Enhanced iron-bound organic carbon preservation on the South China sea slope during the last glacial period and in the basin during the Holocene

Reactive iron (Fe R ) plays an important role in the long-term burial of sedimentary organic carbon (OC). However, the temporal changes in the iron-bound OC (Fe R -OC) preservation since the last glacial period and the controlling factors remain unclear. Here, we analyzed the Fe R , Fe R -OC and stable carbon isotopes in core DZ39 (slope) and JW2 (basin) from the South China Sea (SCS). We investigated the effects of productivity, terrestrial input and redox conditions on Fe R -OC preservation and quantified the burial flux and stock of Fe R -OC. In core DZ39, the fraction of Fe R -OC in total OC (fFe R -OC) averaged 16.8% during the last glacial period, 9.0% during the deglaciation and 8.6% during the Holocene. In core JW2, fFe R -OC averaged 11.5% during the deglaciation and 19.3% during the Holocene. The sedimentary records from the two cores diverge during the Holocene. These variations were jointly controlled by marine OC supply, terrestrial Fe R input and redox conditions. During the last glacial period, more oxygenated conditions and sufficient marine OC and terrestrial Fe R inputs promoted high fFe R -OC in DZ39. During the deglaciation, relatively reducing conditions and declining marine OC and terrestrial Fe R inputs lowered fFe R -OC in both cores. In the Holocene, increasingly reducing conditions further decreased fFe R -OC in DZ39, whereas the more oxygenated conditions increased fFe R -OC in JW2. The Fe R -OC stock of SCS since the last glacial period was estimated at 21 Pg C. These results reveal contrasting Fe R -OC preservation patterns between the slope and basin and highlight the importance of Fe R in OC sequestration on glacial-interglacial timescales.