Paleoenvironmental change in the middle Okinawa Trough since the last deglaciation : evidence from the sedimentation rate and planktonic foraminiferal record

Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 243 (2007): 378-393, doi:10.1016/j.palaeo.2006.08.016.Well-dated, high-resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores, A7 and E017, in the middle Okinawa Trough reveal strong and rapid millennial-scale climate changes since ~18 to 17 thousand years before present (kyr B.P.). Sedimentation rate shows a sudden drop at ~11.2 cal. kyr B.P. due to a rapid rise of sea-level after the Younger Dryas (YD) and consequently submergence of the large continental shelf on the East China Sea (ECS) and the retreat of the estuary providing sediment to the basin. During the last deglaciation, the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly, consistent with the timing of sea surface temperature (SST) variations determined from Mg/Ca measurements of planktonic foraminifera from one of the two cores. These fluctuations are coeval with climate variation recorded in the Greenland ice cores and North Atlantic sediments, namely Heinrich event 1 (H1), Bølling-Allerød (B/A) and YD events. At about 9.4 kyr B.P., a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the Kuroshio Current in the Okinawa Trough, which was synchronous with a rapid sea-level rise at 9.5-9.2 kyr B.P. in the ECS, Yellow Sea (YS) and South China Sea (SCS). The abundance of planktonic foraminiferal species, together with Mg/Ca based SST, exhibits millennial-scale oscillations during the Holocene, with 7 cold events (at about 1.7, 2.3-4.6, 6.2, 7.3, 8.2, 9.6, 10.6 cal. kyr BP) superimposed on a Holocene warming trend. This Holocene trend, together with centennial-scale SST variations superimposed on the last deglacial trend, suggests that both high and low latitude influences affected the climatology of the Okinawa Trough.This study was supported by the National Natural Science Foundation of China (Grant Nos. 40206007, 40106006, 90211022 and 40506027), the Chinese Academy of Sciences innovation program (KZCX3-SW-220), and the NSF (OCE05-29600 to DWO)

(Table T1) Diatom stratigraphy of ODP Site 184-1143

Diatoms from Ocean Drilling Program Leg 184 Site 1143 in the southern South China Sea were analyzed for this paper. We found that diatoms are barren or scarce from 27.94 to 304.04 meters below seafloor. The intervals with age-diagnostic species indicate a middle Miocene age from 472.18 to 469.98 mcd, a late Miocene age or younger at 389.42 mcd, and a late Pliocene to Holocene age from 26.7 to 0.0 mcd

(Table 1) Radiolarian accumulation rates and geochemistry of ODP Site 184-1143

Late Miocene–Recent micropaleontological and geochemical records from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS) indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling. A high export production event - a “biogenic bloom” event - occurred in the southern SCS between 12 and 6 Ma. During this period, high ratios of smectite/(illite + chlorite), smectite/quartz and Al/K indicate a high weathering intensity of the Asian continent, possibly due to the intensification of the East Asian Summer Monsoon (EASM), which may have increased the net flux of nutrients to the ocean, both directly through terrestrial input and indirectly through upwelling activity. A drop in Ba/Ti, Al/Ti and Ca/Ti values around 6 Ma may indicate a lowering of productivity, possibly due to the large consumption of sea surface nutrients by the “biogenic bloom”. Alternatively, it may indicate a shift in terrigenous input source area. At about 5.4 Ma, a decrease in weathering intensity, as indicated by a sudden decrease in the values of smectite/(illite + chlorite), smectite/quartz and Al/K, might have led to a sudden decrease of terrestrial nutrient input to the SCS. We suggest that the biogenic bloom ended when nutrients in surface waters were exhausted, because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the EASM. As a result, radiolarians were absent in the studied area between ~6 and 3.2 Ma. At ~3.2 Ma, radiolarians began to recover, possibly because the start of Northern Hemispheric glaciation and the rapid uplift of the Tibet Plateau led to intensification of the East Asian monsoon. After the Mid-Pleistocene Climate Transition at 0.9 Ma, the abundance and mass accumulation rates of radiolarians increased, probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon

(Table 1) Geochemistry of sediment core NS93-5

The biogenic-related elements Ca, Sr, Ba, P, Cd, scavenged Al, and Ti were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) for Core NS93-5 from the west slope of the South China Sea. Terrestrial input as estimated from the accumulation of Ti was higher during glacials than during interglacials. Carbonate accumulation rates are inversely related to those of terrestrial input, suggesting higher production of calcareous phytoplankton during interglacials. The accumulation patterns of authigenic Sr, Ba, P, and Cd match that of carbonate, further indicating higher calcareous phytoplankton production during interglacials. Scavenged Al and excess SiO2, which is related to biogenic opal, exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input. This indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production. As calcareous phytoplankton is the dominant component of the biogenic sediments in the South China Sea, particularly during interglacials, previous inference of higher productivity in the South China Sea during glacials based on only the biogenic opal proxy needs to be reconsidered

Late Miocene biostratigraphy of ODP Site 184-1143 (Table 1)

Abundant radiolarians are preserved in the relatively complete upper Miocene section of ODP Site 1143. Three radiolarian zones, RN6, RN7 and RN8, are recognized on the basis of Diartus petterssoni (total range in RN6, 6.7 Ma). Variations in the abundance of radiolarians,especially Pyloniid forms,radiolarian flux and species diversity are good proxies of upwelling which,similar to today's,was likely driven by summer monsoons. These radiolarian paleomonsoon proxies indicate that the east Asian summer monsoon first initiated close to the middle/late Miocene boundary at ~12-11 Ma and reached a maximum strength at ~8.24 Ma. Therefore,the initiation of the east Asian summer monsoon was likely earlier than the first Indian monsoon,which appeared ~8 myr ago

Age determination and benthic foraminifera abundance of an onshore sediment core from the Miaodao stratigraphic section (MDS) in the northwest region of the Miaodao Archipelago in the Bohai Sea

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