Kenji M. Matsuzaki

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

Significance In coastal Alaska and the St. Elias orogen, over the past 1.2 million years, mass flux leaving the mountains due to glacial erosion exceeds the plate tectonic input. This finding underscores the power of climate in driving erosion rates, potential feedback mechanisms linking climate, erosion, and tectonics, and the complex nature of climate−tectonic coupling in transient responses toward longer-term dynamic equilibration of landscapes with ever-changing environments. Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

Middle to Upper Pleistocene Polycystine Radiolarians from Hole 902-C9001C, Northwestern Pacific

A continuous 740-kyr Quaternary sedimentary sequence containing abundant siliceous microfossils was recovered from Hole C9001C during the D/V Chikyu 2006 Mission off the Shimokita Peninsula, Japan. This region is characterized by mixed water reflecting the influences of one warm current (Tsugaru Current), one cold current (the Oyashio Current), and several intermediate and deep water masses. Polycystine radiolarians (a siliceous microfossil group) are useful for reconstructing paleoceanographic changes in this region during the Quaternary because of their ecological properties in these types of deep-sea sediments. This paper illustrates and reviews the taxonomic features of all the polycystine species encountered during this study. A detailed taxonomy is presented because different taxonomic names have been applied, even to the same morphospecies, in many cases. The taxonomic classification of 104 species belonging to three orders (Collodaria, Spumellaria, and Nassellaria), 16 superfamilies, 33 families, and 66 genera was verified by comparison of the holotypes and the relevant name-bearing specimens in accordance with the International Code of Zoological Nomenclature to the extent possible. The taxonomic classification system was updated with reference to both recent morphological taxonomic schemes and molecular phylogenetic analyses. This paper also provides a detailed synonym list of each previously illustrated species from the northwestern Pacific Ocean in order to standardize applicable taxonomic names for the same morphospecies. In addition, a new family (Amphisphaeridae Suzuki fam. nov.) and a new replacement name (Lithelius haeckelispiralis Matsuzaki and Suzuki, nomen nov. for Lithelius spiralis of Haeckel in 1861 [not Ehrenberg in 1840]) are described, and the diagnoses of the genus Tholomura and the family Lychnocaniidae are emended.

Middle to Late Pleistocene radiolarian biostratigraphy in the water-mixed region of the Kuroshio and Oyashio currents, northeastern margin of Japan (JAMSTEC Hole 902-C9001C)

A continuous Quaternary sediment sequence was recovered from Hole 902-C9001C during the D/V Chikyu 2006 mission along the northeastern margin of Japan. The age and rate of deposition of this core were estimated using calcareous nannofossil biostratigraphy and oxygen isotope curves measured from benthic foraminifera (Uvigerina akitaensis) and dated from 740 ka to the present, a period that spanned the Brunhes normal polarity epoch. Sediment consisted of diatomaceous siltstone and contained an abundance of radiolarians. A total of 91 radiolarian species was found in the core, of which 74 were analysed. Of these radiolarian species, 36 demonstrated continuous stratigraphical distribution over the past 740 ka and 38 had shorter ranges of biostratigraphical interest. Three of the 38 species were determined to be novel and are described in the present study (Amphisphaera tanzhiyuani sp. nov., Schizodiscus japonicus sp. nov. and Siphonosphaera? paraphoros sp. nov.). Based on 17 radiolarian bioevents, including four datums which have been commonly used across a wide area of the North Pacific, the radiolarian sequence of this core was divided into 8 zones: Amphirhopalum virchowii Zone (613–740 ka), Spongaster tetras irregularis Zone (516–613 ka), Cyrtidosphaera reticulata Zone (357–516 ka), Spongurus cylindricus Zone (238–357 ka), Pterocanium depressum Zone (209–238 ka), Spongoliva ellipsoides Zone (131–209 ka), Ceratospyris problematica Zone (33–131 ka), and the Acanthodesmia vinculata Zone (0–33 ka).

