Intermediate water ventilation change in the subarctic northwest Pacific during the last deglaciation

Pulses of enhanced North Pacific Intermediate Water ventilation from the Okhotsk Sea and Bering Sea during the last deglaciation

“…5). In general, this pattern is consistent with ventilation ages from the intermediate-depth northwest Pacific during HS-1 and YD and, like the results from δ 13 C, suggests a close relationship to NPIW (Duplessy et al, 1989;Adkins and Boyle, 1997;Ahagon et al, 2003;Sagawa and Ikehara, 2008). However, a more complex picture evolves during the Bølling/Allerød.…”

“…These values suggest a strong intermediate-depth convection cell proximal to the Okhotsk Sea during deglacial cold stages, in particular during HS-1. These nutrient-depleted and well-ventilated water masses, indicated by δ 13 C maxima, were subsequently exported into the northwest Pacific and were the likely source of enhanced deglacial NPIW (Duplessy et al, 1989;Adkins and Boyle, 1997;Ahagon et al, 2003;Sagawa and Ikehara, 2008), which probably also ventilated the Bering Sea (Rella et al, 2012). In this context, it is important to note that the vertical expansion of these water masses did not reach the deep-water level in the northwest Pacific.…”

“…Radiocarbon ages between coeval planktic and benthic foraminifers (defined as ventilation ages) were used to measure the difference in the 14 C to C ratio in the dissolved inorganic carbon between surface water and deep water to provide ventilation age changes of the deep water (Broecker et al, 2004). It has been shown that ventilation ages are reduced during HS-1 and the YD and point to a better ventilation of NPIW (Duplessy et al, 1989;Ahagon et al, 2003;Sagawa and Ikehara, 2008). However, necessary information on ventilation changes from shallower sites in the northwest Pacific are not available and important aspects about the mode of formation of deglacial NPIW as well as the respective roles of the Bering Sea or the Okhotsk Sea as possible source regions of NPIW are not well known.…”

A new local marine reservoir correction for the last deglacial period in the Sanriku region, northwestern North Pacific, based on radiocarbon dates from the Towada-Hachinohe (To-H) tephra

“…Ohkushi et al (2007) suggested that their ΔR value (1,000 y or more), which is larger than the modern ΔR value in this area, resulted from active upwelling of deep water during the last deglaciation. However, Sagawa and Ikehara (2008) considered that the upwelling of deep water into intermediate water depths at the western margin of the NW Pacific was not significant during the last deglaciation, based on reconstructed surface and bottom water oxygen isotope ratios, and the age differences between planktonic and benthic foraminifera. Another possible explanation for the slightly larger ΔR value during the deglacial period in the Sanriku region is the uncertainty associated with the terrestrial and marine To-H ages.…”

“…Upwelling of the old seawater in the subarctic North Pacific makes large ΔR in this region. As the circulation of surface and intermediate water in the NW Pacific changed between the last glacial maximum-last deglaciation and the Holocene (e.g., Ahagon et al, 2003 ;Ohkushi et al, 2003 ;Harada et al, 2004 ;Ikehara et al, 2006 ;Shibahara et al, 2007 ;Sagawa and Ikehara, 2008), the extent of the local reservoir effect in this area remains controversial. The local reservoir effect in the modern and former oceans has been estimated using radiocarbon dates from marine materials of known age, and radiocarbon dates from contemporaneous terrestrial and marine materials (e.g., Yoneda et al, 2001 ;Nakamura et al, 2007).…”