Volumetric budget calculation of sediment and carbon storage and export for a late Holocene mid-shelf mudbelt system (NW Iberia)

摘要

Confined fine-grained depoenters (mudbelts) on continental shelves play an important role as common and major fluviogenic submarine depocenters along the source-to-sink pathway and in global sedimentary and carbon cycles. This study provides a complete high-resolution isopach-based budget analysis using closely-spaced, high-resolution seismic-reflection data of an exemplary mid-shelf mudbelt system located on the open and narrow continental shelf of NW Iberia. The budget analysis reveals that 3.957-4.227 km~3 of sediments [i.e., 4073 to 4351 Mt (dry)] are stored in this depocenter. In conjunction with river-discharge estimates, we calculate that, over the past 5300 yr, approximately 34% to 36% of total fluvial sediments supplied to the ocean remain in the shelfal mud depocenter and the balance bypasses the shelf. Total accumulation values for TOC and CaCO_3 amount to 40.31 to 43.46 t and 174.73 to 186.68 Mt, respectively. High-resolution isopach analysis shows high regional morphodynamic variability of the main sediment transit routes, an aspect easily overlooked by core-based or low-resolution profiling studies. The budget analysis reveals persistent low accumulation over the past 5300 yr and thus clarifies that a uniformitarian view of applying modern accumulation rates to the late Holocene can significantly underestimate effective sediment off-shelf transport.