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

Abstract

We used seven 210Pb‐dated sediment cores from the Gaer Arm in the Doubtful Sound fjord complex, Fiordland, New Zealand to evaluate organic carbon (OC) dynamics in a temperate fjord‐head delta. The highly dynamic spatial features of this delta were clearly evident in the observed sediment properties such as mass accumulation rates that varied by a factor of 14, sediment grain size by a factor 5, and sedimentary OC content by a factor 6. Low lignin concentrations (e.g., 2.95 mg (100 mg OC)−1) and syringic/vanillic ratios of lignin phenols (S/V; e.g., 0.44) at the upper deltaic stations were representative of substantial autochthonous OC contributions to delta sediments. Significantly higher acid/aldehyde ratios of vanillic phenols [(Ad/Al)v] at the deltaic stations (0.45–0.82) than the surface grabs (0.26–0.30) indicated rapid degradation of OC within the delta. Despite being a “hot spot” for OC oxidation, the delta likely improves OC preservation in the adjacent fjord by filtering out coarse‐grained particles and exporting fine‐grained particles to fjord sediments. Our results showed that fjord‐head deltas can influence sedimentation and OC dynamics in select regions of fjords and thus warrant more examination of fjord‐head processes, particularly in areas where they are expanding. In particular, as Earth warms and glaciers retreat, the newly exposed fjord‐head platforms in high‐latitude environments may evolve into similar “hot spots” of OC oxidation, thereby altering the dynamics of OC burial in these systems.

Relationships Between Land Use and Terrestrial Organic Matter Transfer to the Baltic Sea Over the Last 500 Years

“…It is highly resistant to microbial degradation and therefore still retains information of its origin after deposition in sediments (Goñi & Hedges, 1992; Hedges et al., 1982; Jex et al., 2014). Thus, lignin composition is widely used to trace the abundance, source, and degradation state of the terrestrial OM deposited in sediment archives (e.g., Chmiel et al., 2015; Cui et al., 2017; Hyodo et al., 2017; Tareq et al., 2011). The aims of this study were (a) to investigate the variation of terrestrial OM export in response to land‐use changes in the coastal area of the Baltic Sea over the last 500 years when human disturbance on the landscape increased and (b) to explore the transport and burial of terrestrial organic carbon from a long‐term perspective by analyzing the difference in the sedimentary OM between the coastal inlet and the upstream lake within the same watershed.…”