Tephrochronological records in two marine sediment cores from the Chilean continental margin (~41 and 41.5°S)

Supplementary material for Martínez Fontaine et al., 2021: Post–glacial tephrochronology record off the Chilean continental margin (~41° S). Including: Table S1.- Globigerina bulloides δ18O and the resulting age model for core MD07-3098 with its respective 1σ and 2σ envelopes. Table S2. Inividual glass shard analyses in core MD07-3100. Major elements not normalized‚ analyzed by EPMA‚ trace elements analyzed by LA-ICP-MS. Table S3. Inividual glass shard analyses in core MD07-3098. Major elements, not normalized, analyzed by EPMA. Table S5.- Planktonic foraminifera radiocarbon ages from core MD07-3098 and the respective marine surface reservoir age correction applied (Rs) in the calibration

Post–glacial tephrochronology record off the Chilean continental margin (∼41° S)

International audienceThe Southern Volcanic Zone of the Andes (∼33–46° S) is a very active volcanic zone with several volcanic centers recording recurrent historical activity (e.g. Llaima, Villarrica, Puyehue-Cordón Caulle, Osorno, Calbuco and Hudson). Tephrochronology is a valuable tool to help better understand the eruptive history of volcanic centers, essential for producing volcanic hazard maps. Additionally, tephrochronology can also be very useful to synchronize stratigraphic records of different nature such as paleoclimatological, paleoceanographical and archaeological records on land, lakes, ice and the ocean. Here we present a (crypto) tephrochronological record from two marine sediment cores retrieved in the Chilean continental margin at ∼41° S and ∼41.6° S. The records display continuous sedimentation since the late glacial, as robustly constrained by planktonic foraminifera δ18O and 14C dates. During this period, twenty three cryptotephras were identified as glass shard peaks together with two ∼25–30 cm–thick visible tephras (one in each core). The source of the (crypto) tephras was mainly constrained by major and trace element geochemistry of individual glass shards together with their stratigraphic position, since it is not possible to observe physical characteristics, such as color and grain size, when analyzing cryptotephras. From these, one cryptotephra was robustly correlated with the HW7 eruption from the Hudson volcano occurring in the Late Holocene at ∼1.5 cal ka BP; and the two visible tephra layers were identified as distant correlatives of the Lepué tephra originating from Michinmahuida volcano and occurring in the Deglaciation/Holocene transition at around 11 cal ka BP. Additionally, eight cryptotephra occurring at ∼3.6, 6.2, 7.0, 8.5, 9.6, 14.2, 15.9 and 18.2 cal ka BP were robustly identified as sourced from Michinmahuida volcano but where otherwise not correlated, providing novel evidence of pre Holocene activity of this volcanic center

Geochemical fingerprints of climate variation and the extreme La Niña 2010–11 as recorded in a Tridacna squamosa shell from Sulawesi, Indonesia

(IF 2.38; Q1)International audienceWe used a Tridacna squamosa (Tridacnidae, Bivalvia) shell that lived between 2006 and 2012 to reconstruct environmental conditions in South East Sulawesi (Indonesia). We focused mainly on estimating the influence of temperature and rainfall on the shell geochemistry, as well as ENSO anomalies. Comparison of the measured and theoretical δ18O values show clear seasonal variations and confirms that this species secretes its shell at isotopic equilibrium. The δ18O in T. squamosa shows how the increased rainfall associated with monsoon precipitations in this area influences the δ18O shell signal during the rainy season, the correlation between shell δ18O and SST (r2 = 0.62) decrease in warm/wet seasons (SST > 28.5 °C). Shell Mg/Ca profiles presents better correlation with SST (r2 = 0.8) than Sr/Ca profiles (r2 = 0.52). Shell Ba/Ca ratio increases during each dry season when primary productivity is maximum. Secondary Ba/Ca peaks also occur during the certain wet seasons and appear associated with abnormal enhanced runoff. Shell δ13C co-varies with primary productivity and salinity, with highest δ13C values occurring during the dry seasons. During 2010–11, abnormal values were detected in all geochemical proxies as result of the strong La Niña event. This calibration study demonstrates the ability of T. squamosa shells to accurately reflect present day environmental processes with seasonal resolutions and to define the local signature of hydrological changes associated with ENSO

Glacial carbonate compensation in the Pacific Ocean constrained from paired oxygen and carbonate system reconstructions

editorial reviewedThe tendency of CaCO_3 dissolution/burial to minimise changes in the carbonate ion concentration of the deep ocean following perturbations to the carbon cycle (‘carbonate compensation’) is thought to act as a first order control on atmospheric CO_2 on timescales of ~10^3 to 10^5 years. Although carbonate compensation could account for up to ~half of the glacial drawdown of CO_2, quantitative estimates of changes in ocean alkalinity are lacking. As such, the role of carbonate compensation in driving glacial-interglacial CO_2 variations remains poorly understood. Here, we combine paired reconstructions of dissolved oxygen from the infaunal-epifaunal benthic foraminiferal δ^13C proxy (Δδ^13C) and the carbonate system from boron proxies (B/Ca, δ^11B) in benthic foraminifera; this approach allows us to quantify both changes in deep ocean respired CO_2 storage, and the response of the carbonate system to this addition/removal of respired CO_2, providing the first quantitative estimates on the amount and timing of alkalinity changes in the deep Pacific during the Last Glacial Maximum (LGM) and over deglaciation. Our results indicate an increase in deep ocean alkalinity during the LGM, and suggest the buffering of the deep ocean may occur substantially faster than the canonical timescale of ~5 kyr (Broecker and Peng, 1987). We present results from a series of sensitivity experiments and long-term simulations using the recently coupled iLOVECLIM-MEDUSA climate/carbon-cycle/sediment model, with implications for our understanding of carbonate compensation in both glacial times, and the long-term future