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North Pacific Subtropical Convergence Zone and the ocean currents involved in the North Pacific Gyre. The North Pacific Gyre , located between the equator and 50 ◦ N latitude and occupying an area of approximately 20 million square kilometers. It is the largest ecosystem in the ocean, one of the five major oceanic gyres, and covers most of the northern Pacific Ocean. The gyre moves clockwise and comprises four prevailing ocean currents: the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south, and the Kuroshio Current to the west. 

North Pacific Subtropical Convergence Zone and the ocean currents involved in the North Pacific Gyre. The North Pacific Gyre , located between the equator and 50 ◦ N latitude and occupying an area of approximately 20 million square kilometers. It is the largest ecosystem in the ocean, one of the five major oceanic gyres, and covers most of the northern Pacific Ocean. The gyre moves clockwise and comprises four prevailing ocean currents: the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south, and the Kuroshio Current to the west. 

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The temporal and spatial distributions of the radiolarian species Spongodiscus biconcavus Haeckel are investigated to understand the paleoceanographic evolution of the Bering Sea region during the last 4.3 Myr based on extensive study of samples collected at Site U1340 during the IODP Expedition 323. The biostratigraphic resolution for the region i...

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Context 1
... The Bering Sea connects the North Pacific and the Arctic Ocean, and plays a critical role in the evolution of global climate and oceanic circulation in the Late Cenozoic, especially during the Quaternary. Nevertheless, the Bering Sea is a marginal sea and there has been little high resolution stratigraphic data due to the lack of calcareous planktonic microfossils. Here we attempt to reveal the processes of paleoceanographic and paleoclimatic evolution in the northern hemisphere since the Pliocene with high-resolution biostratigraphic framework derived from an integrated multidisciplinary study of sediments from the Bering Sea collected during the Integrated Ocean Drilling Program (IODP) Expedition 323. The IODP Expedition 323 provided excellent materials for investigating the stratigraphic as well as paleoceanographic record for the Bering Sea region. This also has implications for the Northern Hemisphere climate because the Bering Sea water mass is affected by North Pacific circumfluence through both the straits and water passes between the Aleutian Islands. The Kamchatka Strait with a water depth of 4420 m is the deep- est sill that allows water exchange between the Bering Sea and the Pacific Ocean, flowing mainly from the Bering Sea to the North Pacific and a weak reverse flow from ocean to sea in the surface layer (Zhabin et al., 2010). The North Pacific Intermediate Water (NPIW) is a water mass composed of sub-Arctic, Okhotsk, and Bering Sea waters (Talley, 1993; Yasuda, 1997), but it was from only the Bering Sea during the last glacial maximum (Tanaka and Takahashi, 2005). The North Pacific waters may also have an influence on the Bering Sea via the Aleutian Current. Interplays of different water masses between the Bering Sea and North Pacific affect the paleobiogeographic evolution of planktonic radiolarians, which, in turn, provide clues for the paleoclimatic change. Spongodiscus sp. was first recorded by Ling (1973) in the core samples from DSDP Leg 19 in the Bering Sea and North Pacific. Its last occurrence datum of 0.3 Ma has widely been used as a biostratigraphic age constraint in the Bering Sea and the high latitude northwestern Pacific area, though its taxonomic status has remained unclear for nearly 40 years. It is interesting that the shell structure of Spongodiscus sp. is very similar to Spongodiscus biconcavus Haeckel, which occurs in present low latitude areas such as in the South China Sea, tropical Pacific and Atlantic Oceans. Investigation of their taxonomic relation- ship and their biostratigraphic and biogeographic distributions may shed light on paleoceanographic processes in the northern Pacific Ocean. This study reports an improved biostratigraphic framework for the Bering Sea region integrating multi-fossil-group data derived from the U1340 cores and our interpretation of the paleoceanographic and paleoclimatic evolution in the northern Pacific, on the basis of Spongodiscus biconcavus Haeckel and related species, such as Spongodiscus sp. Ling (1973), their taxonomy and distribution in the world oceans, and their abundance variation, stratigraphic and geographic evolution at Site U1340 in the Bering Sea in relation to global climate change. The Bering Sea lies between Siberia, Alaska and the Aleutian Islands, consisting of a broad continental shelf and a deep basin (>4000 m deep). The primary surface circulation in the basin is a cyclonic gyre, west-bounded by the southward-flowing Kamchatka Current. The Alaskan Stream flows northward through passes between the Aleutian Islands and is incorporated into this gyre. The water mass from