New northwest Pacific radiolarian data as a tool to estimate past sea surface and intermediate water temperatures

A new radiolarian data set for transfer function estimates of past sea surface temperature (SST) and intermediate water temperature was developed in this study for the northwestern Pacific Ocean covering a region from 1° to 50°N and 120° to 167°E. We analyzed 87 sediments surface samples, selected 30 species and/or species group found in shallow water for estimating past summer SST and 17 species and/or species group found in the intermediate water for estimating past intermediate water temperature. Since the intermediate water temperature changes greatly between 200 and 500 m, our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m. In this context, we estimated past summer SST and intermediate water (at ~500 m) temperature within an error margin of 0.9 and 1.2°C, respectively. A test of the accuracy of our transfer functions, conducted on core samples provided by IODP Expedition 346 Site U1429 in the northern East China Sea, showed that the reconstructed summer SSTs fluctuated between 17.2 and 26.5°C in selected late Pleistocene sequences. These temperatures corresponded to modern winter and summer SST, respectively, which highlights the ability of our new database to accurately reconstruct summer SST. The reconstructed intermediate water temperature fluctuates between 3 and 8°C, which corresponds to the observed temperature range at depths of ~500 m at high and midlatitudes, respectively.

Radiolarian Biostratigraphy from Middle Miocene to Late Pleistocene in the Japan Sea

Abstract. In the Integrated Ocean Drilling Program (IODP) Exp. 346, sampling by drilling was conducted at seven sites (U1422–U1427 and U1430) in the Japan Sea. Radiolarians in moderately well preserved states were found in most samples throughout the sequence in varying abundance. Forty-one radiolarian datum events were identified in this study, and the radiolarian zonation that best divides the middle Miocene to Pleistocene sequences with updated ages of radiolarian datum events (estimates based on the geomagnetic polarity time scale (GTS) 2012) was applied to the sedimentary sequences in the Japan Sea. Here, four new radiolarian zones are proposed for the Quaternary of the Japan Sea, and one zone is slightly revised to adjust for differences among other zones. The sequences collected at the sites extended from the Pleistocene Ceratospyris borealis Zone to progressively deeper zones as follows: Site U1427, four zones to the Pleistocene Schizodiscus japonicus; Site U1422, six zones to the late Pliocene Hexacontium parviakitaense Zone; Sites U1423, U1424 and U1426, eight zones to the early Pliocene Larcopyle pylomaticus Zone; and Sites U1425 and U1430, fourteen zones to the middle Miocene Eucyrtidium inflatum Zone. The absence or extremely rare occurrence of Stylatractus universus and E. matuyamai indicates that S. universus lived in the deep water of the northwestern Pacific and had not been able to migrate into the Japan Sea across the Tsugaru Strait since the Pliocene.

Quaternary radiolarian biostratigraphy of IODP Site 341-U1417A

Expedition 341 of the Integrated Ocean Drilling Program (IODP) retrieved sediment cores spanning the time interval between the Pleistocene and Miocene from the southern Gulf of Alaska. Onboard Pleistocene radiolarian biostratigraphy is hereby refined by increasing the sampling resolution. The 178 core samples from the upper 190 m CCSF-B of Site U1417 contained faunal elements similar to the Northwest Pacific; for example, the three biozones in the Northwest Pacific (i.e., Eucyrtidium matuyamai, Stylatractus universus and Botryostrobus aquilonaris) were also recognized in the Gulf of Alaska, spanning 1.80-1.13 Ma, 1.13-0.45 Ma, and the last 0.45 Myr, respectively. Based on the age model that we used in this study and the shipboard paleomagnetic reversal events, the first occurrences (FOs) of Amphimelissa setosa and Schizodiscus japonicus in the Northeast Pacific were preliminarily determined to be 1.48 and 1.30 Ma, respectively. The last occurrence (LO) of Eucyrtidium matuyamai and the FO of Lychnocanoma sakaii, both well-established bioevents in the Northwest Pacific, were dated at 0.80 Ma and 1.13 Ma, respectively. The LO of E. matuyamai is a synchronous event at 1.05±0.1 Ma in the North Pacific, while the FOs of A. setosa and S. japonicus are significantly older than what found elsewhere at 1.48 Ma and 1.30 Ma, respectively.