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Exportación fluvial de materia orgánica terrestre envejecida hacia el Océano Atlántico Norte

P A Raymond¹, J E Bauer

¹School of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA. praymond@mbl.edu

|February 24, 2001

Resumen

Los ríos exportan carbono orgánico terrestre significativo a los océanos. Paradójicamente, este carbono no se detecta en grandes cantidades. Los estudios muestran que gran parte de este carbono se degrada antes de llegar al océano, alterando su composición.

Área de la Ciencia:

La geoquímica es la geoquímica.
Oceanografía La oceanografía es la oceanografía.
Ciencias ambientales Ciencias ambientales.

Sus antecedentes:

Los ríos mundiales transportan una cantidad sustancial de carbono orgánico terrestre disuelto y particulado a los océanos.
Esta entrada es teóricamente suficiente para explicar la rotación oceánica de carbono orgánico disuelto.
Sin embargo, la materia orgánica terrestre no se encuentra en los océanos en cantidades que coincidan con las entradas fluviales.

Objetivo del estudio:

Investigar la edad y la composición del carbono orgánico terrestre descargado por los ríos en el Atlántico Norte occidental.
Determinar el destino de la materia orgánica terrestre durante su transporte de los ríos al océano.
Conciliar la discrepancia entre las entradas de carbono orgánico fluvial y las reservas oceánicas de carbono orgánico.

Principales métodos:

Análisis del radiocarbono natural (14C) y del isótopo de carbono estable (13C) en materia orgánica disuelta y en partículas fluviales.
Muestreo de cuatro ríos que desembocan en el oeste del Océano Atlántico Norte.
Evaluación de los procesos de degradación de la materia orgánica en ambientes fluviales y costeros.

Principales resultados:

Los ríos exportan tanto carbono orgánico disuelto terrestre viejo (14C empobrecido) como joven (14C enriquecido).
El carbono orgánico particulado terrestre exportado por los ríos es predominantemente viejo.
El carbono orgánico disuelto joven se degrada selectivamente en las aguas fluviales y costeras, dejando un componente más refractario.
Estos hallazgos contradicen las sugerencias anteriores de que la materia orgánica terrestre recién producida domina la exportación fluvial.

Conclusiones:

La materia orgánica fluvial sufre un importante envejecimiento y degradación previo a la exportación.
La degradación selectiva altera la estructura, distribución y cantidad de materia orgánica terrestre antes de su entrega oceánica.
Estos procesos ayudan a explicar la baja detección de materia orgánica terrestre en los sedimentos marinos y el agua de mar.

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