Dataset Information

Temporal and spatial characteristics of sediment sources on the southern Yangtze Shoal over the Holocene.

ABSTRACT: The sediment sources of the Yangtze Shoal were traced by analysing surface and core sediment particle size, detrital and clay minerals, carbon and nitrogen isotopes, and radioisotope dating. In the estuary, the sediments are dominated by silty clay, high stable mineral, and extremely high illite/chlorite. Stable organic carbon isotopes (?¹³C-TOC) indicated a marine-dominated mixture. On the shoal, the sediments are mainly composed of fine sand, high unstable mineral. The ?¹³C-TOC indicated predominantly marine sedimentation. The average TOC of core sediments was ~0.26%, and the average TN was ~0.05%. The TOC/TN was 5.4-7.8, the ?¹³C-TOC was -19.8 to -22.1‰, and the age of the sediments spanned the last ~10.8?ka (Holocene). The sediments and provenance of the Yangtze Shoal have been controlled by the East Asian monsoon, sea level change, riverine sediment flux and ocean circulation. The intervals 8.3-6.3?ka and 3.8-1.5?ka, are characterized by Yangtze River sources, whereas 6.3-3.8?ka and 1.5-0.8?ka, are characterized by a source mixture with Yellow River input. Tracing the multiple sources effectively confirms the hypothesis that the southern Yangtze Shoal was a delta formed by combined sedimentation from the Yangtze River and Yellow River during times of low sea level.

SUBMITTER: Cao C

PROVIDER: S-EPMC6197290 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Temporal and spatial characteristics of sediment sources on the southern Yangtze Shoal over the Holocene.

Cao Chao C Cai Feng F Zheng Yongling Y Wu Chengqiang C Lu Huiquan H Bao Jingjing J Sun Quan Q

Scientific reports 20181022 1

The sediment sources of the Yangtze Shoal were traced by analysing surface and core sediment particle size, detrital and clay minerals, carbon and nitrogen isotopes, and radioisotope dating. In the estuary, the sediments are dominated by silty clay, high stable mineral, and extremely high illite/chlorite. Stable organic carbon isotopes (δ<sup>13</sup>C-TOC) indicated a marine-dominated mixture. On the shoal, the sediments are mainly composed of fine sand, high unstable mineral. The δ<sup>13</sup ...[more]

PMID: 30349016

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Project description:We carried out geochemical analyses on a sediment core from Lake Harris, Florida (USA) to identify sources of organic matter to the sediment throughout the Holocene, and relate changes in those sources to shifts in past climate and environmental conditions. We hypothesized that the sources of organic matter changed in response to regional hydrologic shifts following de-glaciation, and to human population expansion in the state during the 20th century. Hydroclimate shifts in Florida were related to: 1) a steady rise in relative sea level and the fresh water table that began in the early Holocene, 2) wetland formation and expansion ca. 5,000 cal yrs BP, and 3) the onset of the modern El Niño (ENSO) cycle ~3,000 cal yrs BP. Stratigraphic changes in sediment variables from Lake Harris reflect each of these hydroclimate periods. Early in the Holocene, Lake Harris was a marsh-like system in a relatively dry, open-prairie environment. Organic sediments deposited at that time were derived largely from terrestrial sources, as inferred from high TOC/TN ratios, a dominance of longer-chain of n-alkanes (n-C29-31), relatively negative organic carbon isotope values (?13CTOC), and low biogenic silica concentrations. In the middle Holocene, a positive shift in ?13CTOC coincided with the onset of wetter conditions in Florida. Submerged macrophyte biomarkers (n-C21-23) dominated, and during that period bulk organic carbon isotope values were most similar to ?13C values of mid-chain-length n-alkanes. In the late Holocene, ?13CTOC values declined, CaCO3 levels decreased to trace amounts, organic carbon concentrations increased and diatom biogenic silica concentrations increased from 10 to 120 mg g-1. Around 2,900 cal yrs BP, the effects of ENSO intensified and many Florida lakes deepened to their current limnetic state. Concentrations of algal and cyanobacterial biomarkers in the Lake Harris core increased by orders of magnitude after about AD 1940, in response to human-induced eutrophication, an inference supported by values of ?15N that fluctuate around zero.

Dataset Information

Temporal and spatial characteristics of sediment sources on the southern Yangtze Shoal over the Holocene.

Publications

Temporal and spatial characteristics of sediment sources on the southern Yangtze Shoal over the Holocene.

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