase in mixed layer 14C levels in the CEP (up to 1979) indicates the importance of 14C input from these subsurface 14C maxima. Equatorward meridional advection resulting from geostrophic flow is the predominant supply of water upwelling at the equator and controls the 14C distribution in the CEP. The results of multi-layer mixing model calculations indicate an upwelling transport rate of 47 Sverdrups (5S–4N) and a maximum depth of upwelling of 225 m (σ0 = 26.5). These equatorial circulation characteristics explain the 14C, ΣCO2, oxygen, salinity and tritium distributions measured during Leg 3. The time history of mixed layer bomb 14C concentrations in the CEP indicate an exchange time of 4–6 years between the subtropical and equatorial surface oceans

Constraints on mantle ^3He fluxes and deep-sea circulation from an oceanic general circulation model

We have simulated the steady-state distribution of helium in the deep sea to investigate the magnitude and spatial and temporal variability of mantle degassing and to characterize deep-sea circulation and ventilation. The simulation was produced by linking a simple source function for helium injected at mid-ocean ridges with an oceanic general circulation model (GCM). By assuming that the flux of mantle helium is linearly proportional to the seafloor spreading rate and by using previous estimates for the total flux of mantle helium into the oceans, the GCM yields an oceanic ^3He distribution which is in qualitative agreement with observations both in overall magnitude and in general distribution. This provides new evidence that the flux of mantle ^3He into the oceans is about 1000 mol/yr and that mid-ocean ridges are the dominant source of mantle helium. Although the match with observations is good in the Pacific and Indian Oceans, the simulated ^3He anomalies throughout the Atlantic Ocean are much higher than has been measured. Because the GCM is thought to reproduce Atlantic circulation reasonably well, this discrepancy suggests an error in the helium source function. Either helium injection is not a linear function of seafloor emplacement rate, or eruption and concomitant degassing are highly episodic at the slow spreading rates characteristic of the Mid-Atlantic Ridge (MAR). The latter explanation would imply minimal volcanic activity along the entire length of the MAR over the last few centuries. In addition to constraints on the degassing flux, our work provides information on the transport and ventilation of deep ocean waters and constrains the degree to which current GCMs can reproduce deep-water circulation patterns. While the results generally support the GCM's abyssal circulation, our simulation reveals regions of overly-intense lateral diffusion and upwelling in the model, particularly in the equatorial Pacific. Similarly, there appears to be insufficient production of He-ventilated bottom waters in the model Antarctic. These observations suggest that further refinement of the GCM abyssal circulation is required