The impact of recycling of organic carbon on the stable carbon isotopic composition of dissolved inorganic carbon in a stratified marine system (Kyllaren fjord, Norway)

Abstract

A negative carbon isotope shift in sedimentary organic carbon deposited in stratified marine and lacustrine systems has often been inferred to be a consequence of the process of recycling of respired and, therefore, 13 C-depleted, dissolved inorganic carbon (DIC) formed from mineralization of descending organic matter. To study this process, we measured d 13 C DIC and d 13 C values of particulate organic carbon (POC) over an annual cycle in the permanently stratified Kyllaren fjord in Norway. A notable accumulation of respired DIC below the chemocline was evident from the substantially 13 Cdepleted DIC (ca. À19&). Especially in autumn to early spring, respired DIC from the deep anoxic water is mixed into the oxygenated surface water and the calculated respired DIC contribution to the total DIC pool was up to $40% in early spring in the upper 2 m of the water column. At 4 m depth, just below the chemocline, the respired DIC contribution reaches ca. 90% of the total DIC pool. Assimilation of the respired DIC seems to exert only a small effect on d 13 C POC , which has an average d 13 C value of À24&. The measured photoautotrophic fractionation (e p ) was low (<10&) during the majority of the year. This is likely responsible for reducing the apparent impact of recycling of respired DIC on d 13 C POC . However, in June 2002, photoautotrophic use of the 13 C-depleted DIC is obvious from a 13 C-depletion of POC (À33.7&) derived from a bloom of the protist Euglena sp.

Dissolved inorganic carbon and its isotopic differentiation in cascade reservoirs in the Wujiang drainage basin

“…In fresh water, aquatic photosynthesis mainly makes use of dissolved CO 2 , with an isotope fractionation of about 20‰-23‰ [20,25] , thus making the isotopic composition of DIC in the remaining water body 13 C-enriched [11,22,25,29,30,36] . The respiration can induce the decomposition of organic matter; DIC derived from this process is also referred to as respiration-derived DIC [39] , which has a similar δ 13 C to that of the organic source. Although this process is not associated with obvious isotope fractionation, a lot of 12 C would be released from decomposition of organic matter, which may make δ 13 C DIC more negative [11,22,25,29,36,39] , at the same time, may make it increase the DIC concentrations in the water body.…”

“…The respiration can induce the decomposition of organic matter; DIC derived from this process is also referred to as respiration-derived DIC [39] , which has a similar δ 13 C to that of the organic source. Although this process is not associated with obvious isotope fractionation, a lot of 12 C would be released from decomposition of organic matter, which may make δ 13 C DIC more negative [11,22,25,29,36,39] , at the same time, may make it increase the DIC concentrations in the water body.…”

ISO‐CADICA: Isotopic – continuous, automated dissolved inorganic carbon analyser

“…Consequently, the recycling of organic matter becomes proportionally more important and can lead to the more negative d 13 C DIC values observed. [14] However, the diel cycles behave as would be expected when responding to shifts in metabolic balance and the observed variation was far greater than the analytical uncertainty of the ISO-CADICA.…”

Environmental geochemistry of core sediments from Serthalaikkadu creek, East coast of India

“…The increase in OC especially in the central part of creek (from 20 cm in C2) indicates a direct relationship where carbonate dissolution is proportional to OC mineralization in deeper regions (Emerson and Bender 1981;Jahnke et al 1982). In addition, the marginally increasing values in the lower part below 20 cm in C2 also suggest that the increase could be due to phytoplankton-derived materials and mangrove leaves in a highly recalcitrant state (Dittmar 1999) and also that under anoxic conditions the proportion of OC resistant to alteration is much higher than under oxic conditions (Lehmann et al 2002;Van Breugel et al 2005).…”