Hokkaido

Today we collected subtidal samples from Lake Akkeshi. This involved using a grab sampler (below right) to collect material from the lake bottom which will be analysed for microfossils (diatoms and foraminifera) and environmental variables (organic content, partical size analysis, pH and salinity). This information is important to improve the accuracy of the transfer function, although it was sometimes difficult due to the rising tide, and fishing boats getting in the way!

The aim of today's fieldwork was to accurately level the stations which were sampled yesterday, and also to collect short cores to look at the infaunal bahaviour of foraminifera - which is important to understand for determining the appropriate depth for modern sampling.

Today, we first headed to Kiritappu and used the geoslice to collect 2 m sequences of sediment which contained numerous tsuanmi layers. We then headed to Mochirippu where we collected a short core to look in detail at sea-level change over the last 100 years or so, which will be compared with tidal gauge records to check the accuracy of microfossil and sediment transfer functions that have been produced.

At Mochirippu, a detailed lithostratigraphy of the northern marshes was investigated. Particular attention was focused on understanding the deposition of sediments laid down over the last couple of centuries. Numerous cores which extruded, and their lithostratigraphy described and photographed. In addition, a bank exposure was cleaned (below right) and logged. We also recruited another member of the team - a very keen and promising individual... the local dog!

The third transect, covering low and high marshes (left). The doggie kindly looked around us during this fieldwork (right).

A tide gauge station at Akkeshi, set eight years ago, has been recording tidal changes every second. This station provided accurate height and arrival time of the 2003 Tokachi-oki earthquake.

Data from this GPS station are forwarded automatically to Geographical Institute of Japan, Tsukuba (near Geological Survey of Japan).

Historical records -- Akkeshi town has the oldest record of eastern Hokkaido

The earliest written records from eastern Hokkaido postdate the 17th century multi-segment earthquake event -an event that predates A.D. 1694. Colonists of wester n Hok kaido (people in Matsu mae-han) produced many written records throughout the early Edo period (1603-1867). However, most of the rest of Hokkaido remained in control of native peoples (the Ainu) throughout the Edo time. The earliest written records from eastern Hokkaido come from Kokutai Temple in Akkeshi tow n , which was built in 1804. Series of Nikkanki, which means daily records in Japanese, contain well records of tsunami disaster in the 1894 event.

Can you see a volcanic ash layer?

4th June 2005, Onishitoh and Sarukotsutoh

Our research today focused on looking for sites in the north of Hokkaido which may be studied to understand non-seismic sea-level changes. We had a look at a number of sites along the coast, many of which were freshwater but one in particular (Sarukotsutoh) was brackish. Future research may focus on understanding the controls of relative sea-level change at this site, far from the Kuril trench..

Onishitoh

Sarukotsutoh (brackish)

4th June 2005, explore further north

Otoshibe River: name of this river is originated from native Ainu language, O-To-Ushi-Pe, which means "many faggots around the river mouth."

Tokushibetsu River: name of this river is originated from native Ainu language, To-Pu-He, which means "many bamboo grass (or bamboo) near the river."

Tonbetsu River: name of this river is originated from native Ainu language, To-Un-Pe, which means "the river connecting to the pond."

7th June 2005, Tohoro, Notsuke

Today's fieldwork concentrated on looking at the lithostratigraphy on Tohoro, to complement the information that was collected back in October. After an exciting boat trip on the river, we arrived at the saltmarsh and used the geoslice corer to look at the sediments that have accumulated.

These cores were carefully logged and photographed, noting specific changes in sediment composition and the presence and location of tephra layers. We are also interested in understanding the contemporary distribution of microfossils and macrofossils along the intertidal zone (below left).

8th June 2005, Tohoro, Notsuke

The aim of today's research was to further investigate the lithostratigraphy of the saltmarsh using a gauge corer which enabled us to look at deeper sediment sequences over the marsh. Particular attention was focused on extending the transect to high marsh/freshwater environments.

Towards the bottom of the 1.5 m sequences that were typically reocovered over the marsh, a distinctive coarse sand/gravel layer was often found. When cleaned, this material was often composed of pummice, and similar material can be found on the contemporary marsh environment along the beach ridge.

Tidal actions. Pumiceous gravels can easily move by daily tidal actions. Such gravels are probably from older deposits (we can observe at outcrops as in 10th June report).

The sequences that were recovered in the freshwater environments recorded very interesting stratigraphy. Furthermore, distinctive pumice layers found towards the bottom of the sequences may provide good chronological control to date the sea-level changes suggested by the distinct lithological changes and quantified at a later date using microfossils.

Japanese alder (Alnus japonica Steud.)

9th June 2005, Tohoro, Notsuke

The aim of today's research was to collect surface samples to understand the contemporary distribution of microfossils and their controlling environmental parameters (pH, salinity etc.) across the marsh. A transect was established from tidal flat, over the beach ridge, through the marsh, to the freshwater forest. Samples were taken on average at a verticle resolution of 5 cm, but additional samples were also taken at other significant geomorphological changes (i.e. intertidal salt ponds).

10th June 2005, Tohoro, Notsuke

The first part of today's research was studying a coastal outcrop consisting of peat and clastic material, with pumice tephra found within the stratigraphy (below right). Detailed lithostratigraphical analysis was followed by the collection of samples for diatom and plant macrofossil analysis.

The second part of our research in the saltmarsh at Tohoro focused on extending lithostrigraphical analysis further into the freshwater forest found at the back of the marsh. Following which, fossil cores were collected for microfossil, sedimentological, and dating analysis. Two cores were chosen. One in the middle of the marsh, and one in the freshwater swamp which contained interesting gravel sequences showing grading (as shown below) alongside tephra layers which should allow good chronological control.

11th June 2005, Tohoro and Odaito, Notsuke

Levelling to proper benchmarks of Geographical Institute of Japan.

Odaito, the nearest port of Tohoro site.

Benchmark Tide gauge station (?)