Pollen and grain size records in abyssal sediments of the northwest Pacific Ocean as proxies of Plio-Pleistocene climate change /

A distinctive period of global change occurred during the PUocene between the warm Miocene and subsequent Quaternary cooling. Samples from Ocean Drilling Project Site 11 79 (-5586 mbsl, 41°4'N, 159°57'E), Site 881 (-5765 mbsl, 47°6.133'N, 161°29.490'E) and Site 882 (-3255 mbsl, 50°22'N, 167°36'E) were studied to determine the magnitude and composition ofterrigenous flux to the western mid-latitude North Pacific and its relation to climate change in East Asia since the mid-Pliocene. Dust-sized particles (including pollen), sourced from the arid regions and loess plateaus in East Asia are entrained by prevailing westerly winds and transported to the midlatitude northwest North Pacific Ocean. This is recorded by peaks in the total concentration of pollen and spores, as well as the mean grain size of allochthonous and autochthonous silicate material in abyssal marine sediments. Aridification of the Asian interior due to the phased uplift of the Himalayan-Tibetan Plateau created the modem East Asian Monsoon system dominated by a strengthening of the winter monsoon. The winter monsoon is further enhanced during glacials due to the expansion of desert and steppe environments at the expense ofwoodlands and forests recorded by the composition of palynological assemblages. The late Pliocene-Pleistocene glacials at ODP Sites 1 179, 881, and 882 are characterized by increases in grain size, magnetic susceptibility, pollen and spore concentrations around 3.5-3.3, 2.6-2.4, 1.7-1.6, and 0.9-0.7 Ma (ages based on magnetostratigraphic and biostratigraphic datums). The peaks during these times are relatively rich in pollen taxa derived primarily from steppe and boreal vegetation zones, recording cool, dry climates. The overall size increase of sediment and abundance of terrestrial palynomorphs record enhanced wind strength. The increase in magnitude of pollen and spore concentrations as well as grain size record global cooling and Northern Hemisphere glaciation. The peaks in grain size as well as pollen and spore abundance in marine sediments correlate with the mean grain size of loess in East Asia, consistent with the deflation of unarmoured surfaces during glacials. The transport of limiting nutrients to marine environments enhanced sea surface productivity and increased the rate of sediment accumulation.

Spatial and temporal variations of the seasonal sea level cycle in the northwest Pacific

The seasonal sea level variations observed from tide gauges over 1900-2013 and gridded satellite altimeter product AVISO over 1993-2013 in the northwest Pacific have been explored. The seasonal cycle is able to explain 60-90% of monthly sea level variance in the marginal seas, while it explains less than 20% of variance in the eddy-rich regions. The maximum annual and semi-annual sea level cycles (30cm and 6cm) are observed in the north of the East China Sea and the west of the South China Sea respectively. AVISO was found to underestimate the annual amplitude by 25% compared to tide gauge estimates along the coasts of China and Russia. The forcing for the seasonal sea level cycle was identified. The atmospheric pressure and the steric height produce 8-12cm of the annual cycle in the middle continental shelf and in the Kuroshio Current regions separately. The removal of the two attributors from total sea level permits to identify the sea level residuals that still show significant seasonality in the marginal seas. Both nearby wind stress and surface currents can explain well the long-term variability of the seasonal sea level cycle in the marginal seas and the tropics because of their influence on the sea level residuals. Interestingly, the surface currents are a better descriptor in the areas where the ocean currents are known to be strong. Here, they explain 50-90% of inter-annual variability due to the strong links between the steric height and the large-scale ocean currents.

