Organic Carbon and Carbonate as Paleoproductivity Proxies: Examples
from High and Low Productivity Areas of the Tropical Atlantic
C. RUhlemann*, PJ. MUller and RR Schneider
Universitat Bremen, Fachbereich Geowissenschaften, Postfach 33 0440,
D-28334 Bremen, Germany
*correspondingauthor (e-mail):ruehl@uni-bremen.de
Abstract: We reviewed the factors influencing organic carbon and carbonate preservation in marine
sediments. The application and problems of these two biogenic components as paleoproductivity
proxies are exemplified by comparison of two sediment cores: one from the high productivity upwelling
region off Angola, and the other from the low productivity area off North Brazil. Unlike the upwelling
site, sedimentary organic carbon in the low productivity area is problematic as a paleoproductivity
indicator. There, calcium carbonate, the predominant biogenic material of the pelagic ocean, serves
as an alternative estimator for paleoproductivity. During the last 300,000 years, high and variable
paleoproductivity in the eastern Atlantic contrasts with low and relatively constant values in the
West. Beyond this, a countercyclicity of paleoproductivity variations between the eastern and the
western tropical Atlantic is observed. During cold climatic substages, paleoproductivity was at
maximum in the East, whereas minimum values were recorded in the West. These inverse relationships
are attributed to a lowered nutrient concentration of glacial intermediate waters which are the nutrient
source of open ocean new production. At the same time, the supply of nutrients was enhanced in the
eastern Atlantic due to intensified wind-driven upwelling. Moreover, the increased zonal wind stress
may have caused a deepening of the nutricline in the West coupled with a synchronous shallowing
in the East. The sharp Glacial-to-Holocene decrease in paleoproductivity in the upwelling areas
(dominated by opal producers), occurred contemporaneously with an increase in the oligotrophic
open ocean (dominated by carbonate producers). This should have resulted in a decrease of the
carbon rain ratio (C o ,/CCaC03)' possibly contributing to the observed Glacial-to-Holocene increase in
atmospheric pC0 2 •
Introduction
Unicellular phytoplankton and zooplankton are the
largest sources of organic carbon in the marine
environment. Beside organic matter, some important planktic organisms build tests which consist
either of calcium carbonate (CaCO,) or opal
(Si0 2 ' nH,O). These three components, especially
carbonate, constitute virtually the entire biogenic
fraction in sediments deposited on continental slopes
and on the deep-sea floor. Paleoproductivity studies of marine sediments attempt to document temporal and spatial changes in the production of these
biogenic components and search for the causes and
effects, in particular with respect to the earth's climate. Primary production (synonymous: productivity) of marine phytoplankton is an important factor
in the climate system as it accounts for the partitioning of carbon dioxide (C0 2 ) between ocean and
atmosphere (Broecker 1982). Atmospheric CO 2 , a
major greenhouse gas, affects the global heat balance and hence the climate owing to the absorption of thermal radiation leaving the earth's surface
(Trenberth et al. 1996).
Long-term changes of high interglacial and low
glacial atmospheric CO 2 concentrations, as determined from measurements of gas trapped in continental ice (e.g. Bamolaetal. 1987, 1991; Jouzelet
From FISCHER G, WEFER G (eds), 1999, Use oj Proxies in Paleoceanography: ExamplesJrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 315-344
from High and Low Productivity Areas of the Tropical Atlantic
C. RUhlemann*, PJ. MUller and RR Schneider
Universitat Bremen, Fachbereich Geowissenschaften, Postfach 33 0440,
D-28334 Bremen, Germany
*correspondingauthor (e-mail):ruehl@uni-bremen.de
Abstract: We reviewed the factors influencing organic carbon and carbonate preservation in marine
sediments. The application and problems of these two biogenic components as paleoproductivity
proxies are exemplified by comparison of two sediment cores: one from the high productivity upwelling
region off Angola, and the other from the low productivity area off North Brazil. Unlike the upwelling
site, sedimentary organic carbon in the low productivity area is problematic as a paleoproductivity
indicator. There, calcium carbonate, the predominant biogenic material of the pelagic ocean, serves
as an alternative estimator for paleoproductivity. During the last 300,000 years, high and variable
paleoproductivity in the eastern Atlantic contrasts with low and relatively constant values in the
West. Beyond this, a countercyclicity of paleoproductivity variations between the eastern and the
western tropical Atlantic is observed. During cold climatic substages, paleoproductivity was at
maximum in the East, whereas minimum values were recorded in the West. These inverse relationships
are attributed to a lowered nutrient concentration of glacial intermediate waters which are the nutrient
source of open ocean new production. At the same time, the supply of nutrients was enhanced in the
eastern Atlantic due to intensified wind-driven upwelling. Moreover, the increased zonal wind stress
may have caused a deepening of the nutricline in the West coupled with a synchronous shallowing
in the East. The sharp Glacial-to-Holocene decrease in paleoproductivity in the upwelling areas
(dominated by opal producers), occurred contemporaneously with an increase in the oligotrophic
open ocean (dominated by carbonate producers). This should have resulted in a decrease of the
carbon rain ratio (C o ,/CCaC03)' possibly contributing to the observed Glacial-to-Holocene increase in
atmospheric pC0 2 •
Introduction
Unicellular phytoplankton and zooplankton are the
largest sources of organic carbon in the marine
environment. Beside organic matter, some important planktic organisms build tests which consist
either of calcium carbonate (CaCO,) or opal
(Si0 2 ' nH,O). These three components, especially
carbonate, constitute virtually the entire biogenic
fraction in sediments deposited on continental slopes
and on the deep-sea floor. Paleoproductivity studies of marine sediments attempt to document temporal and spatial changes in the production of these
biogenic components and search for the causes and
effects, in particular with respect to the earth's climate. Primary production (synonymous: productivity) of marine phytoplankton is an important factor
in the climate system as it accounts for the partitioning of carbon dioxide (C0 2 ) between ocean and
atmosphere (Broecker 1982). Atmospheric CO 2 , a
major greenhouse gas, affects the global heat balance and hence the climate owing to the absorption of thermal radiation leaving the earth's surface
(Trenberth et al. 1996).
Long-term changes of high interglacial and low
glacial atmospheric CO 2 concentrations, as determined from measurements of gas trapped in continental ice (e.g. Bamolaetal. 1987, 1991; Jouzelet
From FISCHER G, WEFER G (eds), 1999, Use oj Proxies in Paleoceanography: ExamplesJrom the South Atlantic. Springer-Verlag
Berlin Heidelberg, pp 315-344