『Abstract
The reinvestigation of overturning in the Southern Ocean is hypothesized
to have returned CO2 from the deep ocean
to the atmosphere at the end of the last ice age. Large peaks
in opal accumulation have been put forward as evidence for an
increase in wind driven upwelling between 10 and 15 ka. Here,
we use couples nitrogen and silicon isotope records alongside
opal accumulation rates to provide quasi-quantitative estimates
of Southern Ocean nutrient supply, by upwelling, and nutrient
utilization across this interval. Significant changes in the consumption
of N and Si across the two opal accumulation peaks indicate major
changes in both upwelling and nutrient demand. We find N and Si
consumption to be relatively incomplete during peak opal accumulation
at the onset of the deglaciation. This indicates that nutrient
supply was significantly enhanced. The second deglacial peak in
opal accumulation is associated with more complete Si consumption
and variable N consumption. We suggest that this peak represents
strong upwelling and more complete utilization of the available
silicic acid pool. Differences between the Si and N responses
during opal peaks may stem from decreasing iron availability across
the glacial termination. The nutrient isotope evidence for excess
nutrients during the deglaciation indicates that the high export
productivity was insufficient to overcome the evasion of CO2 to the atmosphere as a result of physical circulation
changes. Previous work has demonstrated that the reinvigoration
of overturning circulation during the deglaciation causes a transient
peak in nutrient supply to the low latitudes. This is supported
by our data, which indicate that relatively high macronutrient
concentrations were maintained in the Southern Ocean surface waters
that are incorporated into mode waters despite high demand.
Keywords: nitrogen isotopes; silicon isotopes; nutrient dynamics;
deglaciation; silicic acid supply』
1. Introduction
2. Methods
3. Results and discussion
4. Conclusions
Acknowledgments
References