Carbon isotopes in the rivers from the Lesser Antilles: origin of the carbonic acid consumed by weathering reactions in the Lesser Antilles

Abstract

International audienceIn this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO2) involved in the neutralization reactions during water-rock interactions. The d13C data span a large range of variations, from -19% to -5 _ 2% for DIC (dissolved inorganic carbon) concentrations ranging from 11 mM to 2000 mM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO2 (enriched in heavy carbon (d13C_-3 _ 5%) and biogenic CO2 produced in soils (enriched in light carbon (d13C<-17%)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO2 consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first-order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO2, either under hydrothermal (hot) or surficial (cold) weathering regimes. This study shows that the contribution of magmatic CO2 to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO2 to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone

Controls on deep critical zone architecture: a historical review and four testable hypotheses

“…Recent studies of tectonically active settings suggest that weathering in the deep CZ may be particularly important in determining the strength of connections between climate and tectonics (Tipper et al , ; Calmels et al , ; West, ). In this special issue, Rivé et al () documented connections between weathering and volcanically sourced carbon dioxide using carbon isotopes in stream water from the Lesser Antilles. They found that deeply sourced carbon dioxide plays a key role in the rapid rates of silicate weathering that they observed on these islands.…”

The effect of regional groundwater on carbon dioxide and methane emissions from a lowland rainforest stream in Costa Rica

“…In addition to biogenic contributions from the surface, dissolved CO 2 and CH 4 in regional groundwater can originate from volcanic degassing, nonvolcanic escape of gases from the upper mantle, intrusive magma chambers, carbonate‐bearing rocks in the crust, hydrocarbon accumulations [ Mörner and Etiope , ], and remineralization of ancient sedimentary organic matter [ Lovley and Anderson , ; Park et al ., ; Liu et al ., ]. Aquifers transporting high concentrations of dissolved C have been identified in numerous places around the world, for example, Portugal [ Cruz and Amaral , ], the Canary Islands [ Marrero et al ., ], the United States [ Evans et al ., ; Kampman et al ., ], Japan [ Yamada et al ., ], Canada, Costa Rica, Italy [ Genereux et al ., , and references therein], the Lesser Antilles [ Rivé et al ., ], and the Slovak Republic [ Kucharič et al ., ]. However, little is known about the fate of that C once it discharges into surface waters and its effects on C balances of the aquatic and surrounding terrestrial ecosystems.…”

Aging of basalt volcanic systems and decreasing CO&lt;sub&gt;2&lt;/sub&gt; consumption by weathering

“…Results may have relevance for the carbon cycle and climate studies exploring the emplacement of large igneous provinces like the CAMP (Schaller et al, 2012) or the Deccan Traps (Caldeira and Rampino, 1990) with production of large basaltic areas within a short time. However, the biological contribution to CO 2 drawdown, via elevated fertilization effects, e.g., P or Si release due to weathering and elevated CO 2 in the atmosphere, should be taken into account, too.…”

“…The sensitivity of basalt weathering to climate change (Dessert et al, 2001Coogan and Dosso, 2015;Li et al, 2016) supports a negative weathering feedback in the carbon cycle that maintains the habitability of the Earth's surface over geological timescales (Walker et al, 1981;Berner et al, 1983;Li and Elderfield, 2013). Changes in volcanic weathering fluxes due to emplacement of large volcanic provinces or shifts in the geographic distribution of volcanic fields associated with continental drift may have contributed to climate change in the past (Goddéris et al, 2003;Schaller et al, 2012;Kent and Muttoni, 2013).…”