Dataset: Decadal variations of hypoxia off the Changjiang Estuary since the 1950s: Sedimentary records from benthic foraminifera

The averages of abundance, number of species and Shannon-Wiener index (H′) are 4182 individuals/40 g, 47 and 3.41, respectively. Based on quantitative analysis, there are a total of 16 dominant species with an average relative abundance of >2% for the overall assemblage. 4. TN contents range from 0.09% to 0.12% (average 0.10%), and TOC contents range from 0.40% to 0.58% (average 0.50%).

C/N ratios range from 4.48 to 5.29 (average 4.92). δ13C values range from –23.93‰ to –23.15‰ (average –23.51‰). 5. Bottom-water hypoxia off the Changjiang Estuary has been persistent throughout the study period. From 1950 to 1980, hypoxia was weak and declining; after 1980, hypoxia was severe and intensifying.

The details for sample collection are as follows: Core YEC1701 was collected using a gravity corer during a summer cruise by the State Key Laboratory of Marine Geology (Tongji University) in August, 2017, and its total length is 405 cm. The coring site (30°57′3.062″N, 122°44′19.792″E) was located in the muddy delta front and adjacent to the modern core hypoxic area (Li et al., 2002), and the water depth was 22.4 m. The core was split lengthwise in the laboratory: one half was sealed with the preservative film and stored at 4℃ for archiving, and the other (working half) was carefully smoothed with a stainless steel knife to expose sedimentary structures.

The working half was photographed, described lithologically, and scanned non-destructively by an X-ray fluorescence (XRF) core scanner before subsampling. Subsamples were collected at 1 cm intervals using a stainless steel cutter, sealed in plastic bags, and stored at 4℃ for subsequent analyses.

Note

All the measurements were conducted at the State Key Laboratory of Marine Geology.