Evaluation of the Abandoned Huanghe Delta as an important carbon source of the Chinese marginal seas in recent decades

The manuscript has been accepted by Journal of Geophysical Research - Oceans. Increasing organic carbon (OC) inputs from coastal erosion contribute large uncertainties to carbon cycling in coastal seas. The Abandoned Huanghe Delta (AHD) is a typical coastal erosion region, with large amounts of eroded sediments transported to the Chinese marginal seas. Here we investigated the organic geochemical characteristics of sedimentary organic matter (OM) from the heavily eroded region of AHD and estimated the OC and lignin fluxes caused by coastal erosion. The eroded sedimentary OM was characterized by low carbon loading and low lignin content with high degradation and influenced by the Changjiang . Owing to the sharp decline in the sediment fluxes from large rivers (Changjiang and Huanghe) since the 1990s, the total fluxes to CMS decreased from 11.5 to 5.0 Mt/yr for OC and from 11.5 ×10-2 to 4.7 ×10-2 Mt/yr for lignin, therefore the contribution from the coastal erosion of AHD increased from 24±8% to 56±10% for OC and from 21±9% to 52±15% for lignin. The high proportion contributed by AHD to the Central Yellow Sea Mud area (74±11%) also accounted for the high terrestrial OC burial efficiency there (69%). Considering the different nature of OM and increasing contribution, as in this case, the significance of OC input caused by coastal erosion to the coastal seas are expected to overwhelmed that of rivers and influnce the regional and even global carbon budgets and cycles under the scenarios of global warming and sea level rising. Keywords :coastal erosion, Abandoned Huanghe Delta, Chinese marginal seas, lignin

本研究论文已被《Journal of Geophysical Research - Oceans》收录。海岸侵蚀导致的有机碳（organic carbon, OC）输入量持续攀升，为近海海域的碳循环带来了显著不确定性。废弃黄河三角洲（Abandoned Huanghe Delta, AHD）是典型的海岸侵蚀区域，其侵蚀产生的大量沉积物会被搬运至中国边缘海。本研究针对废弃黄河三角洲强侵蚀区域的沉积物有机质（sedimentary organic matter, OM）开展了有机地球化学特征分析，并估算了海岸侵蚀引发的有机碳与木质素通量。侵蚀来源的沉积物有机质具有碳负载量低、木质素含量低、降解程度高的特征，且受到长江径流的影响。自20世纪90年代起，长江、黄河等大型河流的沉积物通量大幅下降，导致输入至中国边缘海（Chinese marginal seas, CMS）的总通量发生显著变化：有机碳通量从11.5 Mt/yr降至5.0 Mt/yr，木质素通量从11.5×10^-2 Mt/yr降至4.7×10^-2 Mt/yr；与此同时，废弃黄河三角洲海岸侵蚀对有机碳的贡献占比从24±8%提升至56±10%，对木质素的贡献占比从21±9%提升至52±15%。废弃黄河三角洲对黄海中部泥质区的有机碳贡献占比达74±11%，这也解释了该区域较高的陆源有机碳埋藏效率（69%）。鉴于本研究揭示的有机质性质差异与海岸侵蚀贡献占比的持续提升，在全球变暖与海平面上升的背景下，海岸侵蚀引发的有机碳输入对近海海域的重要性预计将超越河流输入，进而对区域乃至全球的碳收支与循环产生影响。关键词：海岸侵蚀、废弃黄河三角洲、中国边缘海、木质素