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Geology topics

P. Anderson

Publications and source records attributed to P. Anderson.

6 recordsLinked to original sources
USGS2008

Resolving model parameter values from carbon and nitrogen stock measurements in a wide range of tropical mature forests using nonlinear inversion and regression trees

Objectively assessing the performance of a model and deriving model parameter values from observations are critical and challenging in landscape to regional modeling. In this paper, we applied a nonlinear inversion technique to calibrate the ecosystem model CENTURY against carbon (C) and nitrogen (N) stock measurements collected from 39 mature tropical forest sites in seven life zones in Costa Rica. Net primary productivity from the Moderate-Resolution Imaging Spectroradiometer (MODIS), C and N stocks in aboveground live biomass, litter, coarse woody debris (CWD), and in soils were used to calibrate the model. To investigate the resolution of available observations on the number of adjustable parameters, inversion was performed using nine setups of adjustable parameters. Statistics including observation sensitivity, parameter correlation coefficient, parameter sensitivity, and parameter confidence limits were used to evaluate the information content of observations, resolution of model parameters, and overall model performance. Results indicated that soil organic carbon content, soil nitrogen content, and total aboveground biomass carbon had the highest information contents, while measurements of carbon in litter and nitrogen in CWD contributed little to the parameter estimation processes. The available information could resolve the values of 2-4 parameters. Adjusting just one parameter resulted in under-fitting and unacceptable model performance, while adjusting five parameters simultaneously led to over-fitting. Results further indicated that the MODIS NPP values were compressed as compared with the spatial variability of net primary production (NPP) values inferred from inverse modeling. Using inverse modeling to infer NPP and other sensitive model parameters from C and N stock observations provides an opportunity to utilize data collected by national to regional forest inventory systems to reduce the uncertainties in the carbon cycle and generate valuable databases to validate and improve MODIS NPP algorithms.

Ecological Modelling↗
USGS2006

Simulating Arctic climate warmth and icefield retreat in the last interglaciation

In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleoclimatic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic icefields during the Last Interglaciation. Our simulated climate matches paleoclimatic observations of past warming, and the combination of physically based climate and ice-sheet modeling with ice-core constraints indicate that the Greenland Ice Sheet and other circum-Arctic ice fields likely contributed 2.2 to 3.4 meters of sea-level rise during the Last Interglaciation.

Science↗
USGS2005

Modern pollen data from North America and Greenland for multi-scale paleoenvironmental applications

The modern pollen network in North America and Greenland is presented as a database for use in quantitative calibration studies and paleoenvironmental reconstructions. The georeferenced database includes 4634 samples from all regions of the continent and 134 pollen taxa that range from ubiquitous to regionally diagnostic taxa. Climate data and vegetation characteristics were assigned to every site. Automated and manual procedures were used to verify the accuracy of geographic coordinates and identify duplicate records among datasets, incomplete pollen sums, and other potential errors. Data are currently available for almost all of North America, with variable density. Pollen taxonomic diversity, as measured by the Shannon-Weiner coefficient, varies as a function of location, as some vegetation regions are dominated by one or two major pollen producers, while other regions have a more even composition of pollen taxa. Squared-chord distances computed between samples show that most modern pollen samples find analogues within their own vegetation zone. Both temperature and precipitation inferred from best analogues are highly correlated with observed values but temperature exhibits the strongest relation. Maps of the contemporary distribution of several pollen types in relation to the range of the plant taxon illustrate the correspondence between plant and pollen ranges. ?? 2005 Elsevier Ltd. All rights reserved.

Quaternary Science Reviews↗
USGS1991

Report of 1st discussion group: The last interglacial in high latitudes of the Northern Hemisphere: Terrestrial and marine evidence

The paleoclimatic informations preserved at some selected sites from high northern latitudes correlative with the last interglacial maximum of Isotopic Substage 5e have been compiled on a hemisphere scale. The mapped compilation reveals much warmer climate conditions on average than present in both terrestrial and marine environments, and indicates a northward shift of subpolar and boreal bioclimatic zones. The data also suggest that temperature and precipitation gradients were significantly different than those of the Holocene, with particularly efficient latitudinal and eastward transport of warm air masses. The paleoenvironmental and paleoclimate trends through the last interglacial sensu lato (Isotopic Stage 5) are more difficult to assess because the chronostratigraphical framework is poorly constrained. Nevertheless, the data suggest important regionalism in the climatostratigraphical trends. In particular, the large amplitude climatic cyclicity that characterizes the last interglacial of Europe is barely observed elsewhere. Moreover, by the end of the last interglacial (Isotopic Substage 5a), conditions slightly cooler than present are recorded in western Europe, while relatively warm conditions, similar to today, apparently prevailed in circumpolar regions adjacent to the North Atlantic despite the onset of ice growth. The last interglacial provides paleosynoptic situations, unlike those of the present, that may contribute to understanding interactions within the environmental system on a hemispheric scale. There is, however, an imperative need for uniformization of data sets and for more accurate chronological control on regional scales.

Quaternary International↗