GFDL - Geophysical Fluid Dynamics Laboratory

Global calcite cycling constrained by sediment preservation controls

August 10th, 2012

Dunne, J. P., B. Hales, J. R. Toggweiler. Journal: Global Biogeochemical Cycles.

Summary

The primary objective of this work was to build a set of internally consistent and computationally efficient algorithms to represent the regionally varying production, water column dissolution, and sediment preservation of pelagic calcite, and analyze the biogeochemical implications.

This work takes advantage of the combination of satellite, ocean interior, and sediment calcite observations in a unique and holistic way in order to infer a set of algorithms and their regionally varying controls to better understand the global calcite cycle. We compared satellite-derived estimates of surface organic carbon productivity with interior ocean properties and field estimates of sediment calcite burial.

As an added constraint, we utilized the pore water model of Hales (2003), to drive sediment preservation as a function of bottom water conditions.

Additionally, we are able to use this framework to test the quantitative implications of hypotheses about the near-term sensitivity of the calcite cycle to climate warming and acidification, as well as the onset of glacial conditions.

The interpretation helps inform our understanding of global biogeochemical cycles, and the algorithms developed here are being used in GFDL’s Earth System Models. The models are available to the public as part of the Coupled Model Intercomparison Project Phase 5.

This effort is part of NOAA’s research into the global carbon cycle under the influence of anthropogenic forcing to determine future atmospheric carbon dioxide levels and the corresponding climate change, ocean acidification, impacts and feedbacks.

Known weaknesses or uncertainties

Since our estimate is grounded in the sediment data, it is ignorant of water column dissolution processes that are not expressed in seafloor preservation variability. While our estimate of calcite cycling agrees fairly well with upper ocean alkalinity-gradient-based estimates, it is thus only a partial representation of the global CaCO3 cycle. Furthermore, it relies on a suite of empirical algorithms, and so cannot represent the role of regional or temporal variability in the underlying physiological and ecological mechanisms at work driving calcite production variation.

Maps of the final, optimized calcite cycle A: CaCO3 production from the satellite synthesis using the algorithm based on the degree of calcite supersaturation, temperature and small phytoplankton production. B: CaCO3 flux to the ocean bottom using the production map in A. C Optimized map of CaCO3 burial flux based on the 5-parameter metamodel . D: CaCO3 content of modern sediment (%).
Maps of the final, optimized calcite cycle A: CaCO3 production from the satellite synthesis using the algorithm based on the degree of calcite supersaturation, temperature and small phytoplankton production. B: CaCO3 flux to the ocean bottom using the production map in A. C Optimized map of CaCO3 burial flux based on the 5-parameter metamodel . D: CaCO3 content of modern sediment (%).