Comparison of multiple salinity datasets:upper ocean salinity and stratification in the tropical Pacific during the Argo period

Ocean salinity is an important variable that affects the ocean stratification.We compared the salinity and ocean stratification in the tropical Pacific derived from the Argo(Array for Real-time Geostrophic Oceanography data),EN4(Ensemble 4 analysis),SODA(the Simple Ocean Data Assimilation reanalysis),IAP(Institute of Atmospheric Physics data),and ORAS4(Ocean Reanalysis System 4)over 2005–2017.Results show that the spatial distribution of climatological mean of sea surface salinity(SSS)in all the products is consistent,and the low salinity region showed large deviation and strong dispersion.The Argo has the smallest RMSE and the highest correlation with the ensemble mean,while the IAP shows a high-salinity deviations relative to other datasets.All the products show high positive correlations between the sea surface density(SSD)and SSS with respect to the deviations of climatological mean from ensemble mean,suggesting that the SSD deviation may be mainly influenced by the SSS deviation.In the aspect of the ocean stratification,the mixed layer depth(MLD)climatological mean in the Argo shows the highest correlation with the ensemble mean,followed by EN4,IAP,ORAS4,and SODA.The Argo and EN4 show thicker barrier layer(BL)relative to the ensemble mean while the SODA displays the largest negative deviation in the tropical western Pacific.Furthermore,the EN4,ORAS4,and IAP underestimate the stability in the upper ocean at the depths of 20–140 m,while Argo overestimates ocean stability.The salinity fronts in the western-central equatorial Pacific from Argo,EN4,and ORAS4 are consistent,while those from SODA and IAP show large deviations with a westward position in amplitude of 0°–6°and 0°–10°,respectively.The SSS trend patterns from all the products are consistent in having ensemble mean with high spatial correlations of 0.95–0.97.

Numerical investigation of wake-collapse internal waves generated by a submerged moving body

The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body.The model incorporates body geometry,propeller forcing,and stratification magnitude of seawater.The generation mechanism and wave properties are discussed based on model results.It was found that the generation of the wave and its properties depend greatly on the body speed.Only when that speed exceeds some critical value,between 1.5 and 4.5 m/s,can the moving body generate wake-collapse internal waves,and with increases of this speed,the time of generation advances and wave amplitude increases.The generated wake-collapse internal waves are confirmed to have characteristics of the second baroclinic mode.As the body speed increases,wave amplitude and length increase and its waveform tends to take on a regular sinusoidal shape.For three linearly temperature-stratified profiles examined,the weaker the stratification,the stronger the wake-collapse internal wave.

Organic carbon isotope gradient and ocean stratification across the late Ediacaran-Early Cambrian Yangtze Platform

Organic carbon isotope （δ-13 Corg） data from two well-preserved sections across a shallow-to-deep water transect of the late Edi- acaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ-13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24%0. In the deep-water Longbizui section, δ-13Corg values from time-equivalent strata of the Dengying Formation are mostly between -35‰ and -32‰）. These new data, in combination with δ-13Corg data reported from other sections in South China, reveal a 6‰-8‰ shallow-to-deep water δ-13Corg gradient. High δ-13Corg values （〉-30‰） occur mostly in shallow-water carbonate rocks, whereas low δ-13Corg values （〈-32‰） dominate the deep-water black shale and chert. The large temporal and spatial δ-13Corg variations imply limited buffering effect from a large dissolved organic carbon （DOC） reservoir that was inferred to have existed in Edi- acaran-Early Cambrian oceans. Instead, δ-13C-org variations between platform and basin sections are more likely caused by dif- ferential microbial biomass contribution to total organic matter. High δ-13Corg values （〉-30‰） documented from shallow-water carbonates are within the range of typical Phanerozoic δ-13Corg data and may record the isotope signature of organic matter from primary （photosynthetic） production. In contrast, low δ-13Corg values （〈-32‰） from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ-13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.

The large increase of δ^(13)C_(carb)-depth gradient and the end-Permian mass extinction

Carbonate carbon isotope （δ^13Ccarb） has received considerable attention in the Permian-Triassic transition for its rapid negative shift coinciding with the great end-Permian mass extinction event. The mechanism has long been debated for such a c~ δ^13Ccarb negative excursion through the end-Permian crisis and subsequent large perturbations in the entire Early Triassic. A δ^13Ccarb depth gradient is observed at the Permian-Triassic boundary sections of different water-depths, i.e., the Yangou, Meishan, and Shangsi sections, and such a large δ^13Ccarb-depth gradient near the end-Permian mass extinction horizon is believed to result from a stratified Paleotethys Ocean with widespread anoxic/euxinic deep water. The evolution of δ^13Ccarb-depth gradient com- bined with paleontological and geochemical data suggests that abundant cyanobacteria and vigorous biological pump in the immediate aftermath of the end-Permian extinction would be the main cause of the large δ^13Ccarb-depth gradient, and the enhanced continental weathering with the mass extinction on land provides a mass amount of nutriment for the flourishing cyanobacteria. Photic zone anoxia/euxinia from the onset of chemocline upward excursion might be the direct cause for the mass extinction whereas the instability of chemocline in the stratified Early Triassic ocean would be the reason for the delayed and involuted biotic recovery.