Major and rare earth element composition of ODP Site 191-1179 sediments, northwest Pacific

Depth profiles of major element and rare earth element (REE) abundances in sediment samples (mainly siliceous ooze and clay) recovered from Holes 1179B and 1179C at Site 1179, Ocean Drilling Program Leg 191 (41.4°N, 159.6°E) were determined. The oxidation states of Mn and Ce were determined by X-ray absorption near-edge structure. Some geochemical indicators were tested, including the MnO/TiO2 ratios, a bivariate diagram of La/Ce vs. Al2O3/(Al2O3+Fe2O3), and other discrimination diagrams. The oxidation state of Mn is reduced Mn(II) in the depth profile below 0.60 meters below seafloor (mbsf), which is consistent with relatively low and high abundances of Mn in the sediments and pore waters, respectively. It is possible that the diagenetic effect on the oxidation state and abundance of Mn makes it difficult for the MnO/TiO2 ratio to reflect the depositional environment. The normalized ratio of La and Ce does not change very much with depth, suggesting that the diagenetic effect does not affect the REE signature in the sediments. On the diagram of La/Ce vs. Al2O3/(Al2O3+Fe2O3), the sediments studied here plot at the boundary of the pelagic and continental margin fields. This suggests that continental material has contributed to the sediment to some degree, even though Site 1179 is in a pelagic region of the northwestern Pacific Ocean, >1600 km from Japan.

Pollen and spores record, and paleotemperature reconstructions for mid-Holocene sediments of the Northwest Pacific

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabited the Sannai-Maruyama site from 5.9-4.2 +/- 0.1 cal. kyr B.P. However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C37 alkenone SSTs showed clear fluctuations, with four periods of high (8.4-7.9, 7.0-5.9, 5.1-4.1, and 2.3-1.4 cal. kyr B.P.) and four of low (-8.4, 7.9-7.0, 5.9-5.1, and 4.1-2.3 cal. kyr B.P.) SST. Thus, each SST cycle lasted 1.0-2.0 kyr, and the amplitude of fluctuation was about 1.5-2.0 °C. Total organic carbon (TOC) and C37 alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal. kyr B.P., but was clearly increased between 5.9 and 4.0 cal. kyr B.P., because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 +/- 0.1 cal. kyr B.P.), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal. kyr B.P., in spite of warm terrestrial climates, the C37 alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal. kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 +/- 0.1 cal. kyr B.P., abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C37 alkenone SST and an increase in pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0-4.3 cal. kyr B.P.) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ~2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.

Distribution of Pliocene diatom faunas in the Northwest Pacific

High-resolution quantitative diatom data are tabulated for the early part of the late Pliocene ( 3.25 to 2.08 Ma ) at DSDP Site 580 in the northwestern Pacific. Sample spacing averages 11 k.y. between 3.1 and 2.8 Ma, but increases to 14 to 19 k.y. prior to 3.1 Ma and after 2.8 Ma. Q-mode factor analysis of the middle Pliocene assemblage reveals four factors which explain 92.4% of the total variance of the 47 samples studied between 3.25 and 2.55 Ma. Three of the factors are closely related to modern subarctic, transitional, and subtropical elements, while the fourth factor, which is dominated by Coscinodiscus marginatus and the extinct Pliocene species Neodenticula kamtschatica, appears to correspond to a middle Pliocene precursor of the subarctic water mass. Knowledge of the modern and generalized Pliocene paleoclimatic relationships of various diatom taxa is used to generate a paleoclimate curve ("Twt") based on the ratio of warm-water (subtropical) to cold-water diatoms with warm-water transitional taxa (Thalassionema nitzschioides, Thalassiosira oestrupii, and Coscinodiscus radiatus) factored into the equation at an intermediate (0.5) value. The "Twt" ratios at more southerly DSDP Sites 579 and 578 are consistently higher (warmer) than those at Site 580 throughout the Pliocene, suggesting the validity of the ratio as a paleoclimatic index. Diatom paleoclimatic data reveal a middle Pliocene (3.1 to 3.0 Ma) warm interval at Site 580 during which paleotemperatures may have exceeded maximum Holocene values by 3 °- 5.5 °C at least three times. This middle Pliocene warm interval is also recognized by planktic foraminifers in the North Atlantic, and it appears to correspond with generalized depleted oxygen isotope values suggesting polar warming. The diatom "Twt" curve for Site 580 compares fairly well with radiolarian and silicoflagellate paleoclimatic curves for Site 580, planktic foraminiferal sea-surface temperature estimates for the North Atlantic, and benthic oxygen isotope curves for late Pliocene, although higher resolution studies on paired samples are required to test the correspondence of these various paleoclimatic indices.

