Modern deposition rates and patterns of organic carbon burial in Fiordland, New Zealand

Abstract

Fjords are disproportionately important for global organic carbon (OC) burial relative to their spatial extent and may be important in sequestering atmospheric CO2, providing a negative climate feedback. Within fjords, multiple locally variable delivery mechanisms control mineral sediment deposition, which in turn modulates OC burial. Sediment and OC sources in Fiordland, New Zealand, include terrigenous input at fjord heads, sediment reworking over fjord‐mouth sills, and landslide events from steep fjord walls. Box cores were analyzed for sedimentary texture, sediment accumulation rate, and OC content to evaluate the relative importance of each delivery mechanism. Sediment accumulation was up to 3.4 mm/yr in proximal and distal fjord areas, with lower rates in medial reaches. X‐radiograph and 210Pb stratigraphy indicate mass wasting and surface‐sediment bioturbation throughout the fjords. Sediment accumulation rates are inversely correlated with %OC. Spatial heterogeneity in sediment depositional processes and rates is important when evaluating OC burial within fjords.

Carbon Dynamics Along a Temperate Fjord‐Head Delta: Linkages With Carbon Burial in Fjords

“…Fjord‐head deltas, like many other deltas, have long been proposed as traps for coarse particles due to reduced flow energy (Gibson & Hickin, ; Orton & Reading, ). The coarse‐grained particles found at all deltaic stations in this study, in contrast with the fine‐ grained particles in fjord sediments (Ramirez et al, ), indicated that the Gaer Arm fjord‐head delta is comparable to other fjord‐head deltas in trapping the majority of coarse particles in a fjord system. The ability of fjord‐head deltas to trap coarse‐grained sediments has been more attributed to the presence of particle‐trapping vegetation growth on the delta, rather than direct deltaic deposition (Walling et al, ).…”

“…In contrast, the five subtidal surface‐grab samples (F8–F12) showed large variation in median grain size varying between 1250.41 and 45.36 μm, with a consistent decreasing trend in grain size from upper (F8) to lower (F12) stations (Figure S4). It is clear that fjord sediments in the deeper stations have a much finer grain size average (9.43 ± 5.09 μm) (Ramirez et al, ) than found in the Gaer Arm fjord‐head delta.…”

“…On this unique platform, the ability to decompose OC is much greater than can occur if the particles were directly injected into the deeper water with low oxygen, due in part to greater oxygen exposure and inherent high efficiency of OC associated with permeable sediments in deltas (Berg & Kostka, ). On the other hand, this type of delta intercepts coarse particles and exports well‐sorted fine particles to fjords and thereby increasing carbon burial rates in the deeper reaches of fjords by reducing permeability of sediments and increasing coating of OC on fine particles (Cui, Bianchi, Hutchings et al, ; Ramirez et al, ).…”

“…To compare the spatial differences in sediment and OC accumulation rates over same time scales and to ensure accurate geochronology generated using 210 Pb method, post‐1900 sediment layers were used to calculate the average sedimentation rates (SRs), mass accumulation rates (MARs), OC accumulation rates (OCARs), and lignin accumulation rates (LARs). These values were further compared with values from New Zealand fjords (Cui, Bianchi, Savage et al, ; Hinojosa et al, ; Ramirez et al, ).…”

Fate of Organic Carbon Burial in Modern Sediment Within Yangtze River Estuary

“…Differences in the burial of C org in large river‐dominated continental margins are primarily controlled by changes in the terrestrial sediment supply (Syvitski et al, ), SARs (Allison et al, ), hydrodynamics (Tesi et al, ), and biological processes (Ramirez et al, ). There were dramatic alterations in the transfer of suspended particles from the land to the sea between the 1950s and 2015, associated with river damming and cultivated land changes in the drainage basin, and the particle loads and amounts of terrestrial C org to the YRE decreased by >60% and >86%, respectively (Figure S2; Li et al, ; Yang et al, ).…”