400
Walter et al.
ratios on sinking particles between box i and m is
still seen (Fig. 2i), although the overall values are
lower compared to the closed ocean basin (Fig. 2f).
These model results are in agreement with the
,,23 !Pa/,,2 30 Th ratios measured in Holocene
sediments throughout the Atlantic north of 50 0 S
(Fig. Sa).
Based on these results, the interpretation of
changes in the xs23!Palxs230Th ratio through time
caused by changes in paleoproductivity can be
made in the Atlantic Ocean, provided that there is
no substantial change in the basin ventilation rate.
A total shutdown of the global conveyer belt circulation, or changes in the production rate of deep
water in the Atlantic in the past, would strongly
influence the export rate op3!Pa. Hence, variaFig. 5. Distribution of xs 23 !PaI ,.,23°Th ratios in Holocene
Atlantic sediments with isolines of estimated primary
productivity in gCm· 2 a·!, after Berger et aJ. 1987 throughout the entire basin (left) and of the equatorial region
(bottom). (Symbols as in Fig.4). Light shaded: area between Subantarctic Front and Polar Front (Polar Frontal
Zone), and dark shaded: area between Polar Front and
ACC-Weddell Gyre (Antarctic Zone) (after Orsi et al.
1995).
Walter et al.
ratios on sinking particles between box i and m is
still seen (Fig. 2i), although the overall values are
lower compared to the closed ocean basin (Fig. 2f).
These model results are in agreement with the
,,23 !Pa/,,2 30 Th ratios measured in Holocene
sediments throughout the Atlantic north of 50 0 S
(Fig. Sa).
Based on these results, the interpretation of
changes in the xs23!Palxs230Th ratio through time
caused by changes in paleoproductivity can be
made in the Atlantic Ocean, provided that there is
no substantial change in the basin ventilation rate.
A total shutdown of the global conveyer belt circulation, or changes in the production rate of deep
water in the Atlantic in the past, would strongly
influence the export rate op3!Pa. Hence, variaFig. 5. Distribution of xs 23 !PaI ,.,23°Th ratios in Holocene
Atlantic sediments with isolines of estimated primary
productivity in gCm· 2 a·!, after Berger et aJ. 1987 throughout the entire basin (left) and of the equatorial region
(bottom). (Symbols as in Fig.4). Light shaded: area between Subantarctic Front and Polar Front (Polar Frontal
Zone), and dark shaded: area between Polar Front and
ACC-Weddell Gyre (Antarctic Zone) (after Orsi et al.
1995).