Late Holocene precipitation variability recorded in the sediments of Reloncaví Fjord (41°S, 72°W), Chile

Abstract

We present reconstructions of late Holocene changes in the source of organic matter and siliceous export production in the Relocanví Fjord (41°S, 72°W), Northern Chilean Patagonia, based on organic carbon content, δ13Corg, N/C ratio, diatom assemblages and biogenic silica contents from three sediment cores. The age models are based on a combination of 210Pb profiles, AMS 14C dating, and on the first occurrence of the diatom Rhizosolenia setigera f. pungens, as a stratigraphic marker in the fjords. The cores span the last 300 to 700 yr. Diatoms dominate the siliceous assemblages in the three cores (98% on average). Our results suggest that precipitation seasonality in the region of Reloncaví was high in CE 1300–1400 and CE 1700–1850, with a clear decreasing trend since CE 1850. The latter trend is in agreement with instrumental records and tree-ring reconstructions. These fluctuations seem to be associated with the Southern Annular Mode (SAM).

Seasonal Changes in Carbonate Saturation State and Air‐Sea CO2 Fluxes During an Annual Cycle in a Stratified‐Temperate Fjord (Reloncaví Fjord, Chilean Patagonia)

“…On the other hand, the combination of lower pH and higher p CO 2 , as well as the drop in DO observed during the winter months, could be attributed to a number of processes: (a) enhanced postbloom heterotrophic processes (Montero et al, ; Olsen et al, ), (b) the mixing of oxygen‐poor deep water from below the halocline up to the surface layer, as has been suggested for Reloncaví Fjord during winter months (Castillo et al, ; González et al, ; León‐Muñoz et al, ), and (c) allochthonous organic matter transported to the fjord (Rebolledo et al, ) by runoff from heavy rain events during winter months.…”

Quantifying uncertainty of past pCO2 determined from changes in C3 plant carbon isotope fractionation

“…Measurement error for δ 13 C org is almost always better than 0.2‰ and commonly better than 0.1‰ (e.g., Werner et al, 1999;King et al, 2012) and an error of ± 0.12‰ for soil δ 13 C org was used in a recent analysis of the uncertainty in the paleosol carbonate pCO 2 proxy (Breecker, 2013). We note that significant changes in the measured δ 13 C org value can also result from changes in precipitation (e.g., Stewart et al, 1995;Kohn, 2010), plant communities (e.g., O 'Leary, 1988;Flanagan et al, 1997), pO 2 (e.g., Berner et al, 2000;Beerling et al, 2002;Tappert et al, 2013), and source inputs (e.g., Walsh et al, 2008;Rebolledo et al, 2015), and thus can affect the accuracy of the reconstructed pCO 2 value. Similar effects are commonly resolved in other pCO 2 proxies by producing multiple reconstructed pCO 2 values for a given time period, with each reconstructed pCO 2 value having its own uncertainty (e.g., Royer et al, 2014;Whiteside et al, 2015;Steinthorsdottir et al, 2011;Cleveland et al, 2008).…”

Environmental and coastline changes controlling Holocene carbon accumulation rates in fjords of the western Strait of Magellan region

“…Sedimentation rates (SR) in fjord basins depend on the supply of siliciclastic components, allochthonous OC terr from local catchment areas and local productivity within the water column (Cui et al, 2016;Bertrand et al, 2012Bertrand et al, , 2014Harada et al, 2013;Lamy et al, 2010;Rebolledo et al, 2015Rebolledo et al, , 2019. Moreover, open fjord systems may also receive a long-distance terrestrial sediment supply (>100 km), often depending on wind-induced surface currents or freshwater runoff within the fjord water surface layer.…”

“…On longer time-scales, Holocene fjord sediment records show variable contribution of OC from terrestrial vegetation sources, in particular derived from dense rainforests and peatlands (OC terr : 30 to 70 wt%; Bertrand et al, 2017Bertrand et al, , 2012Harada et al, 2013;Lamy et al, 2010;Rebolledo et al, 2015). The amount of terrestrial input to these fjord sediments depends on local and regional factors.…”