摘要:

Previous models have attempted to explain glacial to interglacial changes in atmospheric pCO2by invoking changes in the ocean's nutrient concentration or regional changes in nutrient utilization. Nitrogen is limiting to primary production and has a residence time in the ocean compatible with glacial to interglacial variations. But up to now, there has been no geological indicator for glacial to interglacial changes in the ocean's nitrogen cycle. We propose that15N/14N ratios for the organic matrix of preserved foraminifera yield an interpretable δ15N record. We have developed models to study the relationship between plausible changes in the ocean's nitrogen cycle and resulting changes in the15N/14N ratio of dissolved NO3−. Our model results demonstrate that15N/14N ratios exhibit excursions during periods in which the oceans are accumulating or losing nitrogen regardless of the means by which these changes occur. Foraminifera15N/14N results for a Pacific and an Atlantic core provide evidence against wide spread glacial anoxia, a consequence of many models of ocean chemistry. We suggest that increasing shelf‐sediment denitrification upon deglaciation reduced nitrogen concentrations in the modern ocean. Ambiguities between the two foraminifera15N/14N records indicate that local effects associated with changes in hydrography or ecology need to be studied fur

ISSN:0886-6236    

DOI:10.1029/GB003i002p00107

年代:1989

数据来源: WILEY

摘要:

Nitric oxide (NO), nitrous oxide (N2O), and carbon dioxide (CO2) measurements were made at unburned and burned sites within a semiarid chaparral ecosystem located in southern California. Some sites were burned during the dry season (July); others at the start of the wet season (December). This report primarily describes measurements of gas fluxes and soil parameters at unburned sites and sites burned in December. Burning greatly increased the concentrations of ammonium (NH4+), nitrate (NO3−) and potentially mineralizable nitrogen in soil. Nitrate concentrations at sites burned in December were much higher than those at sites burned in July, indicating active nitrification and decreased water stress. Irrigation usually produced immediate but short‐lived increases in NO flux; however, these increases were more moderate than those observed in July. Diurnal studies performed at irrigated and nonirrigated burned sites both in July and December indicated a high correlation of NO flux with temperature (r2>0.81) at most sites, provided that the soil moisture was greater than 30%. Results of diurnal studies were used to normalize daily fluxes and to calculate semiannual losses of nitrogen from both burned and unburned sites. Over a six‐month period, 0.3 g N m−2was lost as NO from burned chaparral, representing 75% of the exchangeable nitrogen lost over the same period and 3.9% of the potentially mineralizable nitrogen present in the soil. From unburned soil, 0.1 g N m−2was lost as NO, representing 33% of the exchangeable nitrogen and 3.3% of the potentially mineralizable nitrogen in soil. These studies indicate that over a six‐month period following a burn, much of the NH4+produced by the burning of aboveground vegetation is lost to the atmosphere as NO. These emissions may be expected to persist for periods in excess of six months because of the increased mineralizable nitrogen available in soil as a result of the burn. Losses of nitrogen both during and following a burn may impact soil fertility, contribute to both air and water pollution, and yield significant inputs to the global atmospheric budgets of both

ISSN:0886-6236    

DOI:10.1029/GB003i002p00121

年代:1989

数据来源: WILEY

摘要:

The sensitivity of a number of different globally aggregated models of the terrestrial biosphere to changes of atmospheric CO2and temperature is investigated. Net primary production (NPP) or net photosynthesis (NP) is modeled as a logistic function, with enhancement due to increased CO2using the β factor widely used in global carbon cycle models. NPP also increases with temperature using a Q10of 1.4, while respiration and coefficients for translocation and for detritus to soil, and soil to soil, carbon transfers increase with a Q10of 2.0. The pathway of carbon flow to the slowly overturning soil reservoir has a significant effect on equilibrium sensitivity of total carbon mass to temperature increases if the transfer coefficient from the rapidly to slowly overturning soil reservoir is fixed; maximum sensitivity occurs if all the carbon entering the slowly overturning reservoir first passes through the rapidly overturning reservoir. If the transfer coefficient increases in parallel with the increase of soil respiration coefficient, the carbon pathway has no effect on equilibrium sensitivity, although the transient response depends strongly on the subdivision of the soil reservoir. Allowing the detritus to soil transfer coefficient to increase in parallel with the coefficient for detrital respiration reduces the equilibrium sensitivity of total carbon mass to temperature increases by about half. The variation in model response to CO2and temperature increases using different model structures is generally comparable to the variation resulting from uncertainty in feedback parameters

