Organic carbon distribution in the North Atlantic Ocean during the last glacial maximum

Abstract

The organic carbon content of eighty-two last glacial maximum (LGM) sediment samples from the North Atlantic Ocean was determined with a Coulometer. Organic carbon in these sediments averaged about 0.5% by weight, slightly higher than in modern sediments. Factors that control organic carbon distribution were examined in two ways: by mapping the spatial distribution of organic carbon during the LGM and by comparing organic carbon content to sediment characteristics. In general, sediment organic content increases with increasing sedimentation rate, increasing clay content, and decreasing carbonate content. The spatial distribution of LGM organic content is similar in most respects to the mapped modern distribution, the primary exception being areas of high organic content. One area of high organic content off nortwest Africa is situated in the same area geographically but is larger than its modern counterpart perhaps indicating that wind-driven upwelling was more intense and/or widespread during the LGM. The two other areas of high organic carbon content, the North American margin and west of the Mid-Atlantic Ridge (MAR) at about 40°N, have no modern counterpart. On the North American margin, south of Cape Cod, organic carbon content is generally >0.6% and in several samples is >0.9%. The increased organic carbon content of sediment in this area appears to be related to an increase in sedimentation rate and the concomitant increase in inorganic nutrients. The area west of the MAR is more perplexing and appears to be related to changes in LGM surface circulation.