Ecological characteristics and stable isotope compositions of Elphidium batialis Saidova off Hidaka (northern Japan) in the Northwestern Pacific continental margin

Abstract

We investigated the microhabitats of benthic foraminifera and stable oxygen and carbon isotope compositions of living (stained) Elphidium batialis Saidova off Hidaka (northern Japan) in the Northwestern Pacific continental margin. In the study area, six major species reside in three microhabitats that are vertically distributed within the sediment column. Bolivina spissa, Uvigerina akitaensis, and E. batialis tend to be shallow infauna, whereas Chilostomellina fimbriata and Globobulimina pacifica are deep infauna. Nonionellina labradorica is intermediate infauna. The δ18O values of E. batialis and U. akitaensis increased gradually with the water depth, but those of E. batialis contain a systematic offset by about −1.0 to −1.2‰ to U. akitaensis. This offset range is consistent with that observed in previous fossil studies in the Bering Sea. The δ13C values of U. akitaensis are approximately consistent (−1.1‰ to −0.8‰) with the water depth, whereas those of E. batialis increase with water depth from the shallower sites (−3.0 to −2.0‰) to the deeper sites (−2.0 to −1.6‰). Depending on the water depth, the δ13C values of E. batialis are lower than U. akitaensis by −1.4 to −0.7‰. Elphidium batialis may produce slightly 13C-poor calcite at the severely oxygen-poor water depths of the oxygen minimum zone (OMZ), suggesting that dissolved oxygen level may affect δ13C values of E. batialis during calcite precipitation. It is hypothesized that the δ13C values of E. batialis may contain signals arising from food digestion (or an internal respiration effect) and change the proportion of carbonate ions for calcite precipitation between the DIC values of the ambient pore water and food materials, depending on the dissolved oxygen level on the seafloor. Thus, the δ13C difference between E. batialis and Uvigerina spp. might be useful when inferring the past development of the OMZ and/or changes in the evolution of the North Pacific Intermediate Water in the subarctic North Pacific margin including adjacent marginal seas such as the Bering Sea.