Extraordinary slow degradation of dissolved organic carbon (DOC) in a cold marginal sea

Abstract

Dissolved organic carbon (DOC) is the largest organic carbon reservoir in the ocean, and the amount of carbon in this reservoir rivals that in atmospheric CO2. In general, DOC introduced into the deep ocean undergoes a significant degradation over a centennial time scale (i.e., ~50 μM to ~34 μM in the North Atlantic and Mediterranean Sea). However, we here show that high concentrations of DOC (58 ± 4 μM) are maintained almost constantly over 100 years in the entire deep East/Japan Sea (EJS). The degradation rate in this sea is estimated to be 0.04 μmol C kg−1 yr−1, which is 2–3 times lower than that in the North Atlantic and Mediterranean Sea. Since the source of DOC in the deep EJS is found to be of marine origin on the basis of δ13C-DOC signatures, this slow degradation rate seems to be due to low temperature (<1 oC) in the entire deep water column. This observational result suggests that the storage capacity of DOC in the world ocean is very sensitive to global warming and slowdown of global deep-water overturning.

Strong linkages between surface and deep-water dissolved organic matter in the East/Japan Sea

“…The concentrations of DON in surface waters of the EJS were similar to those in the global surface ocean (4.4 ± 0.5 µM) (Letscher et al, 2013). Unlike DOC, the concentrations of DON in deep waters of the EJS were similar to values in the eastern Pacific (2.5 ± 0.4 µM) and slightly lower than those in the Southern Ocean (3.5 ± 0.6 µM), the North Atlantic (3.2 ± 0.3 µM), and the Mediterranean Sea (3.5 ± 0.4 µM) (Loh and Bauer, 2000;Hansell and Carlson, 2001;Pujo-Pay et al, 2011).…”

Sources, fluxes, and behaviors of fluorescent dissolved organic matter (FDOM) in the Nakdong River Estuary, Korea

“…The TOC instrument uses a common high-temperature catalytic combustion method (Kirkels et al, 2014). The analytical method is fully described in Kim et al (2015). Briefly, 10 mL of filtered sample was purged with O 2 gas for 20-30 min to completely remove DIC after the samples were acidified to pH ∼ 2.…”

Tracing terrestrial versus marine sources of dissolved organic carbon in a coastal bay using stable carbon isotopes

“…Relationships between δ 13 C-DOC values and (a) the DOC/DON (C/N) ratio and (b) FDOM P in Masan Bay, Republic of Korea. The ranges of the DOC/DON ratio and δ 13 C-DOC values for each group are based on the values reported by Lamb et al (2006) and Beaupré (2015).…”

“…The values of δ 13 C-DOC were determined using a TOC-IRMS instrument (IR-MS from Isoprime, UK coupled with a Vario TOC cube from Elementar, Germany). The analytical method is the same as that used by Kim et al (2015) and Lee and Kim (2018). Low carbon water (< 2 µM; University of Miami, Hansell Organic Biogeochemistry Lab) was measured for blank corrections and used for preparing all standard samples.…”