Börker, Janine, Hartmann, Jens, Amann, Thorben, Romero‐Mujalli, Gibran, Moosdorf, Nils ORCID: https://orcid.org/0000-0003-2822-8261 and Jenkins, Chris (2020) Chemical weathering of loess and its contribution to global alkalinity fluxes to the coastal zone during the Last Glacial Maximum, Mid‐Holocene and Present. Geochemistry, Geophysics, Geosystems, 21 (7). e2020GC008922. DOI https://doi.org/10.1029/2020GC008922.

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Abstract

Loess sediments are windblown silt deposits with, in general, a carbonate grain content of up to 30%. While regionally, loess was reported to increase weathering fluxes substantially, the influence on global weathering fluxes remains unknown. Especially on glacial‐interglacial timescales, loess weathering fluxes might have contributed to land‐ocean alkalinity flux variability since the loess areal extent during glacial epochs was larger. To quantify loess weathering fluxes, global maps representing the loess distribution were compiled. Water chemistry of rivers draining recent loess deposits suggests that loess contributes over‐proportionally to alkalinity concentrations if compared to the mean of alkalinity concentrations of global rivers (~4110 meq L‐1 for rivers draining loess deposits and ~1850 meq L‐1 for the total of global rivers), showing comparable alkalinity concentration patterns in rivers as found for carbonate sedimentary rocks. Loess deposits, covering ~4% of the ice‐ and water‐free land area, increase calculated global alkalinity fluxes to the coastal zone by 16%. The new calculations lead to estimating a 4% higher global alkalinity flux during the LGM compared to present fluxes. The effect of loess on that comparison is high. Alkalinity fluxes from silicate dominated lithological classes were ~28 and ~30% lower during the LGM than recent (with loess and without loess, respectively) and elevated alkalinity fluxes from loess deposits compensated for this. Enhanced loess weathering dampens due to a legacy effect changes in silicate dominated lithologies over the glacial‐interglacial time scale.

Document Type:	Article
Programme Area:	PA2
Research affiliation:	Biogeochemistry and Geology > Submarine Groundwater Discharge
Refereed:	Yes
Open Access Journal?:	No
DOI:	https://doi.org/10.1029/2020GC008922
ISSN:	1525-2027
Date Deposited:	01 Jul 2020 11:35
Last Modified:	24 Nov 2021 12:51
URI:	http://cris.leibniz-zmt.de/id/eprint/3860

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