Fallacy of paleoproductivity signals by the recycled biogenic components: case study in the Central Basin of the northwestern Ross Sea

Abstract

Core LC42, retrieved from the Central Basin of the northwestern Ross Sea, contains three distinct sediment facies (IRD (ice-rafted debris)-poor bioturbated sandy mud, IRD-rich massive sandy mud, and laminated mud) that are interleaved with each other and deposited over the last 1 Ma. The biogenic components (biogenic opal, total organic carbon, and total nitrogen) of the laminated mud layers are consistently higher than the other two facies throughout the core. Based on the depositional succession of sediment facies and IRD-related depositional processes in the Antarctic continental margin, the laminated mud layers without IRD have been deposited during the glacial periods, but the enhanced paleoproductivity in terms of biogenic components during the mud deposition is unexpected. Backscattered electron imagery substantiates distinctly different componentry of the alternating light and dark laminae in the laminated mud. In particular, the light laminae contain scattered diatom fragments and eroded sand-sized lumps of fossil-bearing mud, whereas the dark laminae are clayey and diatomaceous. Both laminae thus are characterized by the high biogenic components, but they are interpreted to have been principally recycled from older deposits because diatom fragments are mostly reworked and old and their archives are poorly preserved. During the glacial periods, these laminated muds were deposited downward by milky plumes of meltwater discharged underneath the advancing glaciers that scoured the earlier-deposited and semi-consolidated diatom-rich sediments. Our study thus highlights that the recycling of biogenic particles should be precautious to avoid the fallacy of paleoclimatic interpretation in formulating climate-productivity models in the Antarctic continental margin.