the Bering Sea is of relatively low salinity and rich in nutrients, and is an important component of the upper halocline in the Arctic Ocean (Cooper et al., 1997). The Bering Sea is connected to the North Pacific through various straits and passes (Fig. 1), with water exchange mostly across the Aleutian Islands above a water depth of approximately 2000 m (i.e., Near Strait, Cook et al., 2005). However, in the eastern Bering Sea, northward flow through the Unimak Pass (80 m deep) is the major conduit between the North Pacific and the shelf (Stabeno et al., 1999). The North Pacific water entering the Bering Sea is transported by the Aleutian Current, also called Subarctic Current. This surface oceanic current is a mixture of eastward-flowing Kuroshio and the Oyashio Currents, located between the Aleutian Islands and the latitude of 42 ◦ N. The Kuroshio Current plays an important role for the warm waters from low to high latitude areas in the North Pacific (Fig. 1), which originates from the West Pacific Warm Pool and has fluctuated in the past (Chen et al., 2005). The Kuroshio, as a western boundary current in the North Pacific, is north-flowing and arising at the western boundary of the North Equatorial Current. One branch of this current flows into the South China Sea through the Taiwan Strait and the Ryukyu Islands, and skirts the east coast of Kyushu. During the summer, it branches west and then flows northeast through the Korea Strait and parallel to the west coast of Honshu in the Sea of Japan as the Tsushima Current. In the vicinity of latitude 35 ◦ N (about central Honshu), the bulk of the Kuroshio turns east to receive the southward-flowing Oyashio Current. This flow, known as the Kuroshio Extension, eventually becomes the North Pacific Current (also known as the North Pacific West Wind Drift). Much of this current’s force is lost to the west of the Hawaiian Islands as a great south-flowing eddy, the Kuroshio countercur- rent, joins the Pacific North Equatorial Current and directs the warm water back to the Philippine Sea. Approaching the North American coast, the remainder of the original flow continues eastward to split off the west coast of Canada and forms the Alaska and California currents. Therefore, this current probably serves as a main linkage for warm plankton species to migrate from tropic to subarctic areas in the North Pacific through the Kuroshio, Oyashio and Aleutian currents in a relay manner. To investigate the stratigraphic distribution of Spongodiscus biconcavus Haeckel and Spongodiscus sp. Ling (1973), we selected the core samples from IODP Site U1340. This site is located on the Bowers Ridge near the Aleutian Islands at 179 ◦ 31.3 W and 54 ◦ 24.0 N at a water depth of 1306 m (Fig. 2). Three holes were cored at this site to a maximum composite depth of 604.5 m, covering the longest depositional period of all sites drilled during Expedition 323. A total of 293 samples were taken with a sampling interval of 0.2 m from the top 10 m and 3 m for the rest of core. Samples were dried and about 1 g of each was weighed and dispersed in distilled water with 10–15% of hydrogen peroxide and sodium hexa-metaphosphate as oxi- dizing and dispersing agents, respectively. A small amount of hydrochloric acid was added to dissolve calcium carbonate. The samples were washed several times until all clay and organic matters were completely gone and only microfossils were left. All radiolarian specimens were mounted onto two permanent slides with Canada balsam for species identification and quantitative analysis. A total of 184 surface samples from the South China Sea were also analyzed with a method of Chen and Tan (1997) for investigating the present distribution of Spongodiscus biconcavus in the low latitude marginal sea of the North Pacific for comparison. Due to the lack of calcareous biogenic material (i.e., foraminifera) in this region, it is not possible to construct a high resolution oxygen stable isotopic stratigraphy for comparing the evolution of the paleoenvironment within the stratigraphic framework. Therefore, most of the stratigraphic constraints are derived from micropaleontologic and paleomagnetic data (Takahashi et al., 2011a). Biostratigraphic datums were initially derived from diatom, radiolarian, dinoflagellate, ebridian, and silicoflagellate bioevents using core catcher samples. A total of 17 bioevents are recognized, which confine the cored interval at Site U1340A from Pliocene to the Recent (Takahashi et al., 2011a, fig. F19, table T2). Although the biostratigraphic results are somewhat primary, they provide basic information for further constructing the biostratigraphic framework and age control. Potential offset between paleomagnetic and micropaleontologic datums exist, especially for sediments older than 2 Ma (below ∼ 300 mbsf) and the uncertainty of some long-range microfossils. In fact, most uncertainties are not derived from the Bering Sea data. They instead come from other North Pacific sites due to diachronous biostratigraphic datums. Some micropaleontologic bioevents have to be reviewed and modified using integrated biostratigraphy in the Bering Sea. In order to refine radiolarian datums at Site U1340 ...