Origin and evolution of Cycladophora davisiana (Radiolaria) in DSDP Hole 19-192, Northwest Pacific

This paper documents the evolutionary history of Cycladophora davisiana Ehrenberg from an uppermost Miocene to Pleistocene sedimentary record in the high-latitude Northwest Pacific. It apparently evolved from C. sakaii Motoyama through a series of intermediates. C. sakaii has a relatively large shell with an external spongy layer. The evolutionary transition is characterized by a relatively rapid decrease in thorax size with a reduction of the spongy appendage. This change occurred during about 0.4 m.y. from 2.8 to 2.4 Ma without cladogenesis. Following this interval, a decrease in thorax size continued gradually up to the Recent, resulting in a very small morphology. Although the population of C. davisiana first appeared at about 2.5 Ma, some morphotypic specimens may occur in earlier periods as indistinguishable very small endmembers in the C. sakaii populations. Timing of the first appearance events both of morphotypic specimens and of a population of C. davisiana in Site 192 and previously reported cores does not disprove the idea that C. davisiana evolved first in the Northwest Pacific region, and later migrated into other regions of the world ocean. Biometrics clearly indicate no direct phylogenetic relationships between C. davisiana and C. cornutoides Kling in the studied core. Thus, the latter species, which was originally described as a variation and later elevated to a subspecies of the former species, is separated from the former species and raised to the species rank.

Pliocene and Pleistocene diatom datum levels of the Northwest Pacific

Thick sections of Pliocene and Pleistocene biosiliceous clay and ooze were recovered by the Hydraulic Piston Corer (I-IPC) at three northwest Pacific sites (DSDP Sites 578, 579, and 580). They contain a well-preserved paleomagnetic record which made it possible to evaluate diatom events used in low and high latitudes in the transitional region of the northwest Pacific. Equatorial Pacific events are usually isochronons between the equatorial and subarctic regions. However, species which have short ranges in low latitudes tend to have diachronous first and last appearances in higher latitudes. All subarctic North Pacific datum species are present in the sediments at three sites which lie north and south across the subarctic front, but their ranges become shorter in southern regions. They do not penetrate into the equatorial region. Spatial distributions of these events are influenced by the paleo-position of the subarctic front. The migration of species from their home-area outwards, in the form of the first appearance, is related to the fluctuations of the subarctic front. The last appearance of species is a response to the change of the surface water temperature that is beyond the limit of tolerance of the species, or an unstable oceanic environment due to major change of climate.

Eocene to Quaternary planktonic foraminifers from the Northwest Pacific

Eocene through Quaternary planktonic foraminifers were identified in cores recovered during Leg 126. Turbidites and volcanic ash beds are intercalated with hemipelagic sediments. Preservation of foraminifers is variable, ranging from excellent to poor and appears to have been affected by fluctuations in the carbonate compensation depth (CCD), depth of burial, changes in bottom water temperature, current velocity, sediment accumulation rates and seafloor topography. Preservation of foraminifers in Quaternary sediments is generally good, however, species abundance varies by a factor of I05-106 and reflects dilution by volcanogenic as well as terrigenous constituents and cannot be used for paleoceanographic reconstructions. In pre-Quaternary deposits planktonic foraminiferal tests frequently exhibit dissolution effects; biostratigraphic zonation and placement of zonal boundaries is difficult owing to hiatuses, dissolution facies, extraneously deposited sediments, and discontinuous coring. The Eocene foraminiferal faunas include specimens of the Globorotalia cerroazulensis plexus, markers of Zone P16 as well as Globigerina senni and Globigerinatheka spp., which became extinct before the end of the Eocene. Six hiatuses and/or dissolution periods, probably reflecting global cooling events and/or changes in oceanic circulation patterns were recorded at Site 792. Recrystallized, poorly preserved, possibly reworked Eocene species (Globigerina senni and Globigerapsis sp.) were recorded in sediments at Site 793.