Major Geologic Cycles of Carbon Oil Coal Graphite Limestone Marble Sedimentary Organic Matter Calcite Aragonite Inorganic Carbon Cycle Carbonate CO2 Organic Carbon Cycle Biomass 380 380 340 360 CO2 Mauna Loa CO2 South Pole CO2 concentr ation ppm a 320 300 O2 ppm CO2 concentration ppm 360 280 260 240 0 20 40 1988 1992 1996 O2 Cape Grim O2 Barrow 220 200 180 1950 1960 1970 1980 1990 d Vostok 340 320 300 280 260 240 220 200 180 400 2000 300 Year 380 340 320 300 280 260 Mauna Loa Law Dome Adelie Land Siple South Pole 240 220 200 180 800 1000 1200 1400 Year 1600 1800 360 e 0 Pagani et al Pearson and Palmer 340 320 300 280 260 240 220 180 25 2000 20 15 10 Age Myr BP 5 0 7500 c Taylor Dome CO2 concentration ppm CO2 concentration ppm 100 200 380 360 200 Age kyr BP 380 b CO2 concentration ppm CO2 concentration ppm 360 Petit et al Fischer et al 340 320 300 280 260 240 220 f 6000 4500 3000 1500 200 180 12500 0 10000 7500 5000 Age yr BP 2500 0 500 400 300 200 Age Myr BP 100 0 Figure 3 2 Variations in atmospheric CO2 concentration on different time scales a Direct measurements of atmospheric CO2 concentration Keeling and Whorf 2000 and O2 from 1990 onwards Battle et al 2000 O2 concentration is expressed as the change from an arbitrary standard b CO2 concentration in Antarctic ice cores for the past millenium Siegenthaler et al 1988 Neftel et al 1994 Barnola et al 1995 Etheridge et al 1996 Recent atmospheric measurements at Mauna Loa Keeling and Whorf 2000 are shown for comparison c CO2 concentration in the Taylor Dome Antarctic ice core Inderm hleet al 1999 d CO2 concentration in the Vostok Antarctic ice core Petit et al 1999 Fischer et al 1999 e Geochemically inferred CO2 concentrations from Pagani et al 1999a and Pearson and Palmer 2000 f Geochemically inferred CO2 concentrations coloured bars represent different published studies cited by Berner 1997 The data from Pearson and Palmer 2000 are shown by a black line BP before present Figur e 1 Water column O 2 and sedimen t carbon contents for stud y sites from the Washing ton and Mex ican ma rgins a Dissolved O 2 concen tration as a func tion of water depth for the contin ental marg ins of Washing ton State sq uar es and northwestern Mex ico circles Note that the Mex ican O 2 concentrations between 150 and 600 m depth are indis tinguishab le from zer o b Weight per cent organic carbon as a func tion of depth in sedimen ts for repr esent ative station s from the Washing ton empty sq uares 630 m lled sq uares 120 m and Mexican contine ntal ma rgins empty circles 620 m lled circles 150 m Fig ur e 2 Org anic carbon burial ef ciency a s a function of oxygen expo sur e time Symbo ls are as follows the Mexican shelf 100 150 m empty circles Mex ican slop e oxyg en de c ient zone 150 1 000 m lled circles the Washing ton shelf and upp er slope 100 600 m shaded sq uares Washington lower slope J I H et al manu script in preparation 600 2 500 m emp ty diamon ds and the California ma rgin 17 1 500 3 500 m shaded triangl es O 2 exposure time is plotted on a log line ar scale so that variations in burial ef ciency at short expo sur e times can be disti nguished the dotted line is a least squar es t to the data For Mexican slope sta tions with zer o O 2 exposure time the data are plotted at 0 003 yr 2 d as the log scale cannot accommod ate a value of zer o Wher e we calculate a ma ximum and minim um total carbon oxidati on rate we present the corr esponding rang e in carbo n burial ef cienc y as two connec ted symbols Inse t as main gur e but with a linear linear scale to demon str ate the exponen tial nature of the relationship H Hartnett R Keil J Hedges A Devol 1998 Influence of oxygen exposure time on organic carbon preservation in continental margin sediments Nature 391 572 574 source Milkhov 2004 Panel a represents the high range of hydrate estimates panel c represents the low range of estimates