Context 2
... The Bering Sea connects the North Pacific and the Arctic Ocean, and plays a critical role in the evolution of global climate and oceanic circulation in the Late Cenozoic, especially during the Quaternary. Nevertheless, the Bering Sea is a marginal sea and there has been little high resolution stratigraphic data due to the lack of calcareous planktonic microfossils. Here we attempt to reveal the processes of paleoceanographic and paleoclimatic evolution in the northern hemisphere since the Pliocene with high-resolution biostratigraphic framework derived from an integrated multidisciplinary study of sediments from the Bering Sea collected during the Integrated Ocean Drilling Program (IODP) Expedition 323. The IODP Expedition 323 provided excellent materials for investigating the stratigraphic as well as paleoceanographic record for the Bering Sea region. This also has implications for the Northern Hemisphere climate because the Bering Sea water mass is affected by North Pacific circumfluence through both the straits and water passes between the Aleutian Islands. The Kamchatka Strait with a water depth of 4420 m is the deep- est sill that allows water exchange between the Bering Sea and the Pacific Ocean, flowing mainly from the Bering Sea to the North Pacific and a weak reverse flow from ocean to sea in the surface layer (Zhabin et al., 2010). The North Pacific Intermediate Water (NPIW) is a water mass composed of sub-Arctic, Okhotsk, and Bering Sea waters (Talley, 1993; Yasuda, 1997), but it was from only the Bering Sea during the last glacial maximum (Tanaka and Takahashi, 2005). The North Pacific waters may also have an influence on the Bering Sea via the Aleutian Current. Interplays of different water masses between the Bering Sea and North Pacific affect the paleobiogeographic evolution of planktonic radiolarians, which, in turn, provide clues for the paleoclimatic change. Spongodiscus sp. was first recorded by Ling (1973) in the core samples from DSDP Leg 19 in the Bering Sea and North Pacific. Its last occurrence datum of 0.3 Ma has widely been used as a biostratigraphic age constraint in the Bering Sea and the high latitude northwestern Pacific area, though its taxonomic status has remained unclear for nearly 40 years. It is interesting that the shell structure of Spongodiscus sp. is very similar to Spongodiscus biconcavus Haeckel, which occurs in present low latitude areas such as in the South China Sea, tropical Pacific and Atlantic Oceans. Investigation of their taxonomic relation- ship and their biostratigraphic and biogeographic distributions may shed light on paleoceanographic processes in the northern Pacific Ocean. This study reports an improved biostratigraphic framework for the Bering Sea region integrating multi-fossil-group data derived from the U1340 cores and our interpretation of the paleoceanographic and paleoclimatic evolution in the northern Pacific, on the basis of Spongodiscus biconcavus Haeckel and related species, such as Spongodiscus sp. Ling (1973), their taxonomy and distribution in the world oceans, and their abundance variation, stratigraphic and geographic evolution at Site U1340 in the Bering Sea in relation to global climate change. The Bering Sea lies between Siberia, Alaska and the Aleutian Islands, consisting of a broad continental shelf and a deep basin (>4000 m deep). The primary surface circulation in the basin is a cyclonic gyre, west-bounded by the southward-flowing Kamchatka Current. The Alaskan Stream flows northward through passes between the Aleutian Islands and is incorporated into this gyre. The water mass from the Bering Sea is of relatively low salinity and rich in nutrients, and is an important component of the upper halocline in the Arctic Ocean (Cooper et al., 1997). The Bering Sea is connected to the North Pacific through various straits and passes (Fig. 1), with water exchange mostly across the Aleutian Islands above a water depth of approximately 2000 m (i.e., Near Strait, Cook et al., 2005). However, in the eastern Bering Sea, northward flow through the Unimak Pass (80 m deep) is the major conduit between the North Pacific and the shelf (Stabeno et al., 1999). The North Pacific water entering the Bering Sea is transported by the Aleutian Current, also called Subarctic Current. This surface oceanic current is a mixture of eastward-flowing Kuroshio and the Oyashio Currents, located between the Aleutian Islands and the latitude of 42 ◦ N. The Kuroshio Current plays an important role for the warm waters from low to high latitude areas in the North Pacific (Fig. 1), which originates from the West Pacific Warm Pool and has fluctuated in the past (Chen et al., 2005). The Kuroshio, as a western boundary current in the North Pacific, is north-flowing and arising at the western boundary of the North Equatorial Current. One branch of this current flows into the South China Sea through the Taiwan Strait and the Ryukyu Islands, and skirts the east coast of Kyushu. During the summer, it branches west and then flows northeast through the Korea Strait and parallel to the west coast of Honshu in the Sea of Japan as the Tsushima Current. In the vicinity of latitude 35 ◦ N (about central Honshu), the bulk of the