Globally, lakes are currently accumulating organic carbon (OC) at an estimated annual rate of about 42 Tgṁyr−1. Most of the OC in all but the most oligotrophic of these lakes is autochthonous, produced by primary production in the lakes. The sediments of reservoirs accumulate an additional 160 Tg annually, and peatlands contribute 96 Tg annually. These three carbon pools collectively cover less than 2% of the Earth's surface and constitute a carbon sink of about 300 Tgṁyr−1. Although the oceans cover 71% of the Earth's surface, they accumulate OC at a rate of only about 100 Tgṁyr−1.