Abstract. Although it has long been assumed that the glacial–interglacial cycles of
atmospheric CO2 occurred due to increased storage of CO2
in the ocean, with no change in the size of the “active” carbon inventory,
there are signs that the geological CO2 supply rate to the active
pool varied significantly. The resulting changes of the carbon inventory cannot be
assessed without constraining the rate of carbon removal from the system,
which largely occurs in marine sediments. The oceanic supply of alkalinity is
also removed by the burial of calcium carbonate in marine sediments, which
plays a major role in air–sea partitioning of the active carbon inventory. Here, we
present the first global reconstruction of carbon and alkalinity burial in
deep-sea sediments over the last glacial cycle. Although subject to large
uncertainties, the reconstruction provides a first-order constraint on the
effects of changes in deep-sea burial fluxes on global carbon and alkalinity
inventories over the last glacial cycle. The results suggest that reduced
burial of carbonate in the Atlantic Ocean was not entirely compensated by the
increased burial in the Pacific basin during the last glacial period, which
would have caused a gradual buildup of alkalinity in the ocean. We also
consider the magnitude of possible changes in the larger but
poorly constrained rates of burial on continental shelves, and show that
these could have been significantly larger than the deep-sea burial changes. The
burial-driven inventory variations are sufficiently large to have
significantly altered the δ13C of the ocean–atmosphere carbon
and changed the average dissolved
inorganic carbon (DIC) and alkalinity concentrations of the
ocean by more than 100 µM, confirming that carbon burial fluxes
were a dynamic, interactive component of the glacial cycles that
significantly modified the size of the active carbon pool. Our results also
suggest that geological sources and sinks were significantly unbalanced
during the late Holocene, leading to a slow net removal flux on the order of
0.1 PgC yr−1 prior to the rapid input of carbon during the industrial
period.
Organic carbon accumulation in modern sediments of the Angola basin influenced by the Congo deep-sea fan