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Paleotempestology evidence recorded by eolian deposition in the Bohai Sea coastal zone during the last interglacial period
Marine Geology 379 (2016) 78–83
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Letter
Paleotempestology evidence recorded by eolian deposition in the Bohai Sea coastal zone during the last interglacial period Shuhuan Du a,⁎, Baosheng Li b, Muhong Chen a, Rong Xiang a, Donefeng Niu b, Yuejun Si c a b c
Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China Department of Geography, South China Normal University, Guangzhou 510631, China School of Geography and Planning, Guangxi Teachers Education University, Nanning 530001, China
a r t i c l e
i n f o
Article history: Received 10 October 2015 Received in revised form 29 April 2016 Accepted 24 May 2016 Available online 25 May 2016 Keywords: Bohai Sea coastal zone Eolian sediments Marine micropaleontology Paleotempestology record Last interglacial period
a b s t r a c t Reconstruction of the generation, development, and evolution of modern storms through paleotempestology is used to understand the regularity of storm activity and the relationship between storm activity and global climate change. Existing paleotempestology research in China is concentrated mainly on the low latitude sediments deposited since the Holocene (about 7000 a). In this study, we examine the storm deposits in the eolian sediments of the Bohai Sea coastal zone at middle latitudes, choosing the Miaodao stratigraphic section (MDS) as the target area. This area is located in the Bohai Sea strait and shows evidence of storms since the last interglacial period using an analysis of the grain size parameter, element ratios, and marine micropaleontology foraminifera fossils in the sediment during the last 130 ka that can be used in our paleotempestology research. The results include three main findings: (1) the marine micropaleontology foraminifer fossils appear in the eolian sediment of the MDS and, in combination with grain size parameter and element ratios of the sediments, serve as evidence of the paleotempestology record on the Bohai Sea coastal zone; (2) planktonic foraminifera fossils appear in the MDS, indicating that the Yellow Sea warm current affected the Bohai Sea during the last interglacial period; and (3) storm activity in the marine isotope stage (MIS) 5a has been recorded in the MDS 15 times. The findings of this study expand the paleotempestology record from 7000 a to 90 ka and serve as a reference for research for middle latitude storm activity. © 2016 Elsevier B.V. All rights reserved.
1. Introduction In recent years, frequent cyclone strikes, with strong winds and heavy rains brought by powerful typhoons, have caused severe damage to life and property and have made significant impacts on fragile coast ecosystems (Bianchette et al., 2009). These events have led to an increased amount of research focused on the relationship of extreme climate events, including relationships between the storms and global warming (Emanuel, 2005) or periodical typhoon interdecadal change (Goldenberq et al., 2001). Therefore, there is an urgent need for the expansion of the timescale of storm records. The science of paleotempestology uses written records, microfossils, isotopes, and element ratios to reconstruct the variability in tropical cyclone activity prior to the instrumental record. Researchers have focused mainly on the study of paleotempestology frequency in recent decades. Donnelly et al. (2001), Donnelly and Woodruff (2007), and Donnelly et al. (2015), recreated century- to millennial-scale strong storm activity ⁎ Corresponding author at: Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164, West Xiangang Road, Guangzhou 510301, China. E-mail address: [email protected] (S. Du).
http://dx.doi.org/10.1016/j.margeo.2016.05.013 0025-3227/© 2016 Elsevier B.V. All rights reserved.
from the middle latitudes in the western North Atlantic; while others have reconstructed the record for the western North Pacific (Woodruff et al., 2009, 2015), including Japan. Most of the paleotempestology research has focused on the late to middle Holocene (Liu and Fearn, 2000; Mann et al., 2009; Boldt et al., 2010; Lane et al., 2011; Brandon et al., 2014). Relatively fewer paleotempestology studies have been conducted in China, and these are concentrated mainly on the low latitudes. Yu et al. (2004) has rebuilt the storm activity of the late Holocene, showing an average of about 160 year cycles. Huang and Yan (1997) uses foraminifera assemblages to identify the Holocene storm activity in the Pearl River estuary region and estimates a typhoon return period of about 350 years. Both the sample resolution and deposition site affect the detection of storm frequency. Global differences have also been noted, with more activity occurring at low latitudes than that at higher latitudes, therefore paleotempestology research in the middle latitude Bohai Sea coastal zone is difficult, the stratigraphic record is influenced by storm deposits that retain the evidence. The Bohai Sea, an enclosed sea with an average depth of only about 18 m, is connected by the Bohai Strait and the Yellow Sea. The strait is only 100 km wide and includes the Miaodao Archipelago. The Bohai Sea is a region of strong storm activity with high frequency because storm surges occur throughout the year (State Meteorological
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Administration, 1990) by the East Asian monsoon. The onset of the East Asian paleomonsoon in China was in the late Oligocene Epoch to early Miocene Epoch (An et al., 1990); while the Bohai Sea coastal zone sediment that formed in the late to middle Pleistocene was influenced by East Asian paleomonsoon (Cao et al., 1987). Therefore, sediment in the Bohai Sea coastal zone has maintained a good record for reconstructing the paleotempestology over a long time scale. Specifically, this study presents the Miaodao stratigraphic section (MDS) as the target area. Reconstruction is performed by determining the ages and proxy paleoclimatic indices, such as the marine micropaleontology, the element ratios, and the grain size parameters to reveal the paleotempestology information recorded since the last interglacial period.
following the procedures used for loess grains reported by Lu and An (1997). The mean grain size (Mz; Φ) and its σ of the MDS samples were calculated by using a formula developed by Fork and Ward (1957). For the foraminifera analysis, a 50 g (dry weight) specimen was split from each sample. The specimens were weighed and soaked in distilled water for ~24 h for disaggregation before washing over a 150 μm sieve and floating in carbon tetrachloride. The foraminifera were counted in the fractions smaller than 150 μm. The TOC and TN were determined in 2–5 mg sediment samples. The quantification was performed by calibration curves and using cystine as the standard. The detection limits were 0.01% for TOC and 0.001% for TN.
