Biogenic silica in surface sediments of the South China Sea: Controlling factors and paleoenvironmental implications

Zhang, Lanlan; Wang, Rujian; Chen, Mu‐Hong; Liu, Jianguo; Zeng, Lili; Xiang, Rong; Zhang, Qiang

doi:10.1016/j.dsr2.2015.11.008

Cited by 26 publications

(9 citation statements)

References 49 publications

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“…In short, a diatom buried in the Paleocene had a very low chance of making it into the fossil record, while the same diatom buried in more recent times was much more likely to be preserved. Furthermore, although radiolarian preservation potential would also have increased over the Cenozoic, the effect would have been less pronounced given the lower k values of radiolarian tests (48)(49)(50)(51)(52)(53)76), due to the effect of temperature and sedimentation rate on burial efficiency being nonlinear with regard to k (77). The dramatic increase in preservation potential would thus have resulted in a concomitant increase in the ratio of diatoms to radiolarians (Fig.…”

Section: Discussionmentioning

confidence: 99%

Revisiting the sedimentary record of the rise of diatoms

Westacott

Planavsky

Hull

2021

Proc. Natl. Acad. Sci. U.S.A.

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Diatoms are a major primary producer in the modern oceans and play a critical role in the marine silica cycle. Their rise to dominance is recognized as one of the largest shifts in Cenozoic marine ecosystems, but the timing of this transition is debated. Here, we use a diagenetic model to examine the effect of sedimentation rate and temperature on the burial efficiency of biogenic silica over the past 66 million years (i.e., the Cenozoic). We find that the changing preservation potential of siliceous microfossils during that time would have overprinted the primary signal of diatom and radiolarian abundance. We generate a taphonomic null hypothesis of the diatom fossil record by assuming a constant flux of diatoms to the sea floor and having diagenetic conditions driven by observed shifts in temperature and sedimentation rate. This null hypothesis produces a late Cenozoic (∼5 Ma to 20 Ma) increase in the relative abundance of fossilized diatoms that is comparable to current empirical records. This suggests that the observed increase in diatom abundance in the sedimentary record may be driven by changing preservation potential. A late Cenozoic rise in diatoms has been causally tied to the rise of grasslands and baleen whales and to declining atmospheric CO2 levels. Here we suggest that the similarity among these records primarily arises from a common driver—the cooling climate system—that drove enhanced diatom preservation as well as the rise of grasslands and whales, rather than a causal link among them.

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Section: Discussionmentioning

confidence: 99%

Revisiting the sedimentary record of the rise of diatoms

Westacott

Planavsky

Hull

2021

Proc. Natl. Acad. Sci. U.S.A.

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“…Thus, the deep-water chemical properties in the SCS are similar to those in the Western Pacific (Miao;Thunell, 1994;Chen et al, 2001). Intense deep-water ventilation, and warm deep (>2 °C) and surface (>28 °C) waters, favor SCS surface sediments CaCO3 preservation, which present CaCO3 contents above 10% at depths ~3500 m, close to the position of the modern CCD (Figure 1.1b) (Wang, 1999;Li, 2009;Zhang et al, 2015).…”

Section: Regional Settingmentioning

confidence: 56%

“…In contrast, PC2 is strongly correlated with Ca and Sr elements, reflecting biogenic sediments input. Since, at the northeast subbasin of the SCS, the authigenic contribution of minerals usually associated with terrestrial materials is negligible (Wei et al, 2003;Zhang et al, 2015), our elemental composition results changes are interpreted primarily as variations in the input of sediments derived from the adjacent continent and marine biogenic contribution.…”

Section: Discussionmentioning

confidence: 91%

“…It is important to highlight that previous studies have shown that substantial carbonate dissolution occurs in the deep central SCS basin, leaving carbonate-poor surface sediments (Zhang et al, 2015;Luo et al, 2018). Therefore, at the deep western and northern SCS subbasins, the enrichment of PF in deep-sea records has been attributed…”

Section: Discussionmentioning

confidence: 96%

“…The contribution of biogenic particles to deep-sea sediments at the SCS is mainly controlled by the dilution of biogenic particles by terrigenous input, carbonate saturation thresholds (dissolution), or biogenic flux (Thunell et al, 1992;Chen et al, 1999;Li et al al., 2001;Wei et al, 2003;Zhang et al, 2015). The modern northeast SCS sub-basin surface sediments present CaCO3 values between 0 and 10%, configuring one of the SCS regions with the lowest carbonate concentration (Zhang et al, 2015). At Hole U1432C retrieval site and depth (3829 m), biogenic particles' contribution to modern sediments is primarily controlled by dilution and dissolution inherent to below lysocline and CCD depths (Zhang et al, 2015).…”

