Chapter 6 The Carbon Cycle © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

2 Figure 6.1 Simplified diagram of some of the key fluxes in the global carbon cycle. The values inside the boxes are standing stocks (in Pg C); the arrows represent annual fluxes (Pg C/y). The black arrows and numbers show the preindustrial values of standing stocks and fluxes; the red arrows and numbers indicate the changes due to anthropogenic activity. Note there are some differences in the values shown on this figure and in Table 6.1 due to different levels of aggregation and different time periods for the estimates. (The diagram is redrawn from Climate Change (2007): The Physical Scientific Basis, Intergovernmental Panel on Climate Change.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

3 Figure 6.2 Variation in atmospheric CO 2 over three timescales. Panel (a) shows direct measurements of atmospheric CO 2 at Mauna Loa, Hawaii. The data for panels (b) and (c) come from ice cores for (b) the Law Dome ice core in Antarctica and (c) the Vostok ice core in Antarctica. The x-axis for panel (c) is in years before present; for panels (a) and (b) the x-axis is the calendar year. ((a) is drawn from data available at Dr. Pieter Tans, NOAA/ESRL ( and Dr. Ralph Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/); (b) is drawn from data available at (Etheridge et al. 1996); and (c) is drawn from data available at (Petit et al. 1999).) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

4 Figure 6.3 Rough diagram of the long-term (4 billion year) record of oxygen in Earth’s atmosphere. Arrows show the appearance of major groups of the biota. (Modified from Berner and Kothavala 2001.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

5 Figure 6.4 Carbon storage and export for the past 12,000 years at the Hubbard Brook Experimental Forest. (Redrawn from Cole and Caraco 2001.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

6 Figure 6.5 Changes in the concentration of dissolved organic C as it passes through a forest. Values are mg C/L. Precipitation has low concentrations of DOC, but as this water moves through the forest canopy it acquires DOC from the trees (throughfall) and even more in the rich organic layers of the forest floor. DOC concentrations are reduced due to both decomposition and sorption in the mineral layers of the soil (upper and lower B horizons). As water exits the system in stream water it has concentrations much lower than in throughfall or forest floor soils. (Redrawn from the data in McDowell and Likens 1988.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

7 Figure 6.6 An eight-year record of the partial pressures in the tidal, freshwater Hudson River. Upper panel: CO 2 in the water (closed symbols) and air (open symbols); lower panel: O 2 in the water; the solid line pO 2 = 0.2 represents O 2 in air. (Modified from Raymond et al and Cole and Caraco 2001.) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).

8 Figure 6.7 Net ecosystem gas exchange (upper; NEE = NEP = GPP−R); GPP (middle) and ecosystem respiration (R; lower) in a temperate grassland in Alberta, Canada. Shown are three years of data based on eddy flux towers. Negative values represent the uptake of CO 2 by the system; positive values represent the net release of CO 2. In this system GPP is almost always larger than R, leading to negative values (net uptake) of CO 2 for the system as a whole (NEE) during the growing season. (Data from Flanagan et al ) © 2013 Elsevier, Inc. All rights reserved. From Fundamentals of Ecosystem Science, Weathers, Strayer, and Likens (eds).