2. Regional setting
4.1. Chronology
The MDS is located at N 37° 56′ 31.9″, E 120° 40′ 35.9″ at an elevation of 12 m above sea level in the northwest region of the Miaodao Archipelago in the Bohai Sea (Fig. 1). A total of 15 layers exist in the MDS (MD1 to MD15), and the chronology indicates that layers MD1 to MD14 have accumulated since the marine isotope stage (MIS) 5e (Fig. 2). 3. Methods and materials
The AMS-14C specific sampling layer, depth, calibration age, and relevant parameters of the OSL are listed in Table 1. We use the known ages and segmentation sedimentation rates to establish the MDS chronology since the Marine Isotope Stage 5e (Eemian, i.e. 124–119 ka) as shown in Fig. 2. The MDS is first divided into five stratigraphic segments (MDS1–MDS5) on the basis of the determined ages. The other ages are calculated by using regression lines for the sedimentation rates (Fig. 2). The results are listed in Table 2.
3.1. AMS-14C and OSL age test
4.2. Grain size
This study obtained 11 sets of age data, including three sets of accelerator mass spectrometry radiocarbon dating (AMS-14C) data and eight optically stimulated luminescence (OSL) datasets from 10 layers in the MDS. The AMS-14C age determination was completed in the AMS-14C Key Laboratory of Nuclear Physics and Technology at Beijing University. The OSL procedure was conducted by the Daybreak 2200 OSL reader at the OSL Laboratory of Chinese Academy of Geological Sciences and the 1100B OSL instrument in the Isotope and OSL Dating Laboratory of Sun. Yat\\sen University. Organic matter was used as the test material for the AMS-14C test. The results of the 14C age were corrected through the CALIB 5.01 program and the IntCal04 database (Stuiver et al., 1998) and showed a range from 0 ka to 21.381 ka with an error of 2σ.
The results of the Mz analysis in the MDS show that Mz ranges from 3.46 Φ (90 μm) to 6.32 Φ (13 μm), with an average of 4.80 Φ (36 μm). The content is mainly sand, which varies from 15.09% to 76.05%, followed by silt at 18.03% to 71.54%, and clay at 5.22% to 25.81% (Fig. 2). The average sand, silt, and clay contents are 44.64%, 43.75%, and 11.61%, respectively. The standard deviation (σ) of the MDS grain sizes ranges from 1.53 to 2.53, with an average of 1.91.
3.2. Proxy paleoclimate indices The samples, n = 314, were analyzed to determine the grain size from the top of the section downward through the MDS. In addition, some samples were collected for foraminifera, total organic carbon (TOC), and total nitrogen (TN) testing. A Malvern Mastersizer 2000 M laser grain size analyzer with a measuring range of 0.02–2000 μm was used for grain size analysis by
4. Results
4.3. Foraminifera analysis The examination of 197 samples of marine micropaleontology in the MDS1 and MDS5 sections identifies 139 foraminifera in 15 samples, all concentrated in MDS5a. Of these foraminifera, 79.8% are benthic foraminifera, including eight genera and nine species (Table 3). Pseudononion sp. A is the most abundant at 33.1% and is identified in 11 of the 15 samples of benthic foraminifera, followed by Guembelitria vivans at 12.2% in eight of 15 samples, Ammonia beccarii at 10.8% in six of 15 samples , and Elphidium magellanicum at 7.91% in five of 15 samples. Other species comprise b5% of the total. Eight samples contain planktonic foraminifera and indicated Globigerina bulloides at 20.1%. All of the individual foraminifera specimens in the sediments are b 100 um in size, and a small amount have broken shells.
Fig. 1. Location of the Miaodao stratigraphical section (MDS).
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Fig. 2. Sequence and time scale of the Miaodao stratigraphical section during the last 130 ka.
4.4. TOC and TN The TOC and TN testing was performed on samples from the MDS5a section. The results indicate a small TOC/TN value in the sample including marine micropaleontology, with an average of 2.3. The TOC/TN in the samples not including marine micropaleontology is 2.5.