Kuroshio turns east to receive the southward-flowing Oyashio Current. This flow, known as the Kuroshio Extension, eventually becomes the North Pacific Current (also known as the North Pacific West Wind Drift). Much of this current’s force is lost to the west of the Hawaiian Islands as a great south-flowing eddy, the Kuroshio countercur- rent, joins the Pacific North Equatorial Current and directs the warm water back to the Philippine Sea. Approaching the North American coast, the remainder of the original flow continues eastward to split off the west coast of Canada and forms the Alaska and California currents. Therefore, this current probably serves as a main linkage for warm plankton species to migrate from tropic to subarctic areas in the North Pacific through the Kuroshio, Oyashio and Aleutian currents in a relay manner. To investigate the stratigraphic distribution of Spongodiscus biconcavus Haeckel and Spongodiscus sp. Ling (1973), we selected the core samples from IODP Site U1340. This site is located on the Bowers Ridge near the Aleutian Islands at 179 ◦ 31.3 W and 54 ◦ 24.0 N at a water depth of 1306 m (Fig. 2). Three holes were cored at this site to a maximum composite depth of 604.5 m, covering the longest depositional period of all sites drilled during Expedition 323. A total of 293 samples were taken with a sampling interval of 0.2 m from the top 10 m and 3 m for the rest of core. Samples were dried and about 1 g of each was weighed and dispersed in distilled water with 10–15% of hydrogen peroxide and sodium hexa-metaphosphate as oxi- dizing and dispersing agents, respectively. A small amount of hydrochloric acid was added to dissolve calcium carbonate. The samples were washed several times until all clay and organic matters were completely gone and only microfossils were left. All radiolarian specimens were mounted onto two permanent slides with Canada balsam for species identification and quantitative analysis. A total of 184 surface samples from the South China Sea were also analyzed with a method of Chen and Tan (1997) for investigating the present distribution of Spongodiscus biconcavus in the low latitude marginal sea of the North Pacific for comparison. Due to the lack of calcareous biogenic material (i.e., foraminifera) in this region, it is not possible to construct a high resolution oxygen stable isotopic stratigraphy for comparing the evolution of the paleoenvironment within the stratigraphic framework. Therefore, most of the stratigraphic constraints are derived from micropaleontologic and paleomagnetic data (Takahashi et al., 2011a). Biostratigraphic datums were initially derived from diatom, radiolarian, dinoflagellate, ebridian, and silicoflagellate bioevents using core catcher samples. A total of 17 bioevents are recognized, which confine the cored interval at Site U1340A from Pliocene to the Recent (Takahashi et al., 2011a, fig. F19, table T2). Although the biostratigraphic results are somewhat primary, they provide basic information for further constructing the biostratigraphic framework and age control. Potential offset between paleomagnetic and micropaleontologic datums exist, especially for sediments older than 2 Ma (below ∼ 300 mbsf) and the uncertainty of some long-range microfossils. In fact, most uncertainties are not derived from the Bering Sea data. They instead come from other North Pacific sites due to diachronous biostratigraphic datums. Some micropaleontologic bioevents have to be reviewed and modified using integrated biostratigraphy in the Bering Sea. In order to refine radiolarian datums at Site U1340 (Takahashi et al., 2011a), 0.2 m sample interval for the youngest 10 m and 3 m spacing for the older section were applied to investigate the vertical distribution of radiolarians in this work. Other datums (diatoms and ebridians) are adopted from Takahashi et al. (2011a). The following biostratigraphic datums are observed in descending order in the U1340A borehole: 1. The first downhole datum of 0.05 Ma at 5.9 mbsf for the LO (last occurrence) of radiolarian Lychnocanoma nipponica sakaii (Morley et al., 1995); 2. The 0.3 Ma datum at 37.6 mbsf with the LOs of Proboscia curvirostris , Thalassiosira jouseae and Proboscia barboi ; 3. The 0.9 Ma datum for the LOs of diatom Actinocyclus oculatus and radiolarian Eucyrtidium ...
Context 3
... Bering Sea is connected to the North Pacific through various straits and passes (Fig. 1), with water exchange mostly across the Aleutian Islands above a water depth of approximately 2000 m (i.e., Near Strait, Cook et al., 2005). However, in the eastern Bering Sea, northward flow through the Unimak Pass (80 m deep) is the major conduit between the North Pacific and the shelf ( Stabeno et al., 1999). The North Pacific water ...
Context 4
... Kuroshio Current plays an important role for the warm waters from low to high latitude areas in the North Pacific ( Fig. 1), which originates from the West Pacific Warm Pool and has fluctuated in the past ( Chen et al., 2005). The Kuroshio, as a western boundary current in the North Pacific, is north-flowing and arising at the western boundary of the North Equatorial Current. One branch of this current flows into the South China Sea through the Taiwan ...
