The distribution and utility of sea‐level indicators in Eurasian sub‐Arctic salt marshes (White Sea, Russia)

Abstract

In support of efforts to reconstruct relative sea level (RSL), we investigated the utility of foraminifera, diatoms and bulk-sediment geochemistry (d 13 C, C:N and parameters measured by Rock-Eval pyrolysis) as sea-level indicators in Eurasian sub-Arctic salt marshes. At three salt marshes (<15 km apart) in Dvina Bay (White Sea, Russia), we collected surface sediment samples along transects from subtidal to Taiga forest environments. Foraminifera at all sites formed bipartite assemblages, where elevations below mean high higher water (MHHW) were dominated by Miliammina spp. and elevations between MHHW and the highest occurrence of foraminifera were dominated by Jadammina macrescens and Balticammina pseudomacrescens. Five high-diversity groups of diatoms were identified and they displayed pronounced variability amongst the study sites. Bulk-sediment geochemistry recognized two groups (clastic-dominated environments below MHHW and organic-rich environments above MHHW). As one group included subtidal elevations and the other included supratidal elevations, we conclude that the measured geochemical parameters are not stand-alone sea-level indicators. Core JT2012 captured a regressive sediment succession of clastic, tidal-flat sediment overlain by salt-marsh organic silt and freshwater peat. The saltmarsh sediment accumulated at 2804AE52 years before present and preserved foraminifera (Jadammina macrescens and Balticammina pseudomacrescens) with good analogy to modern assemblages indicating that RSL was +2.60AE0.47 m at this time. Diatoms confirm that marine influence decreased through time, but the lack of analogy between modern and core assemblages limited their utility as sea-level indicators. Geochemical parameters also indicate a reduction in marine influence through time. We conclude that RSL reconstructions derived from salt-marsh sediment preserved beneath Eurasian sub-Arctic peatlands can provide valuable insight into the spatio-temporal evolution of the Fennoscandian and Eurasian ice sheets.

Does litter input determine carbon storage and peat organic chemistry in tropical peatlands?

“…The strong differences in T max in the surface peat among the vegetation communities supported the first part of our fourth hypothesis, suggesting that litter inputs strongly affects the thermostability of the peat. The low Tmax values found at the Cyperus site are most likely due to low lignin and higher carbohydrate content of grasses (Figure 6; Kemp et al, 2017;Vane et al, 2001;Nimz et al, 1981). The larger Cl pool at the Rhizophora site, despite higher Tmax compared to the Cyperus site, might be linked to low molecular weight organic compounds, for example because sugars are not included in the S2 signal (which is used for calculating the C pools) but are captured by the S1 signal (Carrie et al, 2012).…”

“…Rock-Eval pyrolysis is a technique which has been used recently to track bulk changes in organic matter composition and degree of decomposition (Disnar et al, 2003;Kemp et al, 2017;Newell et al, 2016). Sediments (2 cm 2 ) were sub-sampled at 10 cm intervals, with samples also taken before and after obvious changes in texture and/or colour in the peat stratigraphy.…”

“…Sediments (2 cm 2 ) were sub-sampled at 10 cm intervals, with samples also taken before and after obvious changes in texture and/or colour in the peat stratigraphy. Freeze dried, powdered samples, were analysed using a Rock-Eval(6) analyser, configured in standard mode (Kemp et al, 2017;Newell et al, 2016). Pyrolysis was performed under an inert atmosphere of N2, with an initial isothermal stage where the samples were heated at 200 °C for 3 minutes, before the oven temperature was raised to 650 °C at 25 °C min -1 .…”

“…Rock-Eval 6 pyrolysis has been used to investigate carbon dynamics within a range of systems e.g. mangrove (Marchand et al, 2008), marine sediments (Hare et al, 2014), freshwater and saltmarsh peats (Engelhart et al, 2013Newell et al, 2016Kemp et al, 2017), as well as trends in SOM dynamics through soil profiles (Sebag et al, 2006, Delarue et al, 2013Biester et al, 2014;Sebag et al, 2016), providing a powerful tool for rapid assessment of shifts in peat organic geochemistry among vegetation types and depth.…”

Development of a Training Set of Contemporary Salt-Marsh Foraminifera for Late Holocene Sea- Level Reconstructions in southeastern Australia

“…While there are numerous Northern Hemisphere high-resolution salt marsh sea-level reconstructions based on such microfossil proxies, especially from the North Atlantic region (e.g. Barnett et al 2019;Gehrels et al 2020;Kemp et al 2017b;2018;Kopp et al 2015;Saher et al 2015), there are very few from the Southern Hemisphere. Highresolution reconstructions are available for Tasmania (Gehrels et al 2012), New Zealand (Gehrels et al 2008;Grenfell et al 2012), South America (Frederikse et al 2021) and South Africa (Strachan et al 2014).…”