Pollen Incidence and Wind Transport in Central Hokkaido (I)

Four pollen traps at different levels were used in a natural broad- leafed forest near Tomakomai, central Hokkaido, to investigate pollen incidence and wind transport. The trap at trunk level captured a lesser amount of pollen than the other traps. The pollen period of the canopy trees was from March to the middle of June and it was characterized by a gradual increase in amount of pollen but a sharp decrease. Among the canopy trees, Carpinus, Quercus, Alnus, Betula and Cryptomeria showed the highest pollen frequency. Pollen transported into the sampling site were those of Crypromeria, Fagus, Aesculus Castanea and Tsuga. Although Cryptomeria pollen accounted for 38-48% of the total amount of the canopy tree pollen in the middle of April 1978, the nearest Cryptomeria-bearing forest is about 16 km west of the sampling site

Fluctuations in the East Asian monsoon over the last 144ka in the northwest Pacific based on a high-resolution pollen analysis of IMAGES core MD01-2421

A high-resolution pollen analysis of IMAGES core MD01-2421 (45.83 m) from the northwest Pacific off central Japan was used to clarify the vegetation history of central Japan over the past 144 ka. An age model was constructed using the oxygen isotope stratigraphy of benthic foraminifera, 12 accelerator mass spectrometry (AMS) 14C datings, and two tephra layers with known eruption ages. The pollen temperature index Tp[=100×Tw/(Tc+Tw), where Tw is the sum of temperate taxa and Tc the sum of subalpine taxa] values were high during 129–119, 115–100, 82–76, 53–49, and 15–0 ka. Cool-temperate broad-leaved forests developed during the high-Tp periods and subalpine conifer forests grew during the low-Tp periods. The Tp fluctuated synchronously with summer insolation at 36°N, where the core was collected. During periods with abundant Cryptomeria or Sciadopitys (120–118, 115–89, 78–70, and 4–0.3 ka), the East Asian summer monsoon was stronger and the annual precipitation was greater in central Japan than at present (>2000 vs. 1500 mm). Fluctuations in the sea-surface temperature (SST) calculated from the oxygen isotopes of foraminifera in core MD01-2421 and changes in the strength of the summer monsoon were synchronous. The SST was determined by the currents passing over the core site, rather than by the strength of summer insolation. Northward movement (high SST) of the Kuroshio Current, which is under the influence of the summer Okhotsk high pressure, was strong near the summer insolation minima when precipitation was high, particularly around 116, 94, and 71 ka. Thus, the strengths of both summer insolation and the East Asian summer monsoon have determined the vegetation history of central Japan for the last 144 ka

Late Quaternary variation of lignin composition in core MD01-2421 off central Japan, NW Pacific

In order to understand the responses of terrestrial vegetation in central Japan to global climate changes, we have generated the record of lignin composition from Core MD01-2421 off central Japan in the NW Pacific during the last 145,000 years by tetramethylammonium hydroxide (TMAH)-pyrolysis-gas chromatography–mass spectrometry (GC/MS). The relative abundance of lignin was significantly low in early MIS-1 and MIS-5e and higher in MIS-5c to early MIS-4. This reflects glacial–interglacial changes in sea level and riverine runoff. The ratio of syringyl (S)- to vanillyl (V)-phenols (S / V ratio), which is a contribution index of angiosperms against gymnosperms, was lower in MIS-2, MIS-4 and MIS-6, reflecting the glacial–interglacial variation of air temperature. The ratio of cinnamyl (C)- to vanillyl (V)-phenols (C / V ratio), which indicates the contribution of grasses, was higher in late MIS-2, early-mid MIS-3 and MIS-6. The periods of higher C / V ratio correspond to the periods of lower sea surface temperatures (SSTs), suggesting a dry and cold climate in late MIS-2, mid-MIS-3 and MIS-6