Section: Scs Ne Sub-basin Potential Sediment Sourcesmentioning

confidence: 99%

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>b<Carbonate system and elementary geochemistry>/b<: Paleoceanographic and paleoclimatic implications in the South China Sea along the Late Quaternary

Gerotto¹

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Understanding past ocean carbonate chemistry changes is critical to elucidate the role of the oceans in the global carbon cycle and Earth's climate control according to its large carbon dioxide (CO2) storage capacity. The South China Sea (SCS) is a tropical basin of great interest for understanding the evolution of the carbonate system. This marginal basin is under the influence of the East Asian Monsoon (EAM) which has a profound impact on the interactions between the atmosphere, land, and oceans. In this context, the present work aims to evaluate changes in SCS carbon system considering the carbonate cycles that acted in the basin along with the Quaternary controlling dissolution and dilution processes. For this, we applied using a multiproxy approach in marine sedimentary samples from cores recovered in the eastern, northeast, and northern subbasins of the SCS -Hole IODP U1431D (4240 m depth), Hole U1432C (3829 m), and ODP 1146 (2092 m) -and in surface sediments collected along the basin (R/V Sonne, at depths between 629-3809 m. We evaluated (i) the abundance, fragmentation, and dissolution indexes of planktonic foraminifera and total organic carbon in the last 600 ka; (ii) terrigenous input by the determination of major and trace elements in sediments and variations in natural gamma radiation; and (iii) performed the calibration of morphological attributes of coccoliths in response to a laboratory dissolution experiment and oceanic environmental parameters, generating a new proxy that was applied in the reconstruction of dissolution patterns in the last 210 kyr. The results showed that the records located below the modern lysocline and carbonate compensation were under strong dissolution. A punctual increase in planktonic foraminifera abundance was related to primary productivity and EAM dynamics, with the occurrence of turbidites influencing CaCO3 preservation. Despite the low carbonate preservation inherent to the depth of these records, the dilution of biogenic sediments by the terrigenous input was recorded due to the more significant terrigenous contribution of sediments potentially sourced from Luzon in response to the strengthened summer EAM. The dissolution experiment and the evaluation of surface sediments showed that changes in coccolith morphology, obtained by the ks factor, are mainly controlled by changes in carbonate saturation, and can be used as a proxy to track changes in carbonate saturation limits. When applied as dissolution proxy the ks factor recorded changes possibly related to variations in lysocline depth over the last 210 kyr consistent with changes in deepwater circulation between the Pacific and the SCS. The results of this thesis demonstrate that post-burial dissolution has a major influence on the composition of micro and nannofossils assemblages and in the carbonate preservation at SCS sediments and that the coccolith ks factor is a reliable proxy for tracking changes in carbonate chemistry.

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Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

Lefebvre

Düring

et al. 2023

Earth Surf Processes Landf

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In deep‐marine environments, the inception of channels can be induced by the interaction between bottom currents and rough topography. However, it is still unclear under which conditions such features can form and what happens in the earliest phase of channel development. In this study, based on the morphological, sedimentary and oceanographic settings of a pockmark field in the NW South China Sea, we reveal the process of channel inception through the erosion of pockmarks by bottom currents. Using numerical simulations, we show that an appropriate current velocity can induce the erosion of pockmark trains in cohesive sediments, leading to the coalescence of discrete pockmarks and the formation of a channel with a rough thalweg. The interaction of bottom currents with the pockmarks induces a significant erosion along the pockmarks axis. Bottom‐current erosion is strongest at the downstream edges of pockmarks, where the horizontal velocity reaches a maximum and an upwelling forms. Erosion increases as the distance between pockmarks reduces. In our simulation results, a channel is only formed by the coalescence of pockmarks if the distance between pockmarks is <6 times the diameter of the pockmark. This study provides evidence of the formation of channels by bottom currents, which helps reconstruct palaeoceanographic conditions based on sediment architecture. It also shows the complex hydrodynamics at these structures that strongly control sedimentary processes and may affect distribution of benthic ecosystems in marine environments.

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Biogenic silica in surface sediments of the South China Sea: Controlling factors and paleoenvironmental implications

Cited by 26 publications

References 49 publications

Revisiting the sedimentary record of the rise of diatoms

Revisiting the sedimentary record of the rise of diatoms

>b<Carbonate system and elementary geochemistry>/b<: Paleoceanographic and paleoclimatic implications in the South China Sea along the Late Quaternary

Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

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