Published online by Cambridge University Press: 22 August 2009
GENERAL INTRODUCTION
Approximately 70% of the Earth's environment is marine, which includes substantial sediment deposits, some of which can be greater than 10 km in depth (Fowler, 1990). Although these sediments contain the largest global organic carbon reservoir (∼15 000 × 1018 g C, Hedges and Keil, 1995), apart from shallow margin sediments (to 200 m water depth), they have been considered to be relatively biogeochemically inactive. For example, Jørgensen (1983) calculated that margin sediments accounted for 83% of global marine sediment oxygen uptake whilst only representing 8.6% of global sediment area. In contrast, deeper sediments (200 to >4000 m water depths), despite being ∼91% of marine sediment area, accounted for only 17% of global oxygen uptake. The situation was considered even more extreme for rates of sulphate reduction, with this being responsible for, respectively, 50% and 0% of all organic matter being degraded in margin and deep water sediments (>4000 m water depths) (Jørgensen, 1983). This low activity was consistent with results demonstrating the limited depth distribution of prokaryotic populations in deep sediments. Morita and ZoBell (1955) concluded that the marine biosphere ended at 7.47 m deep, based on their inability to culture bacteria at this or greater depths. Reports of prokaryotes being isolated from deeper sediments were considered to be contaminants introduced during sampling, or dormant organisms being re-activated (ZoBell, 1938).
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.