Context 5
... datums were initially derived from diatom, radiolarian, dinoflagellate, ebridian, and silicoflagellate bio- events using core catcher samples. A total of 17 bioevents are recognized, which confine the cored interval at Site U1340A from Pliocene to the Recent ( Takahashi et al., 2011a, fig. F19, table T2). Although the biostratigraphic results are somewhat primary, they provide basic information for further constructing the biostratigraphic framework and age control. Potential offset between paleomagnetic and micropaleontologic datums exist, especially for sediments older than 2 Ma (below ∼300 mbsf) and the uncertainty of ...
Context 6
... therefore suggest that S. biconcavus generally lives in tropical seas but becomes less common in sub- tropical and temperate areas. Its occurrence in higher latitude is due to influence of warm currents, such as the Kuroshio Current (Figs. 1 and 5). Kunitomo et al. (2006) analyzed the molecular phylogeny of acantharian and polycystine radiolarians based on ribosomal DNA sequences, using living shells of Spongodiscus bicon- cavus collected from the coast surface water of Shimoda, Izu Peninsula, Japan (ranging from 34 • 35 79 N to 34 • 38 91 N and 138 • 55 45 E to 138 • 57 30 E, near the present Kuroshio front). ...
Context 7
... summarize, Spongodiscus biconcavus probably appeared in the late Pleistocene prior to 239 ka in the Bering Sea as well as in the northeast Pacific covered by the Aleutian current, and Okhotsk Sea and Japan Sea influenced by the enhanced northward-flowing Kuroshio Current (Figs. 1, 2 and 8). Its dis- tribution in space and time provides evidence that past climate affected the ocean currents, which in turn, controls biogeography of planktonic species in the North Pacific. ...
Context 8
... are signs of minor abundance increase of sea ice diatoms and dinoflagellates at site U1340, starting at ∼3.4 Ma for dinoflagellates and ∼2.7 Ma for diatoms respec- tively. The significant progressive increase took place since ∼2 Ma and extends into the present (Takahashi et al., 2011b). ...
Context 9
... SIOAS-R131 deposited in the South China Sea Institute, CAS, from sample SCS D-3-8 of surface sediment in central South China Sea, pictured in Fig. 4H, which is basically similar to reference of Popofsky (1912, p. 143, p1. 6, fig. ...

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Citations

... Anyway, a genetic data from both species need to clearly verify their relationships. Moreover, the Kuril Basin of the Sea of Japan and the western part of the Bering Sea are rather isolated and not currently directly connected by the oceanic currents (see Fig. 18; Chen et al., 2014). ...
... Anyway, according to recent studies, the shallow and deep-sea fauna off California and the NW Pacific are apparently relative, but completely different on the specific level due to the absence of connection and gene flow in the modern time (Briggs, 2003;Durham and MacNeil, 1967;Einarsson et al., 1967). Modern currents of the Northern Pacific (Fig. 18) connect these areas via the Northern Pacific Current only (current speed is about 1 km/h and the distance over 7000 km), which means that planktonic larvae require more than 290 days to reach California from the Asian shores (see Chen et al., 2014). For example, Californian deep-sea M. segonzaci closely related to M. beringana is considered as a valid species (Jones and Macpherson, 2007) based on morphological and genetic data as well as there are many other example among shallow and deep-sea decapod crustaceans with the similar relationships and the amphi-Pacific distribution (vicariant taxa) (e.g., Zenkevich, 1963;Ambler, 1980;Zmarzly, 1992;Kensley and Komai, 1992;Kensley, 1996;Jones and Macpherson, 2007;Maggs et al., 2008;Sakai, 2011;Ayón-Parente and Hendrickx, 2013;Poore, 2014;Marin, 2010Marin, , 2015Marin, , 2018. ...
... The map of distribution (upper), the bathymetric range (vertical rectangle) of the genus Munidopsis, and the map of currents (lower) in the NW Pacific (fromChen et al, 2014). The exact locality of the studied specimen of Munidopsis beringanaBenedict, 1902 in the "western part of the Bering Sea" is unknown. ...
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... All samples were treated based on the method described by Zhang et al. (2014aZhang et al. ( , 2014b as follows: (1) 1-2 g of dried sediments of each sample was transferred to a beaker, to which 25 mL of 10% H2O2 solution was added; (2) after 30 min, the beaker was placed in a sonic oscillator for 2 min to separate the clay adhered to the radiolarian specimens. The beaker was then moved to the laboratory table; (3) after allowing the beaker to stand for 2 min, the clay suspension was removed, Figure 1 The map of the studied areas and the ocean currents in the North Pacific Gyre (revised after Chen et al., 2014). Blue dots indicate sampling locations. ...