5. Discussion The paleotempestology research in China has been focused on the Holocene and low latitudes (Huang and Yan, 1997; Yu et al., 2004), longer storm reconstructions that extend through past climatic epochs and from locations that provide better spatial coverage are required in order to better understand past changes in storm activity and, in turn, the
complex mechanisms governing the storm formation, development, and evolution. The MDS is composed of continuous eolian sediments, which have accumulated since approximately 130 ka without marine facies. However, its coastal zone position influences the material sources in the MDS at different periods of the sea level fluctuations. The sea level reconstruction from the south Bohai Sea (Yi et al., 2012) shown in Fig. 3 is compared with the global sea level change (Waelbroeck et al., 2002) over the last 130 ka. During periods of low sea level, the desertification of the seafloor sediments of the receded Bohai Sea provides the main source material (Zhao, 1991). Some research has been conducted on the marine micropaleontology in the sediments of the last glacial period and in the Holocene (Cheng et al., 1995; Li et al., 2002). During periods of high sea level, the main sources of material in the MDS may have been the eolian dune sand that was captured by the Bohai Sea, sand from the coast of the North Yellow Sea, and silt from the Yellow River
Table 1 The relevant parameters of AMS-14C and OSL. a. AMS-14C ages of some horizons in the Miaodao section and their calibrated results. Horizon and lab record number
Depth/m
Ages of AMS-14C (ka BP)
Calibrated ages (Cal ka BP)
Unit 15-GZ4217 Unit 15-GZ4218 Unit 14-GZ4220
0.25 0.50 0.90
2.210 ± 0.30 4.305 ± 0.30 8.065 ± 0.50
2.237 ± 0.88 4.862 ± 0.30 8.947 ± 0.18
b. OSL ages of some horizons in the Miaodao section and their analytical data. Horizon and lab record number
Depth/m
U/10-6
Th/10-6
K/%
Total dose/E.D. (Gy)
Annual dose/(m Gy)
Water content/%
OSL/ka
MD4-SY01 MD5-10G520 MD6-SY 02 MD8-SY 03 MD10-10G521 MD13-10G522 MD14-SY 04 MD14-SY 05 MD15-10G523
1.50 2.06 2.48 3.02 3.60 5.34 5.40 6.30 6.44
1.8 1.43 1.7 1.4 1.20 1.02 1.5 1.3 1.96
10.4 8.67 11.1 9.1 7.00 6.86 10.6 7.9 8.06
1.75 1.61 1.73 1.78 1.85 1.94 1.96 1.29 1.57
71.05 ± 1.26 81.20 ± 0.94 139.75 ± 2.61 187.69 ± 3.37 246.86 ± 3.48 337.69 ± 4.89 404.39 ± 7.13 309.52 ± 5.01 411.08 ± 9.49
3.66 ± 0.3 3.10 3.64 ± 0.3 3.36 ± 0.3 3.01 3.03 3.51 ± 0.3 2.40 ± 0.2 3.02
3.46 3.69 4.31 4.51 7.58 6.73 11.20 11.67 11.37
19.41 ± 0.26 26.2 ± 0.6 38.39 ± 0.57 55.84 ± 1.02 82.1 ± 3.5 111.4 ± 5.0 115.18 ± 2.43 129.05 ± 2.61 136.1 ± 6.3
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Table 2 Geochronology of major sections and every horizon in Miaodao section. Section
Sequence
Depth/m
Age/ka BP
Section
MDS1
MD1 MD2 MD3 MD4 MD5 MD6 MD7
0.50–0 1.02–0.51 1.22–1.03 1.88–1.23 2.46–1.89 2.64–2.47 2.74–2.65
0–4.862 4.862–11.0 11.0–14.5 14.5–24.0 24.0–37.8 37.8–43.6 43.6–46.8
MDS3 MDS4 MDS5
MDS2 a b MDS3
estuary (Cao et al., 1987). No marine micropaleontology has been detected in this period. If marine micropaleontology are found in the eolian sediment formed at periods of high sea level with no transgression to the sedimentary face, such marine micropaleontology could be used as evidence of storm deposition. Such evidence, combined with the grain size parameter and the element ratio index of the sediment, would be beneficial for restoring the paleotempestology record at middle latitudes since the last interglacial period. The results of the Mz and σ of the MDS (Fig. 3) show that σ ranges from 1.53 to 2.53, with an average of 1.91, since the last interglacial period. Using σ of 2 as an index, with b2 indicating better sorting and N 2 indicating poor sorting, all of the sediments of the MDS belong to the better sorting category. In the various subsections, the better sorting sediments are mainly concentrated in the last glacial period (MDS2– MDS4) and the Holocene (MDS1) period with σ averages of 1.80 and 1.84, respectively. The σ in the last interglacial period is 2.01, indicating poor sorting. As shown in Fig. 3, the Mz values for MDS5e, MDS5a, and MDS1 indicate a fine grain size. A paleosol facies developed under the prevalent East Asian summer monsoon period in which the wind was the major transporting agent, indicating a warm and humid climate as the obvious pedogenesis. However, the σ values of MDS5a and MDS5e are poorer than those in MDS1. All developed in the same climate and with the same sedimentary facies; however, the difference in the sorting coefficient indicates that the sediment of MDS5 was disturbed by climatic events because some marine micropaleontology foraminifer fossils were identified in the eolian sediment of MDS5. The initial hypothesis for the interference seen in the sediment is storm deposition. The benthic foraminifera fossils species in MDS5a include some modern, common types found in the Bohai Sea, such as A. beccarii, Ammonia convexidorsa, Cribrononion incertum, E. magellanicum, and Pseudononionella variabilis Zheng, and in the Yellow Sea and East China Sea continental shelf, such as Pseudononion sp. A. G. vivans, Cassidulina carinata Silvestri, and Rosalina vilarbodeana d'Orbigny. The
c a b c d e
Sequence
Depth/m
Age/ka BP
MD8 MD9 MD10 MD11 MD12 MD13 MD14
3.02–2.75 3.36–3.03 4.02–3.37 4.58–4.03 4.98–4.59 5.38–4.99 6.28–5.39
46.8–55.8 55.8–71.2 71.2–89.2 89.2–98.6 98.6–105.3 105.3–113.9 113.9–129.1
