Morphological variability of the trace fossil Schaubcylindrichnus coronus as a response to environmental forcing

Schaubcylindrichnus is an important trace fossil used in the characterization of offshore and shoreface depositional environments. Our understanding of this trace has followed a winding path including the introduction of several new ichnospecies and the subsequent recent synonymization into one ichnospecies. Likewise, our understanding of the ethological interpretation of the trace fossil has evolved from gregarious headdown deposit feeders to filter feeders, until it recently was shown that the tracemaker probably was a funnel feeder. Although several ichnospecies were recently synonymized into one ichnospecies, Schaubcylindrichnus coronus, variability in the number of tubes per sheaf and abundance of nested tubes, i.e., tubes that break up older tubes, were observed between different settings. These differences were studied in close detail at Miocene outcrops in Japan and Taiwan where the trace fossil occurs copiously and therefore allows the intraspecific morphological variability to be addressed. Around 2000 specimens from Japan and Taiwan were studied. The results show a distinct tendency for higher tube numbers in the offshore facies where sediments are characterized by higher silt/mud content, suggesting that S. coronus with higher tube numbers were constructed in a calm environment allowing longer dwelling periods. The increased abundance of nested tubes in settings characterized by thin sand layers indicate that the nested tubes are a reparation response to erosional events destroying the feeding funnels at the sediment-water interface. Consequently, tube number per sheaf and abundance of nested tubes may be used to further characterize the depositional environment in shoreface to offshore facies

Morphology, ethology and taxonomy of the ichnogenus Schaubcylindrichnus : Notes for clarification

Two recent publications dealing with the trace fossil Schaubcylindrichnus (Frey and Howard, 1981) in Cenozoic outcrops have been published independently in the same year (Löwemark and Hong, 2006; Nara, 2006). The two studies came to similar conclusions regarding morphology, somewhat different conclusions with respect to the behavior of the trace maker, and diametrically opposed conclusions regarding the ichnotaxonomy. The two studies (Löwemark & Hong, 2006; Nara, 2006) were published in parallel without taking the other into consideration. During the 2nd International Ichnological Congress in Krakow 2008 the authors had the opportunity to compare their results (Löwemark and Nara, 2008). We therefore feel that a clarifying note is timely. Morphologically, S. coronus is shown to typically consist of three distinct parts: a bundle of thickly lined, often crossing tubes that have been constructed after each other, a feeding funnel connected to one end of the burrow system, and a fecal mound connected to the other end (Nara, 2006). Löwemark & Hong (2006) introduced a new ichnospecies, S. formosus, based on the differences in morphology to the original description of S. coronus that outlined a congruent bundle as the typical form. However, subsequent comparison of S. formosus with Nara's (2006) descriptions of S. coronus showed that the former can be accommodated in the latter. S. formosus therefore should be considered as a junior synonym of S. coronus and be abandoned

Changes in soil CO2 concentration and soil respiration during rainfall events

降雨が土壌中二酸化炭素（CO2）濃度及び土壌呼吸速度に与える影響を調べるため，2008 年5 月（降雨イベント1）と9 月（降雨イベント2）の2 回の降雨を対象に降雨中の土壌中CO2 濃度，土壌呼吸速度の連続観測を行った。その結果，両降雨で観測値の変化に違いが見られた。土壌中CO2 濃度の変化は，特に深度15cm において大きく異なっていた。降雨イベント1 では，降雨開始から数時間後にCO2 濃度が大きく低下し，その後降雨終了時までに回復した。一方，降雨イベント2 では，降雨終了直前にCO2 濃度が上昇を開始し，降雨終了後にピークを迎えた後も降雨前より高い濃度を保っていた。土壌呼吸速度に関しては，降雨前の値は両降雨で同程度であり，降雨開始後に大きく低下するという点でも共通していた。しかしながら，降雨イベント1では降雨終了後も土壌呼吸速度が回復しなかったのに対して，降雨イベント2 後には，降雨前と同程度まで土壌呼吸速度が回復した。土壌各層のCO2 湧き出し速度，CO2 貯留量の推定結果から，降雨イベント1 では，雨水が土壌表面を被覆することによるCO2 拡散の停止に加えて，雨水に伴って侵入する低濃度CO2 による土壌中高濃度CO2 の押し出しという2 つの現象が生じたと考えられた。一方，降雨イベント2 では，CO2 拡散の停止が卓越していたと考えられた。降雨中に生じる現象が2 回の降雨イベントで異なった要因は，降雨前の土壌中CO2 環境の違いにあることが示唆された。Soil respiration and soil CO2 concentration were measured during two rainfall events in May(Event 1) and September (Event 2) 2008 to investigate the effect of rainfall on soil respirationand soil CO2 concentration. The behavior of soil respiration and soil CO2 concentration duringrainfall differed between Events 1 and 2. Soil CO2 concentrations were significantly different ata depth of 15 cm. During Event 1, soil CO2 concentration decreased rapidly in the first severalhours after rainfall began, but returned to the initial concentration by the time rainfall stopped.In contrast, during Event 2, soil CO2 concentration increased at the end of rainfall and reacheda peak after rainfall stopped, thereafter retaining a higher CO2 concentration than that beforerainfall. Soil respiration during both Events 1 and 2 was similar at the beginning of rainfalland decreased rapidly after rainfall began. However, after rainfall, soil respiration in Event 2recovered to the same level observed before rainfall, whereas soil respiration in Event 1 remainedlower. From the estimated soil CO2 production profile and soil CO2 storage, lack of gas diffusioninduced by coverage of the soil surface with rainwater and gas exchange enforced by infiltratingrainwater affected soil respiration and soil CO2 concentration during Event 1. During Event 2,on the other hand, only the lack of gas diffusion was dominant. It is inferred that such differentprocesses during different rainfall events depend on the initial condition of the soil CO2 regime