... Among these species, L. polyacantha, L. spiralis, and L. minor show higher composition in the Bering Sea than in the Philippine Sea. Since warm-water masses of the Kuroshio Current extension may eventually flow into the Bering Sea driven by the ocean circulation (Chen et al., 2014), the distribution pattern of subcluster B3 may be associated with the ocean circulation in the subarctic Pacific. ...
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Overall abundance and species composition of radiolarian faunas were analyzed in surface sediment samples from representative areas of South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea, Philippine Sea, and the western boundary current regions of the North Pacific, in order to understand the biogeographic distribution of radiolarians in the Northwest Pacific and explore its relationship with the main environmental factors and the North Pacific circulation. The results showed that radiolarians in the Northwest Pacific surface sediments can be divided into two large biogeographic provinces—cluster A and cluster B. Cluster A is characterized by the dominance of warm-water species and distributed primarily in tropical and subtropical seas with high radiolarian abundance and diversity; whereas cluster B is predominated by cold water species and distributed mainly in the Arctic and subarctic seas with comparably low abundance and diversity. Cluster A is further divided into five subclusters, A1 to A5, which correspond to East China Sea, Philippine Sea, South China Sea, Sea of Japan, and Kuroshio Current, respectively; cluster B is divided into three subclusters, B1 to B3, which correspond to Sea of Okhotsk, Bering Sea, and subarctic gyre area, respectively. Based on the relationships between radiolarian faunas and major environment parameters in different biogeographic provinces, we suggest that the sea surface temperature (SST) and sea surface salinity (SSS) are primary factors that influence productivity, composition, and distribution pattern of the radiolarian fauna in the Northwest Pacific regions, while water depth is likely responsible for regional differences in the radiolarian fauna in each marginal sea. In addition, according to the distribution and abundance patterns of common radiolarian species in different areas, we identified five special radiolarian assemblages, which may be used as indicators for main Kuroshio Current, Kuroshio-East China Sea Branch, Kuroshio-South China Sea Branch, Tsushima Current, and Oyashio Current water masses.
... The age model used in this study is an update of the preliminary one [Takahashi et al., 2011], and was revised by using the generally accepted datums for the recognized biostratigraphic and magnetostratigraphic events (see supporting information) [Takahashi et al., 2011; Chen et al., 2014a; Zhang et al., 2014b Zhang et al., ,2015. Each Journal of Geophysical Research: Oceans 10.1002/2016JC011750 sample's age was estimated using linear interpolation between two control points. ...
... Ma) was likely caused by climate cooling in the BS. This is indicated by an increase in sea-ice diatom percentages [Takahashi et al., 2011] and an extremely low abundance of the warm-water radiolarian species Spongodiscus biconcavus at Site U1340 [Chen et al., 2014a], probably induced by the onset of the NHG. At 2.73 Ma, the subarctic Pacific halocline resulting from an intensifying NHG led to a decrease in the transport of nutrient-rich deep water into the euphotic zone [Haug et al., 1999] . ...
... The age model used in this study is an update of the preliminary one [Takahashi et al., 2011], and was revised by using the generally accepted datums for the recognized biostratigraphic and magnetostratigraphic events (see supporting information) [Takahashi et al., 2011; Chen et al., 2014a; Zhang et al., 2014b Zhang et al., ,2015. Each Journal of Geophysical Research: Oceans 10.1002/2016JC011750 sample's age was estimated using linear interpolation between two control points. ...
... Ma) was likely caused by climate cooling in the BS. This is indicated by an increase in sea-ice diatom percentages [Takahashi et al., 2011] and an extremely low abundance of the warm-water radiolarian species Spongodiscus biconcavus at Site U1340 [Chen et al., 2014a], probably induced by the onset of the NHG. At 2.73 Ma, the subarctic Pacific halocline resulting from an intensifying NHG led to a decrease in the transport of nutrient-rich deep water into the euphotic zone [Haug et al., 1999] . ...