appearance of the latter four species in the MDS may be attributed to the differences in the water environment from the Yellow Sea Warm current (YSWC). The planktonic foraminifera G. bulloides in MDS5a was also carried by the YSWC. G. bulloides is a temperate distribution specie and is the most widely distributed specie in the modern Globigerina genera. This cold water specie has a strong tolerance to low temperatures and low salt content (Zheng and Zheng, 1960). Modern planktonic foraminifera live mostly in the high salinity of the open ocean and are rare in the shelf basin, and their northern distribution in China is limited to about 36° N (Zheng and Zheng, 1960). Some researchers have reported that planktonic foraminifera were brought by the warm current from the Yellow Sea during high sea level during the last interglacial period and deposited with the benthic foraminifera by the winter monsoon during low sea level periods (Li et al., 1992; Cheng et al., 1991). Research on the impact of the YSWC in the Bohai Sea has focused on the Holocene and the last glacial maximum (Li et al., 2007; Wang et al., 2011). However, no direct evidence has been reported on the effects of the YSWC on the Bohai Sea during the last interglacial period. The foraminifera fossils appearing in MDS5a, particularly G. bulloides planktonic foraminifera confirm that the YSWC affected the Bohai Sea during the last interglacial period. During that period, global sea level fluctuations occurred multiple times (Potter and Lambeck, 2004; Waelbroeck et al., 2002) (see Fig. 3). The Bohai Sea coastal zone also experienced sea level oscillations during the last interglacial period. Yi et al. (2012) reconstructed the reference water level in the south Bohai Sea (Fig. 3) and showed the highest sea level in MDS5a was caused by tectonic movement at about 100–80 ka that resulted in the uplift of the surrounding mountains. Species of planktonic and benthic foraminifera living in the Yellow and East China seas appear in MDS5a, revealing that the Yellow Sea warm water mass moved northward along the Yellow Sea trough into the Bohai Sea during the highest sea level in MDS5a, causing their heterochthonous burial in the MDS by the extreme high
Table 3 Results of foraminiferal identification in MDS5a. Samples Species
MD10-01 MD10-02 MD10-03 MD10-07 MD10-10 MD10-11 MD10-17 MD10-18 MD10-21 MD10-22 MD10-24 MD10-25 MD10-26 MD10-28 MD10-33
Ammonia beccarii
Ammonia convexidorsa
Guembelitria Cribrononion vivans incertum
+ − − − − − − − − + + + + − +
− − − − − − − − − + + − − − −
+ + − − − − − + − + + + − + +
− − + − + − − − − + − − − − −
Elphidium magellanicum
Cassidulina carinata Silvestri
Pseudononion Pseudononionella sp. A variabilis Zheng
− − + − − − − − + + − − − + +
− − − − − − − − − + − + + + +
+ − − + − + + + − + + + + + +
− − − − − − − − − + − − − − −
Rosalina vilarbodeana
Globigerina bulloides
− − − − − + + − − − − − − − +
− − − − − + − + − + + + + + +
Note: MDS5a, layer MD10, which depth 66 cm, divided into 33 samples (e.g. MD10-01 and MD10-02), each sample was collected by 2 cm depth. “+” means contain this species of foraminifer and “−” means inexistence in each sample.
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Fig. 3. Change curves of the grain size parameter Mz (Φ, green line), standard deviation (σ, blue line) in the MDS compared to relative sea level in the south Bohai Sea (Yi et al., 2012, black line) and global sea level changes (Waelbroeck et al., 2002, gray line).
sea level (storm surge) deposition event. The foraminifera group in these layers, including a mixture of the euryhaline and the stenohaline species, shows high differentiation and low dominance. The shells appear in yellow ground glass, and most are small individual shells. A similar sediment grain size distribution and marine micropaleontology of the foraminifera fossils can be found in the eolian sediment of the MDS on the rocky coast; therefore, the most likely mechanism is storm surge. The paleotempestology includes marine matter with smaller TOC/ TN than in the terrigenous matter (Fan et al., 2007). The TOC/TN results of the MDS5a also indicate low TOC/TN values in the sample containing the foraminifera fossils and high values in other terrigenous sediments. For example, MD10-33, containing marine micropaleontology, has a TOC/TN value of 1.6; and MD10-31, which does not contain foraminifera fossils, has a ratio of 3.3. The TOC/TN results for the MDS5a confirmed that foraminifera fossils represent storm deposition, which serves as evidence of paleotempestology recorded in the Bohai Sea coastal zone during the last interglacial period. Although the MDS1 and MDS5c subsections were deposited during periods of high sea level (Fig. 3), no evidence of storm deposits were found. It is possible that this is related to the altitude of the MDS beyond the storm surge depositional surface at that time. The sediment accumulation was 66 cm during 73.4–88.9 ka of the MDS5a. Of the 33 samples from this subsection, 15 included foraminifera fossils. If each sample represents one storm event, then 15 strong storm events occurred during MDS5a, representing a millennial scale periodicity. This millennial scale frequency record of storm deposition events in the MDS during the last interglacial period is similar to that of the Holocene record in the low latitude areas of China (Huang and Yan, 1997; Yu et al., 2004). This reconstruction of the storm deposits from the last interglacial period can serve as a reference for Quaternary climate change research and can provide an important basis in forecasting storm activity under global warming conditions.
6. Conclusions The results of this study are summarized in the following points: 1. The marine micropaleontology of the MDS in the Bohai Sea coastal zone includes foraminifera fossils in the eolian sediment from periods of high sea level during the last interglacial period. These fossils, in combination with the grain size parameter and the element ratios of the sediments, serve as evidence for the paleotempestology record. 2. The planktonic foraminifera fossils appearing in the MDS confirm that the YSWC affected the Bohai Sea during the last interglacial period. 3. The MDS record shows 15 strong storm events during MIS5a. This deposition frequency is similar to the millennial scale frequency of the Holocene at low latitudes. Therefore, the paleotempestology record from 7000 a in the Holocene to the last interglacial period of 90 ka records the middle latitude storm activity. Acknowledgements We thank reviewer Dr. Jonathan D. Woodruff for his comments that greatly improved this manuscript. This work was supported by the National Natural Science Foundation of China under Grant Nos. 41206036, 41290254, 91228207, and 41471159; the Guangdong Province Science and Technology Project under Grant No. 2015A020216015; and by the Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences under Grant No. SQ201306. References An, Z.S., Liu, T.S., Lu, Y.C., Porter, S.C., Kukla, G., 1990. The long-term paleomonsoon variation recorded by the loess sequence in Central China. Quat. Int. 7-8, 91–95.
