PP14B-06:
Toward the Inference of Deglacial Ocean Dynamics from the Spatial Pattern of LGM-to-Modern d13C and d18O Change
Monday, 15 December 2014: 5:15 PM
Geoffrey Gebbie1, Carlye D Peterson2, Lorraine E Lisiecki2 and Howard J Spero3, (1)Woods Hole Oceanographic Inst., Woods Hole, MA, United States, (2)University of California Santa Barbara, Santa Barbara, CA, United States, (3)University of California Davis, Davis, CA, United States
Abstract:
Estimates of the whole-ocean d13C change between
the Last Glacial Maximum (LGM) and the modern-day are converging to
values of about 0.4 per mil, and are of great use in partitioning
land versus ocean contributions to the deglacial carbon cycle. To
determine which specific oceanic processes are at play, however,
knowledge of the spatial pattern of LGM-to-modern d13C and d18O
change is critical. Spatial maps have mostly focused on Atlantic
d13C, with less progress for d18O and the Pacific and Indian sectors,
due to the concentration of sediment-core observations in the Atlantic and the
difficulty in making meaningful maps from sparse data. Here, we
demonstrate that a state estimation (or data assimilation) method
based on recently compiled data and a simple kinematic ocean model
simultaneously produces reasonable results for: 1) global maps of d13C and d18O,
2) uncertainty in the estimated properties, and 3) oceanic water-mass
geometry. The observations include benthic d13C and d18O data from
493 marine sediment cores that were collected from the scientific
literature and NOAA, PANGEA, and Delphi databases. The
kinematic model permits each data point to have influence both up- and
downstream along a water-mass pathway, typically allowing a larger
geographical range than a statistical interpolation method. No
assumption regarding the state of the circulation is necessary, and
the modern-day circulation need not be assumed to be representative
of the LGM. With this method, meridional (or other) sections
can be compared between ocean basins. Furthermore, the internally-consistent d18O and d13C maps
are used to determine the LGM-to-modern spatial changes that are robust given the uncertainty and
sparsity of data. Rather than simply focus on property maps, we suggest that the
link between observations and circulation changes (as
reflected by the paths that water travels), points the way toward
dynamical processes that must be explained. A particular application
of our result is the geographic constraint of possible unobserved
reservoirs of d13C or radiocarbon and calculation of their potential
impact on the global chain of events during the deglaciation.