THE USE OF STABLE CARBON ISOTOPE, TOC AND C/N GEOCHEMISTRY OFCOASTAL WETLAND SEDIMENTS AS INDICATORS OF SEA-LEVEL CHANGE, EARTHQUAKES, TSUNAMIS AND TROPICAL CYCLONES

Stable carbon isotope, TOC and C/N geochemistry of organic remains preserved in tidal wetland sediments are potential sea-level indicators. Stable carbon isotopes (δ¹³C), total organic carbon (TOC) and the ratio of organic carbon to total nitrogen (C/N) together are able to differentiate sources of organic matter that accumulate in coastal depositional sequences, in particular between C₃ and C₄vegetation and freshwater and marine organic matter. They hold value as sea-level indicators because modern intertidal depositional environments (e.g., tidal flat, low marsh, high marsh, and freshwater environments) with distinct bulk sediment and plant δ¹³C, TOC and C/N values occur at specific elevation ranges relative to the tidal frame.

Here, we describe the factors controlling the δ¹³C, TOC and C/N of wetland plants and sediments and outline basic methods for its use as a sea-level indicator. We present a database (n = 374) of sediment δ¹³C, TOC and C/N values from contemporary mangrove and marsh depositional environments from temperate and tropical environments of Europe, North America and the Caribbean. We provide examples of how the database can be employed to reconstruct Holocene sea levels and the occurrence of paleo- earthquakes, tsunamis and tropical cyclones from the sedimentary record. We draw attention to strengths and weaknesses of this approach and offer suggestions for future research directions to further develop this technique.