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Letter
Paleotempestology evidence recorded by eolian deposition in the Bohai Sea coastal zone during the last interglacial period Shuhuan Du a,⁎, Baosheng Li b, Muhong Chen a, Rong Xiang a, Donefeng Niu b, Yuejun Si c a b c
Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China Department of Geography, South China Normal University, Guangzhou 510631, China School of Geography and Planning, Guangxi Teachers Education University, Nanning 530001, China
a r t i c l e
i n f o
Article history: Received 10 October 2015 Received in revised form 29 April 2016 Accepted 24 May 2016 Available online 25 May 2016 Keywords: Bohai Sea coastal zone Eolian sediments Marine micropaleontology Paleotempestology record Last interglacial period
a b s t r a c t Reconstruction of the generation, development, and evolution of modern storms through paleotempestology is used to understand the regularity of storm activity and the relationship between storm activity and global climate change. Existing paleotempestology research in China is concentrated mainly on the low latitude sediments deposited since the Holocene (about 7000 a). In this study, we examine the storm deposits in the eolian sediments of the Bohai Sea coastal zone at middle latitudes, choosing the Miaodao stratigraphic section (MDS) as the target area. This area is located in the Bohai Sea strait and shows evidence of storms since the last interglacial period using an analysis of the grain size parameter, element ratios, and marine micropaleontology foraminifera fossils in the sediment during the last 130 ka that can be used in our paleotempestology research. The results include three main findings: (1) the marine micropaleontology foraminifer fossils appear in the eolian sediment of the MDS and, in combination with grain size parameter and element ratios of the sediments, serve as evidence of the paleotempestology record on the Bohai Sea coastal zone; (2) planktonic foraminifera fossils appear in the MDS, indicating that the Yellow Sea warm current affected the Bohai Sea during the last interglacial period; and (3) storm activity in the marine isotope stage (MIS) 5a has been recorded in the MDS 15 times. The findings of this study expand the paleotempestology record from 7000 a to 90 ka and serve as a reference for research for middle latitude storm activity. © 2016 Elsevier B.V. All rights reserved.
1. Introduction In recent years, frequent cyclone strikes, with strong winds and heavy rains brought by powerful typhoons, have caused severe damage to life and property and have made significant impacts on fragile coast ecosystems (Bianchette et al., 2009). These events have led to an increased amount of research focused on the relationship of extreme climate events, including relationships between the storms and global warming (Emanuel, 2005) or periodical typhoon interdecadal change (Goldenberq et al., 2001). Therefore, there is an urgent need for the expansion of the timescale of storm records. The science of paleotempestology uses written records, microfossils, isotopes, and element ratios to reconstruct the variability in tropical cyclone activity prior to the instrumental record. Researchers have focused mainly on the study of paleotempestology frequency in recent decades. Donnelly et al. (2001), Donnelly and Woodruff (2007), and Donnelly et al. (2015), recreated century- to millennial-scale strong storm activity ⁎ Corresponding author at: Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164, West Xiangang Road, Guangzhou 510301, China. E-mail address: [email protected] (S. Du).
http://dx.doi.org/10.1016/j.margeo.2016.05.013 0025-3227/© 2016 Elsevier B.V. All rights reserved.
from the middle latitudes in the western North Atlantic; while others have reconstructed the record for the western North Pacific (Woodruff et al., 2009, 2015), including Japan. Most of the paleotempestology research has focused on the late to middle Holocene (Liu and Fearn, 2000; Mann et al., 2009; Boldt et al., 2010; Lane et al., 2011; Brandon et al., 2014). Relatively fewer paleotempestology studies have been conducted in China, and these are concentrated mainly on the low latitudes. Yu et al. (2004) has rebuilt the storm activity of the late Holocene, showing an average of about 160 year cycles. Huang and Yan (1997) uses foraminifera assemblages to identify the Holocene storm activity in the Pearl River estuary region and estimates a typhoon return period of about 350 years. Both the sample resolution and deposition site affect the detection of storm frequency. Global differences have also been noted, with more activity occurring at low latitudes than that at higher latitudes, therefore paleotempestology research in the middle latitude Bohai Sea coastal zone is difficult, the stratigraphic record is influenced by storm deposits that retain the evidence. The Bohai Sea, an enclosed sea with an average depth of only about 18 m, is connected by the Bohai Strait and the Yellow Sea. The strait is only 100 km wide and includes the Miaodao Archipelago. The Bohai Sea is a region of strong storm activity with high frequency because storm surges occur throughout the year (State Meteorological
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Administration, 1990) by the East Asian monsoon. The onset of the East Asian paleomonsoon in China was in the late Oligocene Epoch to early Miocene Epoch (An et al., 1990); while the Bohai Sea coastal zone sediment that formed in the late to middle Pleistocene was influenced by East Asian paleomonsoon (Cao et al., 1987). Therefore, sediment in the Bohai Sea coastal zone has maintained a good record for reconstructing the paleotempestology over a long time scale. Specifically, this study presents the Miaodao stratigraphic section (MDS) as the target area. Reconstruction is performed by determining the ages and proxy paleoclimatic indices, such as the marine micropaleontology, the element ratios, and the grain size parameters to reveal the paleotempestology information recorded since the last interglacial period.
following the procedures used for loess grains reported by Lu and An (1997). The mean grain size (Mz; Φ) and its σ of the MDS samples were calculated by using a formula developed by Fork and Ward (1957). For the foraminifera analysis, a 50 g (dry weight) specimen was split from each sample. The specimens were weighed and soaked in distilled water for ~24 h for disaggregation before washing over a 150 μm sieve and floating in carbon tetrachloride. The foraminifera were counted in the fractions smaller than 150 μm. The TOC and TN were determined in 2–5 mg sediment samples. The quantification was performed by calibration curves and using cystine as the standard. The detection limits were 0.01% for TOC and 0.001% for TN.
