Two-year-resolved δ11B records of a modern coral from the South China Sea and the regional composite records

<p>This dataset reports two-year-resolved δ<sup>11</sup>B measurements of a modern <em>Porites </em>coral collected from the Xisha Islands in the South China Sea. The δ<sup>11</sup>B measurements were carried out using a Neptune Plus multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). The international coral standard JCp-1 was measured along with the samples, yielding an average value of 24.28‰ ± 0.45‰ (2SD, n = 6). Additionally, in conjunction with previously published δ<sup>11</sup>B records, this dataset also includes the regional composite results of multiple records from the same reef site, specifically the Xisha Islands (Kang et al., 2021), Hainan Island (Chen et al., 2021; Liu et al., 2014; Wei et al., 2015), Belize (Fowell et al., 2018), and GBR (D'Olivo et al., 2015; D'Olivo et al., 2019; Pelejero et al., 2005; Wei et al., 2009).</p&gt

Super instrumental El Nio events recorded by a Porites coral from the South China Sea

The 2-7-year periodicities recorded in fossil coral records have been widely used to identify paleo-El Nio events. However, the reliability of this approach in the South China Sea (SCS) has not been assessed in detail. Therefore, this paper presents monthly resolution geochemical records covering the period 1978-2015 obtained from a Porites coral recovered from the SCS to test the reliability of this method. The results suggest that the SCS coral reliably recorded local seawater conditions and the super El Nio events that occurred over the past 3 decades, but does not appear to have been sensitive enough to record all the other El Nios. In detail, the Sr/Ca series distinctly documents only the two super El Nios of 1997-1998 and 2014-2016 as obvious low values, but does not match the Oceanic Nio Index well. The super El Nio of 1982-1983 was identified by the growth hiatus caused by the coral bleaching and subsequent death of the coral. Three distinct stepwise variations occur in the delta C-13 series that are coincident with the three super El Nios, which may be related to a substantial decline in endosymbiotic zooxanthellae density caused by the increase in temperature during an El Nio or the selective utilization of different zooxanthellaes that was required to survive in the extreme environment. The increase in rainfall and temperatures over the SCS during El Nios counteracts the effects on seawater delta O-18 (delta O-18(sw)) and salinity; consequently, coral Delta delta O-18 series can be used as a proxy for delta O-18(sw) and salinity, but are not appropriate for identifying El Nio activity. The findings presented here suggest that the method to identify paleo-El Nio activity based on the 2-7-year periodicities preserved in the SCS coral records might not be reliable, because the SCS is on the edge of El Nio anomalies due to its great distance from the central equatorial Pacific and the imprints of weak and medium strength El Nio events may not be recorded by the corals there

Exploring the temperature dependence of clumped isotopes in modern Porites corals

Porites corals are valuable geological archives for reconstructing past sea surface temperature (SST) in tropical oceans. Their clumped isotope compositions (indicated by Δ values) provide a potential proxy for SST. The Δ value in Porites coral usually departs from thermodynamic equilibrium due to vital effects. To explore the temperature dependence of Δ values in corals, we determined δC, δO, and Δ values in two modern Porites corals from the South China Sea. Our results indicate no intercolony or intracolony biases in Δ values on annual timescales. However, on seasonal timescales, Δ enrichment associated with δC depletion is observed at an intracolony level. This cannot be explained by incomplete hydration and/or hydroxylation of metabolic CO; instead, we interpret this new pattern of isotopic anomalies as a peculiar evidence of vital effects on Δ and δC fractionation. Although complicated by vital effects, the Δ signature in Porites corals still preserved a robust SST dependence, similar to those of recently published Δ-T calibrations. The observed Δ offset relative to inorganic carbonate due to the vital effects is consistent, and relative variations in seasonal SST can be obtained. This study refines the Δ thermometer in Porites corals and strengthens its capacity to be used to reconstruct past SST

Human impact overwhelms long-term climate control of weathering and erosion in southwest China

During the Holocene there has been a gradual increase in the influence of humans on Earth systems. High-resolution sedimentary records can help us to assess how erosion and weathering have evolved in response to recent climatic and anthropogenic disturbances. Here we present data from a high-resolution (∼75 cm/k.y.) sedimentary archive from the South China Sea. Provenance data indicate that the sediment was derived from the Red River, and can be used to reconstruct the erosion and/or weathering history in this river basin. Accelerator mass spectrometry 14C dating provides direct age control and reveals coherent variations in clay mineralogy, geochemistry, and terrigenous flux, indicative of strong chemical weathering and physical erosion during the mid-Holocene warm period (6400–4000 cal [calibrated] yr B.P.), followed by weakening from ca. 4000–1800 cal yr B.P., and renewed intensification since 1800 cal yr B.P.. Comparison with climatic records from China indicates that precipitation and temperature controlled both physical erosion and chemical weathering intensity before 1800 cal yr B.P.. However, weathering proxies in the offshore sediment indicate recent increased soil erosion. We suggest that enhanced human activity (deforestation, cultivation, and mining) since the end of the Chinese Han Dynasty (220 CE) has overwhelmed the natural climatic controls on erosion in the Red River