C. Hillairemarcel et al., CARBON PRODUCTIVITY AND CARBON FLUX IN TH E LABRADOR SEA DURING THE LAST 40,000 YEARS, Canadian journal of earth sciences, 31(1), 1994, pp. 139-158
Geochemical and micropaleontological analyses of Labrador Sea sediment
s allowed us to intercalibrate indicators of paleoproductivity and pal
eofluxes of carbon and to reconstitute biogeochemical fluxes, notably
in relation to deep sea circulation changes (Western Boundary Undercur
rent and North Atlantic Deep Water). Linear or logarithmic relations a
re observed between the subrecent fluxes of paleoproductivity indicato
rs (coccoliths, diatoms, dinocysts, Th-230), the C-13 content of left-
coiling or sinistral Neogloboquadrina pachyderma, the modern surface w
ater carbon production, and the rates of organic and inorganic carbon
(C(org), C(inorg)) burial. All indicators increase by a factor of 10(2
) to 10(3) in response to the evolution of paleosea-surface conditions
since the last glacial maximum. Correlations are observed between aut
higenic C(inorg), Th-230, coccoliths, and C-13 content (left-coiling o
r sinistral Neogloboquadrina pachyderma), and also between authigenic
C(org), dinocysts, uranium, and sulfur. Relative C(inorg)/C(org) buria
l rates in the deep sediments ( > 3000 m) allow us to calculate a net
CO2 production in the basin. The net CO2 flux was slightly negative be
tween approximately 20 and approximately 15 ka BP. It reached a first
maximum at about 9 ka BP (approximately 30 mumol . cm-2 . a-1 CO2) fol
lowed by a decrease at approximately 8 ka BP (approximately 20 mumol .
cm-2 . a-1). Since about 7 ka BP, it stabilized at - 35 mumol . cm-2
. a-1. The minimum observed at about 8 ka BP corresponds to a signific
ant rate of C(org) burial accompanied with a maximum flux of redox-sen
sitive indicators (uranium, sulfur). This event does not correspond to
any change in sea-surface temperature or salinity, nor in deep circul
ation, but may be related to the reorganization of the atmospheric cir
culation during a major breakup stage of the Laurentide ice sheet. The
close correlation between the change in CO2 production in the Labrado
r Sea with variations of atmospheric CO2 concentrations during the las
t 20 ka BP suggests that the production of biogenic carbonates in subp
olar basins plays a role in the global carbon cycle on the scale of gl
acial-interglacial climate changes.