2. Regional setting
4.1. Chronology
The MDS is located at N 37° 56′ 31.9″, E 120° 40′ 35.9″ at an elevation of 12 m above sea level in the northwest region of the Miaodao Archipelago in the Bohai Sea (Fig. 1). A total of 15 layers exist in the MDS (MD1 to MD15), and the chronology indicates that layers MD1 to MD14 have accumulated since the marine isotope stage (MIS) 5e (Fig. 2). 3. Methods and materials
The AMS-14C specific sampling layer, depth, calibration age, and relevant parameters of the OSL are listed in Table 1. We use the known ages and segmentation sedimentation rates to establish the MDS chronology since the Marine Isotope Stage 5e (Eemian, i.e. 124–119 ka) as shown in Fig. 2. The MDS is first divided into five stratigraphic segments (MDS1–MDS5) on the basis of the determined ages. The other ages are calculated by using regression lines for the sedimentation rates (Fig. 2). The results are listed in Table 2.
3.1. AMS-14C and OSL age test
4.2. Grain size
This study obtained 11 sets of age data, including three sets of accelerator mass spectrometry radiocarbon dating (AMS-14C) data and eight optically stimulated luminescence (OSL) datasets from 10 layers in the MDS. The AMS-14C age determination was completed in the AMS-14C Key Laboratory of Nuclear Physics and Technology at Beijing University. The OSL procedure was conducted by the Daybreak 2200 OSL reader at the OSL Laboratory of Chinese Academy of Geological Sciences and the 1100B OSL instrument in the Isotope and OSL Dating Laboratory of Sun. Yat\\sen University. Organic matter was used as the test material for the AMS-14C test. The results of the 14C age were corrected through the CALIB 5.01 program and the IntCal04 database (Stuiver et al., 1998) and showed a range from 0 ka to 21.381 ka with an error of 2σ.
The results of the Mz analysis in the MDS show that Mz ranges from 3.46 Φ (90 μm) to 6.32 Φ (13 μm), with an average of 4.80 Φ (36 μm). The content is mainly sand, which varies from 15.09% to 76.05%, followed by silt at 18.03% to 71.54%, and clay at 5.22% to 25.81% (Fig. 2). The average sand, silt, and clay contents are 44.64%, 43.75%, and 11.61%, respectively. The standard deviation (σ) of the MDS grain sizes ranges from 1.53 to 2.53, with an average of 1.91.
3.2. Proxy paleoclimate indices The samples, n = 314, were analyzed to determine the grain size from the top of the section downward through the MDS. In addition, some samples were collected for foraminifera, total organic carbon (TOC), and total nitrogen (TN) testing. A Malvern Mastersizer 2000 M laser grain size analyzer with a measuring range of 0.02–2000 μm was used for grain size analysis by
4. Results
4.3. Foraminifera analysis The examination of 197 samples of marine micropaleontology in the MDS1 and MDS5 sections identifies 139 foraminifera in 15 samples, all concentrated in MDS5a. Of these foraminifera, 79.8% are benthic foraminifera, including eight genera and nine species (Table 3). Pseudononion sp. A is the most abundant at 33.1% and is identified in 11 of the 15 samples of benthic foraminifera, followed by Guembelitria vivans at 12.2% in eight of 15 samples, Ammonia beccarii at 10.8% in six of 15 samples , and Elphidium magellanicum at 7.91% in five of 15 samples. Other species comprise b5% of the total. Eight samples contain planktonic foraminifera and indicated Globigerina bulloides at 20.1%. All of the individual foraminifera specimens in the sediments are b 100 um in size, and a small amount have broken shells.
Fig. 1. Location of the Miaodao stratigraphical section (MDS).
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Fig. 2. Sequence and time scale of the Miaodao stratigraphical section during the last 130 ka.
4.4. TOC and TN The TOC and TN testing was performed on samples from the MDS5a section. The results indicate a small TOC/TN value in the sample including marine micropaleontology, with an average of 2.3. The TOC/TN in the samples not including marine micropaleontology is 2.5.
