Ocean carbon sequestration by fertilization: An integrated bioeochemical assessment

Gruber, N. ; Sarmiento, J.L. ; Gnandesikan, A.

University of California (System). Regents.

关键词: Fertilization;    Biogeochemistry;    Carbon Dioxide;    Seas;    Nutrients;   

DOI  :  10.2172/840613
RP-ID  :  NONE
RP-ID  :  FG03-00ER63010
RP-ID  :  840613

美国|英语

来源: UNT Digital Library

【 摘 要 】

Under this grant, the authors investigated a range of issues associated with the proposal to fertilize the ocean with nutrients (such as iron) in order to increase the export of organic matter from the ocean's near surface waters and consequently increase the uptake of CO{sub 2} from the atmosphere. There are several critical scientific questions that have the potential to be make-or-break issues for this proposed carbon sequestration mechanism: (1) If iron is added to the ocean, will export of organic carbon from the surface actually occur? Clearly, if no export occurs, then there will be no sequestration. (2) if iron fertilization does lead to export of organic carbon from the surface of the ocean, how much CO{sub 2} will actually be removed from the atmosphere? Even if carbon is removed from the surface of the ocean, this does not guarantee that there will be significant removal of CO{sub 2} from the atmosphere, since the CO{sub 2} may be supplied by a realignment of dissolved inorganic carbon within the ocean. (3) What is the time scale of any sequestration that occurs? If sequestered CO{sub 2} returns to the atmosphere on a relatively short time scale, iron fertilization will not contribute significantly to slowing the growth of atmospheric CO{sub 2}. (4) Can the magnitude of sequestration be verified? If verification is extremely difficult or impossible, this option is likely to be viewed less favorably. (5) What unintended consequences might there be from fertilizing the ocean with iron? If these are severe enough, they will be a significant impact on policy decisions. Most research on carbon sequestration by fertilization has focused on the first of these issues. Although a number of in situ fertilization experiments have successfully demonstrated that the addition of iron leads to a dramatic increase in ocean productivity, the question of whether this results in enhanced export remains an open one. The primary focus of the research was on the development of models to examine topics (2) through (5), although some of the research they have accomplished has implications for the first of these topics as well. In this report, they present and discuss their main results and products. They start with a discussion of the results from large-scale fertilization experiments using a relatively simple ecosystem model. While these experiments are very instructive in highlighting the mechanisms and consequences, it is very unlikely that fertilization will ever be carried out on such scales. They therefore conducted a detailed study to investigate how patch-scale fertilization differs from that conducted at basin scale. After presenting the results of this study, they then discuss the results they obtained with regard to consequences of fertilization on ocean biogeochemistry and radiative forcing. Since the existing ecological/biogeochemical models at the beginning of the grant were not adequate to investigate many important components of how ocean ecology and biogeochemistry will respond to the addition of iron, a substantial fraction of their effort went also into the development of a model that would allow them to quantitatively predict phytoplankton functional group diversity. After reporting on their model development work, they close with a summary of their outreach activities and publications.