ISSN:0886-6236    

DOI:10.1029/GB003i002p00137

年代:1989

数据来源: WILEY

摘要:

Preliminary data obtained in the operation of a nested‐network dry deposition measurement program in the eastern United States are used in conjunction with wet deposition data obtained at (or near) the same sites to investigate the variability of ratios of dry to wet deposition of sulfur (as sulfur dioxide and submicron sulfate for dry deposition, and as sulfate for wet deposition). On a monthly basis, the ratio is extremely variable at every location; however, a more coherent picture arises when the average annual cycle is considered. The sites studied here (Oak Ridge, Tennessee; State College, Pennsylvania; Whiteface Mountain, New York; and Bondville, Illinois) yield dry/wet ratios for sulfur deposition that minimize in the summer, with values of about 0.3. At other times of the year, values sometimes exceeding 2.0 are obtained. A summer peak at Oak Ridge is tentatively attributed to the effects of a local drought. The variability is such that use of dry/wet ratios to estimate dry deposition rates when only wet deposition data are available cannot be recommende

ISSN:0886-6236    

DOI:10.1029/GB003i002p00155

年代:1989

数据来源: WILEY

摘要:

The Guinea Dome area (12°N, 22°W) is characterized by a summertime O2maximum which lies at the top of the thermocline. The vertical distributions of molecular nitrogen and argon are used to discuss the physical and biological contributions to oxygen supersaturation in that region. Whereas this subsurface O2maximum is as sharp as those encountered elsewhere in the ocean, it is not at a high supersaturation level (maximum 4.4% on average). Thus the O2maximum does not seem to be mainly due to photosynthesis and hence Reid's [1962] physical hypothesis appears to be like the major explanatio

ISSN:0886-6236    

DOI:10.1029/GB003i002p00163

年代:1989

数据来源: WILEY

摘要:

The average difference between the partial pressure of CO2in ocean surface water and the overlying atmosphere (ΔpCO2= pCO2,ocean) ‐ pCO2,atm) has been changing ever since the beginning of the anthropogenic era due to the dumping of CO2as a waste gas into the atmosphere. However, the change in the difference has not been uniform over the surface of the oceans. This work assesses regional variations in the Earth scale patterns of sources (ΔpCO2>0) and sinks (ΔpCO2<0) during this anthropogenic transient. The regional correction, ΔpCO2*, is defined as the quantity that must be added to a region's preanthropogenic ΔpCO2to give its present value. Using a five‐box ocean model with special surface regions for the prominent equatorial Pacific source and north Atlantic sink, we show that a larger magnitude of ΔpCO2*is necessary for these two regions than for the average ocean. Analytical results with a multiple one‐and‐one‐half‐box model, in which horizontal water exchanges are neglected, indicate that the ratio Of ΔpCO2*values for any two regions should vary inversely with the ratio of their gas exchange coefficients and nearly directly with the ratio of their deep‐to‐surface water piston velocities. The ΔpCO2*values for regions of the five‐box model vary by as much as a factor of six; predictions of the multiple one‐and‐one‐half‐box model are within a factor of two. Discrepancies from these predictions are believed to be due to horizontal and intermediate‐depth water exchanges, which tend to equalize the ΔpCO2*values. Our best estimate is that regions with large vertical water exchanges (equatorial and high‐latitude zones) and/or low gas exchange coefficients (equatorial zones) have ΔpCO2*magnitudes at least twice as large as the magnitud

ISSN:0886-6236    

DOI:10.1029/GB003i002p00179

年代:1989

数据来源: WILEY