5. Discussion The paleotempestology research in China has been focused on the Holocene and low latitudes (Huang and Yan, 1997; Yu et al., 2004), longer storm reconstructions that extend through past climatic epochs and from locations that provide better spatial coverage are required in order to better understand past changes in storm activity and, in turn, the
complex mechanisms governing the storm formation, development, and evolution. The MDS is composed of continuous eolian sediments, which have accumulated since approximately 130 ka without marine facies. However, its coastal zone position influences the material sources in the MDS at different periods of the sea level fluctuations. The sea level reconstruction from the south Bohai Sea (Yi et al., 2012) shown in Fig. 3 is compared with the global sea level change (Waelbroeck et al., 2002) over the last 130 ka. During periods of low sea level, the desertification of the seafloor sediments of the receded Bohai Sea provides the main source material (Zhao, 1991). Some research has been conducted on the marine micropaleontology in the sediments of the last glacial period and in the Holocene (Cheng et al., 1995; Li et al., 2002). During periods of high sea level, the main sources of material in the MDS may have been the eolian dune sand that was captured by the Bohai Sea, sand from the coast of the North Yellow Sea, and silt from the Yellow River
Table 1 The relevant parameters of AMS-14C and OSL. a. AMS-14C ages of some horizons in the Miaodao section and their calibrated results. Horizon and lab record number
Depth/m
Ages of AMS-14C (ka BP)
Calibrated ages (Cal ka BP)
Unit 15-GZ4217 Unit 15-GZ4218 Unit 14-GZ4220
0.25 0.50 0.90
2.210 ± 0.30 4.305 ± 0.30 8.065 ± 0.50
2.237 ± 0.88 4.862 ± 0.30 8.947 ± 0.18
b. OSL ages of some horizons in the Miaodao section and their analytical data. Horizon and lab record number
Depth/m
U/10-6
Th/10-6
K/%
Total dose/E.D. (Gy)
Annual dose/(m Gy)
Water content/%
OSL/ka
MD4-SY01 MD5-10G520 MD6-SY 02 MD8-SY 03 MD10-10G521 MD13-10G522 MD14-SY 04 MD14-SY 05 MD15-10G523
1.50 2.06 2.48 3.02 3.60 5.34 5.40 6.30 6.44
1.8 1.43 1.7 1.4 1.20 1.02 1.5 1.3 1.96
10.4 8.67 11.1 9.1 7.00 6.86 10.6 7.9 8.06
1.75 1.61 1.73 1.78 1.85 1.94 1.96 1.29 1.57
71.05 ± 1.26 81.20 ± 0.94 139.75 ± 2.61 187.69 ± 3.37 246.86 ± 3.48 337.69 ± 4.89 404.39 ± 7.13 309.52 ± 5.01 411.08 ± 9.49
3.66 ± 0.3 3.10 3.64 ± 0.3 3.36 ± 0.3 3.01 3.03 3.51 ± 0.3 2.40 ± 0.2 3.02
3.46 3.69 4.31 4.51 7.58 6.73 11.20 11.67 11.37
19.41 ± 0.26 26.2 ± 0.6 38.39 ± 0.57 55.84 ± 1.02 82.1 ± 3.5 111.4 ± 5.0 115.18 ± 2.43 129.05 ± 2.61 136.1 ± 6.3
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Table 2 Geochronology of major sections and every horizon in Miaodao section. Section
Sequence
Depth/m
Age/ka BP
Section
MDS1
MD1 MD2 MD3 MD4 MD5 MD6 MD7
0.50–0 1.02–0.51 1.22–1.03 1.88–1.23 2.46–1.89 2.64–2.47 2.74–2.65
0–4.862 4.862–11.0 11.0–14.5 14.5–24.0 24.0–37.8 37.8–43.6 43.6–46.8
MDS3 MDS4 MDS5
MDS2 a b MDS3
estuary (Cao et al., 1987). No marine micropaleontology has been detected in this period. If marine micropaleontology are found in the eolian sediment formed at periods of high sea level with no transgression to the sedimentary face, such marine micropaleontology could be used as evidence of storm deposition. Such evidence, combined with the grain size parameter and the element ratio index of the sediment, would be beneficial for restoring the paleotempestology record at middle latitudes since the last interglacial period. The results of the Mz and σ of the MDS (Fig. 3) show that σ ranges from 1.53 to 2.53, with an average of 1.91, since the last interglacial period. Using σ of 2 as an index, with b2 indicating better sorting and N 2 indicating poor sorting, all of the sediments of the MDS belong to the better sorting category. In the various subsections, the better sorting sediments are mainly concentrated in the last glacial period (MDS2– MDS4) and the Holocene (MDS1) period with σ averages of 1.80 and 1.84, respectively. The σ in the last interglacial period is 2.01, indicating poor sorting. As shown in Fig. 3, the Mz values for MDS5e, MDS5a, and MDS1 indicate a fine grain size. A paleosol facies developed under the prevalent East Asian summer monsoon period in which the wind was the major transporting agent, indicating a warm and humid climate as the obvious pedogenesis. However, the σ values of MDS5a and MDS5e are poorer than those in MDS1. All developed in the same climate and with the same sedimentary facies; however, the difference in the sorting coefficient indicates that the sediment of MDS5 was disturbed by climatic events because some marine micropaleontology foraminifer fossils were identified in the eolian sediment of MDS5. The initial hypothesis for the interference seen in the sediment is storm deposition. The benthic foraminifera fossils species in MDS5a include some modern, common types found in the Bohai Sea, such as A. beccarii, Ammonia convexidorsa, Cribrononion incertum, E. magellanicum, and Pseudononionella variabilis Zheng, and in the Yellow Sea and East China Sea continental shelf, such as Pseudononion sp. A. G. vivans, Cassidulina carinata Silvestri, and Rosalina vilarbodeana d'Orbigny. The
c a b c d e
Sequence
Depth/m
Age/ka BP
MD8 MD9 MD10 MD11 MD12 MD13 MD14
3.02–2.75 3.36–3.03 4.02–3.37 4.58–4.03 4.98–4.59 5.38–4.99 6.28–5.39
46.8–55.8 55.8–71.2 71.2–89.2 89.2–98.6 98.6–105.3 105.3–113.9 113.9–129.1
