2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 99-1
Presentation Time: 9:00 AM-6:00 PM

THE SHORTEST DISTANCE BETWEEN TWO POINTS ISN'T ALWAYS A GREAT CIRCLE: GETTING AROUND LAND MASSES IN THE CALIBRATION OF MARINE GEODISPARITY

WU, Shuang-Ye, Geology, University of Dayton, 300 College Park Ave, Dayton, OH 45469, swu526@gmail.com and MILLER, Arnold I., Department of Geology, Univ of Cincinnati, 500 Geology Physics Building, University of Cincinnati, Cincinnati, OH 45221-0013

In the assessment of Phanerozoic marine global biodiversity, there has been longstanding interest in quantifying compositional dissimilarities among sampling points as a function of their distances from one another (geodisparity). Previous research has demonstrated that dissimilarity tends to increase significantly with great-circle distance (GCD), but begins to stabilize at transoceanic distances. The accuracy of these assessments, and absolute comparisons among different temporal intervals, may suffer, however, because of intervening land masses that are not accounted for when distance is calibrated simply as GCD. Here, we present a new method for determining the shortest over-water distance (WD) between two marine locations, and we use the method to recalibrate for several Phanerozoic intervals previous measures of global geodisparity in the taxonomic compositions of marine biotas.

WD was determined using a cost-distance approach in ArcGIS, modified to work on a spherical, as opposed to a planar, surface. For a given time interval, a paleogeographic map with water and landmasses delineated was first digitized and converted to a raster with a cell size of 0.5 by 0.5 degrees. All cells covering water were assigned a value of 1, whereas land cells were assigned “No Value” so they would be excluded in calculations. The cost-distance algorithm was then used to determine the shortest over-water cell path and distance between any two sample points, taking into account latitudinal variations in the distances traversed across individual cells.

Results demonstrate two major effects of using WD. First, compositional dissimilarity between locations tends to increase more slowly with WD than with GCD. Second, pairs of locations with WDs that are at least 50% greater than their GCDs tend to have greater compositional dissimilarity to one another than those with more closely matching WDs and GCDs. These differences are expected as WD better represents the “true” distance between locations; they diminish at GCDs of 6000 km or more, when clear transoceanic paths between locations become more common. Despite these effects, using WD does not alter fundamental patterns of global geodisparity observed in previous research, but it does add interesting details to the picture.

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 99--Booth# 89
Paleontology (Posters) II: Extinction and Environment
Minneapolis Convention Center: Hall C
9:00 AM-6:00 PM, Monday, 10 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 259

© Copyright 2011 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.