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We reconstructed changes in biogenic opal export productivity (BOEP) in the southern Bering Sea (BS) over the last 4.3Ma, based on mass accumulation rate (MAR) of biogenic opal from Integrated Ocean Drilling Program (IODP) Site U1340. The results show that the BOEP in the BS was high and variable between ∼4.3Ma and ∼1.9Ma, extremely low and relatively stable from ∼1.9Ma to ∼1.1Ma, and then fluctuated frequently (generally high during interglacials and low during glacials) during the last ∼1.1Ma. One interval of enhanced BOEP from 4.3Ma∼3.2Ma is a response to the Late Miocene–Early Pliocene “Biogenic Bloom Event”. Another interval from 2.8Ma∼1.9Ma correlates with global opal burial shifting from high-latitude oceans to upwelling-influenced regions following the intensification of the Northern Hemisphere Glaciation (NHG). Whereas, the increase in BS opal export productivity during the last 1.1Ma tends to be a “local” phenomenon. Overall, the BOEP shows a similar trend and good correspondence to the input of the Alaskan Stream (AS), which can be traced using the Na2O/K2O ratio. We thus conclude that the AS may be the direct, and primary factor on BOEP variability in the BS during the last ∼4.3Ma. In addition, although the poor correlation between opal MAR and volcanic glass suggests that BOEP variability was not controlled by long-term variations in the volcanism or ash abundance, increased ash abundance indicated by high contents of volcanic glasses was also a possible reason for enhanced BOEP during the period from ∼4.3Ma to ∼3.2Ma and the last ∼0.5Ma. This article is protected by copyright. All rights reserved.
... Zhang et al. (2014a) reconstructed the vertical water-mass conditions mainly on the basis of the radiolarian assemblages. Using the warm-water radiolarian species Spongodiscus biconcavus at Site U1340, Chen et al. (2014) revealed the water-mass exchanges between high and low latitudes and their relations to the global climate changes. However, these studied were focused primarily on the paleoceanophic changes and their responses to global climate change events. ...
... Moreover, high illite chemistry index (average of 0.8) and well crystalline smectite (average of 0.7) (Figure 4) suggest the chemical weathering prevailing in the Aleutian Islands and the eastern Siberian continent under warm and wet climate condition. These findings are in agreement with the warm climate in the Bering Sea revealed by low percentages of sea-ice diatoms (Takahashi et al., 2011), high radiolarian accumulation rates (Zhang et al., 2014a) and relatively high abundance of warm radiolarian species Spongodiscus biconcavus (Chen et al., 2014) in the studied core, and well respond to the global warm climate during this period, which was shown by the LR04 benthic oxygen isotope values (Lisiecki and Raymo, 2005). During stage Ib (3.94 to 3.6 Ma), the smectite/(illite+chlorite) ratios distinctly increased ( Figure 4), indicating the enhanced contribution of the terrigenous materials from the Aleutian Islands. ...
... During stage II (3.6 to 2.74 Ma), clay minerals from the Alaskan continent distinctly increased (Figure 5), and smectite/(illite+chlorite) ratios decreased (Figure 4), suggesting a cold climate in the Bering Sea. However, good to moderate smectite crystallinity indicates that the weak chemical weathering probably still prevailed in the Aleutian Islands, and the Bering Sea was characterized by a cold and wet climate during this period, which was probably resulted from the strengthened Alaskan Stream indicated by relatively high abundance of radiolarian species Spongodiscus biconcavus (Chen et al., 2014). Iliites exhibited the good to moderate crystallinity and low values of chemistry index (Figure 4), indicating that the Alaskan continent was controlled by the cold and dry climate. ...
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Clay mineral assemblages and crystallinities in sediments from IODP Site 1340 in the Bering Sea were analyzed in order to trace sediment sources and reconstruct the paleoclimatic history of the Bering Sea since Pliocene (the last ∼4.3 Myr). The results show that clay minerals at Site U1340 are dominated by illite, with a moderate amount of smectite and chlorite, and minor kaolinite. Sediment source studies suggest that the clay mineral assemblages and their sources in the studied core are controlled primarily by the climate conditions. During the warm periods, clay minerals originated mainly from the adjacent Aleutian Islands, and smectite/(illite+chlorite) ratios increased. During the cold periods, clay minerals were derived primarily from the Alaskan region, and smectite/(illite+chlorite) ratios decreased. Based on smectite/(illite+chlorite) ratios and clay mineral crystallinities, the evolutionary history of the paleoclimate was revealed in the Bering Sea. In general, the Bering Sea was characterized by warm and wet climate condition from 4.3 to 3.94 Myr, and then cold and dry condition associated with the enhanced volcanism from 3.94 to 3.6 Myr. Thereafter, the climate gradually became cold and wet, and then was dominated by a cold and dry condition since 2.74 Myr, probably induced by the intensification of the Northern Hemisphere Glaciation. The interval from 1.95 to 1.07 Myr was a transitional period of the climate gradually becoming cold and wet. After the middle Pleistocene transition (1.07 to 0.8 Myr), the Bering Sea was governed mainly by cold and wet climate with several intervals of warm climate at ∼0.42 Ma (MIS 11), ∼0.33 Ma (MIS 9) and ∼0.12 Ma (MIS 5), respectively. During the last 9.21 kyr (the Holocene), the Bering Sea was characterized primarily by relatively warm and wet climatic conditions.