appearance of the latter four species in the MDS may be attributed to the differences in the water environment from the Yellow Sea Warm current (YSWC). The planktonic foraminifera G. bulloides in MDS5a was also carried by the YSWC. G. bulloides is a temperate distribution specie and is the most widely distributed specie in the modern Globigerina genera. This cold water specie has a strong tolerance to low temperatures and low salt content (Zheng and Zheng, 1960). Modern planktonic foraminifera live mostly in the high salinity of the open ocean and are rare in the shelf basin, and their northern distribution in China is limited to about 36° N (Zheng and Zheng, 1960). Some researchers have reported that planktonic foraminifera were brought by the warm current from the Yellow Sea during high sea level during the last interglacial period and deposited with the benthic foraminifera by the winter monsoon during low sea level periods (Li et al., 1992; Cheng et al., 1991). Research on the impact of the YSWC in the Bohai Sea has focused on the Holocene and the last glacial maximum (Li et al., 2007; Wang et al., 2011). However, no direct evidence has been reported on the effects of the YSWC on the Bohai Sea during the last interglacial period. The foraminifera fossils appearing in MDS5a, particularly G. bulloides planktonic foraminifera confirm that the YSWC affected the Bohai Sea during the last interglacial period. During that period, global sea level fluctuations occurred multiple times (Potter and Lambeck, 2004; Waelbroeck et al., 2002) (see Fig. 3). The Bohai Sea coastal zone also experienced sea level oscillations during the last interglacial period. Yi et al. (2012) reconstructed the reference water level in the south Bohai Sea (Fig. 3) and showed the highest sea level in MDS5a was caused by tectonic movement at about 100–80 ka that resulted in the uplift of the surrounding mountains. Species of planktonic and benthic foraminifera living in the Yellow and East China seas appear in MDS5a, revealing that the Yellow Sea warm water mass moved northward along the Yellow Sea trough into the Bohai Sea during the highest sea level in MDS5a, causing their heterochthonous burial in the MDS by the extreme high
Table 3 Results of foraminiferal identification in MDS5a. Samples Species
MD10-01 MD10-02 MD10-03 MD10-07 MD10-10 MD10-11 MD10-17 MD10-18 MD10-21 MD10-22 MD10-24 MD10-25 MD10-26 MD10-28 MD10-33
Ammonia beccarii
Ammonia convexidorsa
Guembelitria Cribrononion vivans incertum
+ − − − − − − − − + + + + − +
− − − − − − − − − + + − − − −
+ + − − − − − + − + + + − + +
− − + − + − − − − + − − − − −
Elphidium magellanicum
Cassidulina carinata Silvestri
Pseudononion Pseudononionella sp. A variabilis Zheng
− − + − − − − − + + − − − + +
− − − − − − − − − + − + + + +
+ − − + − + + + − + + + + + +
− − − − − − − − − + − − − − −
Rosalina vilarbodeana
Globigerina bulloides
− − − − − + + − − − − − − − +
− − − − − + − + − + + + + + +
Note: MDS5a, layer MD10, which depth 66 cm, divided into 33 samples (e.g. MD10-01 and MD10-02), each sample was collected by 2 cm depth. “+” means contain this species of foraminifer and “−” means inexistence in each sample.
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Fig. 3. Change curves of the grain size parameter Mz (Φ, green line), standard deviation (σ, blue line) in the MDS compared to relative sea level in the south Bohai Sea (Yi et al., 2012, black line) and global sea level changes (Waelbroeck et al., 2002, gray line).
sea level (storm surge) deposition event. The foraminifera group in these layers, including a mixture of the euryhaline and the stenohaline species, shows high differentiation and low dominance. The shells appear in yellow ground glass, and most are small individual shells. A similar sediment grain size distribution and marine micropaleontology of the foraminifera fossils can be found in the eolian sediment of the MDS on the rocky coast; therefore, the most likely mechanism is storm surge. The paleotempestology includes marine matter with smaller TOC/ TN than in the terrigenous matter (Fan et al., 2007). The TOC/TN results of the MDS5a also indicate low TOC/TN values in the sample containing the foraminifera fossils and high values in other terrigenous sediments. For example, MD10-33, containing marine micropaleontology, has a TOC/TN value of 1.6; and MD10-31, which does not contain foraminifera fossils, has a ratio of 3.3. The TOC/TN results for the MDS5a confirmed that foraminifera fossils represent storm deposition, which serves as evidence of paleotempestology recorded in the Bohai Sea coastal zone during the last interglacial period. Although the MDS1 and MDS5c subsections were deposited during periods of high sea level (Fig. 3), no evidence of storm deposits were found. It is possible that this is related to the altitude of the MDS beyond the storm surge depositional surface at that time. The sediment accumulation was 66 cm during 73.4–88.9 ka of the MDS5a. Of the 33 samples from this subsection, 15 included foraminifera fossils. If each sample represents one storm event, then 15 strong storm events occurred during MDS5a, representing a millennial scale periodicity. This millennial scale frequency record of storm deposition events in the MDS during the last interglacial period is similar to that of the Holocene record in the low latitude areas of China (Huang and Yan, 1997; Yu et al., 2004). This reconstruction of the storm deposits from the last interglacial period can serve as a reference for Quaternary climate change research and can provide an important basis in forecasting storm activity under global warming conditions.
6. Conclusions The results of this study are summarized in the following points: 1. The marine micropaleontology of the MDS in the Bohai Sea coastal zone includes foraminifera fossils in the eolian sediment from periods of high sea level during the last interglacial period. These fossils, in combination with the grain size parameter and the element ratios of the sediments, serve as evidence for the paleotempestology record. 2. The planktonic foraminifera fossils appearing in the MDS confirm that the YSWC affected the Bohai Sea during the last interglacial period. 3. The MDS record shows 15 strong storm events during MIS5a. This deposition frequency is similar to the millennial scale frequency of the Holocene at low latitudes. Therefore, the paleotempestology record from 7000 a in the Holocene to the last interglacial period of 90 ka records the middle latitude storm activity. Acknowledgements We thank reviewer Dr. Jonathan D. Woodruff for his comments that greatly improved this manuscript. This work was supported by the National Natural Science Foundation of China under Grant Nos. 41206036, 41290254, 91228207, and 41471159; the Guangdong Province Science and Technology Project under Grant No. 2015A020216015; and by the Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences under Grant No. SQ201306. References An, Z.S., Liu, T.S., Lu, Y.C., Porter, S.C., Kukla, G., 1990. The long-term paleomonsoon variation recorded by the loess sequence in Central China. Quat. Int. 7-8, 91–95.
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