Processes determining the marine alkalinity and calcium carbonate saturation state distributions
We introduce a composite tracer for the marine system, Alk<sup>*</sup>, that has a global distribution primarily determined by CaCO<sub>3</sub> precipitation and dissolution. Alk<sup>*</sup> is also affected by riverine alkalinity from dissolved terrestrial carbon...
Main Authors: | , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2014-12-01
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Series: | Biogeosciences |
Online Access: | http://www.biogeosciences.net/11/7349/2014/bg-11-7349-2014.pdf |
Summary: | We introduce a composite tracer for the marine system, Alk<sup>*</sup>, that has a
global distribution primarily determined by CaCO<sub>3</sub> precipitation and
dissolution. Alk<sup>*</sup> is also affected by riverine alkalinity from dissolved
terrestrial carbonate minerals. We estimate that the Arctic receives
approximately twice the riverine alkalinity per unit area as the Atlantic,
and 8 times that of the other oceans. Riverine inputs broadly elevate Alk<sup>*</sup>
in the Arctic surface and particularly near river mouths. Strong net
carbonate precipitation results in low Alk<sup>*</sup> in subtropical gyres,
especially in the Indian and Atlantic oceans. Upwelling of dissolved CaCO<sub>3</sub>-rich deep water elevates North Pacific and
Southern Ocean Alk<sup>*</sup>. We use the Alk<sup>*</sup> distribution to estimate the
variability of the calcite saturation state resulting from CaCO<sub>3</sub> cycling
and other processes. We show that regional differences in surface calcite
saturation state are due primarily to the effect of temperature differences
on CO<sub>2</sub> solubility and, to a lesser extent, differences in freshwater
content and air–sea disequilibria. The variations in net calcium carbonate
cycling revealed by Alk<sup>*</sup> play a comparatively minor role in determining
the calcium carbonate saturation state. |
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ISSN: | 1726-4170 1726-4189 |