... Since the initial work by Ling (1973a) specimens equivalent of this taxon appeared in the literature (e.g., Sakai, 1980;Matul et al., 2002Matul et al., , 2009. At Site U1340 in the southern Bering Sea (Fig. 1), Chen et al. (2014) emended this taxon as S. biconcavus. However, original description of S. biconcavus by Haeckel (1887) (and repeated by Popofsky (1912)) states that the shell is a biconcave (thinnest in the center) disk while the emended form by Chen et al. (2014) is a biconvex disk. ...
... At Site U1340 in the southern Bering Sea (Fig. 1), Chen et al. (2014) emended this taxon as S. biconcavus. However, original description of S. biconcavus by Haeckel (1887) (and repeated by Popofsky (1912)) states that the shell is a biconcave (thinnest in the center) disk while the emended form by Chen et al. (2014) is a biconvex disk. Thus there is a fundamental difference in morphology between S. biconcavus by Haeckel (1887) and S. biconcavus emended by Chen et al. (2014). ...
... However, original description of S. biconcavus by Haeckel (1887) (and repeated by Popofsky (1912)) states that the shell is a biconcave (thinnest in the center) disk while the emended form by Chen et al. (2014) is a biconvex disk. Thus there is a fundamental difference in morphology between S. biconcavus by Haeckel (1887) and S. biconcavus emended by Chen et al. (2014). In addition, the disk diameters of S. biconcavus in Chen et al. (2014) were sometimes greater than the specimens observed in our study. ...
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This paper presents, for the first time ever, a complete list of Cenozoic Polycystinea reported between 1834 and 2020. It records 6898 names of taxa originally described as new species or subspecies, assigned to the Class of Polycystinea, the most important group in the infraphylum Radiolaria. This list only attempts to provide an objective record of available and unavailable names, the latter including nomina oblita, nomina nuda, homonyms, invalid nomenclatorial acts, species wrongly described as Polycystinea and nomina dubia species with inexistent name-bearing specimens.
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Our understanding of the paleoceanography of the Bering Sea has been considerably advanced by IODP Expedition 323. The expedition aimed to create a high-resolution record of changes in paleoceanography since the Pliocene in a relatively high-latitude region of the North Pacific, subject to polar amplification. The expedition recovered 660 cores, mainly high-quality Advanced Piston Cores (APC), with a total length of 5741 m of continuous cores from seven sites distributed around the perimeter of the Aleutian Basin, including the Bowers Ridge, the Bering Slope edge, and the Umnak Plateau. These cores are crucial to our understanding of sea-ice distribution, productivity, laminated sediments, input of detrital materials, the formation of the North Pacific Intermediate Water mass, the Pacific water mass entry, the history of the Arctic gateway, and the enigma of the intensification of the Northern Hemisphere Glaciation and the mid-Pleistocene Transition. The maximum ages of the cores are ~5 Ma at the Bowers Ridge sites and 2.5 Ma at the Bering Slope sites. Meltwater from the Alaskan Ice Sheet has influenced the Bering Sea since 4.3 Ma, increasing in influence at 3.3 and 2.8-2.5 Ma. The significant development of sea-ice formation was identified at two sites on the Bowers Ridge at 2.7 and 2.2-2.0 Ma, based on analysis of sea-ice related diatoms and silicoflagellates. Such sea-ice formation affected the extent of the North Pacific Intermediate Water in the Bering Sea, which was strengthened during cold intervals such as when the Bering Strait closed due to falling sea level.
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The Bering Sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the Arctic Ocean and into the subarctic North Pacific Ocean. Cores from IODP Expedition 323 to the Bering Sea provide the first opportunity to obtain reconstructions from the region that extend back to the Pliocene. Previous research at Bowers Ridge, south Bering Sea, has revealed stable levels of siliceous productivity over the onset of major Northern Hemisphere Glaciation (NHG) (c. 2.85-2.73 Ma). However, diatom silica isotope records of oxygen (δ18Odiatom) and silicon (δ30Sidiatom) presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region, superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice. This concluded at 2.58 Ma with a sharp increase in diatom productivity, further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions. These transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest Pacific Ocean, with increases in productivity further aided by increased sea-ice and wind-driven mixing in the Bering Sea. In suggesting a linkage in biogeochemical cycling between the south Bering Sea and subarctic Northwest Pacific Ocean, mainly via the Kamchatka Strait, this work highlights the need to consider the inter-connectivity of these two systems when future reconstructions are carried out in the region.